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  • 1.
    Araujo, Carlos Moyses
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Nagar, Sandeep
    Ramzan, Muhammad
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Shukla, R.
    Jayakumar, O. D.
    Tyagi, A. K.
    Liu, Yi-Sheng
    Chen, Jeng-Lung
    Glans, Per-Anders
    Chang, Chinglin
    Blomqvist, Andreas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Lizárraga, Raquel
    Holmstrom, Erik
    Belova, Lyubov
    Guo, Jinghua
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori. Applied Materials Physics, Department of Materials and Engineering, Royal Institute of Technology (KTH), SE-100 44 Stockholm, Sweden.
    Rao, K. V.
    Disorder-induced Room Temperature Ferromagnetism in Glassy Chromites2014Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 4, s. 4686-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report an unusual robust ferromagnetic order above room temperature upon amorphization of perovskite [YCrO3] in pulsed laser deposited thin films. This is contrary to the usual expected formation of a spin glass magnetic state in the resulting disordered structure. To understand the underlying physics of this phenomenon, we combine advanced spectroscopic techniques and first-principles calculations. We find that the observed order-disorder transformation is accompanied by an insulator-metal transition arising from a wide distribution of Cr-O-Cr bond angles and the consequent metallization through free carriers. Similar results also found in YbCrO3-films suggest that the observed phenomenon is more general and should, in principle, apply to a wider range of oxide systems. The ability to tailor ferromagnetic order above room temperature in oxide materials opens up many possibilities for novel technological applications of this counter intuitive effect.

  • 2. Arslanov, Temirlan R.
    et al.
    Mollaev, Akhmedbek Yu.
    Kamilov, Ibragimkhan K.
    Arslanov, Rasul K.
    Kilanski, Lukasz
    Minikaev, Roman
    Reszka, Anna
    Lopez-Moreno, Sinhue
    Romero, Aldo H.
    Ramzan, Muhammad
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Panigrahi, Puspamitra
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Trukhan, Vladimir M.
    Chatterji, Tapan
    Marenkin, Sergey F.
    Shoukavaya, Tatyana V.
    Pressure control of magnetic clusters in strongly inhomogeneous ferromagnetic chalcopyrites2015Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 5, s. 7720-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Room-temperature ferromagnetism in Mn-doped chalcopyrites is a desire aspect when applying those materials to spin electronics. However, dominance of high Curie-temperatures due to cluster formation or inhomogeneities limited their consideration. Here we report how an external perturbation such as applied hydrostatic pressure in CdGeP2:Mn induces a two serial magnetic transitions from ferromagnet to non-magnet state at room temperature. This effect is related to the unconventional properties of created MnP magnetic clusters within the host material. Such behavior is also discussed in connection with ab initio density functional calculations, where the structural properties of MnP indicate magnetic transitions as function of pressure as observed experimentally. Our results point out new ways to obtain controlled response of embedded magnetic clusters.

  • 3.
    Belonoshko, Anatoly B.
    et al.
    Condensed Matter Theory, Department of Theoretical Physics, AlbaNova University Center, KTH Royal Institute of Technology, SE- 106 91 Stockholm, Sweden.
    Ramzan, Muhammad
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Mao, Ho-kwang
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori. Applied Materials Physics, Department of Materials and Engineering, Royal Institute of Technology (KTH), SE-100 44 Stockholm, Sweden.
    Atomic Diffusion in Solid Molecular Hydrogen2013Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 3, s. 2340-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We performed ab initio molecular dynamics simulations of the C2c and Cmca-12 phases of hydrogen at pressures from 210 to 350 GPa. These phases were predicted to be stable at 0 K and pressures above 200 GPa. However, systematic studies of temperature impact on properties of these phases have not been performed so far. Filling this gap, we observed that on temperature increase diffusion sets in the Cmca-12 phase, being absent in C2c. We explored the mechanism of diffusion and computed melting curve of hydrogen at extreme pressures. The results suggest that the recent experiments claiming conductive hydrogen at the pressure around 260 GPa and ambient temperature might be explained by the diffusion. The diffusion might also be the reason for the difference in Raman spectra obtained in recent experiments.

  • 4.
    Hussain, Tanveer
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Pathak, Biswarup
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Maark, Tuhina Adit
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ramzan, Muhammad
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Functionalization of graphane with alkali and alkaline-earth metals: An insulator-to-metallic transition2012Ingår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 99, nr 4, s. 47004-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In view of interest in functionalized carbon nanostructures due to their potential applications in nanotechnology and nanoelectronics, we have performed a systematic and thorough density functional theory (DFT) study on the interaction of the elements in the first two groups of the periodic table with graphane (hydrogenated graphene) sheet. GGA approximation as employed in DFT has been used to study in detail the binding configuration, bond length, charge transfer and band gap of each of these adatoms doped graphane (CH) systems. To have a better understanding of the adatoms-CH interaction, different doping concentrations varying from 3.125% to 50% have been considered. A certain trend in binding strength, bond length and charge transfer has been found in the case of both alkali metal and alkaline-earth metal adatoms. In the case of alkali-metal adatoms at the low doping concentration of 3.125%, semiconductor behavior was found, whereas at doping higher than this the compound showed metallic behavior. In contrast, alkaline-earth metal-doped CH exhibited metallic behavior at all the doping concentrations. Copyright (C) EPLA, 2012

  • 5.
    Hussain, Tanveer
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Pathak, Biswarup
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ramzan, Muhammad
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Maark, Tuhina Adit
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Calcium doped graphane as a hydrogen storage material2012Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 100, nr 18, s. 183902-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    On the basis of first principle density functional theory, we have studied the stability, electronic structure, and hydrogen storage capacity of a monolayer calcium doped graphane (CHCa). The stability of CHCa was further investigated using the ab initio molecular dynamics study. The binding energy of Ca on graphane sheet was found to be higher than its bulk cohesive energy, which indicates the stability of CHCa. It was observed that with a doping concentration of 11.11% of Ca on graphane sheet, a reasonably good H-2 storage capacity of 6 wt. % could be attained. The adsorption energies of H-2 were found to be 0.1 eV, within the range of practical H-2 storage applications.

  • 6.
    Kaewmaraya, Thanayut
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ramzan, Muhammad
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Guill´en, J. M. Osorio
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori. Applied Materials Physics, Department of Materials and Engineering, Royal Institute of Technology (KTH), SE-100 44 Stockholm, Sweden.
    The electronic structure and the metal-insulator transition of Mg2Mo6S8Manuskript (preprint) (Övrigt vetenskapligt)
  • 7.
    Kaewmaraya, Thanayut
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ramzan, Muhammad
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Löfås, Henrik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Hybrid density functional study of electronic and optical properties of phase change memory material: Ge2Sb2Te52013Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 113, nr 3, s. 033510-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this article, we use hybrid density functional (HSE06) to study the crystal and electronic structures and optical properties of well known phase change memory material Ge2Sb2Te5. We calculate the structural parameters, band gaps, and dielectric functions of three stable structures of this material. We also analyze the electron charge distribution using the Bader's theory of charge analysis. We find that hybrid density functional slightly overestimates the value of "c" parameter. However, overall, our results calculated with the use of hybrid density functional (HSE06) are very close to available experimental values than calculated with the use of Perdew Burke-Ernzerhof functional. Specifically, the electronic band gap values of this material calculated with HSE06 are in good agreement with the available experimental data in the literature. Furthermore, we perform the charge analysis and find that naive ionic model fails to explain the charge distribution between the constituent atoms, showing the complex nature of this compound.

  • 8.
    Kaewmaraya, Thanayut
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ramzan, Muhammad
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Osorio-Guillen, J. M.
    Ahuja, R.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Electronic structure and ionic diffusion of green battery cathode material: Mg2Mo6S82014Ingår i: Solid State Ionics, ISSN 0167-2738, E-ISSN 1872-7689, Vol. 261, s. 17-20Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report ab-initio density functional theory calculations of crystal and electronic structure of Mg2Mo6S8, a candidate material to be used in rechargeable magnesium batteries, by employing hybrid exchange-correlation functionals. We find that Mg2Mo6S8 crystalizes in a triclinic geometry and it is a semiconductor with an indirect band gap. Ab-initio molecular dynamics shows that Mg ions present progressive diffusion starting at 200 K with a preferable path through the channel between Mo6S8 blocks along the [010] direction. The intercalation voltage of the system is also determined and the results show that the voltage evaluated by PBE and hybrid functionals likely implies the lower and the upper limit of the experimental value. Lastly, we confirm the dynamical stability of the crystal structure by the calculated phonon dispersion relation. 

  • 9.
    Kaewmaraya, Thanayut
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ramzan, Muhammad
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Sun, W.
    Sagynbaeva, Myskal
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori. Applied Materials Physics, Department of Materials and Engineering, Royal Institute of Technology (KTH), SE-100 44 Stockholm, Sweden.
    Atomistic study of promising catalyst and electrode material for memory capacitors: Platinum Oxides2013Ingår i: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 79, s. 804-810Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Platinum oxides have the technological importance as evidenced by numerous studies concentrating on their crystal structures to attain the clear atomistic understanding but the controversy exists between the experimental and theoretical studies. In our present study, we report the electronic and optical properties of crystalline PtO and PtO2 on the basis of Heyd-Scuseria-Ernzerhof (HSE06) functional within the framework of the density functional theory (DFT). We present the structural parameters, electronic and optical properties of several proposed structures of PtO and PtO2. We find that PtS-type structure of PtO and CaCl2-type structure of PtO2 are the most stable structures of these materials on the basis of hybrid functional and they appear to be semiconductors with band gap values of 0.87 eV and 1.85 eV, respectively. The mechanical stability of these structures is also confirmed by calculating the phonon band structures. The corresponding structural parameters are found in good agreement with experimental values. Furthermore, we present the bader charge analysis and optical properties of these phases. 

  • 10. Lebegue, Sebastien
    et al.
    Araujo, Carlos Moyses
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Kim, Duck Young
    Ramzan, Muhammad
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Mao, Ho-kwang
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Semimetallic dense hydrogen above 260 GPa2012Ingår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 109, nr 25, s. 9766-9769Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Being the lightest and the most abundant element in the universe, hydrogen is fascinating to physicists. In particular, the conditions of its metallization associated with a possible superconducting state at high temperature have been a matter of much debate in the scientific community, and progress in this field is strongly correlated with the advancements in theoretical methods and experimental techniques. Recently, the existence of hydrogen in a metallic state was reported experimentally at room temperature under a pressure of 260-270 GPa, but was shortly after that disputed in the light of more experiments, finding either a semimetal or a transition to an other phase. With the aim to reconcile the different interpretations proposed, we propose by combining several computational techniques, such as density functional theory and the GW approximation, that phase III at ambient temperature of hydrogen is the Cmca-12 phase, which becomes a semimetal at 260 GPa. From phonon calculations, we demonstrate it to be dynamically stable; calculated electron-phonon coupling is rather weak and therefore this phase is not expected to be a high-temperature superconductor.

