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  • 1.
    Hussain, Tanveer
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kaewmaraya, Thanayut
    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. Department of Materials and Engineering, Royal Institute of Technology (KTH).
    Functionalization of hydrogenated silicene with alkali and alkaline earth metals for efficient hydrogen storage2013In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, no 43, p. 18900-18905Article in journal (Refereed)
    Abstract [en]

    First principles density functional theory has been employed to investigate the electronic structure along with the stability, bonding mechanism, band gap and charge transfer of metal functionalized hydrogenated silicene (SiH), or silicane, in order to envisage the hydrogen storage capacity. Various metal adatoms including Li, Na, K, Be, Mg and Ca have been doped on the most stable chair like configuration of silicane. The corresponding binding energies and charge transfer mechanism have been discussed from the perspective of H-2 storage ability. The Li and Na metal adatoms have been found to be ideally suitable not only for their strong metal to substrate binding and uniform distribution over the substrate but also for their high capacity for storage of hydrogen. The stability of both Li and Na functionalized SiH has also been confirmed by MD simulations. It was found that both Li+ and Na+ adsorbed four H-2 molecules attaining reasonably high storage capacities of 6.30 wt% and 5.40 wt% respectively with average adsorption energies lying within the range suitable for practical H-2 storage applications, in contrast with alkaline earth metals.

  • 2.
    Kaewmaraya, Thanayut
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    First-Principles Studies of Materials Properties: Pressure-Induced Phase Transitions & Functional Materials2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis presents the first-principles studies of materials properties within the framework of the density functional theory (DFT). The thesis constitutes three main parts, i. e., pressure-induced phase transitions in solids, data-storage and clean-energy materials.

    The first part focuses on the predictions of crystal structures and the determinations of electronic properties of Xe-H2, FeB4 and Co3O4. Pressurizing Xe-H2 compound yields the formation of H-rich Xe(H2)8, which can exhibit a metallic feature at comparatively lower pressure than pure hydrogen. Hard superconducting FeB4 gets transformed into a novel transparent phase under pressure owing to the enhanced overlap of atomic cores. Spinel Co3O4 undergoes the phase transition from a cubic to a monoclinic because of the charge transfer between cations via the increased 3d-3d interactions.

    The second part involves the study of structural and electronic properties of phase-change memory materials (PCMs), i. e., Ge2Sb2Te5 (GST) and Ga-doped In2O3. Van der Waals (vdW) interaction must be considered to obtain accurate crystal structure of layered GST. For Ga-doped In2O3 (GIO), the local structure of amorphous GIO is found to resemble that of amorphous In2O3, except the vicinity of doping atoms. The electronic property of a-GIO is metallic, which considerably differs from the semiconducting feature of the crystalline GIO. This emphasizes the contrast in the conductivity of the crystalline and amorphous upon phase switching of GIO.

    The third part associates with the search for clean-energy materials, viz., hydrogen production, hydrogen storage and green Mg-ion batteries. For hydrogen production, the role of intrinsic point defects to water adsorption on ZnO(10-10) surface is investigated. The findings show that the Zn and O defect-sites are energetically not favorable for the water adsorption and dissociation. For the purpose of storing hydrogen in a solid phase, silicene, doped by alkaline and alkaline earth metals, is investigated. We find that Li-doped and Na-doped silicene can attain the superior storage capacity. For cathode material of Mg-ion batteries, Mg2Mo6S8, the diffusivity of Mg ions occurs through an available channel in the bulk with the onset temperature of 200 K.

    List of papers
    1. Theoretical investigation of xenon-hydrogen solids under pressure using ab initio DFT and GW calculations
    Open this publication in new window or tab >>Theoretical investigation of xenon-hydrogen solids under pressure using ab initio DFT and GW calculations
    Show others...
    2011 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, no 9, p. 092101-Article in journal (Refereed) Published
    Abstract [en]

    We have calculated crystal structures and electronic properties of Xe-H(2) compounds under high pressures using first-principles density functional theory calculations and ab-initio random structure searching. We present results for the equation of state, Xe-Xe separations, and the electronic charge transfer between the Xe and H atoms. Our results are broadly consistent with experimental results by M. Somayazulu et al. [Nature Chem. 2, 50 (2010)]. We have in addition calculated the metallization pressure within the GW approximation, finding it to be around 250 GPa, which is close to the maximum pressure reached in the experiment.

