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  • 501.
    Shukla, Vivekanand
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Grigoriev, Anton
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Jena, Naresh K.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Royal Inst Technol KTH, Dept Mat & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden.
    Strain controlled electronic and transport anisotropies in two-dimensional borophene sheets2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 35, p. 22952-22960Article in journal (Refereed)
    Abstract [en]

    Two recent reports on realization of an elemental 2D analogue of graphene:borophene (Science, 2015, 350, 1513-1516; Nat. Chem., 2016, 8, 563-568) focus on the inherent anisotropy and directional dependence of the electronic properties of borophene polymorphs. Achieving stable 2D borophene structures may lead to some degree of strain in the system because of the substrate-lattice mismatch. We use first principles density functional theory (DFT) calculations to study the structural, electronic and transport properties of (12) and -borophene polymorphs. We verified the directional dependency and found the tunable anisotropic behavior of the transport properties in these two polymorphs. We find that strain as low as 6% brings remarkable changes in the properties of these two structures. We further investigate current-voltage (I-V) characteristics in the low bias regime after applying a strain to see how the anisotropy of the current is affected. Such observations like the sizeable tuning of transport and I-V characteristics at the expense of minimal strain suggest the suitability of 2D borophene for futuristic device applications.

  • 502.
    Shukla, Vivekanand
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Jena, Naresh K.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Grigoriev, Anton
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. KTH, Stockholm, Sweden.
    Prospects of Graphene-hBN Heterostructure Nanogap for DNA Sequencing2017In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 9, no 46, p. 39945-39952Article in journal (Refereed)
    Abstract [en]

    Recent advances in solid-state nano-device-based DNA sequencing are at the helm of the development of a new paradigm, commonly referred to as personalized medicines. Paying heed to a timely need for standardizing robust nanodevices for cheap, fast, and scalable DNA detection, in this article, the nanogap formed by the lateral heterostructure of graphene and hexagonal boron nitride (hBN) is explored as a potential architecture. These heterostructures have been realized experimentally, and our study boasts the idea that the passivation of the edge of the graphene electrode with hBN will solve many of practical problems, such as high reactivity of the graphene edge and difficulty in controlled engineering of the graphene edge structure, while retaining the nanogap setup as a useful nanodevice for sensing applications. Employing first-principle density-functional-theory-based nonequilibrium Greens function methods, we identify that the DNA building blocks, nucleobases, uniquely couple with the states of the nanogap, and the resulting induced states can be attributed as leaving a fingerprint of the DNA sequence in the computed current-voltage (I-V) characteristic. Two bias windows are put forward: lower (1-1.2 V) and higher (2.7-3 V), where unique identification of all four bases is possible from the current traces, although higher sensitivity is obtained at the higher voltage window. Our study can be a practical guide for experimentalists toward development of a nanodevice DNA sensor based on graphene-hBN heterostructures.

  • 503.
    Shukla, Vivekanand
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Jena, Naresh K.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Naqvi, S. Rabab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Modeling High-performing Batteries with Mxenes: The case of S-functionalized two- Dimensional Nitride Mxene Electrode2019In: Nano Energy, ISSN 2211-2855, E-ISSN 2211-3282, Vol. 58, p. 877-885Article in journal (Refereed)
    Abstract [en]

    Recent upsurge in the two-dimensional (2D) materials have established their larger role on energy storage applications. To this end, Mxene represent a new paradigm extending beyond the realm of oft-explored elemental 2D materials beginning with graphene. Here in, we employed first principles modelling based on density functional theory to investigate the role of S-functionalized Nitride Mxenes as anodes for Li/Na ion batteries. To be specific, V2NS2 and Ti2NS2 have been explored with a focus on computing meaningful descriptors to quantify these 2D materials to be optimally performing electrodes. The Li/Na ion adsorption energies are found to be high (> -2 eV) on both the surfaces and associated with significant charge transfer. Interestingly, this ion intercalation can reach up to multilayers which essentially affords higher specific capacity for the substrate. Particularly, these two 2D materials (V2NS2 and Ti2NS2) have been found to be more suitable for Li-ion batteries with estimated theoretical capacities of 299.52 mAh g(-1) and 308.28 mAh g(-1) respectively. We have also probed the diffusion barriers of ion migration on these two surfaces and these are found to be ultrafast in nature. All these unique features qualify these Mxenes to be potential anode materials for rechargeable batteries and likely to draw imminent attention.

  • 504.
    Shukla, Vivekanand
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Wärnå, John
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Jena, Naresh K.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Grigoriev, Anton
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Royal Inst Technol KTH, Dept Mat & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden..
    Toward the Realization of 2D Borophene Based Gas Sensor2017In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 48, p. 26869-26876Article in journal (Refereed)
    Abstract [en]

    To the league of rapidly expanding 2D materials, borophene is a recent addition. Herein, a combination of ab initio density functional theory (DFT) and nonequilibrium Green's function (NEGF) based methods is used to estimate the prospects of this promising elemental 2D material for gas sensing applications. We note that the binding of target gas molecules such as CO, NO, NO2, NH3, and CO2 is quite strong on the borophene surface. Interestingly, our computed binding energies are far stronger than several other reported 2D materials like graphene, MoS2, and phosphorene. Further rationalization of stronger binding is made with the help of charge transfer analysis. The sensitivity of the borophene for these gases is also interpreted in terms of computing the vibrational spectra of the adsorbed gases on top of borophene, which show dramatic shift from their gas phase reference values. The metallic nature of borophene enables us to devise a setup considering the same substrate as electrodes. From the computation of the transmission function of system (gas + borophene), appreciable changes in the transmission functions are noted compared to pristine borophene surface. The measurements of current-voltage (I-V) characteristics unambiguously demonstrate the presence and absence of gas molecules (acting as ON and OFF states), strengthening the plausibility of a borophene based gas sensing device. As we extol the extraordinary sensitivity of borophene, we assert that this elemental 2D material is likely to attract subsequent interest.

  • 505.
    Silvearv, Fredrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Larsson, Peter
    Jones, Sarah. L. T.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Larsson, J. Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Establishing the most favorable metal-carbon bond strength for carbon nanotube catalysts2015In: Journal of Materials Chemistry C, ISSN 2050-7526, E-ISSN 2050-7534, Vol. 3, no 14, p. 3422-3427Article in journal (Refereed)
    Abstract [en]

    We have studied a wide range of transition metals to find potential carbon nanotube (CNT) catalysts for chemical vapor deposition (CVD) production. The adhesion strengths between a CNT and a metal cluster were calculated using first principle density functional theory (DFT) for all 1st, 2nd and 3rd row transition metals. We have developed the criterion that the metal-carbon adhesion strength per bond must fulfill a Goldilocks principle for catalyzing CNT growth and used it to identify, besides the well known catalysts Fe, Co and Ni, a number of other potential catalysts, namely Y, Zr, Rh, Pd, La, Ce and Pt. Our results are consistent with previous experiments performed either in a carbon arc discharge environment or by a CVD-process with regard to CNT catalyst activity.