  • 11.
    Lebègue, Sébastien
    et al.
    Nancy University France.
    Araujo, Carlos Moyses
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Kim, Duck Young
    Ramzan, Muhammad
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Mao, Ho-kwang
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori. Applied Materials Physics, Department of Materials and Engineering, Royal Institute of Technology (KTH), SE-100 44 Stockholm, Sweden.
    Semimetallic dense hydrogen above 260 GPa2012Ingår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 109, nr 25, s. 9766-9769Artikel i tidskrift (Refereegranskat)
  • 12. Lizarraga, Raquel
    et al.
    Ramzan, Muhammad
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Araujo, Carlos Moyses
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Blomqvist, Andreas
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori. Applied Materials Physics, Department of Materials and Engineering, Royal Institute of Technology (KTH), SE-100 44 Stockholm, Sweden.
    Holmstrom, Erik
    Structural characterization of amorphous YCrO3from first principles2012Ingår i: EPL, Vol. 99, s. 57010-Artikel i tidskrift (Refereegranskat)
  • 13. Lizarraga, Raquel
    et al.
    Ramzan, Muhammad
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Araujo, Carlos Moyses
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Blomqvist, Andreas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Holmström, Erik
    Structural characterization of amorphous YCrO3 from first principles2012Ingår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 99, nr 5, s. 57010-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We perform a theoretical prediction of the structure of amorphous YCrO3. We obtained equivalent amorphous structures by means of two independent first principles density functional theory based methods: molecular dynamics and stochastic quenching. In our structural analysis we include radial and angle distribution functions as well as calculations of bond lengths and average coordination numbers. We find Cr+3 atoms situated in slightly distorted oxygen octahedra throughout the amorphous structures and that the distribution of these octahedra is disordered. The presence of the same Cr+3 local environments that give rise to ferroelectricity in the orthorhombic perovskite structure suggests that the amorphous phase of YCrO3 may also exhibit ferroelectric properties. Copyright (c) EPLA, 2012

  • 14. Lykissa, Iliana
    et al.
    Li, Shuyi
    Ramzan, Muhammad
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori. Applied Materials Physics, Department of Materials and Engineering, Royal Institute of Technology (KTH), SE-100 44 Stockholm, Sweden.
    Granqvist, Claes-Goran
    Niklasson, Gunnar A.
    Electronic density of states of amorphous vanadium pentoxide films: Electrochemical measurements and density functional theory calculationsManuskript (preprint) (Övrigt vetenskapligt)
  • 15.
    Lykissa, Iliana
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Li, Shu-Yi
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Ramzan, Muhammad
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Chakraborty, Sudip
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Granqvist, Claes Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Electronic density-of-states of amorphous vanadium pentoxide films: Electrochemical data and density functional theory calculations2014Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 115, nr 18, s. 183701/1-/5Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Thin films of V2O5 were prepared by sputter deposition onto transparent and electrically conducting substrates and were found to be X-ray amorphous. Their electrochemical density of states was determined by chronopotentiometry and displayed a pronounced low-energy peak followed by an almost featureless contribution at higher energies. These results were compared with density functional theory calculations for amorphous V2O5. Significant similarities were found between measured data and computations; specifically, the experimental low-energy peak corresponds to a split-off part of the conduction band apparent in the computations. Furthermore, the calculations approximately reproduce the experimental band gap observed in optical measurements.

  • 16. Mollaev, A. Yu.
    et al.
    Kamilov, I. K.
    Arslanov, R. K.
    Kilanski, L.
    Lόpez-Moreno, S.
    Ramzan, Muhammad
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Panigrahi, P.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori. Applied Materials Physics, Department of Materials and Engineering, Royal Institute of Technology (KTH), SE-100 44 Stockholm, Sweden.
    Troyanchuk, I. O.
    Trukhan, V. M.
    Novotortsev, V. M.
    Marenkin, S. F.
    Arslanov, T. R.
    Pressure-Induced and Mn Content Driven Phase Transitions in Ternary ChalcopyriteManuskript (preprint) (Övrigt vetenskapligt)
  • 17. Nellis, W. J.
    et al.
    Ozaki, N.
    Mashimo, T.
    Ramzan, Muhammad
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Kaewmaraya, Thanayut
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori. Applied Materials Physics, Department of Materials and Engineering, Royal Institute of Technology (KTH), SE-100 44 Stockholm, Sweden.
    Optical reflectivities of Gd3Ga5O12 at ~TPa (10 Mbar) shock pressuresManuskript (preprint) (Övrigt vetenskapligt)
  • 18.
    Ramzan, Muhammad
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Structural, Electronic and Mechanical Properties of Advanced Functional Materials2013Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The search for alternate and renewable energy resources as well as the efficient use of energy and development of such systems that can help to save the energy consumption is needed because of exponential growth in world population, limited conventional fossil fuel resources, and to meet the increasing demand of clean and environment friendly substitutes. Hydrogen being the simplest, most abundant and clean energy carrier has the potential to fulfill some of these requirements provided the development of efficient, safe and durable systems for its production, storage and usage.

    Chemical hydrides, complex hydrides and nanomaterials, where the hydrogen is either chemically bonded to the metal ions or physiosorbed, are the possible means to overcome the difficulties associated with the storage and usage of hydrogen at favorable conditions. We have studied the structural and electronic properties of some of the chemical hydrides, complex hydrides and functionalized nanostructures to understand the kinetics and thermodynamics of these materials.

    Another active field relating to energy storage is rechargeable batteries. We have studied the detailed crystal and electronic structures of Li and Mg based cathode materials and calculated the average intercalation voltage of the corresponding batteries. We found that transition metal doped MgH2 nanocluster is a material to use efficiently not only in batteries but also in fuel-cell technologies.

    MAX phases can be used to develop the systems to save the energy consumption. We have chosen one compound from each of all known types of MAX phases and analyzed the structural, electronic, and mechanical properties using the hybrid functional. We suggest that the proper treatment of correlation effects is important for the correct description of Cr2AlC and Cr2GeC by the good choice of Hubbard 'U' in DFT+U method.

    Hydrogen is fascinating to physicists due to predicted possibility of metallization and high temperature superconductivity. On the basis of our ab initio molecular dynamics studies, we propose that the recent claim of conductive hydrogen by experiments might be explained by the diffusion of hydrogen at relevant pressure and temperature.

    In this thesis we also present the studies of phase change memory materials, oxides and amorphization of oxide materials, spintronics and sulfide materials.

    Delarbeten
    1. Structural and energetic analysis of the hydrogen storage materials LiNH2BH3 and NaNH2BH3 from ab initio calculations
    Öppna denna publikation i ny flik eller fönster >>Structural and energetic analysis of the hydrogen storage materials LiNH2BH3 and NaNH2BH3 from ab initio calculations
    Visa övriga...
    2009 (Engelska)Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, nr 13, s. 132102-Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    Ammonia borane (NH3BH3) possesses many appealing properties as a hydrogen storage material; however, the release of trace amounts of borazine during the desorption process is troublesome. Recently, it was found that substitution of one of the H atoms in the NH3 group by Li or Na could significantly improve the hydrogen desorption properties. The resulting lithium amidoborane (LiNH2BH3) and sodium amidoborane (NaNH2BH3) compounds have been studied by us using density-functional theory. Specifically, we have succeeded in determining the detailed crystal structures of LiNH2BH3 and NaNH2BH3, including the atomic positions in their respective unit cells. Calculated hydrogen removal energies of the hydrogen release reactions are found to be in good agreement with the experimental trend.

    Nyckelord
    ab initio calculations, ammonium compounds, boron compounds, crystal structure, density functional theory, desorption, hydrogen storage, lithium compounds, reaction kinetics theory, surface chemistry
    Nationell ämneskategori
    Fysik
    Identifikatorer
    urn:nbn:se:uu:diva-129060 (URN)10.1103/PhysRevB.79.132102 (DOI)000265942800002 ()
    Tillgänglig från: 2010-08-06 Skapad: 2010-08-05 Senast uppdaterad: 2017-12-12
    2. High pressure phase determination and electronic properties of lithiumamidoborane
    Öppna denna publikation i ny flik eller fönster >>High pressure phase determination and electronic properties of lithiumamidoborane
    2012 (Engelska)Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 101, nr 11, s. 111902-Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    In this study we report on the high pressure phase of the promising hydrogen storage material lithiumamidoborane (LiNH2BH3), on the basis of density functional theory calculations with generalized gradient approximation. We take the five possible candidate structures, Pbca, Pbcn, Pcca, Pnma, and Pnnm for the high pressure study of LiNH2BH3. The corresponding structures are relaxed with respect to fractional atomic coordinates and cell parameters, with the use of fully self-consistent ab initio electronic structure calculations to get the equilibrium parameters and total enemies. Then we compare the energies of these phases and find that Pbcn is the most favorable phase at approximate to 100 GPa. Then we calculate the structural parameters of this phase. Finally, we calculate the density of states, Bader charge analysis, and corresponding electron density of this phase.

    Nationell ämneskategori
    Naturvetenskap
    Identifikatorer
    urn:nbn:se:uu:diva-187104 (URN)10.1063/1.4752237 (DOI)000309329300023 ()
    Tillgänglig från: 2012-12-04 Skapad: 2012-12-03 Senast uppdaterad: 2017-12-07Bibliografiskt granskad
    3. High pressure and temperature study of hydrogen storage material BH3NH3 from ab initio calculations
    Öppna denna publikation i ny flik eller fönster >>High pressure and temperature study of hydrogen storage material BH3NH3 from ab initio calculations
    2010 (Engelska)Ingår i: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 71, nr 8, s. 1137-1139Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    We report on BH3NH3, which is material considered promising to use as hydrogen storage, using density functional theory with generalized gradient approximation (GGA). We study the phase transition of BH3NH3 at high pressure and temperature. Our observed phase transition of BH3NH3 from body-centered tetragonal to orthorhombic at 220 K supports the recent and earlier studies. We observe the phase transformation of BH3NH3 at approximate to 11.5 GPa, which is in good agreement with experimental value. Specifically, we predict the phase transition at 11.5 GPa to be orthorhombic to body-centered tetragonal on the basis of our first principles calculations.