    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:uu:diva-158866 (URN)10.1103/PhysRevB.84.092101 (DOI)000294402200001 ()
    Available from: 2011-09-20 Created: 2011-09-19 Last updated: 2017-12-08Bibliographically approved
    2. Revealing an unusual transparent phase of superhard iron tetraboride under high pressure
    Open this publication in new window or tab >>Revealing an unusual transparent phase of superhard iron tetraboride under high pressure
    Show others...
    2014 (English)In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 111, no 48, p. 17050-17053Article in journal (Refereed) Published
    Abstract [en]

    First principles-based electronic structure calculations of super-hard iron tetraboride (FeB4) under high pressure have been undertaken in this study. Starting with a "conventional" superconducting phase of this material under high pressure leads to an unexpected phase transition toward a semiconducting one. This transition occurred at 53.7 GPa, and this pressure acts as a demarcation between two distinct crystal symmetries, metallic orthorhombic and semiconducting tetragonal phases, with Pnnm and I4(1)/acd space groups, respectively. In this work, the electron-phonon coupling-derived superconducting T-c has been determined up to 60 GPa and along with optical band gap variation with increasing pressure up to 300 GPa. The dynamic stability has been confirmed by phonon dispersion calculations throughout this study.

    Keywords
    metal-semiconductor phase transition, superhard material, first principle study, high pressure, superconductivity
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:uu:diva-240205 (URN)10.1073/pnas.1419244111 (DOI)000345920800029 ()25404295 (PubMedID)
    Available from: 2015-01-07 Created: 2015-01-06 Last updated: 2017-12-05Bibliographically approved
    3. A new layered monoclinic phase of Co3O4 at high pressure
    Open this publication in new window or tab >>A new layered monoclinic phase of Co3O4 at high pressure
    Show others...
    (English)Manuscript (preprint) (Other academic)
    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:uu:diva-251335 (URN)
    Available from: 2015-04-15 Created: 2015-04-15 Last updated: 2015-05-12
    4. Hybrid density functional study of electronic and optical properties of phase change memory material: Ge2Sb2Te5
    Open this publication in new window or tab >>Hybrid density functional study of electronic and optical properties of phase change memory material: Ge2Sb2Te5
    2013 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 113, no 3, p. 033510-Article in journal (Refereed) Published
    Abstract [en]

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

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:uu:diva-195377 (URN)10.1063/1.4775715 (DOI)000313670600020 ()
    Available from: 2013-02-25 Created: 2013-02-25 Last updated: 2017-12-06Bibliographically approved
    5. Structural and Vibrational Properties of Layered Data Storage Material: Ge2Sb2Te5
    Open this publication in new window or tab >>Structural and Vibrational Properties of Layered Data Storage Material: Ge2Sb2Te5
    Show others...
    2013 (English)In: SCI ADV MATER, ISSN 1947-2935, Vol. 5, no 10, p. 1493-1497Article in journal (Refereed) Published
    Abstract [en]

    Ge2Sb2Te5 is a prototype material for phase-change memory, while its stable layered phase was recently predicted to be a topological insulator. In this work, we show that standard density functional theory (DFT) calculations provide much larger Te-Te bond length and lattice parameters for layered Ge2Sb2Te5 compared with experimental results. However, by considering van der Waals interactions in DFT calculations, we obtained correct structure information and lattice dynamics properties. It is clear that the discrepancy results from the neglecting the van der Waals interaction between directly weak bonded adjacent Te atoms.

    Keywords
    Chalcogenide, Density Functional Theory Calculations, Weak Bond, Layered Structure
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:uu:diva-208353 (URN)10.1166/sam.2013.1610 (DOI)000323356200021 ()
    Available from: 2013-10-01 Created: 2013-09-30 Last updated: 2015-05-12Bibliographically approved
    6. Molecular dynamics study of amorphous Ga-doped In2O3: a promising material for phase change memory devices
    Open this publication in new window or tab >>Molecular dynamics study of amorphous Ga-doped In2O3: a promising material for phase change memory devices
    2013 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 103, no 7, article id 072113Article in journal (Refereed) Published
    Abstract [en]

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

    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:uu:diva-204964 (URN)10.1063/1.4818788 (DOI)000323769000044 ()
    Funder
    Swedish Research Council
    Available from: 2013-08-13 Created: 2013-08-13 Last updated: 2017-12-06Bibliographically approved
    7. Water adsorption on ZnO(10(1)over-bar0): The role of intrinsic defects
    Open this publication in new window or tab >>Water adsorption on ZnO(10(1)over-bar0): The role of intrinsic defects
    Show others...
    2012 (English)In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 97, no 1, p. 17014-Article in journal (Refereed) Published
    Abstract [en]

    Density functional theory (DFT) calculations have been performed to investigate the interaction of water molecules with bare and defective ZnO(10 (1) over bar0) surfaces. We show that at high coverages water molecules avoid adsorption close to defect sites, whereas at low coverages adsorption on defective surfaces show a similar adsorption pattern to those adsorbed on the defect-free surface, adsorbing in a molecular fashion. Finally we show that the electronic structure of the defective non-polar surface is not much affected by the adsorption of water, with exception of the O-defect surfaces.