  • 506.
    Silvearv, Fredrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Rosa, A. L.
    Lebegue, S.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    An ab-initio study of (Mn,Al) doped ZnO including strong correlation effects2012In: Physica. E, Low-Dimensional systems and nanostructures, ISSN 1386-9477, E-ISSN 1873-1759, Vol. 44, no 6, p. 1095-1097Article in journal (Refereed)
    Abstract [en]

    (Mn,Al)-codoped ZnO has been investigated by means of first-principles calculations using density-functional theory within the generalized-gradient approximation plus on-site Coulomb interaction (GGA + U) to take into the strong correlations on the Mn site. It is found that for several Al-Mn distances, the system shows always an antiferromagnetic behavior. This is explained by the fact that even with the correct electronic structure described with the GGA + U scheme, the extra electron brought by Al is localized in the host conduction band, and therefore does not modify the occupation of the Mn atoms, suggesting that the antiferromagnetic interaction is still dominant. 

  • 507.
    Singh, Deobrat
    et al.
    SV Natl Inst Technol, Dept Appl Phys, Adv Mat Lab, Surat 395007, India..
    Gupta, Sanjeev K.
    St Xaviers Coll, Dept Phys, Computat Mat & Nanosci Grp, Ahmadabad 380009, Gujarat, India..
    Sonvane, Yogesh
    SV Natl Inst Technol, Dept Appl Phys, Adv Mat Lab, Surat 395007, India..
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    High performance material for hydrogen storage: Graphenelike Si2BN solid2017In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 42, no 36, p. 22942-22952Article in journal (Refereed)
    Abstract [en]

    Recently, two dimensional graphenelike i.e. Si2BN solid monolayer have attracted much attention for the use of hydrogen developments. The work is based on first principles calculations using density functional theory with long range van der Waal (vdW) interactions. The optimized structure is energetically more stable due to high formation energy 45.39 eV with PBE and 50.82 eV with HSE06 functionals, respectively. Our ab-initio studies show that Pd (palladium) adatoms secured graphenelike Si2BN solid via two types of interactions; physisorption and chemisorptions reactions, which engrossing up to 3H(2) molecules signifying gravimetric limits of approximate to 6.95-10.21 wt %. The absorption energies vary from -0.31 eV to -1.93 eV with Pd-adatom and without Pd-adatom respectively, and it varies up to -1.24 eV. The work function of pure Si2BN is 5.36 eV while metal-adatom on monolayer Si2BN with (1 to 6)H-2 molecules is 3.53 eV -4.99 eV and reaches up to 5.85 eV. The theoretical study suggests that the functionalized graphenelike Si2BN is efficient for hydrogen storage and propose a possible improvement for advantageous storage of hydrogen at ambient conditions.

  • 508.
    Singh, Deobrat
    et al.
    Govt Coll Engn & Technol, Dept Phys, Bikaner 334004, Rajasthan, India;SV Natl Inst Technol, Dept Appl Phys, Adv Mat Lab, Surat 395007, India.
    Gupta, Sanjeev K.
    St Xaviers Coll, Dept Phys, Computat Mat & Nanosci Grp, Ahmadabad 380009, Gujarat, India.
    Sonvane, Yogesh
    SV Natl Inst Technol, Dept Appl Phys, Adv Mat Lab, Surat 395007, India.
    Hussain, Tanveer
    Univ Queensland, Australian Inst Bioengn & Nanotechnol, Ctr Theoret & Computat Mol Sci, Brisbane, Qld 4072, Australia;Univ Western Australia, Sch Mol Sci, Perth, WA 6009, Australia.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Achieving ultrahigh carrier mobilities and opening the band gap in two-dimensional Si2BN2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 33, p. 21716-21723Article in journal (Refereed)
    Abstract [en]

    Recently, a two-dimensional (2D) Si2BN monolayer material made of silicon, boron and nitrogen, was theoretically predicated and has attracted interest in the scientific community. Due to its 2D planar nature with high formation energy, Si2BN monolayers can be flexible and strong like graphene and also exhibit captivating properties like those of other 2D materials. Motivated by this fascinating graphene-like monolayer of Si2BN, we have investigated its structural and electronic properties based on first-principles calculations. The electronic band structure of pure Si2BN shows metallic behaviour. We have discovered that the band gap of Si2BN monolayer can be tuned to 102 meV by applying external electric fields and mechanical strain. The band gap opening occurs at 5% strain, where the bond angles between the nearest neighbours become nearly equal. The band gap opening occurs at a small external electric field of 0.4 V angstrom(-1). More interestingly, at room temperature, the electron mobility of Si2BN is 4.73 x 10(5) cm(2) V-1 s(-1), which is much larger than that of graphene, while the hole mobility is 1.11 x 10(5) cm(2) V-1 s(-1), slightly smaller than the electron mobility. The ultrahigh carrier mobility of Si2BN may lead to many novel applications in high-performance electronic and optoelectronic devices. These theoretical results suggest that the Si2BN monolayer exhibits multiple effects that may significantly enhance the performance of Si2BN based electronic devices.

  • 509.
    Skorodumova, Natalia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV.
    Belonoshko, Anatoly
    Huang, Lunmei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV.
    Stability of MgCO3 structures at the lower mantle conditions2005In: Amer. Mineral., Vol. 90, p. 1008-Article in journal (Refereed)
  • 510.
    Skorodumova, Natalia V.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Ahuja, Rajeev
    Simak, SI
    Abrikosov, IA
    Johansson, Börje
    Lundqvist, BI
    Electronic, bonding, and optical properties of CeO2 and Ce2O3 from first principles - art. no. 1151082001In: PHYSICAL REVIEW B, ISSN 0163-1829, Vol. 6411, no 11, p. 5108-+ Language: EnglishArticle in journal (Refereed)
    Abstract [en]

    First-principles electronic structure calculations of cerium oxide in two forms, CeO2 and Ce2O3, are Presented. The 4f state of Ce is treated as a part of the inner core in Ce2O3 and as a valence-band-like state in CeO2,. The calculated ground-state and m