    Nyckelord
    Phase transition, High pressure
    Nationell ämneskategori
    Fysik
    Identifikatorer
    urn:nbn:se:uu:diva-136514 (URN)10.1016/j.jpcs.2010.03.021 (DOI)000280977000022 ()
    Tillgänglig från: 2010-12-13 Skapad: 2010-12-13 Senast uppdaterad: 2017-12-11Bibliografiskt granskad
    4. Electronic Structure from First-Principles of LiBH4. NH3, Sr(NH2BH3)2, and Li2Al(BH4)5 . 6NH3 for Hydrogen Storage Applications
    Öppna denna publikation i ny flik eller fönster >>Electronic Structure from First-Principles of LiBH4. NH3, Sr(NH2BH3)2, and Li2Al(BH4)5 . 6NH3 for Hydrogen Storage Applications
    2011 (Engelska)Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, nr 40, s. 20032-20042Artikel i tidskrift (Refereegranskat) Published
    Nationell ämneskategori
    Den kondenserade materiens fysik
    Identifikatorer
    urn:nbn:se:uu:diva-204930 (URN)10.1021/jp206142f (DOI)
    Tillgänglig från: 2013-08-13 Skapad: 2013-08-13 Senast uppdaterad: 2017-12-06
    5. Hybrid density functional and molecular dynamics study of promising hydrogen storage materials: Double metal amidoboranes and metal amidoborane ammoniates
    Öppna denna publikation i ny flik eller fönster >>Hybrid density functional and molecular dynamics study of promising hydrogen storage materials: Double metal amidoboranes and metal amidoborane ammoniates
    2012 (Engelska)Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, nr 33, s. 17351-17359Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    In this paper, the recently synthesized materials, Na2Mg-(NH 2BH 3) 4, NaLi(NH 2BH 3) 2, Mg(NH 2BH 3) 2·NH 3, and Ca-(NH 2BH 3) 2·2NH 3, are studied, which were found suitable for hydrogen storage applications. The hybrid density exchange-correlation functional is employed to explore the structural and electronic properties of these materials using the first-principles method on the basis of density functional theory calculations. From the detailed study of electronic structures, it is found that the mixed cation amidoboranes and [NH 3] molecules play an important role in the dehydrogenation process. Bader charge analysis is performed to show the charge distribution between the constituent atoms. The corresponding electron densities and related properties of these compounds are also calculated. Furthermore, ab initio molecular dynamics simulations are performed to study the diffusion of hydrogen in these compounds, which consist of boron, nitrogen, and hydrogen atoms. The common features of these compounds are also revealed by explaining the electronic properties. Finally, it is shown that the mobility of hydrogen in Na 2Mg(NH 2BH 3) 4 and NaLi(NH 2BH 3) 2 is slightly higher than that in Mg(NH 2BH 3) 2·NH 3 and Ca(NH 2BH 3) 2·2NH 3 at the same temperatures.

    Nationell ämneskategori
    Naturvetenskap
    Identifikatorer
    urn:nbn:se:uu:diva-186758 (URN)10.1021/jp304261f (DOI)000307748700006 ()
    Tillgänglig från: 2012-11-29 Skapad: 2012-11-29 Senast uppdaterad: 2017-12-07Bibliografiskt granskad
    6. Ab initio molecular dynamics study of the hydrogen-deuterium exchange in bulk lithiumborohydride (LiBH4)
    Öppna denna publikation i ny flik eller fönster >>Ab initio molecular dynamics study of the hydrogen-deuterium exchange in bulk lithiumborohydride (LiBH4)
    2009 (Engelska)Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 94, nr 14, s. 141903-Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    The hydrogen storage is still a challenge for mobile applications. The diffusion of hydrogen in solids is considered as a general model system but there is limited knowledge available for the dynamics of hydrogen in complex hydrides. In this letter, we present a systematic approach to study the hydrogen-deuterium exchange in bulk LiBH4 based on ab initio molecular dynamics. Our results predict the single hydrogen (deuterium) exchange in LiBH4, which supports the experimental results. The self-diffusion constant < D > of deuterium in LiBH4 is around 1.42x10(-8) m(2) s(-1).

    Nyckelord
    ab initio calculations, boron compounds, diffusion, hydrogen storage, isotope exchanges, lithium compounds, molecular dynamics method
    Nationell ämneskategori
    Fysik
    Identifikatorer
    urn:nbn:se:uu:diva-129123 (URN)10.1063/1.3115032 (DOI)000265083700016 ()
    Tillgänglig från: 2010-08-09 Skapad: 2010-08-05 Senast uppdaterad: 2017-12-12
    7. Ab initio molecular dynamics study of the hydrogen diffusion in sodium and lithium hydrides
    Öppna denna publikation i ny flik eller fönster >>Ab initio molecular dynamics study of the hydrogen diffusion in sodium and lithium hydrides
    2009 (Engelska)Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 106, nr 016104Artikel i tidskrift (Refereegranskat) Published
    Nationell ämneskategori
    Naturvetenskap
    Forskningsämne
    Fysik med inriktning mot atom- molekyl- och kondenserande materiens fysik
    Identifikatorer
    urn:nbn:se:uu:diva-205241 (URN)10.1063/1.3159896 (DOI)
    Tillgänglig från: 2013-08-14 Skapad: 2013-08-14 Senast uppdaterad: 2017-12-06
    8. Hydrogen diffusion in bulk and nanoclusters of MgH2 and the role of catalysts on the basis of ab initio molecular dynamics
    Öppna denna publikation i ny flik eller fönster >>Hydrogen diffusion in bulk and nanoclusters of MgH2 and the role of catalysts on the basis of ab initio molecular dynamics
    2009 (Engelska)Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 94, nr 22, s. 221910-Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    We present ab initio molecular dynamics calculations based on density functional theory to study the hydrogen-deuterium exchange in bulk and nanoclusters of MgH2. Our calculations reveal the important role of catalysts to diffuse the hydrogen at low temperatures and increase the diffusion rate. We determine the diffusion constants, < D > of deuterium, and show the single hydrogen-deuterium exchange in bulk and nanocluster of MgH2. Our calculated value of diffusion constant of deuterium in bulk MgH2 is in excellent agreement with the experimental value. Furthermore, we show the edge site importance of catalysts in the fast diffusion of hydrogen.

    Nyckelord
    ab initio calculations, catalysis, catalysts, chemical exchanges, density functional theory, diffusion, hydrogen storage, magnesium compounds, molecular dynamics method, nanostructured materials
    Nationell ämneskategori
    Fysik
    Identifikatorer
    urn:nbn:se:uu:diva-129006 (URN)10.1063/1.3152250 (DOI)000266674300023 ()
    Tillgänglig från: 2010-08-05 Skapad: 2010-08-05 Senast uppdaterad: 2017-12-12
    9. Transition metal doped MgH2: a material to potentially combine fuel-cell and battery technologies
    Öppna denna publikation i ny flik eller fönster >>Transition metal doped MgH2: a material to potentially combine fuel-cell and battery technologies
    2010 (Engelska)Ingår i: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 35, nr 19, s. 10373-10376Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    MgH2 is studied as a negative electrode material for rechargeable batteries on the basis of density functional theory calculations. We calculate the average voltage of the corresponding Li-ion battery, which is in good agreement with the experimental value, and we predict the average voltage for the Na-ion battery. Then, molecular dynamics simulations are used to study the diffusive properties of lithium in MgH2 clusters. In particular, we dope MgH2 with transition metals (Fe, Ni, Ti, and V), and analyze the effect on the diffusion of lithium, which is shown to be essentially unaffected. Therefore, we propose that transition metal doped MgH2 is a material that can be used efficiently in both batteries and fuel-cell technologies.

    Nyckelord
    Metal hydrides, Negative electrodes, Hydrogen storage
    Nationell ämneskategori
    Fysik
    Identifikatorer
    urn:nbn:se:uu:diva-135351 (URN)10.1016/j.ijhydene.2010.07.024 (DOI)000283977100041 ()
    Tillgänglig från: 2010-12-07 Skapad: 2010-12-06 Senast uppdaterad: 2017-12-11Bibliografiskt granskad
    10. Calcium doped graphane as a hydrogen storage material
    Öppna denna publikation i ny flik eller fönster >>Calcium doped graphane as a hydrogen storage material
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    2012 (Engelska)Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 100, nr 18, s. 183902-Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    On the basis of first principle density functional theory, we have studied the stability, electronic structure, and hydrogen storage capacity of a monolayer calcium doped graphane (CHCa). The stability of CHCa was further investigated using the ab initio molecular dynamics study. The binding energy of Ca on graphane sheet was found to be higher than its bulk cohesive energy, which indicates the stability of CHCa. It was observed that with a doping concentration of 11.11% of Ca on graphane sheet, a reasonably good H-2 storage capacity of 6 wt. % could be attained. The adsorption energies of H-2 were found to be 0.1 eV, within the range of practical H-2 storage applications.

    Nationell ämneskategori
    Fysik
    Identifikatorer
    urn:nbn:se:uu:diva-174925 (URN)10.1063/1.4710526 (DOI)000303598600068 ()
    Tillgänglig från: 2012-05-30 Skapad: 2012-05-30 Senast uppdaterad: 2017-12-07Bibliografiskt granskad
    11. Functionalization of graphane with alkali and alkaline-earth metals: An insulator-to-metallic transition
    Öppna denna publikation i ny flik eller fönster >>Functionalization of graphane with alkali and alkaline-earth metals: An insulator-to-metallic transition
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    2012 (Engelska)Ingår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 99, nr 4, s. 47004-Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    In view of interest in functionalized carbon nanostructures due to their potential applications in nanotechnology and nanoelectronics, we have performed a systematic and thorough density functional theory (DFT) study on the interaction of the elements in the first two groups of the periodic table with graphane (hydrogenated graphene) sheet. GGA approximation as employed in DFT has been used to study in detail the binding configuration, bond length, charge transfer and band gap of each of these adatoms doped graphane (CH) systems. To have a better understanding of the adatoms-CH interaction, different doping concentrations varying from 3.125% to 50% have been considered. A certain trend in binding strength, bond length and charge transfer has been found in the case of both alkali metal and alkaline-earth metal adatoms. In the case of alkali-metal adatoms at the low doping concentration of 3.125%, semiconductor behavior was found, whereas at doping higher than this the compound showed metallic behavior. In contrast, alkaline-earth metal-doped CH exhibited metallic behavior at all the doping concentrations. Copyright (C) EPLA, 2012

    Nationell ämneskategori
    Naturvetenskap
    Identifikatorer
    urn:nbn:se:uu:diva-183905 (URN)10.1209/0295-5075/99/47004 (DOI)000308376100023 ()
    Tillgänglig från: 2012-11-07 Skapad: 2012-11-05 Senast uppdaterad: 2017-12-07Bibliografiskt granskad
    12. Electronic structure and metalization of a silane-hydrogen system under high pressure investigated using density functional and GW calculations
    Öppna denna publikation i ny flik eller fönster >>Electronic structure and metalization of a silane-hydrogen system under high pressure investigated using density functional and GW calculations
    2010 (Engelska)Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, nr 23, s. 233103-Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    We have computed the electronic structure and the vibrational properties of the recently discovered hydrogen-rich compound silane-hydrogen [SiH4(H-2)(2)] from first principles, using density-functional theory. We have also studied the metallization under pressure of SiH4(H-2)(2) by the GW approximation, and obtained that the metallization occurs around 164 GPa, whereas the standard GGA calculations predict a metallization pressure around 145 GPa. Our results are compared with the recent experiment data of Strobel et al. [Phys. Rev. Lett. 103, 065701 (2009)] and Wang et al. [Proc. Natl. Acad. Sci. USA. 106, 14763 (2009)] and it is found that our calculated value of the metallization pressure is higher than the proposed experimental data. Some possible reasons for such a discrepancy are discussed in the text.

