| 1. |
- Burakovsky, L., et al.
(författare)
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High-Pressure-High-Temperature Polymorphism in Ta : Resolving an Ongoing Experimental Controversy
- 2010
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Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 104:25, s. 255702-
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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.
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| 2. |
- Haeusserman, Ulrich, et al.
(författare)
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Structure and Bonding of gamma-B-28: Is the High Pressure Form of Elemental Boron Ionic?
- 2010
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Ingår i: INORGANIC CHEMISTRY. - : ACS American Chemical Society. - 0020-1669 .- 1520-510X. ; 49:24, s. 11270-11275
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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.
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| 3. |
- Haeussermann, Ulrich, et al.
(författare)
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Electron-poor antimonides: complex framework structures with narrow band gaps and low thermal conductivity
- 2010
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry. - 1477-9226 .- 1477-9234. ; 39:4, s. 1036-1045
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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).
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| 4. |
- Mikhaylushkin, Arkady S
(författare)
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The influence of hydrogen contamination on the structural stability of CoSn under compression
- 2010
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Ingår i: JOURNAL OF PHYSICS-CONDENSED MATTER. - : Iop Publishing Ltd. - 0953-8984 .- 1361-648X. ; 22:43, s. 435501-
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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.
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