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  • 501.
    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)
  • 502. 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)
  • 503. 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)
  • 504.
    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.

  • 505.
    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.

  • 506. 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.

  • 507.
    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.

  • 508. 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.

  • 509. 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.

  • 510. 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.

  • 511. 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.

  • 512. 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.

  • 513. 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.

  • 514.
    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.

  • 515.
    Susanne, Höfner
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Astronomy and Space Physics.
    Bladh, S.
    Univ Padua, Dipartimento Fis & Astron Galileo Galilei, Vicolo Osservatorio 3, I-35122 Padua, Italy..
    Aringer, B.
    Univ Padua, Dipartimento Fis & Astron Galileo Galilei, Vicolo Osservatorio 3, I-35122 Padua, Italy.;Osserv Astron Padova, INAF, Vicolo Osservatorio 5, I-35122 Padua, Italy..
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Dynamic atmospheres and winds of cool luminous giants I. Al2O3 and silicate dust in the close vicinity of M-type AGB stars2016In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 594, article id A108Article in journal (Refereed)
    Abstract [en]

    Context. In recent years, high spatial resolution techniques have given valuable insights into the complex atmospheres of AGB stars and their wind-forming regions. They make it possible to trace the dynamics of molecular layers and shock waves, to estimate dust condensation distances, and to obtain information on the chemical composition and size of dust grains close to the star. These are essential constraints for understanding the mass loss mechanism, which presumably involves a combination of atmospheric levitation by pulsation-induced shock waves and radiation pressure on dust, forming in the cool upper layers of the atmospheres. Aims. Spectro-interferometric observations indicate that Al2O3 condenses at distances of about 2 stellar radii or less, prior to the formation of silicates. Al2O3 grains are therefore prime candidates for producing the scattered light observed in the close vicinity of several M-type AGB stars, and they may be seed particles for the condensation of silicates at lower temperatures. The purpose of this paper is to study the necessary conditions for the formation of Al2O3 and the potential effects on mass loss, using detailed atmosphere and wind models. Methods. We have constructed a new generation of Dynamic Atmosphere and Radiation-driven Wind models based on Implicit Numerics (DARWIN), including a time-dependent treatment of grain growth and evaporation for both Al2O3 and Fe-free silicates (Mg2SiO4). The equations describing these dust species are solved in the framework of a frequency-dependent radiation hydrodynamical model for the atmosphere and wind structure, taking pulsation-induced shock waves and periodic luminosity variations into account. Results. Condensation of Al2O3 at the close distances and in the high concentrations implied by observations requires high transparency of the grains in the visual and near-IR region to avoid destruction by radiative heating. We derive an upper limit for the imaginary part of the refractive index k around 10(-3) at these wavelengths. For solar abundances, radiation pressure due to Al2O3 is too low to drive a wind. Nevertheless, this dust species may have indirect effects on mass loss. The formation of composite grains with an Al2O3 core and a silicate mantle can give grain growth a head start, increasing both mass loss rates and wind velocities. Furthermore, our experimental core-mantle grain models lead to variations of visual and near-IR colors during a pulsation cycle which are in excellent agreement with observations. Conclusions. Al2O3 grains are promising candidates for explaining the presence of gravitationally bound dust shells close to M-type AGB stars, as implied by both scattered light observations and mid-IR spectro-interferometry. The required level of transparency at near-IR wavelengths is compatible with impurities due to a few percent of transition metals (e.g., Cr), consistent with cosmic abundances. Grains consisting of an Al2O3 core and an Fe-free silicate mantle with total grain radii of about 0.1-1 micron may be more efficient at driving winds by the scattering of stellar photons than pure Fe-free silicate grains.

  • 516. Tay, Qiuling
    et al.
    Kanhere, Pushkar
    Ng, Chin Fan
    Chen, Shi
    Chakraborty, Sudip
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Huan, Alfred Cheng Hon
    Sum, Tze Chien
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Chen, Zhong
    Defect Engineered g-C3N4 for Efficient Visible Light Photocatalytic Hydrogen Production2015In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 27, no 14, p. 4930-4933Article in journal (Refereed)
  • 517. Tien, Nguyen Thanh
    et al.
    Phuc, Vo Trung
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Tuning electronic transport properties of zigzag graphene nanoribbons with silicon doping and phosphorus passivation2018In: AIP Advances, ISSN 2158-3226, E-ISSN 2158-3226, Vol. 8, no 8, article id 085123Article in journal (Refereed)
    Abstract [en]

    Density-functional theory in combination with the non-equilibrium Green's function formalism is used to study the effect of silicon doping and phosphorus passivation on the electronic transport properties of zigzag graphene nanoribbons (ZGNRs). We study the edge structures passivated by H atoms and by P atoms. In this work, Si atoms are used to substitute C atoms located at the edge of the samples. We consider ZGNRs terminated by H and P atoms with four zigzag carbon chains (4-ZGNRs) in case of six various configurations. Our calculated results determine that the Si doping improves significantly the current of samples by the number of dopants. Moreover, there is dramatical difference in the transmission spectrum of P-passivated ZGNRs and H-passivated ZGNRs i.e. P passivation not only destroys an enhanced transmission at the Fermi level, which is typical for graphene nanoribbons, but also increases considerably the intensity of transmission spectrum with ballistic transport properties. Furthermore, the numerical results illustrate that pristine H-terminated samples have a broadening band gap in transmission spectra when the bias voltage increases. The relationship between the outcomes indicates that such silicon doping and phosphorus passivation are effective and providing a promising way to modulate the properties of ZGNRs for nanoelectronic device applications. 

