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  • 1. Ahuja, R.
    et al.
    Rekhi, S.
    Saxena, S. K.
    Johansson, Börje
    High-pressure structural phase transitions in RuO2 and its geophysical implications2001In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 62, no 11, p. 2035-2037Article in journal (Refereed)
  • 2.
    Belonoshko, Anatoly B.
    et al.
    KTH, Superseded Departments, Physics.
    Li, S.
    Ahuja, R.
    Johansson, Börje
    KTH, Superseded Departments, Materials Science and Engineering.
    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 09-aug, 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).

  • 3. Blanter, M. S.
    et al.
    Dmitriev, V. V.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Interstitial-interstitial interactions in bcc VB group metals: Ab initio calculations2013In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 74, no 5, p. 716-722Article in journal (Refereed)
    Abstract [en]

    Chemical and strain-induced interactions of oxygen and nitrogen interstitials in bcc V and Ta have been obtained for the first 12 coordination shells in the supercell first-principles calculations by the Viena ab initio simulation package (VASP). It is shown that the chemical interactions are dominating at the first several coordination shells while the strain-induced interactions become important at more distant coordination shells. The latter are in reasonable agreement with the earlier results of a microscopic phenomenological Krivoglaz-Kanzaki-Khachaturyan model (KKKM). The obtained interstitial-interstitial interactions have been used in calculations of the concentration dependence of the oxygen Snoek peak, which is in good agreement with the existing experimental data.

  • 4.
    Blanter, M. S.
    et al.
    Moscow State University of Instrumental Engineering and Information Science, Department of Nanomaterials.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Dmitriev, V. V.
    Moscow State University of Instrumental Engineering and Information Science, Department of Nanomaterials.
    Strain-induced interaction of interstitials in IVA group hcp metals2010In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 71, no 10, p. 1416-1420Article in journal (Refereed)
    Abstract [en]

    Strain-induced (elastic) interactions of oxygen, nitrogen and carbon atoms in IVA group metals, alpha-Ti, Zr, and -Hf, are calculated in the framework of the microscopic Krivoglaz-Kanzaki-Khachaturyan theory. The experimental elastic constants, lattice spacing of the host metal, and concentration expansion coefficients are used as the input numerical parameters. The resulting interactions are stronger in a-Ti than in alpha-Zr and alpha-Hf. A comparative analysis of interactions in the hcp IVA group metals with those in bcc and fcc solid solutions reveals the crystal structure effect. In general, the strain-induced interactions of O, N, and C in hcp IVA group metals are weaker than in bcc solid solutions and are stronger than in fcc solid solutions.

  • 5. De Sarkar, Abir
    et al.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Uppsala University, Sweden.
    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.

  • 6. Dmitriev, V. V.
    et al.
    Blanter, M. S.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ab initio based investigation of interstitial interactions and Snoek relaxation in Nb-O2012In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 73, no 2, p. 182-187Article in journal (Refereed)
    Abstract [en]

    Chemical and strain-induced effective pair interactions of interstitial oxygen atoms in bcc Nb have been determined in supercell first-principles calculations using Vienna ab initio simulation package (VASP). The strain-induced interactions are in reasonable agreement with those obtained earlier within a phenomenological microscopic Krivoglaz-Kanzaki-Khachaturyan model (KKKM). At the same time, the chemical interactions, which have been considered to be small in earlier theoretical considerations, turned out to be dominating at the first several coordination shells. The obtained interactions have been used in calculations of the concentration- and temperature-dependence of the internal friction Snoek peak. The theoretical results are found to be in good agreement with the existing experimental data.

  • 7. Fries, S. G.
    et al.
    Sundman, Bo
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
    Development of multicomponent thermodynamic databases for use in process modelling and simulations2005In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 66, no 04-feb, p. 226-230Article in journal (Refereed)
    Abstract [en]

    Thermodynamic databases describe the Gibbs energy of each phase in a given system, as a function of temperature, pressure and its constitution taking into account various properties like crystal structure, solubility of different element on different types of sites, magnetism, etc. The energetics from first principles calculations, crystallographic information and atomistic modelling results can be incorporated into the parametric Gibbs energies models in order to construct thermodynamic databases, being, however, experimental data obtained, e.g. from calorimetry, emf, thermal analyse, metallography, etc. which provides enthalpies, chemical potentials, phase boundary, etc. the basic type of information used. These thermodynamic databases can be an intermediate level between atomistic and macroscopic modelling, bridging scales and theoretical and empirical modelling. Thermodynamic databases provide consistent and accurate information for understanding the macroscopic behaviour of processes and transformations in real materials. This is essential to make realistic modelling and simulations for improving the production as well as teaching of phenomena which are too complex to be modelled directly from a pure theoretical approach. The majority of the phases present in materials for technical applications are solution phases, being its modelling the most complex part of the development of databases. In this paper, we show some features of the making of these databases, as well as the feedback obtained from their different applications and how that results in improvements.

  • 8. Huang, L.
    et al.
    Ramzan, M.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Anomalous temperature dependence of elastic constant c(44) 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 anomalous temperature dependence of elastic constant c(44) for elements V. Nb, Ta, Pd, and Pt, has been calculated using first-principles theory. It is shown that the variation of elastic constant for simple elements can be approximated as the sum of thermal expansion and electronic components. The thermal expansion contributes the normal linearly decreasing effect to the elastic constant with temperature, while electronic contribution is determined by the unique character of electronic structure of elements and leads to the anomalous effect to the elastic constant with temperature.

