| 1. |
|
|
| 2. |
- Asker Göransson, Christian, et al.
(författare)
-
First-principles solution to the problem of Mo lattice stability
- 2008
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 77:22
-
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.
|
|
| 3. |
- Belonoshko, Anatoly B., et al.
(författare)
-
Molybdenum at High Pressure and Temperature : Melting from Another Solid Phase
- 2008
-
Ingår i: Physical review letters / publ. by the American Physical Society. ; 100:13, s. 135701-
-
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.
|
|
| 4. |
- Belonoshko, Anatoly B., et al.
(författare)
-
Quenching of bcc-Fe from high to room temperature at high-pressure conditions : a molecular dynamics simulation
- 2009
-
Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 11
-
Tidskriftsartikel (refereegranskat)abstract
- The new high-temperature (T), high-pressure (P), body-centered cubic (bcc) phase of iron has probably already been synthesized in recent diamond anvil cell (DAC) experiments (Mikhaylushkin et al 2007 Phys. Rev. Lett. 99 165505). These DAC experiments on iron revealed that the high-PT phase on quenching transforms into a mixture of close-packed phases. Our molecular dynamics simulation and structural analysis allow us to provide a probable interpretation of the experiments. We show that quenching of the high-PT bcc phase simulated with the embedded-atom model also leads to the formation of the mixture of close-packed phases. Therefore, the assumption of the stability of the high-PT bcc iron phase is consistent with experimental observation.
|
|
| 5. |
- Burakovsky, L., et al.
(författare)
-
High-Pressure-High-Temperature Polymorphism in Ta : Resolving an Ongoing Experimental Controversy
- 2010
-
Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 104:25, s. 255702-
-
Tidskriftsartikel (refereegranskat)abstract
- Phase diagrams of refractory metals remain essentially unknown. Moreover, there is an ongoing controversy over the high-pressure melting temperatures of these metals: results of diamond anvil cell (DAC) and shock wave experiments differ by at least a factor of 2. From an extensive ab initio study on tantalum we discovered that the body-centered cubic phase, its physical phase at ambient conditions, transforms to another solid phase, possibly hexagonal omega phase, at high temperature. Hence the sample motion observed in DAC experiments is very likely not due to melting but internal stresses accompanying a solid-solid transformation, and thermal stresses associated with laser heating.
|
|
| 6. |
- Ekholm, Marcus, et al.
(författare)
-
Configurational thermodynamics of Fe-Ni alloys at Earths core conditions
- 2011
-
Ingår i: Earth and Planetary Science Letters. - : Elsevier. - 0012-821X .- 1385-013X. ; 308:1-2, s. 90-96
-
Tidskriftsartikel (refereegranskat)abstract
- 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 Earths 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 Earths inner core, Ni acts as an agent to stabilise the hcp phase.
|
|
| 7. |
- Ghafoor, Naureen, et al.