  • 518.
    Triana, Carlos A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Araujo, Carlos Moyses
    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.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Edvinsson, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Disentangling the intricate atomic short-range order and electronic properties in amorphous transition metal oxides2017In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 2044Article in journal (Refereed)
    Abstract [en]

    Solid state materials with crystalline order have been well-known and characterized for almost a century while the description of disordered materials still bears significant challenges. Among these are the atomic short-range order and electronic properties of amorphous transition metal oxides [aTMOs], that have emerged as novel multifunctional materials due to their optical switching properties and high-capacity to intercalate alkali metal ions at low voltages. For decades, research on aTMOs has dealt with technological optimization. However, it remains challenging to unveil their intricate atomic short-range order. Currently, no systematic and broadly applicable methods exist to assess atomic-size structure, and since electronic localization is structure-dependent, still there are not well-established optical and electronic mechanisms for modelling the properties of aTMOs. We present state-of-the-art systematic procedures involving theory and experiment in a self-consistent computational framework to unveil the atomic short-range order and its role for the electronic properties. The scheme is applied to amorphous tungsten trioxide aWO(3), which is the most studied electrochromic aTMO in spite of its unidentified atomic-size structure. Our approach provides a one-to-one matching of experimental data and corresponding model structure from which electronic properties can be directly calculated in agreement with the electronic transitions observed in the XANES spectra.

  • 519.
    Tsuppayakorn-aek, Prutthipong
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Chulalongkorn Univ, ECPRL, Dept Phys, Fac Sci, Bangkok 10330, Thailand.;Chulalongkorn Univ, PEMRU, Dept Phys, Fac Sci, Bangkok 10330, Thailand.;Commiss Higher Educ, Thailand Ctr Excellence Phys, 328 Si Ayutthaya Rd, Bangkok 10400, Thailand..
    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. Royal Inst Technol KTH, Appl Mat Phys, Dept Mat & Engn, SE-10044 Stockholm, Sweden..
    Bovornratanaraks, Thiti
    Chulalongkorn Univ, ECPRL, Dept Phys, Fac Sci, Bangkok 10330, Thailand.;Chulalongkorn Univ, PEMRU, Dept Phys, Fac Sci, Bangkok 10330, Thailand.;Commiss Higher Educ, Thailand Ctr Excellence Phys, 328 Si Ayutthaya Rd, Bangkok 10400, Thailand..
    The High-Pressure Superconducting Phase of Arsenic2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 3026Article in journal (Refereed)
    Abstract [en]

    Ab initio random structure searching (AIRSS) technique is predicted a stable structure of arsenic (As). We find that the body-centered tetragonal (bct) structure with spacegroup I4(1)/acd to be the stable structure at high pressure. Our calculation suggests transition sequence from the simple cubic (sc) structure transforms into the host-guest (HG) structure at 41 GPa and then into the bct structure at 81 GPa. The bct structure has been calculated using ab initio lattice dynamics with finite displacement method confirm the stability at high pressure. The spectral function alpha F-2 of the bct structure is higher than those of the body-centered cubic (bcc) structure. It is worth noting that both bct and bcc structures share the remarkable similarity of structural and property. Here we have reported the prediction of temperature superconductivity of the bct structure, with a T-c of 4.2 K at 150 GPa.

  • 520.
    Tsuppayakorn-aek, Prutthipong
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Chulalongkorn Univ, Fac Sci, ECPRL, Bangkok 10330, Thailand;Chulalongkorn Univ, Fac Sci, PEMRU, Dept Phys, Bangkok 10330, Thailand;Thailand Ctr Excellence Phys, Commiss Higher Educ, 328 Si Ayutthaya Rd, Bangkok 10400, Thailand.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Watcharatharapong, Teeraphat
    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.
    Bovornratanaraks, Thiti
    Chulalongkorn Univ, Fac Sci, ECPRL, Bangkok 10330, Thailand;Chulalongkorn Univ, Fac Sci, PEMRU, Dept Phys, Bangkok 10330, Thailand;Thailand Ctr Excellence Phys, Commiss Higher Educ, 328 Si Ayutthaya Rd, Bangkok 10400, Thailand.
    Structural prediction of host-guest structure in lithium at high pressure2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 5278Article in journal (Refereed)
    Abstract [en]

    Ab initio random structure searching (AIRSS) technique is used to identify the high-pressure phases of lithium (Li). We proposed the transition mechanism from the fcc to host-guest (HG) structures at finite temperature and high pressure. This complex structural phase transformation has been calculated using ab initio lattice dynamics with finite displacement method which confirms the dynamical harmonic stabilization of the HG structure. The electron distribution between the host-host atoms has also been investigated by electron localization function (ELF). The strongly localized electron of p bond has led to the stability of the HG structure. This remarkable result put the HG structure to be a common high-pressure structure among alkali metals.

  • 521. Umrao, Sima
    et al.
    Abraham, Shiju
    Theil, Frank
    Pandey, Shobhit
    Ciobota, Valerian
    Shukla, P. K.
    Rupp, Caroline J.
    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.
    Popp, Juergen
    Dietzek, Benjamin
    Srivastava, Anchal
    A possible mechanism for the emergence of an additional band gap due to a Ti-O-C bond in the TiO2-graphene hybrid system for enhanced photodegradation of methylene blue under visible light2014In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 4, no 104, p. 59890-59901Article in journal (Refereed)
    Abstract [en]

