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  • 101. Dubrovinsky, L.
    et al.
    Dubrovinskaia, N.
    Crichton, W. A.
    Mikhaylushkin, A. S.
    Simak, S. I.
    Abrikosov, I. A.
    de Almeida, J. S.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Luo, W.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Noblest of all metals is structurally unstable at high pressure2007Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 98, nr 4Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In a series of experiments in externally electrically heated diamond anvil cells we demonstrate that at pressures above similar to 240 GPa gold adopts a hexagonal-close-packed structure. Ab initio calculations predict that at pressures about 250 GPa different stacking sequences of close-packed atomic layers in gold become virtually degenerate in energy, strongly supporting the experimental observations.

  • 102.
    Dubrovinsky, L.
    et al.
    Bayerisches Geoinstitut, Universität Bayreuth.
    Dubrovinskaia, N.
    Bayerisches Geoinstitut, Universität Bayreuth.
    Langenhorst, F.
    Bayerisches Geoinstitut, Universität Bayreuth.
    Dobson, D.
    Bayerisches Geoinstitut, Universität Bayreuth.
    Rubie, D.
    Bayerisches Geoinstitut, Universität Bayreuth.
    Gessgmann, C.
    Max-Planck-Institut für Chemie, Mainz.
    Abrikosov, I. A.
    Condensed Matter Theory Group, Department of Physics, Uppsala University.
    Johansson, Börje
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Baykov, Vitaly
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Vitos, Levente
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Le Bihan, T.
    European Synchrotron Radiation Facility, Grenoble.
    Crichton, W. A.
    European Synchrotron Radiation Facility, Grenoble.
    Dmitriev, V.
    Swiss-Norwegian Beam Lines at ESRF, Grenoble.
    Weber, H. P.
    Swiss-Norwegian Beam Lines at ESRF, Grenoble.
    Iron-silica interaction at extreme conditions and the electrically conducting layer at the base of Earth's mantle2003Ingår i: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 422, nr 6927, s. 58-61Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The boundary between the Earth's metallic core and its silicate mantle is characterized by strong lateral heterogeneity and sharp changes in density, seismic wave velocities, electrical conductivity and chemical composition(1-7). To investigate the composition and properties of the lowermost mantle, an understanding of the chemical reactions that take place between liquid iron and the complex Mg-Fe-Si-Al-oxides of the Earth's lower mantle is first required(8-15). Here we present a study of the interaction between iron and silica (SiO2) in electrically and laser-heated diamond anvil cells. In a multianvil apparatus at pressures up to 140 GPa and temperatures over 3,800 K we simulate conditions down to the core-mantle boundary. At high temperature and pressures below 40 GPa, iron and silica react to form iron oxide and an iron-silicon alloy, with up to 5 wt% silicon. At pressures of 85-140 GPa, however, iron and SiO2 do not react and iron-silicon alloys dissociate into almost pure iron and a CsCl-structured (B2) FeSi compound. Our experiments suggest that a metallic silicon-rich B2 phase, produced at the core-mantle boundary (owing to reactions between iron and silicate(2,9,10,13)), could accumulate at the boundary between the mantle and core and explain the anomalously high electrical conductivity of this region(6).

  • 103. Dubrovinsky, L.
    et al.
    Dubrovinskaia, N.
    Narygina, O.
    Kantor, I.
    Kuznetzov, A.
    Prakapenka, V. B.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Mikhaylushkin, A. S.
    Simak, S. I.
    Abrikosov, I. A.
    Body-centered cubic iron-nickel alloy in Earth's core2007Ingår i: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 316, nr 5833, s. 1880-1883Artikel i tidskrift (Refereegranskat)
  • 104. Dubrovinsky, L. S.
    et al.
    Dubrovinskaia, N. A.
    McCammon, C.
    Rozenberg, G. K.
    Ahuja, R.
    Osorio-Guillen, J. M.
    Dmitriev, V.
    Weber, H. P.
    Le Bihan, T.
    Johansson, Börje
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    The structure of the metallic high-pressure Fe3O4 polymorph: experimental and theoretical study2003Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 15, nr 45, s. 7697-7706Artikel i tidskrift (Refereegranskat)
  • 105. Dubrovinsky, L. S.
    et al.
    Dubrovinskaia, N. A.
    Swamy, V.
    Muscat, J.
    Harrison, N. M.
    Ahuja, Rajeev
    Holm, B.
    Johansson, Börje
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Materials science - The hardest known oxide2001Ingår i: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 410, nr 6829, s. 653-654Artikel i tidskrift (Refereegranskat)
  • 106. Ekholm, M.
    et al.
    Mikhaylushkin, A. S.
    Simak, S. I.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Abrikosov, I. A.
    Configurational thermodynamics of Fe-Ni alloys at Earth's core conditions2011Ingår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 308, nr 1-2, s. 90-96Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    By means of ab-initio calculations, we perform an analysis of the configurational thermodynamics, effects of disorder, and structural energy differences in Fe-Ni alloys at the pressure and temperature conditions of the Earth's core. We show from ab-initio calculations that the ordering energies of fcc and hcp-structured Fe-Ni solid solutions at these conditions depend sensitively on the alloy configuration, i.e., on the degree of chemical disorder, and are on a scale comparable with the structural energy differences. From configurational thermodynamic simulations we find that a distribution of Fe and Ni atoms in the solutions should be very close to completely disordered at these conditions. Using this model of the Fe-Ni system, we have calculated the fcc-hcp structural free energy difference in a wide pressure-temperature range of 120-360 GPa and 1000-6600K. Our calculations show that alloying of Fe with Ni below 3000 K favours stabilisation of the fcc phase over the hcp, in agreement with experiments. However, above 3000 K the effect is reversed, and at conditions corresponding to those of the Earth's inner core, Ni acts as an agent to stabilise the hcp phase.