(författare)
-
Effects of O and N impurities on the nanostructural evolution during growth of Cr/Sc multilayers
- 2009
-
Ingår i: Journal of Materials Research. - 0884-2914 .- 2044-5326. ; 24:1, s. 79-95
-
Tidskriftsartikel (refereegranskat)abstract
- Transition metal multilayers are prime candidates for high reflectivity soft x-ray multilayer mirrors. In particular, Cr/Sc multilayers in the amorphous state have proven to give the highest reflectivity in the water window. We have investigated the influence of impurities N and O as residual gas elements on the growth, structure, and optical performance of Cr/Sc multilayers deposited in high vacuum conditions by a dual cathode direct current magnetron sputter deposition. Multilayer structures with the modulation periods in the range of 0.9–4.5 nm and Cr layer to bilayer thickness ratios in the range of 0.17–0.83 were deposited with an intentionally raised base pressure (pB), ranging from 2 × 10-7 to 2 × 10-5 Torr. Compositional depth profiles were obtained by elastic recoil detection analysis and Rutherford backscattering spectroscopy, while the structural investigations of the multilayers were carried out using hard x-ray reflectivity and transmission electron microscopy. By investigating stacked multilayers, i.e., several multilayers with different designs of the modulation periods, stacked on top of each other in the samples, we have been able to conclude that both N and O are incorporated preferentially in the interior of the Sc layers. At pB = 2 × 10-6 Torr, typically <3 at.% of N and <1.5 at.% of O was found, which did not influence the amorphous nanostructure of the layers. Multilayers deposited with a high pB ~2 × 10-5 Torr, a N content as high as ~37 at.% was measured by elastic recoil detection analysis. These multilayers mainly consist of understoichiometric face-centered cubic CrN x /ScN y nanocrystalline layers, which could be grown as thin at 0.3 nm and is explained by a stabilizing effect on the ScN y layers during growth. It is also shown that by adding a background pressure of as little as 5 × 10-6 Torr of pure N2 the soft x-ray reflectivity (? = 3.11 nm) can be enhanced by more than 100% by N incorporation into the multilayer structures, whereas pure O2 at the same background pressure had no effect.
|
|
| 8. |
- Haeusserman, Ulrich, et al.
(författare)
-
Structure and Bonding of gamma-B-28: Is the High Pressure Form of Elemental Boron Ionic?
- 2010
-
Ingår i: INORGANIC CHEMISTRY. - : ACS American Chemical Society. - 0020-1669 .- 1520-510X. ; 49:24, s. 11270-11275
-
Tidskriftsartikel (refereegranskat)abstract
- The recently characterized crystal structure of metastable gamma-B-28 is analyzed from a crystal chemical point of view, and the electron requirement of its building units and that of their linkage is determined. The structure consists of unique B-2 dumbbells and B-12 icosahedra, which are connected through two-center and three-center, two-electron bonds. The different bonding motifs are ascertained by theoretical calculations of difference charge distributions. Chemical bonding in high pressure gamma-B-28 bears great resemblance to alpha-B-12 which is the simplest boron modification. The previously made description of gamma-B-28 as ionic in terms of (B2)(delta+) and (B-12)(delta-) is not supported.
|
|
| 9. |
- Haeussermann, Ulrich, et al.
(författare)
-
Electron-poor antimonides: complex framework structures with narrow band gaps and low thermal conductivity
- 2010
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry. - 1477-9226 .- 1477-9234. ; 39:4, s. 1036-1045
-
Tidskriftsartikel (refereegranskat)abstract
- Binary zinc and cadmium antimonides and their ternary relatives with indium display complex crystal structures, but reveal at the same time narrow band gaps in their electronic structure at or close to the Fermi level. It is argued that these systems represent "electron-poor framework semiconductors" (EPFS) with average valence electron concentrations between three and four. EPFS materials constituted of metal and semimetal atoms form a common, weakly polar framework containing multi-center bonded structural entities. The localized multi-center bonding feature is thought to be the key to structurally complex semiconductors. In this respect electron-poor antimonides become related to modifications of elemental boron. Electron-poor antimonides show promising thermoelectric properties, especially through a remarkably low thermal conductivity. At the same time the thermal stability of these compounds is rather limited because of temperature polymorphism and/or comparatively low melting or decomposition temperatures ( usually below 600 K).
|
|
| 10. |
- Isaev, Eyvas, et al.
(författare)
-
Impact of lattice vibrations on equation of state of the hardest boron phase
- 2011
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 83:13, s. 132106-
-
Tidskriftsartikel (refereegranskat)abstract
- An accurate equation of state (EOS) is determined for the high-pressure orthorhombic phase of boron, B(28), experimentally as well as from ab initio calculations. The unique feature of our experiment is that it is carried out on the single crystal of B(28). In theory, we take into consideration the lattice vibrations, often neglected in first-principles simulations. We show that the phonon contribution has a profound effect on the EOS of B(28), giving rise to anomalously low values of the pressure derivative of the bulk modulus and greatly improving the agreement between theory and experiment.
|
|
| 11. |
- Kochetov, A. E., et al.