    Here we report the experimental and theoretical study of two TiO2-graphene oxide (TG) and TiO2-reduced graphene oxide (TR) composites synthesized by a facile and ecological route, for enhanced visible light (similar to 470 nm) photocatalytic degradation of Methylene Blue (MB) (99% efficiency), with high rate constant values (1800% over bare TiO2). TG couples TiO2 nanopowder with Graphene Oxide (GO) while TR couples it with reduced graphene oxide (RGO). The present study, unlike previous reports, discusses never-before-reported double absorption edges obtained for both TG (3.51 eV and 2.51 eV) and TR (3.42 eV and 2.39 eV) composites, which represents the reason behind feasible visible light (2.56 eV) induced photocatalysis. TiO2 domains in the composites dominate the higher band edge, while GO/RGO domains explain the lower band edge. Formation of Ti-O-C bonds in both TG and TR drives the shifting upwards of the valence band edge and reduction in band gap. Further, these bonds provide a conductive pathway for charge carriers from TiO2 nanopowder to the degraded species via the GO/RGO matrix, resulting in decreased charge carrier recombination in TiO2 and enhanced efficiency. To attest that the developed theory is correct, density function theory (DFT) calculations were performed. DFT obtained energetics and electronic structures support experimental findings by demonstrating the role of the Ti-O-C bond, which results in double band edge phenomenon in composites. Finally, the mechanism behind MB degradation is discussed comprehensively and the effect of the weight percent of GO/RGO in the composite on the rate constant and photodegradation efficiency has been studied experimentally and explained by developing analytical equations.

  • 522.
    Vitos, Levente
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Magyari-Kope, B
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Kollar, J
    Grimvall, G
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Phase transformations between garnet and perovskite phases in the Earth's mantle: A theoretical study2006In: Physics of the Earth and Planetary Interiors, Vol. 156, p. 108-116Article in journal (Refereed)
  • 523. Wang, B. C.
    et al.
    Nisar, Jawad
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Pathak, Biswarup
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kang, T. W.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Band gap engineering in BiNbO4 for visible-light photocatalysis2012In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 100, no 18, p. 182102-Article in journal (Refereed)
    Abstract [en]

    We have investigated the electronic structure of anionic mono- (S, N, and C) and co-doping (N-N, C-N, S-C, and S-N) on BiNbO4 for the visible-light photocatalysis. The maximum band gap reduction of pure BiNbO4 is possible with the (C-S) co-doping and minimum with N mono-doping. The calculated binding energies show that the co-doped systems are more stable than their mono-doped counterparts. Our optical absorption curves indicate that the mono- (C) and co-anionic doped (N-N and C-S) BiNbO4 systems are promising materials for visible light photocatalysis.

  • 524. Wang, Baochang
    et al.
    Arhammar, Cecilia
    Jiang, Xue
    Araujo, Carlos Moyses Graca
    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.
    A Comparison Between Hybrid Functional, GW Approach and the Bethe Salpether Equation: Optical Properties of High Pressure Phases of TiO22014In: Science of Advanced Materials, ISSN 1947-2935, Vol. 6, no 6, p. 1170-1178Article in journal (Refereed)
    Abstract [en]

    Titanium dioxide has good corrosion resistance in aqueous solutions and is a good candidate for photoelectrodes. The limitation of the anatase phase of TiO2 is its large band gap. High pressure phases of TiO2 like fluorite, pyrite and cotunnite may possess a more suitable band gap than the well known atmospheric phases. In this paper, the electronic properties of high pressure phases of TuO(2), fluorite, pyrite and cotunnite, have been investigated by hybrid functional and GW methods. Our calculations suggest that the band gap of fluorite and pyrite phases have optimal band gaps to absorb visible light for photocatalysis to decompose water. The imaginary part of the dielectric function has also been calculated for fluorite, pyrite, cotunnite and anatase phases using the Bethe-Salpether (BSE) method. The dielectric function calculated by BSE for the anatase phase agrees well with experiment and with previous studies, using the same level of theory. Therefore we expect that we are also able to predict the optical properties of the high pressure phases of TiO2 by the BSE method. The spatial properties and the localization character of excitons in these high pressure phases were investigated and discussed in terms of photoconversion efficiency.

  • 525. Wang, Baochang
    et al.
    Kanhere, Pushkar D.
    Chen, Zhong
    Nisar, Jawad
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Pathak, Biswarup
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Anion-Doped NaTaO3 for Visible Light Photocatalysis2013In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 44, p. 22518-22524Article in journal (Refereed)
    Abstract [en]

    In this paper, we have employed DFT and HSE06 methods to study the doping effects on the NaTaO3 photocatalyst. N, S, C, and P monodoping and N-N, C-S, P-P, and N-P codoping have been studied. The redopants' formation energies have been calculated, and we find S monodoping is energetically more favorable than any other elemental doping. The mechanism of anion doping on the electronic properties of NaTaO3 is discussed. We find the band gap reduces significantly if we dope with anionic elements whose p orbital energy is higher than the O 2p orbitals. N and S can shift the valence band edge upward without losing the ability to split water into H-2 and O-2. Double-hole-mediated codoping can decrease the band gap significantly. On the basis of our calculations, codoping with N-N, C-S, and P-P could absorb visible light. However, they can only decompose water into H-2 when the valence band edge is above the water oxidation level.