  • 107. Gorbatov, O. I.
    et al.
    Korzhavyi, Pavel A.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialteknologi.
    Ruban, Andrei V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Gornostyrev, Yu. N.
    Vacancy-solute interactions in ferromagnetic and paramagnetic bcc iron: Ab initio calculations2011Ingår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 419, nr 1-3, s. 248-255Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Vacancy-solute interactions play a crucial role in diffusion-controlled processes, such as ordering or decomposition, which occur in alloys under heat treatment or under irradiation. Detailed knowledge of these interactions is important for predicting long-term behavior of nuclear materials (such as reactor steels and nuclear-waste containers) as well as for advancing our general understanding of kinetic processes in alloys. Using first-principles calculations based on the density functional theory and employing the locally self-consistent Green's function technique, we develop a database of vacancy-solute interactions in dilute alloys of bcc Fe with 3p (Al, Si, P, S), 3d (Sc-Cu), and 4d (Y-Ag) elements. Unrelaxed interactions within the first three coordination shells have been computed in the ferromagnetic state as well as in the paramagnetic (disordered local moment) state of the iron matrix. Magnetism is found to have a strong effect on the vacancy-solute interactions. Implications of the obtained results for interpreting the effects of vacancy trapping and enhanced impurity diffusion are discussed.

  • 108. Grechnev, G. E.
    et al.
    Ahuja, R.
    Johansson, Börje
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Eriksson, O.
    Electronic structure and magnetic properties of lithium manganese spinels2003Ingår i: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 258, s. 287-289Artikel i tidskrift (Refereegranskat)
  • 109. Grechnev, G. E.
    et al.
    Ahuja, Rajeev
    Johansson, Börje
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Eriksson, O.
    Electronic structure, magnetic, and cohesive properties of LixMn2O4: Theory2002Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 65, nr 17Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The volume dependent electronic structure of the spinel-type lithium manganese oxides LixMn2O4, x=0,0.5,1, is studied ab initio by employing a full-potential electronic structure method. The electronic structure, total energies, open-circuit voltage, and magnetic moments were obtained for various spin configurations of LixMn2O4 in the cubic spinel structure and the low-temperature orthorhombic structure. The effect of magnetic ordering on the band structure and structural stability has been investigated and an antiferromagnetic ordering proved to be the ground state of the LixMn2O4 spinels. Our calculations show that the manganese majority t(2g) d band is filled for all LixMn2O4 compounds studied, and the filling of the minority t(2g) band is expected in the lithiation process. The lithium intercalation potential, bulk modulus, magnetic moments, and optical properties are calculated within the itinerant band approach and are found to be in good agreement with available experimental data, indicating, that the density-functional theory provides reliable electronic structure of the LixMn2O4 system. The effect of the orthorhombic distortion on electronic structure and magnetism of LiMn2O4 was investigated, and our calculations do not show a substantial charge ordering at the structural transition from the cubic spinel to the orthorhombic structure, as proposed earlier. Instead, the low-temperature orthorhombic structure is found to possess the lowest energy via a Jahn-Teller distortion driven by the d band.

  • 110. Grigoriev, A.
    et al.
    Skorodumova, N. V.
    Simak, S. I.
    Wendin, G.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ahuja, R.
    Electron transport in stretched monoatomic gold wires2006Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 97, nr 23Artikel i tidskrift (Refereegranskat)
  • 111. Guo, J. H.
    et al.
    Vayssieres, L.
    Persson, Clas
    Ahuja, R.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Nordgren, J.
    Polarization-dependent soft-x-ray absorption of a highly oriented ZnO microrod-array2005Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 17, nr 1, s. 235-240Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Polarization-dependent x-ray absorption measurements were performed on a crystalline ZnO three-dimensional array consisting of highly oriented microrods as well as on particulate thin film consisting of monodisperse spherical nanoparticles. Strong anisotropic effects have been observed for the highly oriented ZnO rods, unlike for the isotropic spherical ones. Full-potential calculations of orbital-resolved x-ray absorption of a ZnO wurtzite periodic crystal, including the Zn 3d as part of the valence states, shows a very good agreement with the experimental findings. Comprehensive fundamental knowledge of the electronic structure of ZnO is obtained by probing and demonstrating the orbital symmetry of oxygen and its contribution to the conduction band of this important II-VI semiconductor.

  • 112. Guo, J. H.
    et al.
    Vayssieres, L.
    Persson, Clas
    Ahuja, R.
    Johansson, Börje
    Nordgren, J.
    Polarization-dependent soft-x-ray absorption of highly oriented ZnO microrod arrays2002Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 14, nr 28, s. 6969-6974Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Polarization-dependent x-ray absorption measurements were performed on crystalline ZnO three-dimensional arrays consisting of highly oriented microrods as well as on particulate thin films consisting of monodisperse spherical nanoparticles. Strong anisotropic effects have been observed for the highly oriented ZnO rods, but not for the isotropic spherical nanoparticles. Full-potential calculations of the orbital-resolved x-ray absorption of a ZnO wurtzite periodic crystal, including Zn 3d among the valence states, show very good agreement with the experimental findings. Comprehensive fundamental knowledge of the electronic structure of ZnO is obtained by probing and demonstrating the orbital symmetry of oxygen and its contribution to the conduction band of this important II-VI semiconductor.