(författare)
-
Interaction of Au nanowires with impurities
- 2008
-
Ingår i: European Physical Journal B. - : Springer Science and Business Media LLC. - 1434-6028 .- 1434-6036. ; 61:4, s. 441-444
-
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.
|
|
| 12. |
- Lane, Nina J, et al.
(författare)
-
First-principles study of dislocations in hcp metals through the investigation of the (11(2)over-bar1) twin boundary
- 2011
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 84:18, s. 184101-
-
Tidskriftsartikel (refereegranskat)abstract
- Herein, we use first principles calculations to study the energy of the (11 (2) over bar1) twin boundary in Zr, Zn, Mg, Ti, and Be. This boundary is important for understanding the microyielding and damping of hexagonal close-packed metals. The (11 (2) over bar1) twin boundary is unique in that it is composed of-and can form by the glide of-basal dislocations nucleating at every c lattice parameter. The effect of the number of atoms between boundaries on the boundary energy, and the resulting lattice strains of the relaxed structures are quantified. It is shown that the energies obtained converge within 32-64 atoms/supercell. The structures with a higher second-order elastic constant term, c(44), also have higher boundary energies. It is further shown that the critical resolved shear stresses of the basal dislocations at 0 K, which make up the (11 (2) over bar1) twin, are so low as to be below the threshold of the first principles calculations.
|
|
| 13. |
|
|
| 14. |
- Mikhaylushkin, Arkady, et al.
(författare)
-
Instability of the body-centered tetragonal phase of iron under extreme conditions
- 2009
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 79:13
-
Tidskriftsartikel (refereegranskat)abstract
- The influence of the tetragonal and orthorhombic axial distortions on the body-centered cubic (bcc) phase of Fe at extreme conditions has been studied by means of first-principles calculations. We unambigiously demonstrate that the energy minimum corresponding to the body-centered tetragonal (bct) (c/a approximate to 0.9) structure, previously found in Fe upon the axial tetragonal distortion of the bcc phase along the Bain's path under compression at zero temperature, is an artifact of the structural constraint. When the bcc structure is examined using the orthorhombic distortion involving the tetragonal distortion as a particular case, the bct (c/a approximate to 0.9) structural framework represents a saddle point between two mirrored face-centered cubic minima rather than a local minimum. Therefore we conclude that there is no ground to emphasize on possible thermal stabilization of the bct structure with a particular c/a ratio apart from the whole family of structures obtained by tetragonal, orthorhombic, or another type of axial distortions.
|
|
| 15. |
|
|
| 16. |
|
|
| 17. |
|
|
| 18. |
- Mikhaylushkin, Arkady S, et al.
(författare)
-
High-pressure structural behavior of large-void CoSn-type intermetallics: Experiments and first-principles calculations
- 2008
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : Institutionen för fysik, kemi och biologi. - 1098-0121 .- 1550-235X. ; 77:1, s. 014102-
-
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.
|
|
| 19. |
|
|
| 20. |
- Mikhaylushkin, Arkady S
(författare)
-
The influence of hydrogen contamination on the structural stability of CoSn under compression
- 2010
-
Ingår i: JOURNAL OF PHYSICS-CONDENSED MATTER. - : Iop Publishing Ltd. - 0953-8984 .- 1361-648X. ; 22:43, s. 435501-
-
Tidskriftsartikel (refereegranskat)abstract
- The binary CoSn compound has a unique ground state large-void crystal structure, whose stability under pressure has recently been examined. Whereas theoretical results predicted a series of phase transformations, the room temperature experiments did not observe any structural change. We suggest that the large void of a CoSn-type structure could contain natural impurities such as hydrogen, which can influence the thermodynamic stability of a CoSn system and explain the unusual disagreement between the theoretical and experimental results. Based on first-principles calculations we reveal that the contamination of CoSn by hydrogen only results in a subtle change of structural parameters and the equation of state of CoSn, but drastically increases the stability of the CoSn-type phase in comparison with the high-pressure phases predicted earlier. We argue that the hardly detectable natural impurities of light elements in porous compounds like CoSn are able to change the phase equilibria.
|
|
| 21. |
- Mikhaylushkin, Arkady, et al.
