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  • 1. Belonoshko, A. B.
    et al.
    Li, Sa
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    High-pressure crystal structure studies of Fe, Ru and Os2004In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 65, no 8-9, p. 1565-1571Article in journal (Refereed)
    Abstract [en]

    In order to reveal structural trends with increasing pressure in d transition metals, we performed full potential linear muffin-tin orbital calculations for Fe, Ru, and Os in the hexagonal close packed structure. The calculations cover a wide volume range and demonstrate that all these hexagonal close-packed metals have non-ideal c/a at low pressures which, however, increases with pressure and asymptotically approaches the ideal value at very high compressions. These results are in accordance with most recent experiment for Ru and Os. The experimental data for iron is not conclusive, but it is believed that the c/a ratio decreases weakly with increasing pressure at moderate compression. Since, the experimental and calculated equations of state for iron are in increasingly good agreement with increasing pressure, it is possible that either the negative c/a trend is valid only for a restricted pressure range, or related to the experimental difficulties (e.g. non-hydrostaticity).

  • 2. Benyahia, K
    et al.
    Nabi, Z
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Boukabrine, F
    Khalfi, A
    Ab-initio calculations of the optical and magnetic properties of erbium silicide ErSi22009In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 70, no 10, p. 1378-1384Article in journal (Refereed)
    Abstract [en]

    We present a computational method for the ab-initio study of the optical and magnetic properties using the augmented plane wave plus local orbitals (APW+lo) method. The calculations are presented within the local density (LDA) approximation. Erbium silicide (ErSi2) is representative of the whole trivalent heavy-rare-earth disilicides family, and its study will provide information valid for all of them. Thus, the study of its optical and magnetic properties is very important, especially for the calculation of magneto-optical quantities. In this paper the optical and magnetic properties are well described. Up to now no theoretical study on optical and magnetic properties of ErSi2 is available in the literature. We report theoretical calculations of the reel and imaginary parts of the dielectric function (DF), the refractive index and the extinction coefficient, the spectra of the reflectivity, the absorption coefficient, the energy-loss function (ELF), and the magnetic moments. (C) 2009 Elsevier Ltd. All rights reserved.

  • 3. De Sarkar, Abir
    et al.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Electronic charge transport through ZnO nanoribbons2014In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 75, no 11, p. 1223-1228Article in journal (Refereed)
    Abstract [en]

    I-V characteristics of ZnO nanoribbons (NRs) have been investigated using density functional theory coupled to non-equilibrium Green's Function. The current through the NRs drops with the increasing NR width, leveling off to 1.66 and 0.42 mu A in zig-zag and arm-chair NRs respectively for widths similar to 20 angstrom at 3 V of electrical bias. The transconductance as well as the current flowing through the arm-chair NRs decays exponentially with NR width for both odd and even number of dimer lines traversed. The current through the zig-zag NRs falls off exponentially with NR width, being insensitive to the odd or even numbers of zig-zag lines appearing along the normal to the charge transport direction.

  • 4.
    Huang, Lunmei
    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.
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    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.
    Anomalous temperature dependence of elastic constant c44 in V, Nb, Ta, Pd, and Pt2010In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 71, no 8, p. 1065-1068Article in journal (Refereed)
    Abstract [en]

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

  • 5.
    Kim, Duck Young
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Kwon, S. K.
    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.
    Ab initio study of the pressure effects on R2Mo2O72008In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 69, no 9, p. 2245-2247Article in journal (Refereed)
    Abstract [en]

    Structural parameters and Mo 4d bands in geometrically frustrated pyrochlore R2Mo2O7 (R: Nd, Sm, Gd, Tb, Dy) have been studied using ab initio methods. Both of chemical pressure and external pressure give linear behaviors of structural parameters. The chemical pressure affects more strongly on Mo–O–Mo bond angle, oxygen coordinate and lattice constant, whereas one electron bandwidth varies more rapidly with external pressure in good agreement with experimental results.

  • 6. Li, Sa
    et al.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Araújo, C. Moysés
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Jena, Puru
    Dehydrogenation associated with Ti catalyst in sodium alanate2010In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 71, no 8, p. 1073-1076Article in journal (Refereed)
    Abstract [en]

    Addition of small amount of Ti precursors to sodium alanate has recently been found to substantially improve the kinetics and thermodynamics of hydrogen sorption in sodium alanate. In spite of several attempts, a fundamental understanding of how the catalyst works has remained unattainable. Using first principles methods we have investigated the mechanisms for hydrogen desorption in this material. We conclude that Ti substituted at Al site is energetically most favorable. The small amount of Ti substitution does not introduce large lattice distortion. The Ti atom serves as a magnet that continues to attract nearby H atoms as the nearest ones are successively desorbed. The number of Al atoms near to the Ti site remains at four upon hydrogen desorption when Ti is substituted at the Al site. These results provide important new insight into the design of future catalysts for hydrogen storage materials.

  • 7.
    Luo, Wei
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    de Almeida, J. Souza
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Osorio-Guillen, J. M.
    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.
    Electronic structure of a thermoelectric material: CsBi4Te62008In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 69, no 9, p. 2274-2276Article in journal (Refereed)
    Abstract [en]

    We have calculated the electronic structure of CsBi4Te6 by means of first-principles self-consistent total-energy calculations within the local-density approximation using the full-potential linear-muffin-tin-orbital method. From our calculated electronic structure we have calculated the frequency dependent dielectric function. Our calculations shows that CsBi4Te6 a semiconductor with a band gap of 0.3 eV. The calculated dielectric function is very anisotropic. Our calculated density of state support the recent experiment of Chung et al. [Science 287 (2000) 10241 that CsBi4Te6 is a high performance thermoelectric material for low temperature applications. (C) 2008 Elsevier Ltd. All rights reserved.