  • 526. Wang, Baochang
    et al.
    Lilja, Mirjam
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Ma, Taoran
    Soerensen, Jan
    Steckel, Hartwig
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Strömme, Maria
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Theoretical and experimental study of the incorporation of tobramycin and strontium-ions into hydroxyapatite by means of co-precipitation2014In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 314, p. 376-383Article in journal (Refereed)
    Abstract [en]

    Antibiotic incorporation into hydroxyapatite (HA) coatings by co-precipitation and the impact of bone relevant doping elements on the adsorption kinetics are investigated from both theoretical and experimental points of view. Tobramycin interactions with bioactive TiO2 and HA surfaces are analyzed using density functional theory. According to the calculations, the drug molecule has larger adsorption energy than the Ca+ ion on both surfaces under study in Phosphate Buffered Saline (PBS). The results support the experimental observations that HA nucleation and growth are strongly limited on TiO2 surfaces in the presence of clinically relevant antibiotic concentrations in PBS. The drug molecule is more likely to adopt parallel arrangement onto the HA surface, as the adsorption energy of such arrangement is higher compared to a perpendicular one. Strontium substitution of the HA surface is found to results in a weaker drug-surface interaction, and leads also to a decrease in coating thickness. However, the presence of strontium gives rise to a coating morphology with enhanced drug incorporation capacity and slower antibiotic release compared to non-substituted, co-precipitated counterparts. Our theoretical calculation results were found to be in excellent agreement with experimental data and provide a powerful tool to understand the interaction mechanism between drug and different surface chemistries necessary for development of future versatile orthopedic and dental implant surfaces.  

  • 527.
    Wang, Baochang
    et al.
    Department of Materials and Engineering, The Royal Institute of Technology (KTH).
    Nisar, Jawad
    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.
    Molecular simulation for gas adsorption at NiO (100) surface2012In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 4, no 10, p. 5691-5697Article in journal (Refereed)
    Abstract [en]

    Density functional theory (DFT) calculations have been employed to explore the gas-sensing mechanisms of NiO (100) surface on the basis of energetic and electronic properties. We have calculated the adsorption energies of NO 2, H 2S, and NH 3 molecules on NiO (100) surface using GGA+U method. The calculated results suggest that the interaction of NO 2 molecule with NiO surface becomes stronger and contributes more extra peaks within the band gap as the coverage increases. The band gap of H 2S-adsorbed systems decrease with the increase in coverage up to 0.5 ML and the band gap does not change at 1 ML because H 2S molecules are repelled from the surface. In case of NH 3 molecular adsorption, the adsorption energy has been increased with the increase in coverage and the band gap is directly related to the adsorption energy. Charge transfer mechanism between the gas molecule and the NiO surface has been illustrated by the Bader analysis and plotting isosurface charge distribution. It is also found that that work function of the surfaces shows different behavior with different adsorbed gases and their coverage. The work function of NO 2 gas adsorption has a hill-shaped behavior, whereas H 2S adsorption has a valley-shaped behavior. The work function of NH 3 adsorption decreases with the increase in coverage. On the basis of our calculations, we can have a better understanding of the gas-sensing mechanism of NiO (100) surface toward NO 2, H 2S, and NH 3 gases

  • 528. Wang, Baochang
    et al.
    Nisar, Jawad
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Almeida, Cristiane Gomes
    Santos Mascarenhas, Artur Jose
    Silva, Luciana Almeida
    Francis David, Denis Gilbert
    Bargiela, Pascal
    Araujo, Carlos Moyses
    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.
    da Silva, Antonio Ferreira
    Optical and electronic properties of nanosized BiTaO4 and BiNbO4 photocatalysts: Experiment and theory2014In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 251, no 5, p. 1034-1039Article in journal (Refereed)
    Abstract [en]

    Nanosized BiTaO4 and BiNbO4 were prepared by the citrate method. The electronic and optical properties of BiTaO4 and BiNbO4 have been investigated by means of photo-acoustic spectroscopy (PAS), X-ray photo-electron spectroscopy (XPS), and first-principles calculations based on density functional theory. The measured valence band (from XPS) of both materials agreed well with the theoretical findings. It was also found that the calculated optical properties such as dynamical dielectric function and optical absorption spectra are in good agreement with the experimental findings. According to the absorption spectra, the absorption edges of BiNbO4 and BiTaO4 are located at 370 and 330nm, respectively. Both phases have the ability to harvest UV light and relatively high surface area to volume ratio and can be used as UV/visible light-driven photocatalysts.

  • 529. Wang, Jianhui
    et al.
    Liu, Tao
    Wu, Guotao
    Li, Wen
    Liu, Yongfeng
    Araújo, C 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.
    Blomqvist, Andreas
    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.
    Xiong, Zhitao
    Yang, Ping
    Gao, Mingxia
    Pan, Hongge
    Chen, Ping
    Potassium-modified Mg(NH2)2/2 LiH system for hydrogen storage2009In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 48, no 32, p. 5828-5832Article in journal (Refereed)
  • 530.
    Wang, Peng
    et al.
    Dalian Univ Technol, Key Lab Mat Modificat Laser Ion & Electron Beams, Minist Educ, Dalian 116024, Peoples R China..
    Jiang, Xue
    Dalian Univ Technol, Key Lab Mat Modificat Laser Ion & Electron Beams, Minist Educ, Dalian 116024, Peoples R China..
    Hu, Jun
    Soochow Univ, Coll Phys Optoelect & Energy, Suzhou 215006, Jiangsu, Peoples R China..
    Huang, Xiaoming
    Dalian Univ Technol, Sch Ocean Sci & Technol, Panjin Campus, Panjin 124221, Peoples R China..
    Zhao, Jijun
    Dalian Univ Technol, Key Lab Mat Modificat Laser Ion & Electron Beams, Minist Educ, Dalian 116024, Peoples R China..
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Royal Inst Technol, Dept Mat & Engn, S-10044 Stockholm, Sweden.
    Prediction of huge magnetic anisotropies in 5d transition metallocenes2017In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 29, no 43, article id 435802Article in journal (Refereed)
    Abstract [en]

    The stability, electronic structure and non-collinear magnetic properties of a series of 5d metallocenes, namely, two cyclopentadienyl (Cp) rings sandwiched with a single 5d transition metal atom, are investigated. Our first-principles calculations reveal that Cp rings not only provide a suitable ligand environment for metal atoms, but also result in tunable magnetism depending on the transition metal element. Among them, HfCp2 and WCp2 show a high preference for the magnetization axis perpendicular to the Cp plane, with large magnetic anisotropy energies (MAEs) around 10 meV. We further consider triple decker metallocenes (M2Cp3), and find a huge MAE of above 60 meV in Ta2Cp3. The orbital energy split and shifts induced by composition change in metallocenes is mainly responsible for the significant MAE enhancement. By choosing a suitable crystal field for transition metal atoms, we pave a feasible pathway for designing promising building blocks of future magnetic storage devices.