    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:uu:diva-170802 (URN)10.1209/0295-5075/97/17014 (DOI)000300250800045 ()
    Available from: 2012-03-13 Created: 2012-03-13 Last updated: 2017-12-07Bibliographically approved
    8. Functionalization of hydrogenated silicene with alkali and alkaline earth metals for efficient hydrogen storage
    Open this publication in new window or tab >>Functionalization of hydrogenated silicene with alkali and alkaline earth metals for efficient hydrogen storage
    2013 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, no 43, p. 18900-18905Article in journal (Refereed) Published
    Abstract [en]

    First principles density functional theory has been employed to investigate the electronic structure along with the stability, bonding mechanism, band gap and charge transfer of metal functionalized hydrogenated silicene (SiH), or silicane, in order to envisage the hydrogen storage capacity. Various metal adatoms including Li, Na, K, Be, Mg and Ca have been doped on the most stable chair like configuration of silicane. The corresponding binding energies and charge transfer mechanism have been discussed from the perspective of H-2 storage ability. The Li and Na metal adatoms have been found to be ideally suitable not only for their strong metal to substrate binding and uniform distribution over the substrate but also for their high capacity for storage of hydrogen. The stability of both Li and Na functionalized SiH has also been confirmed by MD simulations. It was found that both Li+ and Na+ adsorbed four H-2 molecules attaining reasonably high storage capacities of 6.30 wt% and 5.40 wt% respectively with average adsorption energies lying within the range suitable for practical H-2 storage applications, in contrast with alkaline earth metals.

    Keywords
    Silicane, Hydrogen Storage, Adsorption Energy
    National Category
    Natural Sciences
    Research subject
    Physics with spec. in Atomic, Molecular and Condensed Matter Physics
    Identifiers
    urn:nbn:se:uu:diva-206631 (URN)10.1039/c3cp52830h (DOI)000325943200017 ()
    Available from: 2013-09-02 Created: 2013-09-02 Last updated: 2017-12-06Bibliographically approved
    9. Electronic structure and ionic diffusion of green battery cathode material: Mg2Mo6S8
    Open this publication in new window or tab >>Electronic structure and ionic diffusion of green battery cathode material: Mg2Mo6S8
    2014 (English)In: Solid State Ionics, ISSN 0167-2738, E-ISSN 1872-7689, Vol. 261, p. 17-20Article in journal (Refereed) Published
    Abstract [en]

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

    Keywords
    Mg-ion batteries, First-principle calculations, Hybrid functionals, Molecular dynamics
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:uu:diva-229710 (URN)10.1016/j.ssi.2014.03.023 (DOI)000338819500004 ()
    Available from: 2014-08-18 Created: 2014-08-12 Last updated: 2017-12-05Bibliographically approved
  • 3.
    Kaewmaraya, Thanayut
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    De Sarkar, Abir
    Sa, Baisheng
    Sun, Z.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Strain-induced tunability of optical and photocatalytic properties of ZnO mono-layer nanosheet2014In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 91, p. 38-42Article in journal (Refereed)
    Abstract [en]

    Strain-induced tunability of several properties of ZnO monolayer nanosheet has been systematically studied using density functional theory. The band gap of the sheet varies almost linearly with uniaxial strain, while it shows a parabola-like behavior under homogeneous biaxial strain. Tensile strain reduces ionicity of Zn-O bonds, while compressive strain increases it. This provides ample implications for the photocatalytic dissociation of water molecules and the scission of polar molecules on ZnO nanosheet. The dynamical stability of the sheet assessed by the calculation of its vibrational frequencies has shown the sheet to be unstable for 10% and 7.5% compressive biaxial homogeneous strain. 