  • 511. Skorodumova, Natalia V.
    et al.
    Belonoshko, A. B.
    Huang, L. M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Ahuja, Rajeev
    Johansson, Börje
    Stability of the MgCO3 structure under lower mantle conditions2005In: American Mineralogist, Vol. 90, p. 1008-Article in journal (Refereed)
  • 512.
    Smazna, Daria
    et al.
    Univ Kiel, Inst Mat Sci, Kaiserstr 2, D-24143 Kiel, Germany.
    Rodrigues, Joana
    Univ Aveiro, Dept Fis, P-3810193 Aveiro, Portugal;Univ Aveiro, I3N, P-3810193 Aveiro, Portugal.
    Shree, Sindu
    Univ Kiel, Inst Mat Sci, Kaiserstr 2, D-24143 Kiel, Germany.
    Postica, Vasile
    Tech Univ Moldova, Dept Microelect & Biomed Engn, 168 Stefan Cel Mare Blvd, MD-2004 Kishinev, Moldova.
    Neubueser, Gero
    Univ Kiel, Inst Mat Sci, Kaiserstr 2, D-24143 Kiel, Germany.
    Martins, A. F.
    Univ Aveiro, Dept Fis, P-3810193 Aveiro, Portugal;Univ Aveiro, I3N, P-3810193 Aveiro, Portugal.
    Ben Sedrine, N.
    Univ Aveiro, Dept Fis, P-3810193 Aveiro, Portugal;Univ Aveiro, I3N, P-3810193 Aveiro, Portugal.
    Jena, Naresh K.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Siebert, Leonard
    Univ Kiel, Inst Mat Sci, Kaiserstr 2, D-24143 Kiel, Germany.
    Schuett, Fabian
    Univ Kiel, Inst Mat Sci, Kaiserstr 2, D-24143 Kiel, Germany.
    Lupan, Oleg
    Univ Kiel, Inst Mat Sci, Kaiserstr 2, D-24143 Kiel, Germany;Tech Univ Moldova, Dept Microelect & Biomed Engn, 168 Stefan Cel Mare Blvd, MD-2004 Kishinev, Moldova.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Correia, M. R.
    Univ Aveiro, Dept Fis, P-3810193 Aveiro, Portugal;Univ Aveiro, I3N, P-3810193 Aveiro, Portugal.
    Monteiro, Teresa
    Univ Aveiro, Dept Fis, P-3810193 Aveiro, Portugal;Univ Aveiro, I3N, P-3810193 Aveiro, Portugal.
    Kienle, Lorenz
    Univ Kiel, Inst Mat Sci, Kaiserstr 2, D-24143 Kiel, Germany.
    Yang, Ya
    Chinese Acad Sci, Beijing Inst Nanoenergy & Nanosyst, CAS Ctr Excellence Nanosci, Beijing 100083, Peoples R China.
    Adelung, Rainer
    Univ Kiel, Inst Mat Sci, Kaiserstr 2, D-24143 Kiel, Germany.
    Mishra, Yogendra Kumar
    Univ Kiel, Inst Mat Sci, Kaiserstr 2, D-24143 Kiel, Germany.
    Buckminsterfullerene hybridized zinc oxide tetrapods: defects and charge transfer induced optical and electrical response2018In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 10, no 21, p. 10050-10062Article in journal (Refereed)
    Abstract [en]

    Buckminster fullerene (C-60) based hybrid metal oxide materials are receiving considerable attention because of their excellent fundamental and applied aspects, like semiconducting, electron transfer, luminescent behaviors, etc. and this work briefly discusses the successful fabrication of C-60 decorated ZnO tetrapod materials and their detailed structure-property relationships including device sensing applications. The electron microscopy investigations indicate that a quite dense surface coverage of ZnO tetrapods with C-60 clusters is achieved. The spectroscopy studies confirmed the identification of the C-60 vibrational modes and the C-60 induced changes in the absorption and luminescence properties of the ZnO tetrapods. An increased C-60 concentration on ZnO results in steeper ZnO bandgap absorption followed by well-defined free exciton and 3.31 eV line emissions. As expected, higher amounts of C-60 increase the intensity of C-60-related visible absorption bands. Pumping the samples with photons with an energy corresponding to these absorption band maxima leads to additional emission from ZnO showing an effective charge transfer phenomenon from C-60 to the ZnO host. The density of states model obtained from DFT studies for pure and C-60 coated ZnO surfaces confirms the experimental observations. The fabricated C-60-ZnO hybrid tetrapod based micro- and nanodevices showed interesting ethanol gas sensing characteristics.

  • 513.
    Souvatzis, Petros
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Katsnelson, Mikhail
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Theoretical Magnetism.
    Simak, Sergei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Theoretical Magnetism.
    Mohn, Peter
    First-principles prediction of superplastic transition-metal alloys2004In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 70, no 1, p. 012201-Article in journal (Refereed)
    Abstract [en]

    Superplastic transition metal alloys and compounds are predicted from first principles calculations. Provided a suitable tuning of the alloying is done, materials with vanishingly low shear modulus C[prime] have recently been identified among the 3d, 4d, and 5d elements if the valence electron average number is close to 4.24 (i.e., Ti-Ta-Nb-V-Zr-O and Ti-Nb-Ta-Zr-O alloys). The vanishingly low C[prime] elastic constant of these bcc alloys is, according to the joint experimental and theoretical studies [T. Saito et al., Science 300, 464 (2003)], the crucial material parameter that is responsible for the superplasticity. We predict here, using first principles calculations, that superplastic alloys should also be found for alloys with drastically different valence electron concentrations, i.e., for W-Re-, W-Tc-, Mo-Re-, Mo-Tc-, and Fe-Co-based alloys.

  • 514.
    Souvatzis, Petros
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Osorio-Guillén, Jorge Mario
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Grechnev, Alexei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Elastic properties of Mg(1-x)AlxB2 from first principles theory2004In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 16, no 29, p. 5241-5250Article in journal (Refereed)
    Abstract [en]

    Elastic properties of Mg(1−x)AlxB2 have been studied from first principles. The elastic constants (c11, c12, c13, c33 and c55) have been calculated, in the regime of x = 0 to 0.25. From these calculations the ratio between the bulk modulus and shear modulus (B/G) as well as the ratio between the two directional bulk moduli (Ba/Bc) have been evaluated. Our calculations show that the ratio Ba/Bc decreases monotonically as the aluminium content is increased, whereas the ratio B/G is well below the empirical ductility limit, 1.75, for all concentrations. In addition, we analyse the electronic structure and the nature of the chemical bonding, using the balanced crystal orbital overlap population (BCOOP) (Grechnev et al 2003 J. Phys.: Condens. Matter 15 7751) and the charge densities. Our analysis suggests that, while aluminium doping decreases the elastic anisotropy of MgB2 in the a and c directions, it will not change the brittle behaviour of the material considerably. 