    Nationell ämneskategori
    Fysik
    Identifikatorer
    urn:nbn:se:uu:diva-136130 (URN)10.1103/PhysRevB.81.233103 (DOI)000279144200001 ()
    Tillgänglig från: 2010-12-10 Skapad: 2010-12-10 Senast uppdaterad: 2017-12-11Bibliografiskt granskad
    13. Semimetallic dense hydrogen above 260 GPa
    Öppna denna publikation i ny flik eller fönster >>Semimetallic dense hydrogen above 260 GPa
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    2012 (Engelska)Ingår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 109, nr 25, s. 9766-9769Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    Being the lightest and the most abundant element in the universe, hydrogen is fascinating to physicists. In particular, the conditions of its metallization associated with a possible superconducting state at high temperature have been a matter of much debate in the scientific community, and progress in this field is strongly correlated with the advancements in theoretical methods and experimental techniques. Recently, the existence of hydrogen in a metallic state was reported experimentally at room temperature under a pressure of 260-270 GPa, but was shortly after that disputed in the light of more experiments, finding either a semimetal or a transition to an other phase. With the aim to reconcile the different interpretations proposed, we propose by combining several computational techniques, such as density functional theory and the GW approximation, that phase III at ambient temperature of hydrogen is the Cmca-12 phase, which becomes a semimetal at 260 GPa. From phonon calculations, we demonstrate it to be dynamically stable; calculated electron-phonon coupling is rather weak and therefore this phase is not expected to be a high-temperature superconductor.

    Nyckelord
    ab initio, solid hydrogen, high-pressure physics, phase transition
    Nationell ämneskategori
    Fysik
    Identifikatorer
    urn:nbn:se:uu:diva-177864 (URN)10.1073/pnas.1207065109 (DOI)000306061400029 ()
    Tillgänglig från: 2012-07-20 Skapad: 2012-07-19 Senast uppdaterad: 2017-12-07Bibliografiskt granskad
    14. Atomic Diffusion in Solid Molecular Hydrogen
    Öppna denna publikation i ny flik eller fönster >>Atomic Diffusion in Solid Molecular Hydrogen
    2013 (Engelska)Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 3, s. 2340-Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    We performed ab initio molecular dynamics simulations of the C2c and Cmca-12 phases of hydrogen at pressures from 210 to 350 GPa. These phases were predicted to be stable at 0 K and pressures above 200 GPa. However, systematic studies of temperature impact on properties of these phases have not been performed so far. Filling this gap, we observed that on temperature increase diffusion sets in the Cmca-12 phase, being absent in C2c. We explored the mechanism of diffusion and computed melting curve of hydrogen at extreme pressures. The results suggest that the recent experiments claiming conductive hydrogen at the pressure around 260 GPa and ambient temperature might be explained by the diffusion. The diffusion might also be the reason for the difference in Raman spectra obtained in recent experiments.

    Nationell ämneskategori
    Den kondenserade materiens fysik
    Identifikatorer
    urn:nbn:se:uu:diva-204936 (URN)10.1038/srep02340 (DOI)000322565300003 ()
    Tillgänglig från: 2013-08-13 Skapad: 2013-08-13 Senast uppdaterad: 2017-12-06Bibliografiskt granskad
    15. Ab initio study of lithium and sodium iron fluorophosphate cathodes for rechargeable batteries
    Öppna denna publikation i ny flik eller fönster >>Ab initio study of lithium and sodium iron fluorophosphate cathodes for rechargeable batteries
    2009 (Engelska)Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 94, nr 15, s. 151904-Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    The cathode materials Li2FePO4F and Na2FePO4F are studied by means of ab initio calculations. The generalized gradient approximation (GGA) and GGA+U are used to describe the crystal structures, and the electronic and magnetic properties of Li2FePO4F, Na2FePO4F, LiFePO4F, and NaFePO4F. Since only the lattice parameters are known for Li2FePO4F, our calculations predict the corresponding atomic positions, and reveal that the iron atom state (Fe-III or Fe-II) is changed during the reaction, which is of importance to understand the reactions taking place in rechargeable batteries. Finally, our calculated intercalation voltage with the GGA+U approximation is in good agreement with experimental value.

    Nyckelord
    ab initio calculations, cathodes, crystal structure, lattice constants, lithium compounds, secondary cells, sodium compounds
    Nationell ämneskategori
    Fysik
    Identifikatorer
    urn:nbn:se:uu:diva-129109 (URN)10.1063/1.3119704 (DOI)000265285200021 ()
    Tillgänglig från: 2010-08-06 Skapad: 2010-08-05 Senast uppdaterad: 2017-12-12Bibliografiskt granskad
    16. Ferromagnetism in the potential cathode material LiNaFePO4F
    Öppna denna publikation i ny flik eller fönster >>Ferromagnetism in the potential cathode material LiNaFePO4F
    2009 (Engelska)Ingår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 87, nr 1, s. 18001-Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    We present the ab initio study of the cathode material LiNaFePO4F, which is suitable for rechargeable batteries. Our calculations reveal the ferromagnetic order to be the ground state of this material. We also predict more than 5.0V intercalation voltage of this material for sodium-ion batteries. The low cost of sodium iron. fluorophasphate batteries and more than 5.0V intercalation voltage makes it the more suitable candidate, commercially and scientifically, than any other cathode materials for rechargeable batteries. Copyright (C) EPLA, 2009

    Nationell ämneskategori
    Fysik
    Identifikatorer
    urn:nbn:se:uu:diva-128289 (URN)10.1209/0295-5075/87/18001 (DOI)000269357900031 ()
    Tillgänglig från: 2010-07-21 Skapad: 2010-07-20 Senast uppdaterad: 2017-12-12
    17. Structural, magnetic, and energetic properties of Na2FePO4F, Li2FePO4F, NaFePO4F, and LiFePO4F from ab initio calculations
    Öppna denna publikation i ny flik eller fönster >>Structural, magnetic, and energetic properties of Na2FePO4F, Li2FePO4F, NaFePO4F, and LiFePO4F from ab initio calculations
    2009 (Engelska)Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 106, nr 4, s. 043510-Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    In this paper, we report on Na2FePO4F and Li2FePO4F, which are materials that are used as cathodes in batteries, using density functional theory with the LDA, LDA + U, GGA, or GGA + U approximations. Specifically, we study their crystal structure, electronic structure, and magnetic properties and provide similar information about the intermediate compounds LiFePO4F and NaFePO4F. Finally, the intercalation voltages of the corresponding batteries are calculated using various exchange-correlation approximations and conclusions are drawn about which one is the most suitable to use for the study of this class of materials.

    Ort, förlag, år, upplaga, sidor
    American Institute of Physics, 2009
    Nationell ämneskategori
    Fysik
    Forskningsämne
    Materialvetenskap
    Identifikatorer
    urn:nbn:se:uu:diva-108262 (URN)10.1063/1.3202384 (DOI)000270083800025 ()
    Tillgänglig från: 2009-09-10 Skapad: 2009-09-10 Senast uppdaterad: 2017-12-13Bibliografiskt granskad
    18. Crystal and electronic structures of lithium fluorosulphate based materials for lithium-ion batteries
    Öppna denna publikation i ny flik eller fönster >>Crystal and electronic structures of lithium fluorosulphate based materials for lithium-ion batteries
    2010 (Engelska)Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, nr 125101Artikel i tidskrift (Refereegranskat) Published
    Nationell ämneskategori
    Naturvetenskap
    Forskningsämne
    Fysik med inriktning mot atom- molekyl- och kondenserande materiens fysik
    Identifikatorer
    urn:nbn:se:uu:diva-205242 (URN)DOI: 10.1103/PhysRevB.82.125101 (DOI)
    Tillgänglig från: 2013-08-15 Skapad: 2013-08-15 Senast uppdaterad: 2017-12-06
    19. Hybrid Density Functional Calculations and Molecular Dynamics Study of Lithium Fluorosulphate, A Cathode Material for Lithium-Ion Batteries
    Öppna denna publikation i ny flik eller fönster >>Hybrid Density Functional Calculations and Molecular Dynamics Study of Lithium Fluorosulphate, A Cathode Material for Lithium-Ion Batteries
    2011 (Engelska)Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, s. 2600-2603Artikel i tidskrift (Refereegranskat) Published
    Nationell ämneskategori
    Den kondenserade materiens fysik
    Identifikatorer
    urn:nbn:se:uu:diva-204941 (URN)10.1021/jp110625a (DOI)
    Tillgänglig från: 2013-08-13 Skapad: 2013-08-13 Senast uppdaterad: 2017-12-06
    20. The electronic structure and the metal-insulator transition of Mg2Mo6S8
    Öppna denna publikation i ny flik eller fönster >>The electronic structure and the metal-insulator transition of Mg2Mo6S8
    (Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
    Nationell ämneskategori
    Den kondenserade materiens fysik
    Identifikatorer
    urn:nbn:se:uu:diva-204947 (URN)
    Tillgänglig från: 2013-08-13 Skapad: 2013-08-13 Senast uppdaterad: 2014-01-08
    21. Electronic structure of MgCuMo6S8
    Öppna denna publikation i ny flik eller fönster >>Electronic structure of MgCuMo6S8
    (Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
    Nationell ämneskategori
    Den kondenserade materiens fysik
    Identifikatorer
    urn:nbn:se:uu:diva-204948 (URN)
    Tillgänglig från: 2013-08-13 Skapad: 2013-08-13 Senast uppdaterad: 2014-01-08
    22. Hybrid exchange-correlation functional study of the structural, electronic, and mechanical properties of the MAX phases
    Öppna denna publikation i ny flik eller fönster >>Hybrid exchange-correlation functional study of the structural, electronic, and mechanical properties of the MAX phases
    2011 (Engelska)Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 98, nr 2, s. 021902-Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    In this letter, we report on our results obtained with the hybrid functional HSE06 on the structural, electronic, and mechanical properties of the MAX phases. As a sample, we choose Ti2AlN, Ti2AlC, V2AlC, Nb2AlC, Ta2AlC, V2GeC, Ti3SiC2, and Ti4AlN3, which cover all the known types of MAX phases. From our calculations, we have found that V2GeC has the magnetically ordered ground state. Our results are compared to available experimental data, and it is shown that the HSE06 functional can be used as a predictive tool to study the properties of this family of compounds.

