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| 2. |
- Asker Göransson, Christian, et al.
(författare)
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First-principles solution to the problem of Mo lattice stability
- 2008
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 77:22
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Tidskriftsartikel (refereegranskat)abstract
- The energy differences between the ground state body-centered structure and closed-packed face-centered structure for transition metals in the middle of the series show unusually large disagreements when they are obtained by the thermochemical approach based on the analysis of experimental data or by first-principles electronic structure calculations. Considering a typical example, the lattice stability of Mo, we present a solution to this long-standing problem. We carry out ab initio molecular dynamics simulations for the two phases at high temperature and show that the configurational energy difference approaches the value derived by means of the thermochemical approach. The main contribution to the effect comes from the modification of the canonical band structure due to anharmonic thermal motion at high temperature.
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| 3. |
- Belonoshko, Anatoly B., et al.
(författare)
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Molybdenum at High Pressure and Temperature : Melting from Another Solid Phase
- 2008
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Ingår i: Physical review letters / publ. by the American Physical Society. ; 100:13, s. 135701-
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Tidskriftsartikel (refereegranskat)abstract
- The Gibbs free energies of bcc and fcc Mo are calculated from first principles in the quasiharmonic approximation in the pressure range from 350 to 850 GPa at room temperatures up to 7500 K. It is found that Mo, stable in the bcc phase at low temperatures, has lower free energy in the fcc structure than in the bcc phase at elevated temperatures. Our density-functional-theory-based molecular dynamics simulations demonstrate that fcc melts at higher than bcc temperatures above 1.5 Mbar. Our calculated melting temperatures and bcc-fcc boundary are consistent with the Mo Hugoniot sound speed measurements. We find that melting occurs at temperatures significantly above the bcc-fcc boundary. This suggests an explanation of the recent diamond anvil cell experiments, which find a phase boundary in the vicinity of our extrapolated bcc-fcc boundary.
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| 4. |
- Kochetov, A. E., et al.
(författare)
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Interaction of Au nanowires with impurities
- 2008
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Ingår i: European Physical Journal B. - : Springer Science and Business Media LLC. - 1434-6028 .- 1434-6036. ; 61:4, s. 441-444
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Tidskriftsartikel (refereegranskat)abstract
- We report the results of our first-principles studies of the interaction between an infinite monoatomic gold nanowire and a carbon-monoxide molecule. We show that the gold monoatomic nanowire is capable of absorbing the CO molecule at the distances of about 1.8 angstrom and forms a bond with the carbon atom. Further, we find that dissociation of the CO molecule as the source of gold nanowire contamination with carbon, which is widely discussed in literature as the possible reason for the striking stability of gold nanowires under stretching, is thermodynamically unfavored.
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| 7. |
- Mikhaylushkin, Arkady S, et al.
(författare)
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High-pressure structural behavior of large-void CoSn-type intermetallics: Experiments and first-principles calculations
- 2008
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : Institutionen för fysik, kemi och biologi. - 1098-0121 .- 1550-235X. ; 77:1, s. 014102-
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Tidskriftsartikel (refereegranskat)abstract
- The high-pressure structural behavior of the binary intermetallic compounds CoSn, FeSn, and NiIn with the peculiar void containing CoSn (B35)-type structure has been studied by means of room-temperature diamond anvil cell and high-temperature multianvil experiments, as well as by first-principles calculations. All three compounds remain structurally stable at pressures up to at least 25 GPa, whereas first-principles calculations predict high-pressure structural changes below 20 GPa. A plausible explanation for the discrepancy is that at room temperature, a sizable activation barrier inhibits kinetically the transformation into more close-packed polymorphs. It is supported by our experiments at temperatures around 1000 °C and a pressure of 10 GPa. At these conditions, NiIn transforms into the temperature-quenchable stoichiometric CsCl-type high-pressure phase, which has been predicted in our first-principles calculations. However, CoSn and FeSn decompose into a mixture of compounds richer and poorer in tin, respectively. Nevertheless, it might be possible that lower temperatures and higher pressures may afford theoretically predicted polymorphs. In particular, a phase transformation to the FeSi-type structure predicted for CoSn is of interest as materials with the FeSi-type structure are known for unusual thermal and transport properties.
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| 8. |
- Mikhaylushkin, Arkady, 1977-
(författare)
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Structural properties of Fe1-xNix compressed and heated to the Earth's core conditions
- 2008
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Ingår i: FPLO Workshop,2008. - Dresden : Germany.
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Konferensbidrag (refereegranskat)abstract
- Cosmochemical, geochemical, and geophysical studies provide evidences that Earth's core contains iron with substantial (5 to 15 at. %) amounts of nickel and/or impurities of light elements. The results of our combined first-principles study and in-situ and temperature-quenched laser-heated diamond anvil-cell experiments on the high-pressure high-temperature structural behavior of pure Fe and Fe_0.9 Ni_0.1 alloy are reported. Our temperature-quenched experiments indicate that the face-centered cubic (fcc) phase of pure iron can exist in the pressure-temperature region above 160 GPa and 3700 K. In accord our theoretical results show that the fcc phase of Fe becomes as stable as the hexagonal-close-packed (hcp) phase at Earth's core condition (P ~ 300-360 GPa and T around 5000-6000 K). Further we demonstrate by means of in-situ angle-dispersive x-ray diffraction in internally heated diamond anvil cells (DACs) that by substantial alloying of Fe with Ni (10 at. %) a body-centered cubic phase can stabilize in the Earth's core. Our results give an evidence that the actual structure of the the Earth's core could be a complex phase, which is very sensitive to the presence of impurities of nickel, sulfur, silicon, etc.
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| 9. |
- Mikhaylushkin, Arkady, et al.
(författare)
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Voyage to the Earth's Deep Interior
- 2008
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Ingår i: NCS News. - : National Supercomputer Centre, Linköpings universitet. ; :3, s. 3-5
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Tidskriftsartikel (populärvet., debatt m.m.)
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