  • 515.
    Souza de Almeida, Jailton
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Tuning the structural, electronic, and optical properties of BexZn1-xTe alloys2006In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 89, no 6, p. 061913-Article in journal (Refereed)
    Abstract [en]

    A series of first principles calculations have been carried out to investigate structural, electronic, and optical properties of BexZn1-xTe alloys for five beryllium compositions. Our results show that the lattice constant scales linearly with beryllium composition and there is a direct-to-indirect band gap crossover nearly at the composition of 20%. It is also found that no bowing effect in the absorption edge is observed unlike other II-VI semiconductor alloys. Our results are in good qualitative agreements with experimental observations.

  • 516. Springell, R.
    et al.
    Detlefs, B.
    Lander, G. H.
    Ward, R. C. C.
    Cowley, R. A.
    Ling, N.
    Goetze, W.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Elemental engineering: Epitaxial uranium thin films2008In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, no 19, p. 193403-Article in journal (Refereed)
    Abstract [en]

    Epitaxial films of the well-known alpha (orthorhombic) structure and an unusual hcp form of uranium have been grown on Nb and Gd buffers, respectively, by sputtering techniques. In a 5000 A film of alpha-U a charge-density wave has been observed, and its properties are different from those found in the bulk. The 500 A hcp-U film has a c/a ratio of 1.90(1), which is unusually large for the hcp structure. Theoretical calculations show that this hcp form is metastable and predict that it orders magnetically.

  • 517. Srepusharawoot, P.
    et al.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Bovornratanaraks, T.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Pinsook, U.
    Evidence of a medium-range ordered phase and mechanical instabilities in strontium under high pressure2012In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 152, no 13, p. 1172-1175Article in journal (Refereed)
    Abstract [en]

    We provided the first theoretical evidence for a medium-range ordered phase in high pressure strontium from the first-principles calculations. At the absolute zero temperature, the enthalpy-pressure relation shows that the bcc and hcp are energetically more favorable than the other experimentally observed phases between 24 and 27 GPa. In the present work, we concentrate on the bcc phase because we found a link to a medium-range ordered phase. Our results reveal that the bcc phonon dispersion at the N and H points starts softening at around 24.1 GPa. The ab initio molecular dynamics at 300 K and 27 GPa showed that the bcc is quickly transformed into a lower energy structure with R3c symmetry and distorted basis. The simulated diffraction patterns showed that the R3c structure has only a single major peak at low angle. The R3c peak locates near the first peak of the bcc structure. This is the evidence of the so-called medium-range ordered phase. This structure is a strong candidate for the unsolved S-phase reported by experiments.

  • 518.
    Srepusharawoot, Pornjuk
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Araujo, C. Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Blomqvist, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Scheicher, Ralph H.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    A comparative investigation of H-2 adsorption strength in Cd- and Zn-based metal organic framework-52008In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 129, no 16, p. 164104-164104-5Article in journal (Refereed)
    Abstract [en]

    Hydrogen binding energies for the primary and secondary adsorption sites in the Cd- and Zn-based metal organic framework-5 (MOF-5) were studied using density functional theory. Out of the three exchange-correlation functionals employed in our study, we find that the local density approximation yields a qualitatively correct description of the interaction strengths of H-2 in MOF-5 systems. The H-2 adsorption energies for all trapping sites in Zn- and Cd-based MOF-5 are seen to be of the same order of magnitude but with a generally stronger binding in Cd- based MOF-5 as compared to Zn- based MOF-5. In particular, the H-2 binding energy at the secondary adsorption sites in Cd- based MOF-5 is increased by around 25% compared to Zn-based MOF-5. This result suggests that Cd- based MOF-5 would be better suited to store hydrogen at higher temperatures than Zn-based MOF-5.

  • 519.
    Srepusharawoot, Pornjuk
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Araújo, C. Moysés
    Blomqvist, Andreas
    Scheicher, Ralph H.
    Ahuja, Rajeev
    A comparative investigation of H2 interaction in Cd- and Zn-based Metal Organic Framework-5Manuscript (Other academic)
  • 520.
    Srepusharawoot, Pornjuk
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Araújo, Moysés
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Scheicher, Ralph
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Li+ and H+ Diffusions in Lithium Amide and Hydride: A first-principles studyManuscript (preprint) (Other academic)
    Abstract [en]

    In the present work, the reaction energies of Li+ and H+ migrations with two different situations, namely inside LiNH2 and between LiNH2 and LiH are determined by the density functional theory. Our results reveal that the Li+ migrations in both cases are rather easy. However, H+ diffusion from LiNH2 to LiH is found to be more difficult than that inside LiNH2. Consequently, diffusions of Li+ and H+ inside LiNH2 are more favorable than those between LiNH2 and LiH. Finally, the migration energies of Li+ and H+ migrations in LiNH2 are determined by the nudged elastic band method and we found that Li+ and H+ migration energy barriers in LiNH2 are 0.30 and 0.58 eV, respectively.

  • 521.
    Srepusharawoot, Pornjuk
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Blomqvist, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Araújo, Moysés
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Scheicher, Ralph
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hydrogen Binding in Alkali-decorated Iso-reticular Metal Organic Framework-16 based on Zn, Mg, and Ca2011In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 36, no 1, p. 555-562Article in journal (Refereed)
    Abstract [en]

    Hydrogen adsorption energies were investigated in three different types of iso-reticular Metal Organic Framework-16, Zn-/Mg-/Ca-MOF16, decorated with either Li, Na, or K. Concerning the binding strengths of the alkali metals, the density functional theory calculations reveal that Li is bound strongest to the host framework, followed by K and Na. Decoration with Li also results in the highest hydrogen adsorption energies among the studied alkali metals. Furthermore, Zn-MOF16 exhibits the highest hydrogen adsorption energies near the metal oxide cluster, while hydrogen binding strengths at organic linker sites do not differ substantially between Zn-/Mg-/Ca-MOF16. Based on these results, we conclude that for Metal Organic Framework-16, Li-decorated Zn-MOF16 appears to be the optimal choice for hydrogen storage among the nine combinations.

  • 522.
    Srepusharawoot, Pornjuk
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Blomqvist, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Araújo, Moysés
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Scheicher, Ralph H.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    One-dimensional polymeric carbon structure based on five-membered rings in alkaline earth metal dicarbides BeC2 and MgC22010In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, no 12, p. 125439-Article in journal (Refereed)
    Abstract [en]

    We studied five alkaline earth dicarbide systems MAEC2 (where M-AE =   Be-Ba) by using ab initio random structure search. For BeC2 and MgC2,   the lowest energy and dynamically stable configuration consists of five-membered carbon rings connected to each other via an individual  arbon atom, stabilized through the donation of electrons from the   surrounding alkaline earth ions. For CaC2, SrC2, and BaC2, our study   shows that the chain crystal structure is more stable than the   predicted structure due to strains induced by the increasing size of   alkaline earth metal ions. The reaction energies of the typical synthesis pathway are comparable to those calculated for the experimental reaction of the known chain-type structure. Finally, the proposed structure should be optically distinguishable due to a   significantly narrower band gap.