  • 4.
    Kaewmaraya, Thanayut
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kim, Duck Young
    Lebegue, S.
    Pickard, C. J.
    Needs, R. J.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Theoretical investigation of xenon-hydrogen solids under pressure using ab initio DFT and GW calculations2011In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, no 9, p. 092101-Article in journal (Refereed)
    Abstract [en]

    We have calculated crystal structures and electronic properties of Xe-H(2) compounds under high pressures using first-principles density functional theory calculations and ab-initio random structure searching. We present results for the equation of state, Xe-Xe separations, and the electronic charge transfer between the Xe and H atoms. Our results are broadly consistent with experimental results by M. Somayazulu et al. [Nature Chem. 2, 50 (2010)]. We have in addition calculated the metallization pressure within the GW approximation, finding it to be around 250 GPa, which is close to the maximum pressure reached in the experiment.

  • 5.
    Kaewmaraya, Thanayut
    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.
    Yang, Xiao
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Panigrahi, Puspamitra
    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 new, layered monoclinic phase of Co3O4 at high pressure2015In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 30, p. 19957-19961Article in journal (Refereed)
    Abstract [en]

    We present the crystal structures and electronic properties of a Co3O4 spinel under high pressure. Co3O4 undergoes a first-order transition from a cubic (CB) Fd (3) over barm to a lower-symmetry monoclinic (MC) P2(1)/c phase at 35 GPa, occurring after the local high-spin to low-spin phase transition. The high-pressure phase exhibits the octahedral coordination of Co(II) and Co(III), whereas the CB phase contains the fourfold coordination of Co(II) and the sixfold coordination of Co(III). The CB-to-MC transition is attributed to the charge-transfer between the di-and trivalent cations via the enhanced 3d-3d interactions.

  • 6.
    Kaewmaraya, Thanayut
    et al.
    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.
    Araujo, Carlos M
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Rosa, A. L.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Water adsorption on ZnO(10(1)over-bar0): The role of intrinsic defects2012In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 97, no 1, p. 17014-Article in journal (Refereed)
    Abstract [en]

    Density functional theory (DFT) calculations have been performed to investigate the interaction of water molecules with bare and defective ZnO(10 (1) over bar0) surfaces. We show that at high coverages water molecules avoid adsorption close to defect sites, whereas at low coverages adsorption on defective surfaces show a similar adsorption pattern to those adsorbed on the defect-free surface, adsorbing in a molecular fashion. Finally we show that the electronic structure of the defective non-polar surface is not much affected by the adsorption of water, with exception of the O-defect surfaces.

  • 7.
    Kaewmaraya, Thanayut
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ramzan, Muhammad
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Löfås, Henrik
    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.
    Hybrid density functional study of electronic and optical properties of phase change memory material: Ge2Sb2Te52013In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 113, no 3, p. 033510-Article in journal (Refereed)
    Abstract [en]

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

  • 8.
    Kaewmaraya, Thanayut
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ramzan, Muhammad
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Osorio-Guillen, J. M.
    Ahuja, R.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Electronic structure and ionic diffusion of green battery cathode material: Mg2Mo6S82014In: Solid State Ionics, ISSN 0167-2738, E-ISSN 1872-7689, Vol. 261, p. 17-20Article in journal (Refereed)
    Abstract [en]

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

  • 9.
    Kaewmaraya, Thanayut
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ramzan, Muhammad
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sun, W.
    Sagynbaeva, Myskal
    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. Applied Materials Physics, Department of Materials and Engineering, Royal Institute of Technology (KTH), SE-100 44 Stockholm, Sweden.
    Atomistic study of promising catalyst and electrode material for memory capacitors: Platinum Oxides2013In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 79, p. 804-810Article in journal (Refereed)
    Abstract [en]

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

  • 10. Kotmool, Komsilp
    et al.
    Kaewmaraya, Thanayut
    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.
    Anversa, Jonas
    Bovornratanaraks, Thiti
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Gou, Huiyang
    Piquini, Paulo Cesar
    Kang, Tae Won
    Mao, Ho-Kwang
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Revealing an unusual transparent phase of superhard iron tetraboride under high pressure2014In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 111, no 48, p. 17050-17053Article in journal (Refereed)
    Abstract [en]

    First principles-based electronic structure calculations of super-hard iron tetraboride (FeB4) under high pressure have been undertaken in this study. Starting with a "conventional" superconducting phase of this material under high pressure leads to an unexpected phase transition toward a semiconducting one. This transition occurred at 53.7 GPa, and this pressure acts as a demarcation between two distinct crystal symmetries, metallic orthorhombic and semiconducting tetragonal phases, with Pnnm and I4(1)/acd space groups, respectively. In this work, the electron-phonon coupling-derived superconducting T-c has been determined up to 60 GPa and along with optical band gap variation with increasing pressure up to 300 GPa. The dynamic stability has been confirmed by phonon dispersion calculations throughout this study.