  • 9. Kim, D. Y.
    et al.
    Kwon, S. K.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    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.

  • 10. Landa, A.
    et al.
    Klepeis, J.
    Soederlind, P.
    Naumov, I.
    Velikokhatnyi, O.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ab initio calculations of elastic constants of the bcc V-Nb system at high pressures2006In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 67, no 10-sep, p. 2056-2064Article in journal (Refereed)
    Abstract [en]

    First-principles total energy calculation based on the exact muffin-tin orbital and full-potential linear muffin-tin orbital methods were used to calculate the equation of state and shear elastic constants of bcc V, Nb, and the V95Nb05 disordered alloy as a function of pressure up to 6 Mbar. We found a mechanical instability in C-44 and a corresponding softening in C at pressures similar to 2 Mbar for V. Both shear elastic constants show softening at pressures similar to 0.5 Mbar for Nb. Substitution of 5 at% of V with Nb removes the instability of V with respect to trigonal distortions in the vicinity of 2 Mbar pressure, but still leaves the softening of C-44 in this pressure region. We argue that the pressure-induced shear instability (softening) of V (Nb) originates from the electronic system and can be explained by a combination of the Fermi surface nesting, electronic topological transition, and band Jahn-Teller effect.

  • 11.
    Larsson, Per-Lennart
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Olsson, Erik
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    A numerical study of the mechanical behavior at contact between particles of dissimilar elastic-ideally plastic materials2015In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 77, p. 92-100Article in journal (Refereed)
    Abstract [en]

    In the present study contact between elastic-ideally plastic dissimilar spheres are investigated in detail. The investigation is based on numerical methods and in particular the finite element method. The numerical results presented are discussed with respect to correlation of global contact properties as well as the behavior of local field variables such as contact pressure distribution and the evolution of the effective plastic strain. Large deformation effects are accounted for and discussed in detail. The constitutive behavior is described by classical Mises plasticity. It is shown that correlation of the dissimilar contact problem can be accurately achieved based on the Johnson contact parameter with the representative stress chosen as the yield stress of the softer material.

  • 12. Li, Sa
    et al.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Araujo, C. Moyses
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    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.

  • 13.
    Luo, Wei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    de Almeida, J. Souza
    Osorio-Guillen, J. M.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    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.

  • 14. Mikhaylushkin, A. S.
    et al.
    Simak, S. I.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Haussermann, U.
    The role of orthorhombic distortions in gallium under high hydrostatic pressure2006In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 67, no 10-sep, p. 2132-2135Article in journal (Refereed)
    Abstract [en]

    We have performed a detailed analysis ofthedouble-well feature ofthetotal energy fortheGa-III phase as a function of tetragonal andorthorhombicdistortionsoftheface-centered cubic (fcc) lattice. We demonstrate that inthelow-pressureregion this double-well feature disappears and only one minimum exists. In order to reveal this result,thepossibility oforthorhombicdistortionshas to be taken into account. At elevatedpressurebetween 58 and 84 GPa,thesecond minimum becomes pronounced, but never develops into a separate local minimum up tothetransformation intothefcc phase.

  • 15. Ramzan, M.
    et al.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    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.

  • 16. Shahid, Robina
    et al.
    Muhammad, Nawshad
    Gonfa, Girma
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Synthesis, COSMO-RS analysis and optical properties of surface modified ZnS quantum dots using ionic liquids2015In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 85, p. 34-38Article in journal (Refereed)
    Abstract [en]

    Zinc sulfide (ZnS) quantum dots (QDs) were synthesized using the microwave assisted ionic liquid (MAIL) route. Three ionic liquids (ILs), namely, 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]), trihexyl(tetradecyl) phosphonium bis(trifluoromethanesulfonyl) amide ([P-6,P-6,P-6,P-14][TSFA]) and trihexyl (tetradecyl) phosphonium chloride ([P-6,P-6,P-6,P-14][Cl]) were used in this study. The size and structure of the QDs were characterized by high-resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED) pattern, respectively. The synthesized QDs were of wurtzite crystalline structure with size less than 5 nm. The QDs were more uniformly distributed while using the phosponium based ILs as a reaction medium during synthesis. The optical properties were investigated by UV-vis absorption and photoluminescence (PL) emission spectroscopy. The optical properties of QDs showed the quantum confinement effect in their absorption and the effect of cation and anion structural moiety was observed on their bandedge emission. The QDs emission intensity was measured higher for [P-6,P-6,P-6,P-14][Cl] due to their better dispersion as well as high charge density of Cl anion. The capability of the ILs in stabilizing the QDs was interpreted by density functional theory (DFT) computations. The obtained results are in good agreement with the theoretical prediction.

  • 17. Watanabe, M.
    et al.
    Haviland, David B.
    KTH, Superseded Departments, Physics.
    Quantum phase transition and Coulomb blockade with one-dimensional SQUID arrays2002In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 63, no 08-jun, p. 1307-1310Article in journal (Refereed)
    Abstract [en]

    We report on experiments with one-dimensional (1D) arrays of small-capacitance superconducting quantum interference devices (SQUIDs), where an external magnetic field can be used to tune in situ the Josephson coupling between neighboring superconducting electrodes. We have studied the superconductor-insulator transition in such arrays, and have also used these arrays to bias a single Josephson junction. In the later experiment, we have observed a clear Coulomb blockade of Cooper-pair tunnelling (CBCPT) in the single junction.

1 - 17 of 17
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