  • 113. Gutierrez, G.
    et al.
    Belonoshko, Anatoly B.
    Ahuja, R.
    Johansson, Börje
    Structural properties of liquid Al2O3: A molecular dynamics study2000Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics: Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, ISSN 1063-651X, E-ISSN 1095-3787, Vol. 61, nr 3, s. 2723-2729Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Molecular dynamics (MD) simulations of liquid aluminum oxide (Al2O3) were carried out on a system with up to 1800 particles, using a pairwise potential. All simulations were done in the microcanonical ensemble, for two densities, 3.0 and 3.175 g/cm(3), at temperatures of 2200, 2600, and 3000 K. A detailed analysis of the interatomic distances, given by the partial pair-distribution functions and the bond-angles distribution, reveals that in the liquid state there is st short range order dominated by a somewhat distorted (AlO4)(5-) tetrahedron, in agreement with recent experimental measurements. This conclusion is supported by the distribution of nearest-neighbor coordinations, where more than 60% of Al atoms have four O as nearest neighbors. This finding does not change over the explored temperature range. Because of the presence of twofold rings, the connectivity of (AlO4)(5-) units consists of corner, edge, and face sharing tetrahedra. Based in this structural information, i.e., bond lengths, coordination numbers, bond-angle distributions, and ring statistics, our MD simulation allows us to put forward a possible structure of liquid Al2O3.

  • 114. Gutierrez, G.
    et al.
    Johansson, Börje
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Molecular dynamics study of structural properties of amorphous Al2O32002Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 65, nr 10Artikel i tidskrift (Refereegranskat)
  • 115. Gutierrez, G.
    et al.
    Taga, A.
    Johansson, Börje
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Theoretical structure determination of gamma-Al2O32002Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 65, nr 1Artikel i tidskrift (Refereegranskat)
  • 116. Haussermann, U.
    et al.
    Simak, S. I.
    Ahuja, R.
    Johansson, Börje
    A unified bonding picture for the metallic triel elements2000Ingår i: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 39, nr 7, s. 1246-+Artikel i tidskrift (Refereegranskat)
  • 117. Haussermann, U.
    et al.
    Simak, S. I.
    Ahuja, Rajeev
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Johansson, Börje
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Metal-nonmetal transition in the boron group elements2003Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 90, nr 6Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Structural competition in boron group elements has been studied by means of ab initio calculations. For boron we predict a structural change alpha-B-->alpha-Ga accompanied by a nonmetal-metal transition at a pressure of about 74 GPa. For Al and Ga we find an icosahedron based elemental modification (alpha-B) 0.22 and 0.05 eV/atom, respectively, higher in energy than the corresponding metallic ground state structures. In particular, the low energy difference for Ga raises expectations into the experimental feasibility of new modifications for these elements, especially in nanosized systems.

  • 118. Heathman, S.
    et al.
    Haire, R. G.
    Le Bihan, T.
    Ahuja, R.
    Li, S.
    Luo, W.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    The unique high-pressure behavior of curiurn probed further using alloys2007Ingår i: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 444, s. 138-141Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The changing role of the 5f electrons across the actinide series has been of prime interest for many years. The remarkable behavior of americium's 5f electrons under pressure was determined experimentally a few years ago and it precipitated a strong interest in the heavy element community. Theoretical treatments of americium's behavior under pressure followed and continue today. Experimental and theoretical findings regarding curium's behavior under pressure have shown that the pressure behavior of curium was not a mirror image of that for americium. Rather, one of the five crystallographic phases observed with curium (versus four for americium) was a unique monoclinic structure whose existence is due to a spin stabilization effect by curium's 5f(7) electronic configuration and its half-filled 5f-shell. We review briefly the behavior of pure curium under pressure but focus on the pressure behaviors of three curium alloys with the intent of comparing them with pure curium. An important experimental finding confirmed by theoretical computations, is that dilution of curium with its near neighbors is sufficient to prevent the formation of the unique C2/c phase that appears in pure Cm metal under pressure. As this unique C2/c phase is very sensitive to having a 5f7 configuration to maximize the magnetic spin polarization, dilution of this state with adjacent actinide neighbors reduces its stability.

  • 119. Heathman, S.
    et al.
    Haire, R. G.
    Le Bihan, T.
    Lindbaum, A.
    Idiri, M.
    Normile, P.
    Li, S.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Lander, G. H.
    A high-pressure structure in curium linked to magnetism2005Ingår i: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 309, nr 5731, s. 110-113Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Curium ties at the center of the actinide series and has a half-filled shell. with seven 5f electrons spatially residing inside its radon core. As a function of pressure, curium exhibits five different crystallographic phases up to 100 gigapascals, of which all but one are also found in the preceding element, americium. We describe here a structure in curium, Cm III, with monoctinic symmetry, space group C2/c, found at intermediate pressures (between 37 and 56 gigapascals). Ab initio electronic structure calculations agree with the observed sequence of structures and establish that it is the spin polarization of curium's 5f electrons that stabilizes Cm Ill. The results reveal that curium is one of a few elements that has a lattice structure stabilized by magnetism.