  • 523.
    Srepusharawoot, Pornjuk
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Scheicher, Ralph H.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Araujo, Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Blomqvist, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Pinsook, Udomsilp
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Ab Initio Study of Molecular Hydrogen Adsorption in Covalent Organic Framework-12009In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 113, no 19, p. 8498-8504Article in journal (Refereed)
    Abstract [en]

    The adsorption energies of hydrogen molecules at all possible adsorption sites of covalent organic framework-1 (COF-1) are studied by density functional theory (DFT) and second-order Moller-Plesset perturbation theory (MP2). The most favorable adsorption sites from our DFT results are on the top of an oxygen atom for the B3O3 ring and on the top of the center of the C-C bond for the benzene ring when a single H-2 is interacting with the COF-1. The adsorption energy trend obtained from the DFT calculations is found to be in good agreement with the MP2 binding energy trend. The binding preferences are slightly changed when high hydrogen loading is considered. H-2 molecules prefer to be trapped on the top of the carbon atoms of the benzene ring and also on the top of the oxygen atoms of the B3O3 ring. These findings are confirmed by hydrogen center-of-mass distribution results obtained using molecular dynamics simulations. Moreover, our DFT results reveal that the hydrogen adsorption energies are boosted when we increase the number of hydrogen loadings due to attractive H-2-H-2 interactions. In addition, the nonavailability of the remaining adsorption sites in the COF-1 leads to a reduction of the H-2 mobility.

  • 524. Srepusharawoot, Pornjuk
    et al.
    Swatsitang, Ekaphan
    Amornkitbamrung, Vittaya
    Pinsook, Udomsilp
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hydrogen adsorption of Li functionalized Covalent Organic Framework-366: An ab initio study2013In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 38, no 33, p. 14276-14280Article in journal (Refereed)
    Abstract [en]

    This work deals with the investigations of hydrogen adsorption energies of the Li functionalized Covalent Organic Framework-366 (COF-366) by using the density functional theory method. Based on total energy calculations, it was found that Li atom is preferentially trapped at the center site of the tetra(p-amino-phenyl) porphyrin and the onN site of a terephthaldehyde chain. Moreover, hydrogen adsorption energies per H-2 for 1-3 H-2 loadings range from 0.03 to 0.22 eV. According to ab initio molecular dynamics simulations, our results found that hydrogen capacities of Li functionalized COF-366 at ambient pressure are 2.06, 1.58, and 1.05 wt% for 77, 150 and 298 K, respectively.

  • 525.
    Srivastava, Anurag
    et al.
    ABV Indian Inst Informat Technol & Management, CNT Lab, Adv Mat Res Grp, Gwalior 474015, MP, India..
    Khan, Md. Shahzad
    ABV Indian Inst Informat Technol & Management, CNT Lab, Adv Mat Res Grp, Gwalior 474015, MP, India..
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Electron transport in NH3/NO2 sensed buckled antimonene2018In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 272, p. 1-7Article in journal (Refereed)
    Abstract [en]

    The structural and electronic properties of buckled antimonene have been analysed using density functional theory based ab-initio approach. Geometrical parameters in terms of bond length and bond angle are found close to the single ruffle mono-layer of rhombohedral antimony. Inter-frontier orbital analyses suggest localization of lone pair electrons at each atomic centre. Phonon dispersion along with high symmetry point of Brillouin zone does not signify any soft mode. With an electronic band gap of 1.8eV, the quasi-2D nano-surface has been further explored for NH3/NO2 molecules sensing and qualities of interaction between NH3/NO2 gas and antimonene scrutinized in terms of electronic charges transfer. A current-voltage characteristic has also been analysed, using Non Equilibrium Green's function (NEGF), for antimonene, in presence of incoming NH3/NO2 molecules.

  • 526. Srivastava, Anurag
    et al.
    Sharma, Vikash
    Kaur, Kamalpreet
    Khan, Md. Shahzad
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Rao, V. K.
    Electron transport properties of a single-walled carbon nanotube in the presence of hydrogen cyanide: first-principles analysis2015In: Journal of Molecular Modeling, ISSN 1610-2940, E-ISSN 0948-5023, Vol. 21, no 7, article id 173Article in journal (Refereed)
    Abstract [en]

    First-principles analysis based on density functional theory was performed to compute the electronic and transport properties of a single-walled carbon nanotube in the presence of hydrogen cyanide. A chiral (4,1) carbon nanotube was found to become less metallic as the number of hydrogen cyanide molecules nearby increased. When there were a sufficient number of hydrogen cyanide molecules close to the nanotube, it became semiconducting. This metallic to semiconducting transformation of the nanotube was verified by analyzing its conductance and current as a function of the number of molecules of hydrogen cyanide present. The conductivity of the carbon nanotube was very high when no hydrogen cyanide molecules were present, but decreased considerably when even just a single hydrogen cyanide molecule approached the surface of the nanotube.

  • 527. Srivastava, Anurag
    et al.
    Tyagi, Neha
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    First-principles study of structural and electronic properties of gallium based nanowires2013In: Solid State Sciences, ISSN 1293-2558, E-ISSN 1873-3085, Vol. 23, p. 35-41Article in journal (Refereed)
    Abstract [en]

    Structural stability and electronic properties of GaX (X = N, P, As and Sb) nanowires have been investigated using first-principles based density function theory approach. Out of linear, zigzag, square and hexagon shaped configuration, the square shaped geometry is energetically most stable. The computation of lattice parameters, bulk modulus and pressure derivatives for these Ga based nanowires observes the highest bulk modulus for hexagonal shaped GaN nanowire amongst all, suggest the mechanical strength of this geometry. Electronic band structures analysis shows the semiconducting as well as metallic behavior of these nanowires.