    Nationell ämneskategori
    Fysik
    Identifikatorer
    urn:nbn:se:uu:diva-149784 (URN)10.1063/1.3536513 (DOI)000286470800021 ()
    Tillgänglig från: 2011-03-23 Skapad: 2011-03-23 Senast uppdaterad: 2017-12-11Bibliografiskt granskad
    23. M(N+1)AX(N)(M=Ti, A=Al, X=H) phase class materials with hydrogen: Ti4AlH3 and Ti3AlH2
    Öppna denna publikation i ny flik eller fönster >>M(N+1)AX(N)(M=Ti, A=Al, X=H) phase class materials with hydrogen: Ti4AlH3 and Ti3AlH2
    2010 (Engelska)Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 96, nr 26, s. 261906-Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    To date more than 50 MAX phases known to exist but all of those are consist of nitrides or carbides. We present a modified type of these phases, Ti4AlH3 and Ti3AlH2, having hydrides in their composition, by our density functional theory (DFT) calculations. We study the structural stability, electronic structure, elastic, thermal, and mechanical properties of these materials which are comparable with well known phases: Ti3SiC2, Ti4AlN3, and Ti3AlC2. Moreover, these materials can also be studied for hydrogen storage purposes. We hope that our work will be helpful to discover the other types of such phases which are important from the technological and industrial point of view.

    Nyckelord
    crystal structure, density functional theory, elastic moduli, electronic structure, hydrogen storage, mechanical properties, thermal properties
    Nationell ämneskategori
    Fysik
    Identifikatorer
    urn:nbn:se:uu:diva-135413 (URN)10.1063/1.3459960 (DOI)000279514400018 ()
    Tillgänglig från: 2010-12-07 Skapad: 2010-12-06 Senast uppdaterad: 2017-12-11
    24. Correlation effects in the electronic and structural properties of Cr2AlC
    Öppna denna publikation i ny flik eller fönster >>Correlation effects in the electronic and structural properties of Cr2AlC
    2011 (Engelska)Ingår i: Physica Status Solidi. Rapid Research Letters, ISSN 1862-6254, E-ISSN 1862-6270, Vol. 5, nr 3, s. 122-124Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    In this Letter, we present the electronic and structural properties calculated by first principles GGA and GGA+U calculations of Cr2AlC, a member of the MAX phases family of compounds. While GGA fails to obtain a correct description, the GGA+U method successfully reproduces the experimental equilibrium volume and bulk modulus values of Cr2AlC, and predict it to be a ferromagnet. Therefore, correlation effects are crucial for the correct description of Cr2AlC, provided that a suitable value of U is chosen.

    Nyckelord
    MAX phases, ab-initio calculations, GGA plus U, correlations
    Nationell ämneskategori
    Fysik
    Identifikatorer
    urn:nbn:se:uu:diva-157668 (URN)10.1002/pssr.201004508 (DOI)000288178800012 ()
    Tillgänglig från: 2011-08-22 Skapad: 2011-08-22 Senast uppdaterad: 2017-12-08
    25. Electronic and mechanical properties of Cr2GeC with hybrid functional and correlation effects
    Öppna denna publikation i ny flik eller fönster >>Electronic and mechanical properties of Cr2GeC with hybrid functional and correlation effects
    2012 (Engelska)Ingår i: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 152, nr 13, s. 1147-1149Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    We present a computational study of the MAX phase material Cr2GeC to obtain its crystal and electronic structure using density functional theory with various exchange-correlation functionals. While the GGA and GGA+U methods are giving a reasonable description of the lattice parameters, the hybrid functional (HSE06) is found to give too large values. Then, on the basis of our GGA+U calculations, the antiferromagnetic ordering is found to be the ground state. Furthermore, we study the charge distribution between the constituent elements of this compound and find that the simple ionic model fails to describe it due to the complex nature of this material. Finally, we conclude that the treatment of the correlated electrons is important for the correct description of this material. 

    Nyckelord
    MAX phases, Hybrid functional, Electronic structure, Mechanical properties
    Nationell ämneskategori
    Fysik
    Identifikatorer
    urn:nbn:se:uu:diva-177581 (URN)10.1016/j.ssc.2012.03.044 (DOI)000305313800015 ()
    Tillgänglig från: 2012-07-16 Skapad: 2012-07-16 Senast uppdaterad: 2017-12-07
    26. Anomalous temperature dependence of elastic constant c44 in V, Nb, Ta, Pd, and Pt
    Öppna denna publikation i ny flik eller fönster >>Anomalous temperature dependence of elastic constant c44 in V, Nb, Ta, Pd, and Pt
    Visa övriga...
    2010 (Engelska)Ingår i: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 71, nr 8, s. 1065-1068Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    The electrochemical reduction processes on stainless-steel substrates from an aqueous electrolyte composed of nitric acid, Bi3+, HTeO2+, SbO+ and H2SeO3 systems were investigated using cyclic voltammetry. The thin films with a stoichiometry of Bi2Te3, Bi0.5Sb1.5Te3 and Bi2Te2.7Se0.3 have been prepared by electrochemical deposition at selected potentials. The structure, composition, and morphology of the films were studied by X-ray diffraction (XRD), environmental scanning electron microscopy (ESEM) and electron microprobe analysis (EMPA). The results showed that the films were single phase with the rhombohedral Bi2Te3 structure. The morphology and growth orientation of the films were dependent on the deposition potentials.

    Nyckelord
    Chalcogenides; Crystal growth; Electron microscopy; Microstructure
    Nationell ämneskategori
    Annan teknik
    Identifikatorer
    urn:nbn:se:uu:diva-95715 (URN)10.1016/j.jpcs.2010.03.007 (DOI)000280977000008 ()
    Tillgänglig från: 2007-04-04 Skapad: 2007-04-04 Senast uppdaterad: 2017-12-14Bibliografiskt granskad
    27. Probing temperature-induced ordering in supersaturated Ti-1 (-) xAlxN coatings by electronic structure
    Öppna denna publikation i ny flik eller fönster >>Probing temperature-induced ordering in supersaturated Ti-1 (-) xAlxN coatings by electronic structure
    Visa övriga...
    2014 (Engelska)Ingår i: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 242, s. 207-213Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    The ordering of supersaturated cubic titanium aluminum nitride (c-Ti0.35Al0.65N) coatings is probed from room temperature up to and above the point of spinodal decomposition, using Near Edge X-ray Absorption Fine-structure (NEXAFS) and first principles calculations. The measured and calculated nitrogen (N) K spectra suggest that unoccupied N p states hybridize with Ti d states. When temperature is raised the N p-Ti d overlap decreases, whereas hybridization between N p and Al p tends to increase. The observed spectral changes with temperature together with calculations of defect heat of formation suggest a depletion of N in the surroundings of Ti in c-Ai(1) (-) xAlxN and/or in the formed c-TiN.

    Nationell ämneskategori
    Den kondenserade materiens fysik
    Identifikatorer
    urn:nbn:se:uu:diva-204951 (URN)10.1016/j.surfcoat.2013.10.054 (DOI)000333782400030 ()
    Tillgänglig från: 2013-08-13 Skapad: 2013-08-13 Senast uppdaterad: 2017-12-06Bibliografiskt granskad
    28. Structural characterization of amorphous YCrO3from first principles
    Öppna denna publikation i ny flik eller fönster >>Structural characterization of amorphous YCrO3from first principles
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    2012 (Engelska)Ingår i: EPL, Vol. 99, s. 57010-Artikel i tidskrift (Refereegranskat) Published
    Nationell ämneskategori
    Den kondenserade materiens fysik
    Identifikatorer
    urn:nbn:se:uu:diva-204953 (URN)10.1209/0295-5075/99/57010 (DOI)
    Tillgänglig från: 2013-08-13 Skapad: 2013-08-13 Senast uppdaterad: 2014-01-08
    29. Disorder-induced Room Temperature Ferromagnetism in Glassy Chromites
    Öppna denna publikation i ny flik eller fönster >>Disorder-induced Room Temperature Ferromagnetism in Glassy Chromites
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    2014 (Engelska)Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 4, s. 4686-Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    We report an unusual robust ferromagnetic order above room temperature upon amorphization of perovskite [YCrO3] in pulsed laser deposited thin films. This is contrary to the usual expected formation of a spin glass magnetic state in the resulting disordered structure. To understand the underlying physics of this phenomenon, we combine advanced spectroscopic techniques and first-principles calculations. We find that the observed order-disorder transformation is accompanied by an insulator-metal transition arising from a wide distribution of Cr-O-Cr bond angles and the consequent metallization through free carriers. Similar results also found in YbCrO3-films suggest that the observed phenomenon is more general and should, in principle, apply to a wider range of oxide systems. The ability to tailor ferromagnetic order above room temperature in oxide materials opens up many possibilities for novel technological applications of this counter intuitive effect.