  • 120. Heathman, S.
    et al.
    Le Bihan, T.
    Yagoubi, S.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Department of Physics and Materials Science, Uppsala University.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Department of Physics and Materials Science, Uppsala University.
    Structural investigation of californium under pressure2013Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 87, nr 21, s. 214111-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The high-pressure structural behavior of californium has been studied experimentally and theoretically up to 100 GPa. A valence change from divalent to trivalent forms was observed under modest pressure revealing californium to be the only actinide to exhibit more than one metallic valence at near to ambient conditions as is the case for cerium in the lanthanide series. Three metallic valencies and four different crystallographic phases were observed in californium as a function of pressure. High-pressure techniques, synchrotron radiation, and ab initio electronic structure calculations of total energies were used to investigate the material and to determine the role which californium's 5f electrons play in influencing these transitions. The crystallographic structures observed are similar to those found in the preceding actinide elements, curium and americium, with the initially localized 5f states becoming completely delocalized under the influence of high pressure.

  • 121. Hoglund, A.
    et al.
    Castleton, C. W. M.
    Göthelid, Mats
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik, Materialfysik, MF.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Mirbt, S.
    Point defects on the (110) surfaces of InP, InAs, and InSb: A comparison with bulk2006Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, nr 7Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The basic properties of point defects, such as local geometries, positions of charge-transfer levels, and formation energies, have been calculated using density-functional theory, both in the bulk and on the (110) surface of InP, InAs, and InSb. Based on these results we discuss the electronic properties of bulk and surface defects, defect segregation, and compensation. In comparing the relative stability of the surface and bulk defects, it is found that the native defects generally have higher formation energies in the bulk. From this it can be concluded that at equilibrium there is a considerably larger fraction of defects at the surface and under nonequilibrium conditions defects are expected to segregate to the surface, given sufficient time. In most cases the charge state of a defect changes upon segregation, altering the charge-carrier concentrations. The photothresholds are also calculated for the three semiconductors and are found to be in good agreement with experimental data.

  • 122. Holm, B.
    et al.
    Ahuja, R.
    Belonoshko, Anatoly B.
    Johansson, Börje
    Theoretical investigation of high pressure phases of carbon dioxide2000Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 85, nr 6, s. 1258-1261Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The recent discovery of a new solid phase of carbon dioxide (CO2-V) has made it apparent that the properties of this vital chemical species are drastically altered under high pressure conditions. The reported transition at around 40 GPa from the Cmca phase (CO2-III), which is a molecular solid, into the novel phase, which was observed to be quartzlike, clearly suggests a dramatic change of the chemical, electronic, and structural properties. We here present a theoretical analysis of the implications of this metamorphosis. At even higher pressures, we predict the existence of a very hard phase of the stishovite type.

  • 123. Holm, B.
    et al.
    Ahuja, Rajeev
    Johansson, Börje
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Ab initio calculations of the mechanical properties of Ti3SiC22001Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 79, nr 10, s. 1450-1452Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present results of first-principles calculations of the elastic constants and other mechanical properties of Ti3SiC2. This knowledge is important from a technological point of view, since the material shows promising characteristics, such as a combined metallic and ceramic appearance. We also confirm a recent experimental observation that the structure of Ti3SiC2 is stable at elevated pressures, and investigate some consequences of this fact.

  • 124. Holm, B.
    et al.
    Ahuja, Rajeev
    Li, S.
    Johansson, Börje
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Theory of the ternary layered system Ti-Al-N2002Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 91, nr 12, s. 9874-9877Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present calculations on the physical properties of Ti4AlN3 obtained from first principles, as well as some general observations concerning this group of materials. We further report mechanical data obtained through numerical simulations for some representative phases, and elaborate on the issue of high pressure stability. By examining the density of states of Ti4AlN3, we conclude that it is a semimetal, and we predict an opening up of the band gap around the Fermi level with increasing pressure.

  • 125. Holmstrom, E.
    et al.
    Olovsson, W.
    Abrikosov, I. A.
    Niklasson, A. M. N.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Gorgoi, M.
    Karis, O.
    Svensson, S.
    Schafers, F.
    Braun, W.
    Ohrwall, G.
    Andersson, G.
    Marcellini, M.
    Eberhardt, W.
    Sample preserving deep interface characterization technique2006Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 97, nr 26Artikel i tidskrift (Refereegranskat)
  • 126. Hu, Q. M.
    et al.
    Kadas, K.
    Hogmark, S.
    Yang, R.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Hardness and elastic properties of covalent/ionic solid solutions from first-principles theory2008Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 103, nr 8Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Most of the engineering materials are alloys (solid solutions) and inevitably contain some impurities or defects such as vacancies. However, theoretical predictions of the hardness of this kind of materials have rarely been addressed in literature. In this paper, a hardness formula for multicomponent covalent solid solution is proposed based on the work of Simunek and Vackar [Phys. Rev. Lett. 96, 085501 (2006)]. With this formula, the composition dependence of the hardness is investigated for titanium nitrogencarbide (TiN1-xCx), off-stoichiometric transition-metal nitrides (TiN1-x and VN1-x), and B-doped semiconductors. The predicted hardness is in good agreement with experiments. To investigate the most frequently quoted correlation between hardness and elastic modulus, the elastic moduli of the systems involved in this paper have also been calculated. The results show that the elastic moduli cannot be used for rigorous predictions of the hardness of the solid solutions.

  • 127. Hu, Q. M.
    et al.
    Li, S. J.
    Hao, Y. L.
    Yang, R.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Phase stability and elastic modulus of Ti alloys containing Nb, Zr, and/or Sn from first-principles calculations2008Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 93, nr 12Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The alloying effects of Nb, Zr, and/or Sn on the phase stability and elastic properties of Ti are investigated by using a first-principles method. Our calculation results indicate that a carefully designed Ti-Nb-Zr-Sn system can be a good candidate for low modulus biomedical materials. We find that the well-known correlation between the e/a ratio and both elastic and phase stabilities for Ti alloyed with transition metal elements breaks down for the Ti-Sn alloy.