  • 528.
    Strömme, Maria
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV.
    Jonsson, Anna-Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV.
    Skorodumova, Natalia V.
    Backholm, Jonas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV.
    Niklasson, A. Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV.
    Chronopotentiometry as a possible probe of the electron density of states of disordered electrochromic oxides2004In: Proc IME-6, International Meeting on Electrochromism, Brno, Czech, 2004, p. Aug. 29-Sept. 2, pp 56Conference paper (Refereed)
  • 529.
    Strømme, Maria
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    A new probe of the electron structure of amorphous materials2004In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 93, no 20, p. 206403-1Article in journal (Refereed)
  • 530.
    Suksaengrat, Pitphichaya
    et al.
    Khon Kaen Univ, Fac Sci, Dept Phys, Khon Kaen 40002, Thailand..
    Amornkitbamrung, Vittaya
    Khon Kaen Univ, Fac Sci, Dept Phys, Khon Kaen 40002, Thailand.;Khon Kaen Univ, Integrated Nanotechnol Res Ctr, Khon Kaen 40002, Thailand.;Nanotec KKU Ctr Excellence Adv Nanomat Energy Pro, Khon Kaen 40002, Thailand..
    Srepusharawoot, Pornjuk
    Khon Kaen Univ, Fac Sci, Dept Phys, Khon Kaen 40002, Thailand.;Khon Kaen Univ, Integrated Nanotechnol Res Ctr, Khon Kaen 40002, Thailand.;Nanotec KKU Ctr Excellence Adv Nanomat Energy Pro, Khon Kaen 40002, Thailand..
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Royal Inst Technol KTH, Dept Mat & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden..
    Density Functional Theory Study of Hydrogen Adsorption in a Ti-Decorated Mg-Based Metal-Organic Framework-742016In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 17, no 6, p. 879-884Article in journal (Refereed)
    Abstract [en]

    The Ti-binding energy and hydrogen adsorption energy of a Ti-decorated Mg-based metal-organic framework-74 (Mg-MOF-74) were evaluated by using first-principles calculations. Our results revealed that only three Ti adsorption sites were found to be stable. The adsorption site near the metal oxide unit is the most stable. To investigate the hydrogen-adsorption properties of Ti-functionalized Mg-MOF-74, the hydrogen-binding energy was determined. For the most stable Ti adsorption site, we found that the hydrogen adsorption energy ranged from 0.26 to 0.48eVH(2)(-1). This is within the desirable range for practical hydrogen-storage applications. Moreover, the hydrogen capacity was determined by using ab initio molecular dynamics simulations. Our results revealed that the hydrogen uptake by Ti-decorated Mg-MOF-74 at temperatures of 77, 150, and 298K and ambient pressure were 1.81, 1.74, and 1.29H(2)wt%, respectively.

  • 531.
    Sun, Weiwei
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Chakraborty, Sudip
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Stabilizing a hexagonal Ru2C via Lifshitz transition under pressure2013In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 103, no 25, p. 251901-Article in journal (Refereed)
    Abstract [en]

    A unique type of heavy transition metal carbide Ru2C was synthesized experimentally at high pressure-high temperature and consequently quenched to ambient condition. The dynamical stability study reveals the instability at ambient condition. We have found that it can be stabilized from 30 to 110 GPa. The stronger 4d-2p hybridization and the formation of a cage like Fermi surface do impact the stability. The mixed bands primarily 2p characteristic weighted crossing the Fermi level form a Fermi surface piece at Gamma point under pressure. The clear change of topology of Fermi surface verifies the Lifshitz transition from ambient condition to high pressure.

  • 532.
    Sun, Weiwei
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hussain, Tanveer
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    De Sarkar, Abir
    Maark, Tuhina Adit
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Improvement in the desorption of H-2 from the MgH2 (110) surface by means of doping and mechanical strain2014In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 86, p. 165-169Article in journal (Refereed)
    Abstract [en]

    In this letter, density functional theory has been employed to investigate the release or desorption of hydrogen from the MgH2 (1 1 0) surface. To improve upon the energetics for hydrogen desorption from this system, the effects of strain and doping by Al, Si, Ti have been explored. Both of these two effects have been found to be effective. The strain applied along the X direction induces more prominent effects than along the Y direction. Regarding the doping, the system doped with Al gives the most noticeable effect. The Si doped system shows the least improvement while the Ti doped system lies in between as compared to the other two. The combination of doping and strain effects is found to be more efficacious.

  • 533.
    Sun, Weiwei
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Role of correlation and relativistic effects in MAX phases2012In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 47, no 21, p. 7615-7620Article in journal (Refereed)
    Abstract [en]

    We have performed the ab initio calculations to study the role of correlation and relativistic effects in MAX phases. As of now, there are more than 50 MAX phases reported in the literature; however, we have chosen two MAX phases, namely Cr2AlC and Ta2AlC, as representatives of MAX phases for our study as they are very poorly described from calculation point of view. Our results show that correlation effects are very important to understand the electronic and mechanical properties of Cr2AlC, but not so important for Ta2AlC. We have also studied the relativistic effects on Ta2AlC and our calculations show that going from scalar to fully relativistic effects does not have any significant effect on the electronic and mechanical properties of Ta2AlC. We conclude that Ta2AlC is a weakly correlated system, whereas Cr2AlC is a strongly correlated system. Further experiments are needed to explain the discrepancy between theory and experiments.

  • 534.
    Sun, Weiwei
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. KTH Royal Inst Technol, Dept Mat Sci & Engn, SE-10044 Stockholm, Sweden..
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. KTH Royal Inst Technol, Dept Mat Sci & Engn, SE-10044 Stockholm, Sweden..
    Stability of a new cubic monoxide of Thorium under pressure2015In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 5, article id 13740Article in journal (Refereed)
    Abstract [en]

    Density functional theory has been applied to elucidate the stability of thorium monoxide (ThO). It is found out that the pressure can stabilize the rocksalt phase of ThO, and the transition pressure is estimated between 14 and 22 GPa. The stability of ThO can be attributed due to the gradually filling 5f orbitals at the expense of 7s and 6d electrons in Th metal. For ThO, the pressure induces stronger Th-O bond reflected by the newly established 6d-2p hybridization which is the dominant cause of its stability. The phonon dispersion curves of the rocksalt phase show the positive frequencies which indicates its dynamical stability. Our successful prediction of the stabilization of the metallic ThO has proposed a route to synthesize novel actinide monoxides.

  • 535.
    Sun, Weiwei
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. KTH Royal Inst Technol, Dept Mat Sci & Engn, SE-10044 Stockholm, Sweden..
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Feng, Qingguo
    Linkoping Univ, Dept Phys Chem & Biol, SE-58183 Linkoping, Sweden.;Linkoping Univ, SeRC, SE-58183 Linkoping, Sweden..
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. KTH Royal Inst Technol, Dept Mat Sci & Engn, SE-10044 Stockholm, Sweden..
    Anisotropic distortion and Lifshitz transition in alpha-Hf under pressure2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 11, article id 115130Article in journal (Refereed)
    Abstract [en]

    In this work we report a theoretical investigation on behavior of the elastic constant C-44 and the transverse optical phonon mode E(2)g of a-Hf under pressure within the density functional theory. In contrast to many other reported transition metals, the above two quantities do not show a synchronous relation as pressure increases. Below 13 GPa, an opposite shifting tendency has been observed. However, once the pressure is raised above 13 GPa, the trend is pulled back to be consistent. This anomalous behavior is figured out to be caused by the large lattice anisotropy of the c/a ratio along with the elastic anisotropy. The synchronous behavior is found to be in accordance with the behavior of c/a ratio with increased pressure. In our band-structure investigations the electronic topological transition has been discovered at 10 GPa, which relates to the change of c/a ratio suggested by recent literature. The presence of the Van Hove singularity shown in the densities of states has been identified and regarded as the origin of the variation of C-44 and E(2)g.