  • 11.
    Ozaki, N.
    et al.
    Osaka Univ, Grad Sch Engn, 2-2 Yamadaoka, Suita, Osaka 5650871, Japan.;Osaka Univ, Photon Pioneers Ctr, 2-2 Yamadaoka, Suita, Osaka 5650871, Japan..
    Nellis, W. J.
    Harvard Univ, Dept Phys, Cambridge, MA 02138 USA..
    Mashimo, T.
    Kumamoto Univ, Shock Wave & Condensed Matter Res Ctr, Kumamoto 8608555, Japan..
    Ramzan, Muhammad
    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, Appl Mat Phys, SE-10044 Stockholm, Sweden..
    Kaewmaraya, Thanayut
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kimura, T.
    Ehime Univ, Geodynam Res Ctr, Matsuyama, Ehime 7908577, Japan..
    Knudson, M.
    Sandia Natl Labs, POB 5800, Albuquerque, NM 87185 USA.;Washington State Univ, Inst Shock Phys, Pullman, WA 99164 USA..
    Miyanishi, K.
    Osaka Univ, Photon Pioneers Ctr, 2-2 Yamadaoka, Suita, Osaka 5650871, Japan..
    Sakawa, Y.
    Osaka Univ, Inst Laser Engn, 2-2 Yamadaoka, Suita, Osaka 5650871, Japan..
    Sano, T.
    Osaka Univ, Inst Laser Engn, 2-2 Yamadaoka, Suita, Osaka 5650871, Japan..
    Kodama, R.
    Osaka Univ, Grad Sch Engn, 2-2 Yamadaoka, Suita, Osaka 5650871, Japan.;Osaka Univ, Photon Pioneers Ctr, 2-2 Yamadaoka, Suita, Osaka 5650871, Japan.;Osaka Univ, Inst Acad Initiat, 2-2 Yamadaoka, Suita, Osaka 5650871, Japan..
    Dynamic compression of dense oxide (Gd3Ga5O12) from 0.4 to 2.6 TPa: Universal Hugoniot of fluid metals2016In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, article id 26000Article in journal (Refereed)
    Abstract [en]

    Materials at high pressures and temperatures are of great current interest for warm dense matter physics, planetary sciences, and inertial fusion energy research. Shock-compression equation-of-state data and optical reflectivities of the fluid dense oxide, Gcl(3)Ga(5)O(12) (GGG), were measured at extremely high pressures up to 2.6TPa (26 Mbar) generated by high-power laser irradiation and magnetically driven hypervelocity impacts. Above 0.75TPa, the GGG Hugoniot data approach/reach a universal linear line of fluid metals, and the optical reflectivity most likely reaches a constant value indicating that GGG undergoes a crossover from fluid semiconductor to poor metal with minimum metallic conductivity (MMC). These results suggest that most fluid compounds, e.g., strong planetary oxides, reach a common state on the universal Hugoniot of fluid metals (UHFM) with MMC at sufficiently extreme pressures and temperatures. The systematic behaviors of warm dense fluid would be useful benchmarks for developing theoretical equation-of-state and transport models in the warm dense matter regime in determining computational predictions.

  • 12.
    Ramzan, Muhammad
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kaewmaraya, Thanayut
    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. Applied Materials Physics, Department of Materials and Engineering, Royal Institute of Technology (KTH), SE-100 44 Stockholm, Sweden.
    Molecular dynamics study of amorphous Ga-doped In2O3: a promising material for phase change memory devices2013In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 103, no 7, article id 072113Article in journal (Refereed)
    Abstract [en]

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

  • 13. Sa, Baisheng
    et al.
    Sun, Zhimei
    Kaewmaraya, Thanayut
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Zhou, Jian
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Structural and Vibrational Properties of Layered Data Storage Material: Ge2Sb2Te52013In: SCI ADV MATER, ISSN 1947-2935, Vol. 5, no 10, p. 1493-1497Article in journal (Refereed)
    Abstract [en]

    Ge2Sb2Te5 is a prototype material for phase-change memory, while its stable layered phase was recently predicted to be a topological insulator. In this work, we show that standard density functional theory (DFT) calculations provide much larger Te-Te bond length and lattice parameters for layered Ge2Sb2Te5 compared with experimental results. However, by considering van der Waals interactions in DFT calculations, we obtained correct structure information and lattice dynamics properties. It is clear that the discrepancy results from the neglecting the van der Waals interaction between directly weak bonded adjacent Te atoms.

1 - 13 of 13
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