(författare)
-
Stability of the ternary perovskites Sc3EN (E=B,Al,Ga,In) from first principles
- 2009
-
Ingår i: PHYSICAL REVIEW B. - 1098-0121. ; 79:13, s. 134107-
-
Tidskriftsartikel (refereegranskat)abstract
- Mechanical and thermodynamic stability of the isoelectronic ternary inverse perovskites Sc3EN (E=B,Al,Ga,In) has been studied from first principles. We confirm stability of recently synthesized cubic phases Sc3AlN and Sc3InN, and predict the stability of cubic Sc3GaN and a triclinic phase aP20-Sc3BN. Substantial phonon softening in Sc3AlN and Sc3GaN is observed indicating a possibility that structural defects could form readily. In accord, our experiments show that magnetron sputter deposited films contain regions with high density of nonperiodic stacking faults along the < 111 > growth direction. We suggest that defect-free crystals may exhibit anomalies in the carrier properties, promising for electronic applications.
|
|
| 22. |
- Mikhaylushkin, Arkady, 1977-
(författare)
-
Structural properties of Fe1-xNix compressed and heated to the Earth's core conditions
- 2008
-
Ingår i: FPLO Workshop,2008. - Dresden : Germany.
-
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.
|
|
| 23. |
- Mikhaylushkin, Arkady, et al.
(författare)
-
Voyage to the Earth's Deep Interior
- 2008
-
Ingår i: NCS News. - : National Supercomputer Centre, Linköpings universitet. ; :3, s. 3-5
-
Tidskriftsartikel (populärvet., debatt m.m.)
|
|
| 24. |
- Mondal, Swastik, et al.
(författare)
-
Electron-Deficient and Polycenter Bonds in the High-Pressure gamma-B-28 Phase of Boron
- 2011
-
Ingår i: PHYSICAL REVIEW LETTERS. - : American Physical Society. - 0031-9007. ; 106:21, s. 215502-
-
Tidskriftsartikel (refereegranskat)abstract
- The peculiar bonding situation in gamma boron is characterized on the basis of an experimental electron-density distribution which is obtained by multipole refinement against low-temperature single-crystal x-ray diffraction data. A topological analysis of the electron-density distribution reveals one-electron-two-center bonds connecting neighboring icosahedral B-12 clusters. A unique polar-covalent two-electron-three-center bond between a pair of atoms of an icosahedral cluster and one atom of the interstitial B-2 dumbbell explains the observed charge separation in this high-pressure high-temperature polymorph of boron.
|
|
| 25. |
- Zarechnaya, E Yu, et al.
(författare)
-
Superhard Semiconducting Optically Transparent High Pressure Phase of Boron
- 2009
-
Ingår i: PHYSICAL REVIEW LETTERS. - 0031-9007. ; 102:18, s. 185501-
-
Tidskriftsartikel (refereegranskat)abstract
- An orthorhombic (space group Pnnm) boron phase was synthesized at pressures above 9 GPa and high temperature, and it was demonstrated to be stable at least up to 30 GPa. The structure, determined by single-crystal x-ray diffraction, consists of B-12 icosahedra and B-2 dumbbells. The charge density distribution obtained from experimental data and ab initio calculations suggests covalent chemical bonding in this phase. Strong covalent interatomic interactions explain the low compressibility value (bulk modulus is K-300=227 GPa) and high hardness of high-pressure boron (Vickers hardness H-V=58 GPa), after diamond the second hardest elemental material.
|
|