  • 531.
    Wang, Y
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Ahuja, Rajeev
    Eriksson, Olle
    Johansson, Börje
    Grimvall, G.
    H-point vibration: precise solution of Mo, Fe and Na2002In: J.Phys. Cond. Matt., Vol. 14, p. L453-Article in journal (Other academic)
  • 532. Wang, Y
    et al.
    Johansson, Börje
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics IV.
    Ahuja, Rajeev
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics IV.
    Mean-field potential calculations of shock-compressed porous carbon2005In: Physical Review B, Vol. 71, p. 054110-Article in journal (Refereed)
  • 533. Wang, Y.
    et al.
    Liu, Z. -K
    Chen, L. -Q
    Burakovsky, L.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    First-principles calculations on MgO: Phonon theory versus mean-field potential approach2006In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 100, no 2, p. 023533-Article in journal (Refereed)
    Abstract [en]

    Various thermodynamic properties of MgO were studied using both ab initio phonon theory and the mean-field potential (MFP) approach. They include thermal pressure, thermal expansion, the 300 K equation of state, and the shock Hugoniot. It is found that the results of ab initio phonon theory and the MFP approach agree with each other, except that ab initio phonon theory gave a poor description of the thermal pressure when temperature became relatively high.

  • 534. Wang, Y
    et al.
    Liu, Z.K.
    Chen, LQ
    Burakovsky, L
    Ahuja, Rajeev
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    First-principles calculation of MgO : Phonon theory vs mean field potential approach2006In: J. Appl. Phys., Vol. 100, p. 023533-Article in journal (Refereed)
  • 535.
    Wani, Ishtiaq Hassan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Jafri, Syed Hassan Mujtaba
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Wärnå, John
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hayat, Aqib
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Li, Hu
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Shukla, Vivekanand
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Orthaber, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Grigoriev, Anton
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Ahuja, Rajeev
    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 and Astronomy, Materials Theory. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical 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, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    LEIFER, KLAUS
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Sub 20 nm metal-conjugated molecule junctions acting as a nitrogen dioxide sensorManuscript (preprint) (Other academic)
  • 536.
    Wani, Ishtiaq Hassan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Orthaber, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Jafri, Syed Hassan Mujtaba
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Grigoriev, Anton
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Ahuja, Rajeev
    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 and Astronomy, Materials Theory. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical 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, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    LEIFER, KLAUS
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Change of random telegraph conductance signal in different gas atmospheres in a nano molecular electronic deviceManuscript (preprint) (Other academic)
  • 537.
    Watcharatharapong, Teeraphat
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sundaram, Manickam Minakshi
    Murdoch Univ, Australia.
    Chakraborty, Sudip
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Li, Dan
    Murdoch Univ, Australia.
    Shafiullah, G. M.
    Murdoch Univ, Australia.
    Aughterson, Robert D.
    Australian Nucl Sci & Technol Org.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Effect of Transition Metal Cations on Stability Enhancement for Molybdate-Based Hybrid Supercapacitor2017In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 9, no 21, p. 17977-17991Article in journal (Refereed)
    Abstract [en]

    The race for better electrochemical energy storage systems has prompted examination of the stability in the molybdate framework (MMoO4; M = Mn, Co, or Ni), based on a range of transition metal cations from both computational and experimental approaches. Molybdate materials synthesized:with controlled nano scale morphologies (such as nanorods, agglomerated nanostructures, and nanoneedles for Mn, Co, and Ni elements, respectively) have been used as a cathode in hybrid energy storage systems. The computational and experimental data confirms that the MnMoO4 crystallized in beta-form with alpha-MnMoO4 type whereas Co and Ni cations crystallized in alpha-form with alpha-CoMoO4 type structure. Among the various transition metal Cations studied, hybrid device comprising NiMoO4 vs activated carbon exhibited excellent electrochemical performance having the specific capacitance 82 F g(-1) at a current density of 0.1 A g(-1) but the cycling Stability, needed to be significantly improved. The specific capacitance of the NiMoO4 electrode material is shown to be directly related to the surface area of the electrode/electrolyte interface, but the CoMoO4 and MnMoO4 favored a bulk formation that could be suitable for structural stability. The useful insights from the electronic structure analysis and effective mass have been provided to: demonstrate the role of cations in the molybdate structure and its influence in electrochemical energy storage. With improved cycling stability, NiMoO4 can be suitable for renewable energy storage. Overall, this study will enable the development of next generation molybdate materials with multiple cation substitution resulting,in better cycling stability and higher specific capacitance.