  • 536.
    Sun, Z
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Ahuja, Rajeev
    Applied Physics Letters2006In: Applied Physics Letters, Vol. 88, no 161914Article in journal (Refereed)
  • 537.
    Sun, Z
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Ahuja, Rajeev
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Structure of Phase Change materials for data storage2006In: Structure of Phase Change materials for data storage, Vol. 96, no 055507Article in journal (Refereed)
  • 538. Sun, Z.
    et al.
    Music, D.
    Ahuja, Rajeev
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics III. Physics IV.
    Li, Sa
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics III. Physics IV.
    Schneider, Jochen
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics III. Physics IV.
    Bonding and classification of nanolayered ternaray carbides2004In: Physical Review, Vol. B 70, p. 092102-Article in journal (Refereed)
  • 539. Sun, Z
    et al.
    Music, D.
    Ahuja, Rajeev
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics III. Physics IV.
    Schneider, Jochen
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics III. Physics IV.
    Calculated elastic properties of M2AlC M = Ti, V, Cr, Nb and Ta2004In: Solid State Comunications, Vol. 129, p. 589-Article in journal (Refereed)
  • 540.
    Sun, Zhimei
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Lowther, J. E.
    Mechanical properties of vanadium carbide and a ternary vanadium tungsten carbide2010In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 150, no 15-16, p. 697-700Article in journal (Refereed)
    Abstract [en]

    Ab initio total energy calculations are performed on non-stoichiometric vanadium carbide with supercells representing vacancy concentrations of VC0.875 and VC0.75. The VC0.875 supercell retains a cubic symmetry whilst in the case of the VC0.75 supercell C vacancies located in close proximity have the lowest energy configuration and the cubic lattice slightly distorts to a monoclinic symmetry. Using a stress strain calculational procedure, the elastic constants of both the cubic and the monoclinic systems are deduced. In all cases C vacancies decrease the elastic moduli. A similar analysis is then applied to consider when W is incorporated into VC. In this case it is found that the elastic moduli increase with W content suggesting that a V-W-C alloy could have significant potential as a novel hard material. (C) 2010 Elsevier Ltd. All rights reserved.

  • 541.
    Sun, Zhimei
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Kyrsta, Stepan
    Music, Denis
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Schneider, Jochen M.
    Structure of the Ge-Sb-Te phase-change materials studied by theory and experiment2007In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 143, no 4-5, p. 240-244Article in journal (Refereed)
    Abstract [en]

    We have studied the structure of GeSb2Te4, GeSb4Te7, and Ge3Sb2Te6 compounds using theoretical and experimental means. Based on ab initio calculations, we propose the stacking sequence in the [111] direction of GeSb2Te4, GeSb4Te7, and Ge3Sb2Te6 phases to be Te-Ge-Te-Sb-Te-v-Te-Sb-, Te-Ge-Te-Sb-Te-v-Te-Sb-Te-Sb-Te-v-Te-Sb-, and Te-Ge-Te-Ge-Te-Sb-Te-v-Te-Sb-Te-Ge-, respectively, where v is an ordered vacancy layer. This structural model agrees with the X-ray diffraction data of sputter-deposited Ge2Sb2Te5, GeSb2Te4, GeSb4Te7, and Ge3Sb2Te6 thin films.

  • 542. Sun, Zhimei
    et al.
    Pan, Yuanchun
    Zhou, Jian
    Sa, Baisheng
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Origin of p-type conductivity in layered nGeTe center dot mSb(2)Te(3) chalcogenide semiconductors2011In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 83, no 11, p. 113201-Article in journal (Refereed)
    Abstract [en]

    Ge2Sb2Te5, an extensively studied narrow-band-gap semiconductor for phase-change memories, always displays p-type conductivity. However, the defect physics and origin of the p-type conductivity are not yet clear. We have studied various types of defects in layered nGeTe center dot mSb(2)Te(3) (GST) using ab initio calculations. The results show that the formation energies of V-Ge are always the lowest followed by Sb-Te in the studied GST. The majority defects are V-Ge and Sb-Te, which results in the p-type conductivity of GST. Although Ge2Sb2Te5 always has a p-type character, one can make both p-and n-type GeSb2Te4 and GeSb4Te7 by tuning the atomic chemical environments.

  • 543.
    Sun, Zhimei
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Zhou, Jian
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Unique melting behavior in phase-change materials for rewritable data storage2007In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 98, no 5, p. 055505-Article in journal (Refereed)
    Abstract [en]

    Ge2Sb2Te5 (GST) is a technologically very important phase-change material for rewritable optical and electrical storage because it can be switched rapidly back and forth between amorphous and crystalline states for millions of cycles by appropriate pulsed heating. However, an understanding of this complicated phenomenon has not yet been achieved. Here, by ab initio molecular dynamics, we unravel the reversible phase transition process of GST. The melting of rocksalt-structured GST is unique in that it forms two-dimensional linear or tangled clusters while keeping order in the perpendicular direction. It is this specific character that results in the fast and reversible phase transition between amorphous and crystalline and hence rewritable data storage.

  • 544. Sun, Zhimei
    et al.
    Zhou, Jian
    Blomqvist, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Fast crystallization of chalcogenide glass for rewritable memories2008In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 93, no 6, p. 061913-Article in journal (Refereed)
    Abstract [en]

    By ab initio molecular dynamics simulations, we unraveled the unique network structure of amorphous Ge1Sb2Te4, which shows high rank of ordering and mostly consists of distorted defective octahedrons with a small portion of distorted tetrahedrons. The phase transition from amorphous to cubic Ge1Sb2Te4 would be mainly a process of angle rearrangements of tetrahedrons to octahedrons and vice versa.

  • 545. Sun, Zhimei
    et al.
    Zhou, Jian
    Blomqvist, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Formation of Large Voids in the Amorphous Phase-Change Memory Ge2Sb2Te5 Alloy2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 102, no 7, p. 075504-Article in journal (Refereed)
    Abstract [en]

    Onthe basis of ab initio molecular dynamics simulations, large voids mainlysurrounded by Te atoms are observed in molten and amorphousGe2Sb2Te5, which is due to the clustering of two- andthreefold coordinated Te atoms. Furthermore, pressure shows a significant effecton the clustering of the under coordinated Te atoms andhence the formation of large voids. The present results demonstratethat both vacancies and Te play an important role inthe fast reversible phase transition process.