    Nationell ämneskategori
    Den kondenserade materiens fysik
    Identifikatorer
    urn:nbn:se:uu:diva-204955 (URN)10.1038/srep04686 (DOI)000334286200001 ()
    Tillgänglig från: 2013-08-13 Skapad: 2013-08-13 Senast uppdaterad: 2017-12-06Bibliografiskt granskad
    30. Electronic density of states of amorphous vanadium pentoxide films: Electrochemical measurements and density functional theory calculations
    Öppna denna publikation i ny flik eller fönster >>Electronic density of states of amorphous vanadium pentoxide films: Electrochemical measurements and density functional theory calculations
    Visa övriga...
    (Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
    Nationell ämneskategori
    Den kondenserade materiens fysik
    Identifikatorer
    urn:nbn:se:uu:diva-204956 (URN)
    Tillgänglig från: 2013-08-13 Skapad: 2013-08-13 Senast uppdaterad: 2015-06-24
    31. Optical reflectivities of Gd3Ga5O12 at ~TPa (10 Mbar) shock pressures
    Öppna denna publikation i ny flik eller fönster >>Optical reflectivities of Gd3Ga5O12 at ~TPa (10 Mbar) shock pressures
    Visa övriga...
    (Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
    Nationell ämneskategori
    Den kondenserade materiens fysik
    Identifikatorer
    urn:nbn:se:uu:diva-204958 (URN)
    Tillgänglig från: 2013-08-13 Skapad: 2013-08-13 Senast uppdaterad: 2014-01-08
    32. Electronic, mechanical and optical properties of Y2O3 with hybrid density functional (HSE06)
    Öppna denna publikation i ny flik eller fönster >>Electronic, mechanical and optical properties of Y2O3 with hybrid density functional (HSE06)
    2013 (Engelska)Ingår i: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 71, s. 19-24Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    In this paper, we have investigated the electronic, optical and mechanical properties of the Y2O3 crystal by first-principle calculations based on the density-functional theory. The generalized gradient approximation (GGA-PBE) and hybrid exchange-correlation functional (HSE06) are both used for comparative study. It is found that, the band gap of Y2O3 calculated by HSE06 method (6.0 eV) is in good agreement with the experimental band gap data (5.5 eV), and HSE06 gives better electronic structure description close to experiments. Then we calculate the elastic constants, and derive the corresponding properties i.e.; bulk, shear and Young's moduli, and Poisson's ratio. Our calculated elastic and mechanical properties correspond well with experimental data. Besides, we also obtain the equilibrium lattice and bulk modulus of yttria by fitting the Birch-Murnaghan equation of state. It is found that, the HSE06 well reproduce the experimental lattice parameters, equilibrium volume and bulk modulus of Y2O3. Based on the accurate described crystal and electronic structure and mechanical properties by HSE06 method, the optical properties of this material are also analyzed.

    Nyckelord
    Hybrid density functional, Electronic structure, Mechanical properties, Optical properties
    Nationell ämneskategori
    Naturvetenskap
    Identifikatorer
    urn:nbn:se:uu:diva-198896 (URN)10.1016/j.commatsci.2012.12.026 (DOI)000316661300003 ()
    Tillgänglig från: 2013-05-02 Skapad: 2013-04-29 Senast uppdaterad: 2017-12-06Bibliografiskt granskad
    33. Electronic structure, mechanical and optical properties of In2O3 with hybrid density functional (HSE06)
    Öppna denna publikation i ny flik eller fönster >>Electronic structure, mechanical and optical properties of In2O3 with hybrid density functional (HSE06)
    (Engelska)Ingår i: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766Artikel i tidskrift (Refereegranskat) Submitted
    Nationell ämneskategori
    Den kondenserade materiens fysik
    Identifikatorer
    urn:nbn:se:uu:diva-204959 (URN)
    Tillgänglig från: 2013-08-13 Skapad: 2013-08-13 Senast uppdaterad: 2017-12-06Bibliografiskt granskad
    34. Surface states and ferromagnetism in crystalline YCrO3
    Öppna denna publikation i ny flik eller fönster >>Surface states and ferromagnetism in crystalline YCrO3
    (Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
    Nationell ämneskategori
    Den kondenserade materiens fysik
    Identifikatorer
    urn:nbn:se:uu:diva-204960 (URN)
    Tillgänglig från: 2013-08-13 Skapad: 2013-08-13 Senast uppdaterad: 2014-01-08
    35. High Pressure Phase Transition and Electronic, Mechanical Properties of Ferroelectric Material: PbTiO3
    Öppna denna publikation i ny flik eller fönster >>High Pressure Phase Transition and Electronic, Mechanical Properties of Ferroelectric Material: PbTiO3
    (Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
    Nationell ämneskategori
    Den kondenserade materiens fysik
    Identifikatorer
    urn:nbn:se:uu:diva-204961 (URN)
    Tillgänglig från: 2013-08-13 Skapad: 2013-08-13 Senast uppdaterad: 2014-01-08
    36. Atomistic study of promising catalyst and electrode material for memory capacitors: Platinum Oxides
    Öppna denna publikation i ny flik eller fönster >>Atomistic study of promising catalyst and electrode material for memory capacitors: Platinum Oxides
    Visa övriga...
    2013 (Engelska)Ingår i: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 79, s. 804-810Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    Platinum oxides have the technological importance as evidenced by numerous studies concentrating on their crystal structures to attain the clear atomistic understanding but the controversy exists between the experimental and theoretical studies. In our present study, we report the electronic and optical properties of crystalline PtO and PtO2 on the basis of Heyd-Scuseria-Ernzerhof (HSE06) functional within the framework of the density functional theory (DFT). We present the structural parameters, electronic and optical properties of several proposed structures of PtO and PtO2. We find that PtS-type structure of PtO and CaCl2-type structure of PtO2 are the most stable structures of these materials on the basis of hybrid functional and they appear to be semiconductors with band gap values of 0.87 eV and 1.85 eV, respectively. The mechanical stability of these structures is also confirmed by calculating the phonon band structures. The corresponding structural parameters are found in good agreement with experimental values. Furthermore, we present the bader charge analysis and optical properties of these phases. 

    Nationell ämneskategori
    Den kondenserade materiens fysik
    Identifikatorer
    urn:nbn:se:uu:diva-204962 (URN)10.1016/j.commatsci.2013.07.021 (DOI)000324471100102 ()
    Tillgänglig från: 2013-08-13 Skapad: 2013-08-13 Senast uppdaterad: 2017-12-06Bibliografiskt granskad
    37. High pressure, mechanical, and optical properties of ZrW2O8
    Öppna denna publikation i ny flik eller fönster >>High pressure, mechanical, and optical properties of ZrW2O8
    2011 (Engelska)Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 109, nr 3, s. 033510-Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    In this paper, we present the high pressure studies of well known negative thermal expansion material ZrW2O8 on the basis of our density functional theory calculations. We reproduce the experimental alpha and gamma crystal structures of ZrW2O8. We calculate the transition pressure (from alpha to gamma) of this material to be approximate to 26 kbar. Our calculated positional and axial parameters are in an excellent agreement with the available experimental values for the both alpha and gamma phases of this material. Then we study the mechanical properties of this material. We calculate the elastic constants, bulk, shear and Young's moduli, Poisson's ratio, and Debye temperature of alpha-ZrW2O8. In our study, we find that the generalized gradient approximation method fails to obtain the correct values while the local density approximation (LDA) method successfully reproduces the experimental bulk modulus of ZrW2O8. Our calculated values of the shear and Young's moduli, Poisson's ratio, and Debye temperature of alpha-ZrW2O8 with LDA method are also in good agreement with the experimental results. Finally, we predict and analyze the optical properties of this material.

    Nationell ämneskategori
    Fysik
    Identifikatorer
    urn:nbn:se:uu:diva-148942 (URN)10.1063/1.3544487 (DOI)000287366000023 ()
    Anmärkning

    Correction in: Journal of Applied Physics, 2011, Vol. 109, issue. 7, article nr. 079903

    Tillgänglig från: 2011-03-15 Skapad: 2011-03-14 Senast uppdaterad: 2017-12-11
    38. Molecular dynamics study of amorphous Ga-doped In2O3: a promising material for phase change memory devices
    Öppna denna publikation i ny flik eller fönster >>Molecular dynamics study of amorphous Ga-doped In2O3: a promising material for phase change memory devices
    2013 (Engelska)Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 103, nr 7, artikel-id 072113Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    In this paper, we employ the ab-initio molecular dynamics simulations, within the framework of density functional theory, to construct and characterize the amorphous structure of gallium-doped indium oxide. The electronic properties of amorphous and crystalline structures of Ga:In2O3 are investigated and compared by calculating the density of states, radial distribution function, bond angle distribution, and Bader charge analysis. We observe the band gap closure in amorphous structure, which corresponds to semiconductor to metallic transition in this material on amorphization. Our calculated results show the same characteristics of Ga:In2O3 with other phase change memory (PCM) materials available in literature and suggest it a promising candidate for PCM devices.

    Nationell ämneskategori
    Den kondenserade materiens fysik
    Identifikatorer
    urn:nbn:se:uu:diva-204964 (URN)10.1063/1.4818788 (DOI)000323769000044 ()
    Forskningsfinansiär
    Vetenskapsrådet
    Tillgänglig från: 2013-08-13 Skapad: 2013-08-13 Senast uppdaterad: 2017-12-06Bibliografiskt granskad
    39. Hybrid density functional study of electronic and optical properties of phase change memory material: Ge2Sb2Te5
    Öppna denna publikation i ny flik eller fönster >>Hybrid density functional study of electronic and optical properties of phase change memory material: Ge2Sb2Te5
    2013 (Engelska)Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 113, nr 3, s. 033510-Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    In this article, we use hybrid density functional (HSE06) to study the crystal and electronic structures and optical properties of well known phase change memory material Ge2Sb2Te5. We calculate the structural parameters, band gaps, and dielectric functions of three stable structures of this material. We also analyze the electron charge distribution using the Bader's theory of charge analysis. We find that hybrid density functional slightly overestimates the value of "c" parameter. However, overall, our results calculated with the use of hybrid density functional (HSE06) are very close to available experimental values than calculated with the use of Perdew Burke-Ernzerhof functional. Specifically, the electronic band gap values of this material calculated with HSE06 are in good agreement with the available experimental data in the literature. Furthermore, we perform the charge analysis and find that naive ionic model fails to explain the charge distribution between the constituent atoms, showing the complex nature of this compound.

    Nationell ämneskategori
    Naturvetenskap
    Identifikatorer
    urn:nbn:se:uu:diva-195377 (URN)10.1063/1.4775715 (DOI)000313670600020 ()
    Tillgänglig från: 2013-02-25 Skapad: 2013-02-25 Senast uppdaterad: 2017-12-06Bibliografiskt granskad
    40. Pressure-Induced and Mn Content Driven Phase Transitions in Ternary Chalcopyrite
    Öppna denna publikation i ny flik eller fönster >>Pressure-Induced and Mn Content Driven Phase Transitions in Ternary Chalcopyrite
    Visa övriga...
    (Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
    Nationell ämneskategori
    Den kondenserade materiens fysik
    Identifikatorer
    urn:nbn:se:uu:diva-204966 (URN)
    Tillgänglig från: 2013-08-13 Skapad: 2013-08-13 Senast uppdaterad: 2014-01-08
    41. Role of correlation effects in the superconducting material: InV6S8
    Öppna denna publikation i ny flik eller fönster >>Role of correlation effects in the superconducting material: InV6S8
    2011 (Engelska)Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 99, nr 22, s. 221904-Artikel i tidskrift, Letter (Refereegranskat) Published
    Abstract [en]

    In this letter, we present the high pressure studies to compute the structural parameters and electronic structure of InV(6)S(8), using the first principles density functional theory (DFT) and DFT+U methods. While LDA and GGA fail to give the correct electronic and structural properties, the DFT+U method performs well to reproduce the experimental observed quantities of InV(6)S(8). We analyze the electronic structures and nesting of InV(6)S(8) at different pressure values and show that the nesting of energy bands reduces with compression. Finally, we conclude that the Hubbard like correction is necessary to take into account the correlation effects, which are very important in the correct description of InV(6)S(8), by choosing the moderate value of U.