  • 538.
    Watcharatharapong, Teeraphat
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    T-Thienprasert, Jiraroj
    Kasetsart Univ, Fac Sci, Dept Phys, Bangkok 10900, Thailand..
    Barpanda, Prabeer
    Indian Inst Sci, Mat Res Ctr, Faraday Mat Lab, Bangalore 560012, Karnataka, India..
    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, S-10044 Stockholm, Sweden..
    Chakraborty, Sudip
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Mechanistic study of Na-ion diffusion and small polaron formation in Kröhnkite Na2Fe(SO4)2·2H2O based cathode materials2017In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 5, no 41, p. 21726-21739Article in journal (Refereed)
    Abstract [en]

    Kröhnkite-type Na2Fe(SO4)2·2H2O mineral is a sustainable and promising polyanionic cathode that has been experimentally found to offer a high redox potential (3.25 V vs. Na/Na+) along with fast-ion diffusion and high reversibility. Owing to the structural complexity, Na+ diffusion was assumed to occur along a convoluted channel along the b-axis. However, theoretical work related to this material still appears missing to support that statement. In this work, DFT+U calculations have been performed with the primary aim to unveil the Na+ diffusion mechanism in this material. The electronic structure and charge transfer are also envisaged to reveal evidence of Fe2+/3+ redox reaction and a vital role of structural H2O. Based on formation energies of this material with varied Na concentration, a calculated voltage profile is determined to show two voltage plateaus at 4.81 and 3.51 V, corresponding to experimental results. Nudged elastic band calculation reveals that Na+ diffusion is primarily occuring in the [01] direction with a moderate ionic mobility due to the structural distortion induced during migration, suggesting the possibility of defect-assisted diffusion. Intriguingly, the formation of small hole polarons is first observed, and could play a key role in the electronic conduction of this material.

  • 539.
    Wilhelmsson, Ola
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
    Palmquist, Jens-Petter
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
    Lewin, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
    Emmerlich, J.
    Eklund, P.
    Persson, P.O.Å.
    Högberg, H.
    Li, S.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Eriksson, O.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Hultman, L.
    Jansson, Ulf
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
    Deposition and characterization of ternary thin films within the Ti–Al–C system by DC magnetron sputtering2006In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 291, no 1, p. 290-300Article in journal (Refereed)
    Abstract [en]

    The formation of ternary compounds within the Ti–Al–C system was studied by magnetron sputtering for thin-film deposition and first-principles calculations for phase stability. As-deposited films were characterized with X-ray diffraction (XRD) and high-resolution transmission electron microscopy (TEM). The hardness and Young's moduli of the material were studied by nanoindentation. Epitaxial and phase-pure films of Mn+1AXn phases Ti3AlC2 and Ti2AlC as well as the perovskite phase Ti3AlC were deposited on Al2O3(00ℓ) wafers kept at temperatures between 800 and 900 °C. The only ternary phases observed at low temperatures (300 °C) were Ti3AlC and cubic (Ti,Al)C, the latter can be described as a metastable solid solution of Al in TiC similar to the more studied (Ti,Al)N system. The difficulties to form MAX phases at low substrate temperatures were attributed of requirement for a sufficient diffusivity to partition the elements corresponding to the relatively complex crystal structures with long c-axes. While MAX-phase synthesis at 800 °C is significantly lower than contemporary bulk sintering processes, a reduction of the substrate temperature towards 300 °C in the present thin-film deposition experiments resulted in stacking sequence variations and the intergrowth of (Ti,Al)C.

  • 540.
    Yang, Xiao
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Yanshan Univ, Coll Civil Engn & Mech, Qin Huangdao 066004, Hebei, Peoples R China..
    Li, Huijian
    Yanshan Univ, Coll Civil Engn & Mech, Qin Huangdao 066004, Hebei, Peoples R China..
    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, S-10044 Stockholm, Sweden..
    Kang, Taewon
    Dongguk Univ, Nano Informat Technol Acad, Seoul 100715, South Korea..
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Dongguk Univ, Nano Informat Technol Acad, Seoul 100715, South Korea..
    Formation and electronic properties of palladium hydrides and palladium-rhodium dihydride alloys under pressure2017In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 3520Article in journal (Refereed)
    Abstract [en]

    We present the formation possibility for Pd-hydrides and Pd-Rh hydrides system by density functional theory (DFT) in high pressure upto 50 GPa. Calculation confirmed that PdH2 in face-centered cubic (fcc) structure is not stable under compression that will decomposition to fcc-PdH and H-2. But it can be formed under high pressure while the palladium is involved in the reaction. We also indicate a probably reason why PdH2 can not be synthesised in experiment due to PdH is most favourite to be formed in Pd and H-2 environment from ambient to higher pressure. With Rh doped, the Pd-Rh dihydrides are stabilized in fcc structure for 25% and 75% doping and in tetragonal structure for 50% doping, and can be formed from Pd, Rh and H-2 at high pressure. The electronic structural study on fcc type PdxRh1-xH2 indicates the electronic and structural transition from metallic to semi-metallic as Pd increased from x = 0 to 1.

  • 541.
    Yang, Xiao
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Yanshan Univ, Coll Civil Engn & Mech, Qin Huangdao 066004, Hebei, Peoples R China.
    Li, Huijian
    Yanshan Univ, Coll Civil Engn & Mech, Qin Huangdao 066004, Hebei, Peoples R China..
    Hu, Minzheng
    Yanshan Univ, Coll Civil Engn & Mech, Qin Huangdao 066004, Hebei, Peoples R China..
    Liu, Zeliang
    Yanshan Univ, Coll Civil Engn & Mech, Qin Huangdao 066004, Hebei, Peoples R China..
    Wärnå, John
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Cao, Yuying
    Deakin Univ, Inst Frontier Mat, Geelong, Vic 3216, Australia..
    Ahuja, Rajeev
    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.
    Mechanical properties investigation on single-wall ZrO2 nanotubes: A finite element method with equivalent Poisson's ratio for chemical bonds2018In: Physica. E, Low-Dimensional systems and nanostructures, ISSN 1386-9477, E-ISSN 1873-1759, Vol. 98, p. 23-28Article in journal (Refereed)
    Abstract [en]

    A method to obtain the equivalent Poisson's ratio in chemical bonds as classical beams with finite element method was proposed from experimental data. The UFF (Universal Force Field) method was employed to calculate the elastic force constants of Zr-O bonds. By applying the equivalent Poisson's ratio, the mechanical properties of single-wall ZrNTs (ZrO2 nanotubes) were investigated by finite element analysis. The nanotubes' Young's modulus (Y), Poisson's ratio (nu) of ZrNTs as function of diameters, length and chirality have been discussed, respectively. We found that the Young's modulus of single-wall ZrNTs is calculated to be between 350 and 420 GPa.