  • 128. Hu, Q. -M
    et al.
    Yang, R.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Vitos, Levante
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Composition dependent hardness of covalent solid solutions and its electronic structure origin2016Ingår i: Ceramic Engineering and Science Proceedings, American Ceramic Society, 2016, nr 8, s. 143-151Konferensbidrag (Refereegranskat)
    Abstract [en]

    Materials with high hardness are technologically important for cutting and forming tools, engine components, valves, seals, gears, many types of wear resistant coatings, etc. The search for harder materials has a long history and remains one of the most active areas in materials science. Predictive tools for hardness will make this effort more efficient. In the past ten years, several hardness models based on electronic structure theory for perfect elemental materials/binary covalent and ionic compounds have been put forward. However, most of the engineering materials are alloys (solid solutions) and inevitably contain some impurities or defects such as vacancies. Theoretical predictions of the hardness of this kind of materials have rarely been touched. We have presented a hardness formula for multi-component covalent solid solutions. Here the composition dependence of the hardness of some covalent/ionic solid solutions, predicted with this formula, taking the parameters from our first-principles calculations, will be reported in comparison with experimental results. Furthermore, the electronic structure origin of the composition dependence of the hardness will be discussed. We will show that the band-filling effect proposed in literature to account for the composition dependence of the hardness of e.g. TiCxN1-x fails for some of the systems. Instead, we suggest that the composition dependence is controlled by the competition between the band-filling effect and the strength of electronic states hybridization. © 2016 by The American Ceramic Society.

  • 129. Hu, Qing Miao
    et al.
    Kadas, K.
    Hogmark, S.
    Yang, R.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Predicting hardness of covalent/ionic solid solution from first-principles theory2007Ingår i: Applied Physics Letters, ISSN 0003-6951, Vol. 91, nr 12, s. 121918-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We introduce a hardness formula for the multicomponent covalent and ionic solid solutions. This expression is tested on nitride spinel materials A(3)N(4) (A=C,Si,Ge) and applied to titanium nitrogen carbide (TiN(1-x)C(x) with 0 <= x <= 1), off-stoichiometric transition-metal nitride (TiN(1-x) and VN(1-x) with x <= 0.25), and B-doped semiconductors (C(1-x)B(x), Si(1-x)B(x), and Ge(1-x)B(x) with x <= 0.1). In all cases, the theoretical hardness is in good agreement with experiments.

  • 130.
    Hu, Qing-Miao
    et al.
    Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, Shenyang 110016, Peoples R China.;Royal Inst Technol, Dept Mat Sci & Engn, S-10044 Stockholm, Sweden..
    Kadas, Krisztina
    Uppsala Univ, Dept Phys, Condensed Matter Theory Grp, SE-75121 Uppsala, Sweden.;Res Inst Solid State Phys & Opt, H-1525 Budapest, Hungary..
    Hogmark, Sture
    Res Inst Solid State Phys & Opt, H-1525 Budapest, Hungary..
    Yang, Rui
    Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, Shenyang 110016, Peoples R China..
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Hardness and elastic properties of covalent/ionic solid solutions from first-principles theory (vol 103, art no 083505, 2008)2008Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 104, nr 3, artikel-id 039901Artikel i tidskrift (Refereegranskat)
  • 131.
    Hu, Qing-Miao
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Chun-Mei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Kulkova, Svetlana E.
    Institute of Strength Physics and Materials Science, Siberian Branch of Russian Academy of Science, Russia.
    Yang, Rui
    Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, China.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Magnetoelastic effects in Ni2Mn1+xGa1-x alloys from first-principles calculations2010Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, nr 6, s. 064108-1-064108-5Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The magnetic coupling between Mn atoms on Ga sublattice (Mn-Ga) and Mn atoms on Mn sublattice (Mn-Mn) in Ni2Mn1+xGa1-x alloy and its effect on the elastic modulus of the alloy are investigated by the use of first-principles methods. It is shown that, for x = 0.25, the state with antiparallel Mn-Ga-Mn-Mn magnetic coupling is slightly more stable than that with parallel coupling, whereas for x = 0.10, both magnetic states are almost degenerated. For both antiparallel and parallel Mn-Ga-Mn-Mn magnetic couplings, the bulk modulus (B) of Ni2Mn1+xGa1-x deviates from the general e/a-B relationship with e/a being the number of valence electrons per atom. The shear modulus C' versus the martensitic transformation temperature T-M for Ni2Mn1+xGa1-x with antiparallel Mn-Ga-Mn-Mn magnetic coupling is in line with the general C'-T-M relationship for Ni2MnGa-based alloys, in contrast to the case of parallel Mn-Ga-Mn-Mn magnetic coupling.