    Nationell ämneskategori
    Fysik
    Identifikatorer
    urn:nbn:se:uu:diva-167654 (URN)10.1063/1.3664219 (DOI)000298244500019 ()
    Anmärkning

    Correction in: Applied Physics Letters, vol. 100, issue 4, article nr. 049901, DOI: 10.1063/1.3679545

    Tillgänglig från: 2012-02-01 Skapad: 2012-01-31 Senast uppdaterad: 2017-12-08
  • 19.
    Ramzan, Muhammad
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Ahuja, R
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Ab initio molecular dynamics study of the hydrogen-deuterium exchange in bulk lithiumborohydride (LiBH4)2009Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 94, nr 14, s. 141903-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The hydrogen storage is still a challenge for mobile applications. The diffusion of hydrogen in solids is considered as a general model system but there is limited knowledge available for the dynamics of hydrogen in complex hydrides. In this letter, we present a systematic approach to study the hydrogen-deuterium exchange in bulk LiBH4 based on ab initio molecular dynamics. Our results predict the single hydrogen (deuterium) exchange in LiBH4, which supports the experimental results. The self-diffusion constant < D > of deuterium in LiBH4 is around 1.42x10(-8) m(2) s(-1).

  • 20.
    Ramzan, Muhammad
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Ahuja, R
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Ferromagnetism in the potential cathode material LiNaFePO4F2009Ingår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 87, nr 1, s. 18001-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present the ab initio study of the cathode material LiNaFePO4F, which is suitable for rechargeable batteries. Our calculations reveal the ferromagnetic order to be the ground state of this material. We also predict more than 5.0V intercalation voltage of this material for sodium-ion batteries. The low cost of sodium iron. fluorophasphate batteries and more than 5.0V intercalation voltage makes it the more suitable candidate, commercially and scientifically, than any other cathode materials for rechargeable batteries. Copyright (C) EPLA, 2009

  • 21.
    Ramzan, Muhammad
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori. Applied Materials Physics, Department of Materials and Engineering, Royal Institute of Technology (KTH), SE-100 44 Stockholm, Sweden.
    Ab initio molecular dynamics study of the hydrogen diffusion in sodium and lithium hydrides2009Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 106, nr 016104Artikel i tidskrift (Refereegranskat)
  • 22.
    Ramzan, Muhammad
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori. Applied Materials Physics, Department of Materials and Engineering, Royal Institute of Technology (KTH), SE-100 44 Stockholm, Sweden.
    Electronic structure of MgCuMo6S8Manuskript (preprint) (Övrigt vetenskapligt)
  • 23.
    Ramzan, Muhammad
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Hybrid density functional and molecular dynamics study of promising hydrogen storage materials: Double metal amidoboranes and metal amidoborane ammoniates2012Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, nr 33, s. 17351-17359Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, the recently synthesized materials, Na2Mg-(NH 2BH 3) 4, NaLi(NH 2BH 3) 2, Mg(NH 2BH 3) 2·NH 3, and Ca-(NH 2BH 3) 2·2NH 3, are studied, which were found suitable for hydrogen storage applications. The hybrid density exchange-correlation functional is employed to explore the structural and electronic properties of these materials using the first-principles method on the basis of density functional theory calculations. From the detailed study of electronic structures, it is found that the mixed cation amidoboranes and [NH 3] molecules play an important role in the dehydrogenation process. Bader charge analysis is performed to show the charge distribution between the constituent atoms. The corresponding electron densities and related properties of these compounds are also calculated. Furthermore, ab initio molecular dynamics simulations are performed to study the diffusion of hydrogen in these compounds, which consist of boron, nitrogen, and hydrogen atoms. The common features of these compounds are also revealed by explaining the electronic properties. Finally, it is shown that the mobility of hydrogen in Na 2Mg(NH 2BH 3) 4 and NaLi(NH 2BH 3) 2 is slightly higher than that in Mg(NH 2BH 3) 2·NH 3 and Ca(NH 2BH 3) 2·2NH 3 at the same temperatures.

  • 24.
    Ramzan, Muhammad
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi.
    M(N+1)AX(N)(M=Ti, A=Al, X=H) phase class materials with hydrogen: Ti4AlH3 and Ti3AlH22010Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 96, nr 26, s. 261906-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    To date more than 50 MAX phases known to exist but all of those are consist of nitrides or carbides. We present a modified type of these phases, Ti4AlH3 and Ti3AlH2, having hydrides in their composition, by our density functional theory (DFT) calculations. We study the structural stability, electronic structure, elastic, thermal, and mechanical properties of these materials which are comparable with well known phases: Ti3SiC2, Ti4AlN3, and Ti3AlC2. Moreover, these materials can also be studied for hydrogen storage purposes. We hope that our work will be helpful to discover the other types of such phases which are important from the technological and industrial point of view.

  • 25.
    Ramzan, Muhammad
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Role of correlation effects in the superconducting material: InV6S82011Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 99, nr 22, s. 221904-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this letter, we present the high pressure studies to compute the structural parameters and electronic structure of InV(6)S(8), using the first principles density functional theory (DFT) and DFT+U methods. While LDA and GGA fail to give the correct electronic and structural properties, the DFT+U method performs well to reproduce the experimental observed quantities of InV(6)S(8). We analyze the electronic structures and nesting of InV(6)S(8) at different pressure values and show that the nesting of energy bands reduces with compression. Finally, we conclude that the Hubbard like correction is necessary to take into account the correlation effects, which are very important in the correct description of InV(6)S(8), by choosing the moderate value of U.

  • 26.
    Ramzan, Muhammad
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Hussain, Tanveer
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    High pressure phase determination and electronic properties of lithiumamidoborane2012Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 101, nr 11, s. 111902-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this study we report on the high pressure phase of the promising hydrogen storage material lithiumamidoborane (LiNH2BH3), on the basis of density functional theory calculations with generalized gradient approximation. We take the five possible candidate structures, Pbca, Pbcn, Pcca, Pnma, and Pnnm for the high pressure study of LiNH2BH3. The corresponding structures are relaxed with respect to fractional atomic coordinates and cell parameters, with the use of fully self-consistent ab initio electronic structure calculations to get the equilibrium parameters and total enemies. Then we compare the energies of these phases and find that Pbcn is the most favorable phase at approximate to 100 GPa. Then we calculate the structural parameters of this phase. Finally, we calculate the density of states, Bader charge analysis, and corresponding electron density of this phase.

  • 27.
    Ramzan, Muhammad
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Hussain, Tanveer
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Hydrogen diffusion in bulk and nanoclusters of MgH2 and the role of catalysts on the basis of ab initio molecular dynamics2009Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 94, nr 22, s. 221910-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present ab initio molecular dynamics calculations based on density functional theory to study the hydrogen-deuterium exchange in bulk and nanoclusters of MgH2. Our calculations reveal the important role of catalysts to diffuse the hydrogen at low temperatures and increase the diffusion rate. We determine the diffusion constants, < D > of deuterium, and show the single hydrogen-deuterium exchange in bulk and nanocluster of MgH2. Our calculated value of diffusion constant of deuterium in bulk MgH2 is in excellent agreement with the experimental value. Furthermore, we show the edge site importance of catalysts in the fast diffusion of hydrogen.

  • 28.
    Ramzan, Muhammad
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Kaewmaraya, Thanayut
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori. Applied Materials Physics, Department of Materials and Engineering, Royal Institute of Technology (KTH), SE-100 44 Stockholm, Sweden.
    Molecular dynamics study of amorphous Ga-doped In2O3: a promising material for phase change memory devices2013Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 103, nr 7, artikel-id 072113Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, we employ the ab-initio molecular dynamics simulations, within the framework of density functional theory, to construct and characterize the amorphous structure of gallium-doped indium oxide. The electronic properties of amorphous and crystalline structures of Ga:In2O3 are investigated and compared by calculating the density of states, radial distribution function, bond angle distribution, and Bader charge analysis. We observe the band gap closure in amorphous structure, which corresponds to semiconductor to metallic transition in this material on amorphization. Our calculated results show the same characteristics of Ga:In2O3 with other phase change memory (PCM) materials available in literature and suggest it a promising candidate for PCM devices.

  • 29.
    Ramzan, Muhammad
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Lebegue, S.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Correlation effects in the electronic and structural properties of Cr2AlC2011Ingår i: Physica Status Solidi. Rapid Research Letters, ISSN 1862-6254, E-ISSN 1862-6270, Vol. 5, nr 3, s. 122-124Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this Letter, we present the electronic and structural properties calculated by first principles GGA and GGA+U calculations of Cr2AlC, a member of the MAX phases family of compounds. While GGA fails to obtain a correct description, the GGA+U method successfully reproduces the experimental equilibrium volume and bulk modulus values of Cr2AlC, and predict it to be a ferromagnet. Therefore, correlation effects are crucial for the correct description of Cr2AlC, provided that a suitable value of U is chosen.

  • 30.
    Ramzan, Muhammad
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Lebegue, S.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Electronic and mechanical properties of Cr2GeC with hybrid functional and correlation effects2012Ingår i: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 152, nr 13, s. 1147-1149Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a computational study of the MAX phase material Cr2GeC to obtain its crystal and electronic structure using density functional theory with various exchange-correlation functionals. While the GGA and GGA+U methods are giving a reasonable description of the lattice parameters, the hybrid functional (HSE06) is found to give too large values. Then, on the basis of our GGA+U calculations, the antiferromagnetic ordering is found to be the ground state. Furthermore, we study the charge distribution between the constituent elements of this compound and find that the simple ionic model fails to describe it due to the complex nature of this material. Finally, we conclude that the treatment of the correlated electrons is important for the correct description of this material. 