  • 542. Yilmaz, S.
    et al.
    Nisar, Jawad
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Atasoy, Y.
    McGlynn, E.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Parlak, M.
    Bacaksiz, E.
    Defect-induced room temperature ferromagnetism in B-doped ZnO2013In: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 39, no 4, p. 4609-4617Article in journal (Refereed)
    Abstract [en]

    ZnO microrods were grown on glass substrates by the spray pyrolysis method and boron was doped into the ZnO microrods by diffusion. X-ray diffraction results confirmed that the incorporation of B leads to a slight reduction in the deposit texture. Scanning electron microscopy measurements showed that the morphology of the ZnO samples changed from a microrod to nanocrystalline structure with B-doping. Photoluminescence data indicate that B-doping leads to a relative increase of the unstructured green band intensity. Magnetic measurements revealed that B-doped ZnO samples exhibited room temperature ferromagnetism related to defects, in agreement with first principles theoretical calculations. 

  • 543.
    Yuldashev, Sh. U.
    et al.
    Dongguk University, Nano-Information Technology Academy (NITA).
    Yunusov, Z. A.
    Dongguk University, Nano-Information Technology Academy (NITA).
    Kwon, Y. H.
    Dongguk University, Quantum-Functional Semiconductor Research Center.
    Lee, S. H.
    Korea University, Department of Physics.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kang, T. W.
    Dongguk University, Nano-Information Technology Academy (NITA).
    Critical behavior of the resistivity of GaMnAs near the Curie temperature2017In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 263, p. 38-41Article in journal (Refereed)
    Abstract [en]

    The effect of the magnetization fluctuations on the resistivity of GaMnAs near the Curie temperature T-C was experimentally studied. It is shown that the determination of T-C from the maximum of the temperature derivative of the resistivity is valid for the samples with a high concentration of free carries. Whereas, for the samples with low concentration of free carriers the T-C coincides with the resistivity maximum. The magnetic specific heat for T > T-C demonstrates the crossover from the one dimensional to the three dimensional critical behavior when the temperature become closer to the Curie temperature. This is explained by the formation of the ferromagnetic phase in the paramagnetic side of the phase transition which is started from Mn-Mn dimers oriented along one direction.

  • 544. Zaoui, A.
    et al.
    Belabbes, A.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ferhat, M.
    Interplay between lattice dynamics and the low-pressure phase of simple cubic polonium2011In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 375, no 15, p. 1695-1697Article in journal (Refereed)
    Abstract [en]

    Low-pressure structural properties of simple cubic polonium are explored through first-principles density-functional theory based relativistic total energy calculations using pseudopotentials and plane-wave basis set, as well as linear-response theory. We have found that Po undergoes structural phase transition at low pressure near 2 GPa, where the element transforms from simple cubic to a mixture of two trigonal phases namely, hR1 (alpha = 86 degrees) and hR2 (alpha = 97.9 degrees) structures. The lattice dynamics calculations provide strong support for the observed phase transition, and show the dynamical stability (instability) of the hR2 (hR1) phase.

  • 545. Zeng, Qiao-Shi
    et al.
    Ding, Yang
    Mao, Wendy L
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Blomqvist, Andreas
    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.
    Yang, Wenge
    Shu, Jinfu
    Sinogeikin, Stas V
    Meng, Yue
    Brewe, Dale L
    Jiang, Jian-Zhong
    Mao, Ho-Kwang
    Substitutional alloy of Ce and Al2009In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 106, no 8, p. 2515-2518Article in journal (Refereed)
    Abstract [en]

    The formation of substitutional alloys has been restricted to elements with similar atomic radii and electronegativity. Using high-pressure at 298 K, we synthesized a face-centered cubic disordered alloy of highly dissimilar elements (large Ce and small Al atoms) by compressing the Ce(3)Al intermetallic compound >15 GPa or the Ce(3)Al metallic glass >25 GPa. Synchrotron X-ray diffraction, Ce L(3)-edge absorption spectroscopy, and ab initio calculations revealed that the pressure-induced Kondo volume collapse and 4f electron delocalization of Ce reduced the differences between Ce and Al and brought them within the Hume-Rothery (HR) limit for substitutional alloying. The alloy remained after complete release of pressure, which was also accompanied by the transformation of Ce back to its ambient 4f electron localized state and reversal of the Kondo volume collapse, resulting in a non-HR alloy at ambient conditions.

  • 546. Zhang, Hualei
    et al.
    Johansson, Börje
    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.
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    First-principles study of solid-solution hardening in steel alloys2012In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 55, p. 269-272Article in journal (Refereed)
    Abstract [en]

    Materials with excellent mechanical properties, such as light mass combined with remarkable hardness and toughness, are technologically important not least for automotive and other transport applications. Solid solution strengthening, due to dislocation pinning by impurities, is an effective route to enhance the intrinsic hardness of alloys. In the present work, we use advanced quantum theory to reveal the mechanical characteristics of iron alloys within and beyond their thermodynamic stability fields. Among the considered alloying elements, magnesium strongly reduces the density of the host alloys and significantly enhances the hardness. Our findings suggest that stainless steel grades containing a few percent of magnesium are promising engineering materials for high-strength and light-weight designs.