  • 132.
    Hu, Qing-Miao
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Chun-Mei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Yang, Rui
    Kulkova, Svetlana E.
    Institute of Strength Physics and Materials Science, Siberian Branch of Russian Academy of Science, Russia.
    Bazhanov, Dmitry I.
    Faculty of Physics, Moscow State University, Russia.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Site occupancy, magnetic moments, and elastic constants of off-stoichiometric Ni2MnGa from first-principles calculations2009Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, nr 14Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The site occupancy and elastic modulus of off-stoichiometric Ni2MnGa alloys are investigated by the use of the first-principles exact muffin-tin orbital method in combination with coherent-potential approximation. The stable site occupancy at 300 K is determined by comparing the free energies of the alloys with different site-occupation configurations. It is shown that, for most of the off-stoichiometric Ni2MnGa, the "normal" site occupation is favorable, i.e., the excess atoms of the rich component occupy the sublattice(s) of the deficient one(s). Nevertheless, for the Ga-rich alloys, the excess Ga atoms have strong tendency to take the Mn sublattice no matter if Mn is deficient or not. Based on the determined site occupancy, the elastic moduli of the off-stoichiometric Ni2MnGa are calculated. We find that, in general, the bulk modulus increases with increasing e/a ratio (i.e., the number of valence electrons per atom). The shear moduli C-' and C-44 change oppositely with e/a ratio: C-' decreases but C-44 increases with increasing e/a. However, the Mn-rich Ga-deficient alloys deviate significantly from this general trend. The correlation of calculated elastic moduli and available experimental martensitic transformation temperatures (T-M) demonstrates that the alloy with larger C-' than that of the perfect Ni2MnGa generally possesses lower T-M except for Ni2Mn1+xGa1-x.

  • 133. Hu, Q.M.
    et al.
    Yang, R.
    Lu, J.M.
    Wang, L.
    Li, Y.J.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Effect of Zr on the properties of (TiZr)Ni alloys from first-principles calculations2007Ingår i: Physical Review B, ISSN 0163-1829, Vol. 76, s. 224201-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The effect of Zr on the martensitic transformation (MT) behavior and mechanical properties of (Ti(0.5-x)Zr(x))Ni(0.5) alloys is investigated by calculating the elastic constants and elastic moduli in the B2 phase as a function of x for 0 <= x <= 0.2. The calculations are performed using the coherent potential approximation implemented within the framework of the exact muffin-tin orbitals method. We find that the theoretical elastic properties correlate well with the behavior of the MT. With increasing Zr concentration, the anisotropy of the alloy decreases, indicating that the nonbasal plane shear on which the modulus C(44) plays an important role, dominates and, therefore, a monoclinic martensitic phase should result. The experimental Zr content dependence of the MT temperature is paralleled with the calculated C(44) versus Zr content. The theoretical elastic moduli demonstrate that the (TiZr)Ni alloys, with Zr distributed randomly on the Ti sublattice, are intrinsically ductile, which suggests that the poor ductility of these alloys may be ascribed to some other factors, for example, impurities, precipitation, and grain boundaries.

  • 134. Huang, L.
    et al.
    Ramzan, M.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Anomalous temperature dependence of elastic constant c(44) in V, Nb, Ta, Pd, and Pt2010Ingår i: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 71, nr 8, s. 1065-1068Artikel i tidskrift (Refereegranskat)
    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.

  • 135. Huang, L.
    et al.
    Skorodumova, N. V.
    Belonoshko, Anatoly B.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Carbon in iron phases under high pressure2005Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 32, nr 21Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The influence of carbon impurities on the properties of iron phases (bcc, hcp, dhcp, fcc) has been studied using the first-principles projector augmented-wave ( PAW) method for a wide pressure range. It is shown that the presence of similar to 6 at. % of interstitial carbon has a little effect on the calculated structural sequence of the iron phases under high pressure. The bcc ! hcp transition both for pure iron and iron containing carbon takes place around 9 GPa. According to the enthalpies comparison, the solubility of carbon into the iron solid is decreased by high pressure. The coexistence of iron carbide (Fe3C) + pure hcp Fe is most stable phase at high pressure compared with other phases. Based on the analysis of the pressure-density dependences for Fe3C and hcp Fe, we suggest that there might be some fraction of iron carbide present in the core.

  • 136. Huang, L.
    et al.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Kwon, S. K.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Thermoelastic properties of random alloys from first-principles theory2006Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 73, nr 10Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a first-principles description of the temperature-dependent elastic constants in random alloys. The substitutional disorder is treated using the coherent potential approximation implemented within the frameworks of exact muffin-tin orbitals theory. The temperature effects are approximated as the sum of electronic and thermal expansion contributions. Calculations on pure Nb demonstrate that this approach correctly accounts for the main temperature dependence of cubic elastic constants. When extended to Nb-Zr solid solution, the theoretical results show good agreement with experiments at temperatures less than or similar to 300 K.

  • 137. Hugosson, Håkan Wilhelm
    et al.
    Eriksson, O.
    Jansson, U.
    Johansson, Börje
    Phase stabilities and homogeneity ranges in 4d-transition-metal carbides: A theoretical study2001Ingår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 6313, nr 13Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    First-principles full-potential linear muffin-tin orbital calculations have been used to study the 4d-transition-metal cal bides ZrC, NbC, and MoC. The experimental phase diagrams at T = 0 of the refractory compounds ZrC, NbC, and MoC have been reproduced with great accuracy from first principles theory. The energy of for marion for these compounds has been calculated for several phases and stoichiometries in order to understand the differences in phase stabilities and the changes in homogeneity ranges found between these systems is explained. The results can be regarded as theoretical zero-temperature phase stability diagrams for the three compounds containing not only the experimentally verified but also hypothetical phases and many of the experimental properties and trends are reproduced and explained. A study of the changes and differences in electronic structure and bonding of the studied compounds, phases and stoichiometries is also presented. As a part of this study the hexagonal Me2C (Me being Zr, Nb, or Mo) phases were studied and the theoretical structures, with relaxed interlayer distances and lattice parameters, were obtained. The phase stabilities and electronic structure of the experimentally reported orthorhombic Nb2C and Mo2C phases were also studied.