  • 8.
    Noor, Saroaut
    et al.
    Dept of Physics, Khulna University of Engineering and Technology, Khulna, Bangladesh.
    Hakim, M. A.
    Material Science Division, Atomic Energy Centre, Dhaka, Bangladesh.
    Sikder, S. S.
    Dept of Physics, Khulna University of Engineering and Technology, Khulna, Bangladesh.
    Manjura Hoque, S.
    Material Science Division, Atomic Energy Centre, Dhaka, Bangladesh.
    Hanium Maria, Kazi
    Dept of Physics, University of Dhaka, Bangladesh.
    Nordblad, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Magnetic behavior of Cd2+ substituted cobalt ferrites2012In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 73, no 2, p. 227-231Article in journal (Refereed)
    Abstract [en]

    The effect of Cd-substitution on the variation of saturation magnetization M,, Curie temperature T-c, and magnetic moments n(B) of Co1-xCdxFe2O4 (x=0.0-1.0 in steps of 0.1) ferrites have been investigated using SQUID magnetometer and impedance analyzer. The samples were prepared by conventional double sintering ceramic technique and found to be single-phase cubic spinel structure by X-ray diffraction. Saturation magnetization M-s, is found to increase with increase of Cd substitution attaining a maximum value at x=0.4 and decreases thereafter. Curie temperature decreases almost linearly with increasing x content up to x=0.7. Samples having x >= 0.8 display complex magnetic behavior with competing antiferromagnetic and ferromagnetic interactions with the manifestation of large hysteresis at low temperature and no sign of saturation. Samples with x > 0.8 show paramagnetic characteristic at T=5 K with no spontaneous magnetization revealed through Arrot-Belov-Kouvel (ABK) plots.

  • 9. Qiu, Liqin
    et al.
    Zhou, Jian
    Cheng, Xuan
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Electrochemical deposition of Bi2Te3-based thin films2010In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 71, no 8, p. 1131-1136Article in journal (Refereed)
    Abstract [en]

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

  • 10.
    Ramzan, Muhammad
    et al.
    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.
    High pressure and temperature study of hydrogen storage material BH3NH3 from ab initio calculations2010In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 71, no 8, p. 1137-1139Article in journal (Refereed)
    Abstract [en]

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

  • 11. Sa, Baisheng
    et al.
    Miao, Nahihua
    Zhou, Jian
    Song, Zhitang
    Sun, Zhimei
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Phase stability and electronic structure of Si2Sb2Te5 phase-change material2010In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 71, no 8, p. 1165-1167Article in journal (Refereed)
    Abstract [en]

    On the basis of an ab initio computational study, the present work provide a full understanding on the atomic arrangements, phase stability as well as electronic structure of Si2Sb2Te5, a newly synthesized phase-change material. The results show that Si2Sb2Te5 tends to decompose into Si1Sb2Te4 or Si1Sb4Te7 or Sb2Te3, therefore, a nano-composite containing Si1Sb2Te4, Si1Sb4Te7 and Sb2Te3 may be self-generated from Si2Sb2Te5. Hence Si2Sb2Te5 based nano-composite is the real structure when Si2Sb2Te5 is used in electronic memory applications. The present results agree well with the recent experimental work.

  • 12.
    Tutti, Faramarz
    et al.
    School of Geology, College of Science, University of Tehran, Iran.
    Lazor, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Temperature-induced phase transition in phlogopite revealed by Raman spectroscopy2008In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 69, no 10, p. 2535-2539Article in journal (Refereed)
    Abstract [en]

    Raman study of a natural hydrous phlogopite was carried out at temperatures up to 500 degrees C for the first time. Evolution of four well-resolved Raman modes at wavenumbers 196, 278, 322, and 682 cm(-1) was followed in detail with temperature increase. The analysis of data reveals linear decrease of vibrational wavenumbers in the studied temperature range, with small but experimentally significant discontinuities occurring at a temperature of 365 +/- 15 degrees C. Although the overall appearance of Raman spectra remains intact on crossing this temperature, the presence of discontinuities, as well as a marked difference between Gruneisen parameters calculated for high- and low-temperature ranges, signifies the presence of a temperature-induced phase transformation. By combining and correlating the results of the present Raman study with the high-temperature X-ray work performed by Tutti et al. [High-temperature study and thermal expansion of phlogopite, Phys. Chem. Miner. 27 (2000) 599-603] we arrive at the interpretation of a temperature-induced structural phase transformation in phlogopite without a significant symmetry change, with an underlying microscopic mechanism involving deformation of Mg octahedra and rotation of tetrahedral grid from ditrigonal toward hexagonal at the transition temperature.

  • 13. Wdowik, U. D.
    et al.
    Legut, D.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    CoO under pressure from first principles2008In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 69, no 7, p. 1698-1703Article in journal (Refereed)
    Abstract [en]

    Density functional theory and the generalized gradient approximation with correction for Hubbard energy was used to study the behavior of cobaltous oxide (CoO) under pressure. COO undergoes an insulator-metal transition which is accompanied by a magnetic collapse. The antiferromagnetic phase of CoO transforms to nonmagnetic phase with the 6-7% reduction in the fractional volume. The magnetic collapse and the energy band gap closure are driven by the lost of correlation which results from the delocalization of 3d electrons. Delocalization process is due to the band broadening with compression. The Hubbard energy influences the transitions pressure. The lower Hubbard terms result in the lower values of transition pressure. The evolution of magnetic moment, energy band gap, and the bandwidth versus increasing pressure is analyzed. The results of calculations are compared to the existing theoretical and experimental data.

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