  • 547. Zhang, Xinyu
    et al.
    Qin, Jiaqian
    Liu, Hanyu
    Zhang, Shiliang
    Ma, Mingzhen
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Liu, Riping
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Pressure-induced zigzag phosphorus chain and superconductivity in boron monophosphide2015In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 5, article id 8761Article in journal (Refereed)
    Abstract [en]

    We report on the prediction of the zinc-blende structure BP into a novel C2/m phase from 113 to 208 GPa which possesses zigzag phosphorus chain structure, followed by another P4(2)/mnm structure above 208 GPa above using the particle-swarm search method. Strong electron-phonon coupling lambda in compressed BP is found, in particular for C2/m phase with the zigzag phosphorus chain, which has the highest lambda (0.56-0.61) value among them, leading to its high superconducting critical temperature T-c (9.4 K-11.5 K), which is comparable with the 4.5 Kto 13 Kvalue of black phosphorus phase I (orthorhombic, Cmca). This is the first system in the boron phosphides which shows superconductivity from the present theoretical calculations. Our results show that pressure-induced zigzag phosphorus chain in BP exhibit higher superconducting temperature T-C, opening a new route to search and design new superconductor materials with zigzag phosphorus chains.

  • 548.
    Zhonglai, Li
    et al.
    Department of Chemistry, Materials Section and Supercritical Fluid Centre, University College Cork.
    Larsson, J. Andreas
    Tyndall National Institute, University College Cork.
    Larsson, Peter
    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.
    Tobin, Joseph M.
    Department of Chemistry, Materials Section and Supercritical Fluid Centre, University College Cork.
    O'Byrne, Justin
    Department of Chemistry, Materials Section and Supercritical Fluid Centre, University College Cork.
    Morris, Michael A.
    Department of Chemistry, Materials Section and Supercritical Fluid Centre, University College Cork.
    Attard, Gary
    School of Chemistry, Cardiff University.
    Holmes, Justin D.
    Department of Chemistry, Materials Section and Supercritical Fluid Centre, University College Cork.
    Copper/Molybdenum Nanocomposite Particles as Catalysts for the Growth of Bamboo-Structured Carbon Nanotubes2008In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 112, no 32, p. 12201-12206Article in journal (Refereed)
    Abstract [en]

    Bamboo-structured carbon nanotubes (BCNTs), with mean diameters of 20 nm, have been synthesized on MgO-supported Cu and Mo catalysts by the catalytic chemical vapor deposition of methane. BCNTs could only be generated using a combination of Cu and Mo catalysts. No BCNTs were produced from either individual Cu or Mo catalysts. In combination, Mo was found to be essential for cracking the methane precursor, while Cu was required for BCNT formation. Energy dispersive X-ray analysis of the individual particles at the tips of the nanotubes suggest that Cu and Mo are present as a “composite” nanoparticle catalyst after growth. First-principles modeling has been used to describe the interaction of the Cu/Mo catalyst with the nanotubes, suggesting that the catalyst binds with the same energy as traditional catalysts such as Fe, Ni, and Co.

  • 549. Zhou, J.
    et al.
    Sun, Z.
    Pan, Y.
    Song, Z.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Vacancy or not: An insight on the intrinsic vacancies in rocksalt-structured GeSbTe alloys from ab initio calculations2011In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 95, no 2, p. 27002-Article in journal (Refereed)
    Abstract [en]

    Rocksalt-structured GeSbTe (GST) phase-change materials contain significant amounts of intrinsic vacancies at one sublattice. On the basis of ab initio total energy calculations, we have shown that the so-called intrinsic vacancies result from geometrical voids that originate from packing spaces for lone pairs of electrons tightly bound to specific Te layers where a weak bonding exists. The existence of such geometrical voids is concomitant with a narrow band gap. The present results will shed new insights on the intrinsic vacancies in rocksalt-structured GST.

  • 550.
    Zhou, Jian
    et al.
    Beihang Univ, Sch Mat Sci & Engn, Beijing 100191, Peoples R China..
    Sa, Baisheng
    Fuzhou Univ, Coll Mat Sci & Engn, Fuzhou 350100, Peoples R China..
    Sun, Zhimei
    Beihang Univ, Sch Mat Sci & Engn, Beijing 100191, Peoples R China.;Beihang Univ, Ctr Integrated Computat Mat Engn, Int Res Inst Multidisciplinary Sci, Beijing 100191, Peoples R China..
    Si, Chen
    Beihang Univ, Sch Mat Sci & Engn, Beijing 100191, Peoples R China.;Beihang Univ, Ctr Integrated Computat Mat Engn, Int Res Inst Multidisciplinary Sci, Beijing 100191, Peoples R China..
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Manipulating carriers' spin polarization in the Heusler alloy Mn2CoAl2015In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 5, no 90, p. 73814-73819Article in journal (Refereed)
    Abstract [en]

    We report that complete spin polarization and controllable spin polarization of carriers can be simultaneously realized in the Heusler alloy Mn2CoAl simply by applying external pressures based on first-principles studies. At ambient conditions, Mn2CoAl is a ferromagnetic spin-gapless semiconductor (SGS) with complete spin polarization. Under hydrostatic pressures up to 40 GPa, Mn2CoAl undergoes a series of electronic transitions from SGS with spin-up as a conducting channel to a ferromagnetic semiconductor and then to SGS with spin-down as a conducting channel and finally to a half metal, during which the magnetic moment remains as 2 mB. Such rich electronic transitions are attributed to different responses of the spin-up and spin-down electrons under pressure. This work highlights a desirable way to control the carrier's spin polarization and provides a new insight into the electron behavior in Mn2CoAl related Heusler alloys under pressure.

89101112 501 - 550 of 558
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