  • 31.
    Ramzan, Muhammad
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Lebègue, Sébastien
    Nancy University France.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori. Applied Materials Physics, Department of Materials and Engineering, Royal Institute of Technology (KTH), SE-100 44 Stockholm, Sweden.
    Crystal and electronic structures of lithium fluorosulphate based materials for lithium-ion batteries2010Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, nr 125101Artikel i tidskrift (Refereegranskat)
  • 32.
    Ramzan, Muhammad
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Lebègue, Sébastien
    Nancy University France.
    Kang, Tae W.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori. Applied Materials Physics, Department of Materials and Engineering, Royal Institute of Technology (KTH), SE-100 44 Stockholm, Sweden.
    Hybrid Density Functional Calculations and Molecular Dynamics Study of Lithium Fluorosulphate, A Cathode Material for Lithium-Ion Batteries2011Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, s. 2600-2603Artikel i tidskrift (Refereegranskat)
  • 33.
    Ramzan, Muhammad
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Li, Y.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori. Applied Materials Physics, Department of Materials and Engineering, Royal Institute of Technology (KTH), SE-100 44 Stockholm, Sweden.
    Electronic structure, mechanical and optical properties of In2O3 with hybrid density functional (HSE06)Ingår i: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766Artikel i tidskrift (Refereegranskat)
  • 34.
    Ramzan, Muhammad
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Li, Y.
    Araujo, Carlos Moyses
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori. Applied Materials Physics, Department of Materials and Engineering, Royal Institute of Technology (KTH), SE-100 44 Stockholm, Sweden.
    Surface states and ferromagnetism in crystalline YCrO3Manuskript (preprint) (Övrigt vetenskapligt)
  • 35.
    Ramzan, Muhammad
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Li, Y.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Chimata, Raghuveer
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Electronic, mechanical and optical properties of Y2O3 with hybrid density functional (HSE06)2013Ingår i: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 71, s. 19-24Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, we have investigated the electronic, optical and mechanical properties of the Y2O3 crystal by first-principle calculations based on the density-functional theory. The generalized gradient approximation (GGA-PBE) and hybrid exchange-correlation functional (HSE06) are both used for comparative study. It is found that, the band gap of Y2O3 calculated by HSE06 method (6.0 eV) is in good agreement with the experimental band gap data (5.5 eV), and HSE06 gives better electronic structure description close to experiments. Then we calculate the elastic constants, and derive the corresponding properties i.e.; bulk, shear and Young's moduli, and Poisson's ratio. Our calculated elastic and mechanical properties correspond well with experimental data. Besides, we also obtain the equilibrium lattice and bulk modulus of yttria by fitting the Birch-Murnaghan equation of state. It is found that, the HSE06 well reproduce the experimental lattice parameters, equilibrium volume and bulk modulus of Y2O3. Based on the accurate described crystal and electronic structure and mechanical properties by HSE06 method, the optical properties of this material are also analyzed.

  • 36.
    Ramzan, Muhammad
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Liu, P.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori. Applied Materials Physics, Department of Materials and Engineering, Royal Institute of Technology (KTH), SE-100 44 Stockholm, Sweden.
    High Pressure Phase Transition and Electronic, Mechanical Properties of Ferroelectric Material: PbTiO3Manuskript (preprint) (Övrigt vetenskapligt)
  • 37.
    Ramzan, Muhammad
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Luo, Wei
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    High pressure, mechanical, and optical properties of ZrW2O82011Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 109, nr 3, s. 033510-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, we present the high pressure studies of well known negative thermal expansion material ZrW2O8 on the basis of our density functional theory calculations. We reproduce the experimental alpha and gamma crystal structures of ZrW2O8. We calculate the transition pressure (from alpha to gamma) of this material to be approximate to 26 kbar. Our calculated positional and axial parameters are in an excellent agreement with the available experimental values for the both alpha and gamma phases of this material. Then we study the mechanical properties of this material. We calculate the elastic constants, bulk, shear and Young's moduli, Poisson's ratio, and Debye temperature of alpha-ZrW2O8. In our study, we find that the generalized gradient approximation method fails to obtain the correct values while the local density approximation (LDA) method successfully reproduces the experimental bulk modulus of ZrW2O8. Our calculated values of the shear and Young's moduli, Poisson's ratio, and Debye temperature of alpha-ZrW2O8 with LDA method are also in good agreement with the experimental results. Finally, we predict and analyze the optical properties of this material.

  • 38.
    Ramzan, Muhammad
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Silvearv, F
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Blomqvist, A
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Scheicher, Ralph H.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Lebegue, S
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Structural and energetic analysis of the hydrogen storage materials LiNH2BH3 and NaNH2BH3 from ab initio calculations2009Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, nr 13, s. 132102-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ammonia borane (NH3BH3) possesses many appealing properties as a hydrogen storage material; however, the release of trace amounts of borazine during the desorption process is troublesome. Recently, it was found that substitution of one of the H atoms in the NH3 group by Li or Na could significantly improve the hydrogen desorption properties. The resulting lithium amidoborane (LiNH2BH3) and sodium amidoborane (NaNH2BH3) compounds have been studied by us using density-functional theory. Specifically, we have succeeded in determining the detailed crystal structures of LiNH2BH3 and NaNH2BH3, including the atomic positions in their respective unit cells. Calculated hydrogen removal energies of the hydrogen release reactions are found to be in good agreement with the experimental trend.

  • 39.
    Ramzan, Muhammad
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Silvearv, Fredrik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Lebègue, Sébastien
    Nancy University France.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori. AppliedMaterials Physics, Department of Materials and Engineering, Royal Institute of Technology (KTH), SE-100 44 Stockholm, Sweden.
    Electronic Structure from First-Principles of LiBH4. NH3, Sr(NH2BH3)2, and Li2Al(BH4)5 . 6NH3 for Hydrogen Storage Applications2011Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, nr 40, s. 20032-20042Artikel i tidskrift (Refereegranskat)
  • 40.
    Ramzan, Muhammad
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Silvearv, Fredrik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Lebègue, Sébastien
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Electronic Structure from First-Principles of LiBH(4)center dot NH(3), Sr(NH(2)BH(3))(2), and Li(2)Al(BH(4))(5)center dot 6NH(3) for Hydrogen Storage Applications2011Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, nr 40, s. 20036-20042Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A series of compounds containing boron, nitrogen, and hydrogen atoms, namely, LiBH(4)center dot NH(3), Sr(NH(2)BH(3))(2), and Li(2)Al(BH(4))(5)center dot 6NH(3), were synthesized recently, and found to be promising for hydrogen storage. We have conducted the corresponding ab initio calculations using density functional theory and analyzed the corresponding electron density as well as derived properties. Also, molecular dynamics simulations were performed to study the diffusion of hydrogen in this series of compounds. We found that despite having widely different crystal structures and difference in their chemical composition, these compounds share common features at the level of their electronic structure. Moreover, diffusion of hydrogen appears to be more favorable in LiBH(4)center dot NH(3) than in Sr(NH(2)BH(3))(2) and Li(2)Al(BH(4))(5)center dot 6NH(3).

  • 41.
    Ramzan, Muhammed
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Li, Yunguo
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Electronic structure, mechanical and optical properties of In2O3 with hybrid density functional (HSE06)2013Ingår i: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 172, s. 37-40Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this study, the hybrid densily correlation functional (HSE06) is used to explore the eleclronic structure and optical properties of In2O3, on the basis of density functional theory (DFT). The calculated equilibrium lattice parameters, volume and bulk modulus of this compound, are comparable with the experimental results available in the literature. The bandgap of In2O3 has been a matter of debate in literatures. However, our calculated bandgap can bridge the gap between experiment and theory, and is in good agreement with the available experimental results. Furthermore, we calculate and analyze the optical and mechanical properties of this compound. We hope that our work will help to understand the correct electronic structure and optical properties of this compound.

  • 42.
    Sagynbaeva, Myskal
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Panigrahi, Puspamitra
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Yunguo, Li
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ramzan, Muhammad
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Tweaking the magnetism of MoS2 nanoribbon with hydrogen and carbon passivation2014Ingår i: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 25, nr 16, s. 165703-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using density functional theory (DFT), we report the modulated electronic and magnetic properties of MoS2 nanoribbon by passivating the ribbon edges with H and C separately. For the modeled symmetric MoS2 nanoribbon with a zig-zag type edge, one side is terminated at Mo and the other side is terminated at S. For the zig-zag type, we have studied two ribbons of width similar to 3 angstrom and 6 angstrom respectively. Both of these pristine zig-zag type nanoribbons are found to be metallic and also ferromagnetic. However, the increase in the ribbon width results in a decrease in the net magnetic moment of the nanoribbon. Thereafter, we study the modulated electronic and magnetic properties of the nanoribbon of similar to 3 angstrom width by saturating the ribbon edges with H and C. In one case, by passivating the zig-zag type ribbon with H at the S terminated edge, we find a net increase in magnetic moment of the ribbon when compared with the pristine one. Furthermore, when the ribbon is passivated with H at both of the edges, the net magnetic moment shows a decreasing trend. In another case, the zig-zag nanoribbon is passivated with C in a similar fashion to H and we find with one edge passivation the net magnetic moment of the ribbon decreases, whereas with both edges C passivated the ribbon magnetism increases significantly. However, the nanoribbon modeled with the armchair type of edge and terminated with Mo at both sides is found to be non-magnetic and semiconducting. Passivating the armchair type nanoribbon with H and C, we find the band gap shows an increasing trend when going from one side to both sides passivation. In all cases, the armchair type nanoribbons show non-magnetic behavior.

  • 43. Århammar, C.
    et al.
    Endrino, J. L.
    Ramzan, Muhammad
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Horwat, D.
    Blomqvist, Andreas
    Rubensson, Jan-Erik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Molekyl- och kondenserade materiens fysik.
    Andersson, Joakim
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Molekyl- och kondenserade materiens fysik.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori. Applied Materials Physics, Department of Materials and Engineering, Royal Institute of Technology (KTH).
    Probing temperature-induced ordering in supersaturated Ti-1 (-) xAlxN coatings by electronic structure2014Ingår i: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 242, s. 207-213Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The ordering of supersaturated cubic titanium aluminum nitride (c-Ti0.35Al0.65N) coatings is probed from room temperature up to and above the point of spinodal decomposition, using Near Edge X-ray Absorption Fine-structure (NEXAFS) and first principles calculations. The measured and calculated nitrogen (N) K spectra suggest that unoccupied N p states hybridize with Ti d states. When temperature is raised the N p-Ti d overlap decreases, whereas hybridization between N p and Al p tends to increase. The observed spectral changes with temperature together with calculations of defect heat of formation suggest a depletion of N in the surroundings of Ti in c-Ai(1) (-) xAlxN and/or in the formed c-TiN.

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