  • 546. Sun, Zhimei
    et al.
    Zhou, Jian
    Blomqvist, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Xu, Lihua
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Local structure of liquid Ge1Sb2Te4 for rewritable data storage use2008In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 20, no 20, p. 205102-Article in journal (Refereed)
    Abstract [en]

    Phase-change materials based on chalcogenide alloys have been widely used for optical data storage and are promising materials for nonvolatile electrical memory use. However, the mechanism behind the utilization is unclear as yet. Since the rewritable data storage involved an extremely fast laser melt-quenched process for chalcogenide alloys, the liquid structure of which is one key to investigating the mechanism of the fast reversible phase transition and hence rewritable data storage, here by means of ab initio molecular dynamics we have studied the local structure of liquid Ge1Sb2Te4. The results show that the liquid structure gives a picture of most Sb atoms being octahedrally coordinated, and the coexistence of tetrahedral and fivefold coordination at octahedral sites for Ge atoms, while Te atoms are essentially fourfold and threefold coordinated at octahedral sites, as characterized by partial pair correlation functions and bond angle distributions. The local structure of liquid Ge1Sb2Te4 generally resembles that of the crystalline form, except for the much lower coordination number. It may be this unique liquid structure that results in the fast and reversible phase transition between crystalline and amorphous states.

  • 547. Sun, Zhimei
    et al.
    Zhou, Jian
    Mao, Ho-Kwang
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Peierls distortion mediated reversible phase transition in GeTe under pressure2012In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 109, no 16, p. 5948-5952Article in journal (Refereed)
    Abstract [en]

    With the advent of big synchrotron facilities around the world, pressure is now routinely placed to design a new material or manipulate the properties of materials. In GeTe, an important phase-change material that utilizes the property contrast between the crystalline and amorphous states for data storage, we observed a reversible phase transition of rhombohedral <-> rocksalt <-> orthorhombic <-> monoclinic coupled with a semiconductor <-> metal interconversion under pressure on the basis of ab initio molecular dynamics simulations. This interesting reversible phase transition under pressure is believed to be mediated by Peierls distortion in GeTe. Our results suggest a unique way to understand the reversible phase transition and hence the resistance switching that is crucial to the applications of phase-change materials in nonvolatile memory. The present finding can also be expanded to other IV-VI semiconductors.

  • 548. Sun, Zhimei
    et al.
    Zhou, Jian
    Pan, Yuanchun
    Song, Zhitang
    Mao, Ho-Kwang
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Pressure-induced reversible amorphization and an amorphous-amorphous transition in Ge2Sb2Te5 phase-change memory material2011In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 108, no 26, p. 10410-10414Article in journal (Refereed)
    Abstract [en]

    Ge2Sb2Te5 (GST) is a technologically very important phase-change material that is used in digital versatile disks-random access memory and is currently studied for the use in phase-change random access memory devices. This type of data storage is achieved by the fast reversible phase transition between amorphous and crystalline GST upon heat pulse. Here we report pressure-induced reversible crystalline-amorphous and polymorphic amorphous transitions in NaCl structured GST by ab initio molecular dynamics calculations. We have showed that the onset amorphization of GST starts at approximately 18 GPa and the system become completely random at approximately 22 GPa. This amorphous state has a cubic framework (c-amorphous) of sixfold coordinations. With further increasing pressure, the c-amorphous transforms to a high-density amorphous structure with trigonal framework (t-amorphous) and an average coordination number of eight. The pressure-induced amorphization is investigated to be due to large displacements of Te atoms for which weak Te-Te bonds exist or vacancies are nearby. Upon decompressing to ambient conditions, the original cubic crystalline structure is restored for c-amorphous, whereas t-amorphous transforms to another amorphous phase that is similar to the melt-quenched amorphous GST.

  • 549. Sun, Zhimei
    et al.
    Zhou, Jian
    Shin, Hyun-Joon
    Blomqvist, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Stable nitride complex and molecular nitrogen in N doped amorphous Ge2Sb2Te52008In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 93, no 24, p. 241908-Article in journal (Refereed)
    Abstract [en]

    Nitrogen doping is identified to be a sufficient way to reduce the power consumption of Ge2Sb2Te5, a phase-change material for data storage. On the basis of ab initio molecular dynamics simulations, we show that the doped N in amorphous Ge2Sb2Te5 coexist as Ge(Sb, Te)N complex and N-2, and high density of the film produces more N-2. Furthermore, both Ge(Sb, Te)N complex and N-2 are stable upon annealing at 600 K.

  • 550.
    Sundaram, Manickam Minakshi
    et al.
    Murdoch Univ, Dept Chem, Murdoch, WA 6150, Australia..
    Watcharatharapong, Teeraphat
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Chakraborty, Sudip
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Duraisamy, Shanmughasundaram
    Indian Inst Sci, Inorgan & Phys Chem, Bangalore 560012, Karnataka, India..
    Rao, Penki Tirupathi
    Indian Inst Sci, Inorgan & Phys Chem, Bangalore 560012, Karnataka, India..
    Munichandraiah, Nookala
    Indian Inst Sci, Inorgan & Phys Chem, Bangalore 560012, Karnataka, India..
    Synthesis, and crystal and electronic structure of sodium metal phosphate for use as a hybrid capacitor in non-aqueous electrolyte2015In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 44, no 46, p. 20108-20120Article in journal (Refereed)
    Abstract [en]

    Energy storage devices based on sodium have been considered as an alternative to traditional lithium based systems because of the natural abundance, cost effectiveness and low environmental impact of sodium. Their synthesis, and crystal and electronic properties have been discussed, because of the importance of electronic conductivity in supercapacitors for high rate applications. The density of states of a mixed sodium transition metal phosphate (maricite, NaMn1/3Co1/3Ni1/3PO4) has been determined with the ab initio generalized gradient approximation (GGA)+Hubbard term (U) method. The computed results for the mixed maricite are compared with the band gap of the parent NaFePO4 and the electrochemical experimental results are in good agreement. A mixed sodium transition metal phosphate served as an active electrode material for a hybrid supercapacitor. The hybrid device (maricite versus carbon) in a nonaqueous electrolyte shows redox peaks in the cyclic voltammograms and asymmetric profiles in the charge-discharge curves while exhibiting a specific capacitance of 40 F g(-1) and these processes are found to be quasi-reversible. After long term cycling, the device exhibits excellent capacity retention (95%) and coulombic efficiency (92%). The presence of carbon and the nanocomposite morphology, identified through X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) studies, ensures the high rate capability while offering possibilities to develop new cathode materials for sodium hybrid devices.

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