  • 138. Hugosson, Håkan Wilhelm
    et al.
    Jansson, U.
    Johansson, Börje
    Eriksson, O.
    Phase stability diagrams of transition metal carbides, a theoretical study2001Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 333, nr 6, s. 444-450Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The experimental phase diagrams at T = 0 of the refractory compounds ZrC, NbC and MoC have been reproduced with great accuracy from first principles theory. The energy of formation for these compounds has been calculated for several phases and stoichiometries in order to understand, for example, the differences and changes in homogeneity ranges found in these systems. This determination of relative phase stabilities for a wide range of concentrations is necessary for first principles determination of phase diagrams for these compounds with complex bonding and structural properties as well as technological importance.

  • 139. Hugosson, Håkan Wilhelm
    et al.
    Jansson, U.
    Johansson, Börje
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Eriksson, O.
    Restricting dislocation movement in transition metal carbides by phase stability tuning2001Ingår i: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 293, nr 5539, s. 2434-2437Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A mechanism to enhance hardness in multilayer coatings is proposed. Using the technologically important hard transition metal carbides as prototypes, although the principle is transferable also to other systems, we demonstrate, from first-principles calculations, that by suitable alloying the energy difference between several competing structures in the transition meta[ carbides is small or tunable. This creates multiphase/polytypic compounds with a random or controllable layer stacking sequence, systems in which the propagation of dislocations can be strongly suppressed by a large number of interfaces between structures with different glide systems, accordingly allowing the possibility of a greatly enhanced hardness. With modern thin-film technologies, it should therefore be possible to deposit such materials that will express multilayer characteristics with only minor changes in the chemical constitution of the material, which is in contrast to conventional superlattices.

  • 140.
    Hugosson, Håkan Wilhelm
    et al.
    Uppsala University.
    Korzhavyi, Pavel A.
    KTH, Tidigare Institutioner, Materialvetenskap.
    Jansson, U.
    Johansson, Börje
    KTH, Tidigare Institutioner, Materialvetenskap.
    Eriksson, O.
    Phase stabilities and structural relaxations in substoichiometric TiC1-x2001Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 63, nr 16, s. 165116-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    First-principles calculations have been used to study the effect of vacancies and relaxation around the vacancy sites in substoichiometric TiC1-x. The effect of relaxation on phase stabilities, equilibrium volumes. and electronic structure of the substoichiometric phases was studied using a combined approach of pseudopotential plane wave and full-potential linear muffin-tin orbital methods. A relaxation away from the vacancies was found for the titanium atoms, the magnitude of which increased with vacancy concentration and the inclusion of nearest-neighbor carbon atom relaxation. The inclusion of local relaxations was found to correctly predict the off-stoichiometric equilibrium composition of titanium carbide. The anomalous volume behavior of TiC at small vacancy concentration is explained as an effect of the local relaxation of the atoms surrounding the vacancy sites, but we do not find that the lattice parameter of any of the studied stoichiometries is larger than that of ideal stoichiometric TiC.

  • 141.
    Hussain, Tanveer
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden.
    Chakraborty, Sudip
    De Sarkar, Abir
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden.
    Enhancement of energy storage capacity of Mg functionalized silicene and silicane under external strain2014Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 105, nr 12, s. 123903-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The electronic structure, stability, and hydrogen storage capacity of strain induced Mg functionalized silicene (SiMg) and silicane (SiHMg) monolayers have been studied by means of van der Waals induced first principles calculations. A drastic increase in the binding energy of Mg adatoms on both the monolayers under the biaxial symmetric strain of 10% ensures the uniform distribution of dopants over the substrates. A significant positive charge on each Mg accumulates a maximum of six H-2 molecules with H-2 storage capacity of 8.10% and 7.95% in case of SiMg and SiHMg, respectively. The average adsorption energy for H-2 molecules has been found ideal for practical H-2 storage materials.

  • 142.
    Hussain, Tanveer
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Chakraborty, Sudip
    Kang, T. W.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    BC3 Sheet Functionalized with Lithium-Rich Species Emerging as a Reversible Hydrogen Storage Material2015Ingår i: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 16, nr 3, s. 634-639Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The decoration of a BC3 monolayer with the polylithiated molecules CLi4 and OLi2 has been extensively investigated to study the hydrogen-storage efficiency of the materials by first principles electronic structure calculations. The binding energies of both lithiated species with the BC3 substrate are much higher than their respective cohesive energies, which confirms the stability of the doped systems. A significant positive charge on the Li atom in each of the dopants facilitates the adsorption of multiple H-2 molecules under the influence of electrostatic and van der Waals interactions. We observe a high H-2-storage capacity of 11.88 and 8.70 wt% for the BC3-CLi4 and BC3-OLi2 systems, respectively, making them promising candidates as efficient energy-storage systems.

  • 143. Hwang, Choongyu
    et al.
    Kim, Duck Young
    Siegel, D. A.
    Chan, Kevin T.
    Noffsinger, J.
    Fedorov, A. V.
    Cohen, Marvin L.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Neaton, J. B.
    Lanzara, A.
    Ytterbium-driven strong enhancement of electron-phonon coupling in graphene2014Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, nr 11, s. 115417-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a high-resolution angle-resolved photoemission spectroscopy study in conjunction with first-principles calculations to investigate how the interaction of electrons with phonons in graphene is modified by the presence of Yb. We find that the charges transferred from Yb to the graphene layer hybridize with the graphene pi bands, leading to a strong enhancement of the electron-phonon interaction. Specifically, the electron-phonon coupling constant is increased by as much as a factor of 10 upon the introduction of Yb with respect to as-grown graphene (<= 0.05). The observed coupling constant constitutes the highest value ever measured for graphene and suggests that the hybridization between graphene and the adatoms might be a critical parameter in realizing superconducting graphene.

