| 1. |
- 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.
|
|
| 2. |
- 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.
|
|
| 3. |
|
|
| 4. |
- 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.
|
|
| 5. |
|
|
| 6. |
- 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.
|
|