  • 144. Isaev, E. I.
    et al.
    Ahuja, R.
    Simak, S. I.
    Lichtenstein, A. I.
    Vekilov, Y. K.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Abrikosov, I. A.
    Anomalously enhanced superconductivity and ab initio lattice dynamics in transition metal carbides and nitrides2005Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 72, nr 6Artikel i tidskrift (Refereegranskat)
  • 145. Isaev, E. I.
    et al.
    Pourovskii, L. V.
    Niklasson, A. M. N.
    Vekilov, Y. K.
    Johansson, Börje
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Abrikosov, I. A.
    Magnetic properties of a Co/Cu/Ni trilayer on the Cu(100) surface2002Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 65, nr 2Artikel i tidskrift (Refereegranskat)
  • 146. Isaev, E. I.
    et al.
    Simak, S. I.
    Abrikosov, I. A.
    Ahuja, R.
    Vekilov, Yu Kh
    Katsnelson, M. I.
    Lichtenstein, A. I.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Phonon related properties of transition metals, their carbides, and nitrides: A first-principles study2007Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 101, nr 12Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    Lattice dynamics of body-centered cubic (bcc) V-b-VIb group transition metals (TM), and B1-type monocarbides and mononitrides of IIIb-VIb transition metals are studied by means of first-principles density functional perturbation theory, ultra soft pseudopotentials, and generalized gradient approximation to the exchange-correlation functional. Ground state parameters of transition metals and their compounds are correctly reproduced with the generated ultrasoft pseudopotentials. The calculated phonon spectra of the bcc metals are in excellent agreement with results of inelastic neutron scattering experiments. We show that the superconductivity of transition metal carbides (TMC) and transition metal nitrides (TMN) is related to peculiarities of the phonon spectra, and the anomalies of the spectra are connected to the number of valence electrons in crystals. The calculated electron-phonon interaction constants for TM, TMC, and TMN are in excellent agreement with experimentally determined values. Phonon spectra for a number of monocarbides and mononitrides of transition metals within the cubic NaCl- and hexagonal WC-type structures are predicted. Ideal stoichiometric B1 crystals of ScC, YC, and VC are predicted to be dynamically stable and superconducting materials. We also conclude that YN is a semiconductor.

  • 147. Isaev, E. I.
    et al.
    Skorodumova, N. V.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Vekilov, Y. K.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Dynamical stability of Fe-H in the Earth's mantle and core regions2007Ingår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 104, nr 22, s. 9168-9171Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The core extends from the depth of 2,900 km to the center of the Earth and is composed mainly of an iron-rich alloy with nickel, with 10% of the mass comprised of lighter elements like hydrogen, but the exact composition is uncertain. We present a quantum mechanical first-principles study of the dynamical stability of FeH phases and their phonon densities of states at high pressure. Our free-energy calculations reveal a phonon-driven stabilization of dhcp FeH at low pressures, thus resolving the present contradiction between experimental observations and theoretical predictions. Calculations reveal a complex phase diagram for FeH under pressure with a dhcp -> hcp -> fcc sequence of structural transitions.

  • 148.
    Isaev, Eyvaz
    et al.
    Moscow State Institute of Steel and Alloys.
    Baykov, Vitaly
    KTH, Tidigare Institutioner, Materialvetenskap.
    Korzhavyi, Pavel A.
    KTH, Tidigare Institutioner, Materialvetenskap.
    Vekilov, Yu. Kh.
    Johansson, Börje
    KTH, Tidigare Institutioner, Materialvetenskap.
    Abrikosov, Igor
    Eriksson, O.
    Intrinsic defects and transition metal impurities in GaAs2004Ingår i: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 272, nr 3, s. 1961-1962Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Thermodynamics of intrinsic point defects, 3d-transition metal (TM) impurities, and various defect pairs in GaAs have been studied by means of the locally self-consistent Green's function method. Antisite defects, As-Ga, are found to be the most energetically favorable defects in the As-rich GaAs. The studied TM impurities (V, Cr, Mn, and Fe) are found to form substitutional alloys on the Ga sublattice. The magnetic moments of TM impurities in the GaAs host are calculated under the assumption that orbital moments of TM are quenched and the total magnetization is due to spill ordering of electrons in the crystal. Thermodynamic possibility of formation of complexes between TM-atoms is investigated.

  • 149. Isaeva, E. I.
    et al.
    Lichtenstein, A. I.
    Vekilov, Y. K.
    Smirnova, E. A.
    Abrikosov, I. A.
    Simak, S. I.
    Ahuja, Rajeev
    KTH, Tidigare Institutioner, Materialvetenskap.
    Johansson, Börje
    KTH, Tidigare Institutioner, Materialvetenskap.
    Ab initio phonon calculations for Ll(2) Ni3Al and B2NiAl2004Ingår i: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 129, nr 12, s. 809-814Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The phonon spectra and phonon density of states of the Ni3Al and NiAl intermetallic compounds are calculated from first principles using the linear response method in conjunction with ultrasoft pseudopotentials. The calculated phonon dispersion curves are in good agreement with available experimental results from inelastic neutron scattering.

  • 150. James, P.
    et al.
    Eriksson, O.
    Hjortstam, O.
    Johansson, Börje
    Nordstrom, L.
    Calculated trends of the magnetostriction coefficient of 3d alloys from first principles2000Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 76, nr 7, s. 915-917Artikel i tidskrift (Refereegranskat)
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