Search

A series of ternary aluminide intermetallics with a new structure type were formed from the reaction of gold and rare-earth metals in aluminum flux. The REAu3Al7 structure was obtained with all rare earths RE with the exception of La and Eu. These materials crystallize in the rhombohedral space group R-3c, with unit cell parameters a=8.0922(6) A˚ and c=21.066(2) A˚ for PrAu3Al7 as an example. The variation in cell edges with rare-earth size is regular with the exception of the Yb analogue. The possible mixed valency indicated by this result was confirmed by magnetic susceptibility measurements. Density functional theory-based band structure calculations on YbAu3Al7 indicate the ytterbium f-orbitals are located just below the Fermi level, further supporting the mixed valence description of this material. [Copyright &y& Elsevier]

Abstract: KSb5S8 and its solid solution analogs with Rb and Tl were found to exhibit a reversible and tunable glass→crystal→glass phase transition. Selected members of this series were analyzed by differential scanning calorimetry to measure the effect of the substitution on the thermal properties. The solid solutions K1− x Rb x Sb5S8 exhibited clear deviations in melting and crystallization behavior and temperatures from the parent structure. The crystallization process of the glassy KSb5S8 as a function of temperature could clearly be followed with Raman spectroscopy. The thermal conductivity of both glassy and crystalline KSb5S8 at room temperature is ∼0.40W/mK, among the lowest known values for any dense solid-state material. Electronic band structure calculations carried out on KSb5S8 and TlSb5S8 show the presence of large indirect band-gaps and confirm the coexistence of covalent Sb-S bonding and predominantly ionic K(Tl)⋯S bonding. Pair distribution function analyses based on total X-ray scattering data on both crystalline and glassy K1− x Rb x Sb5S8 showed that the basic structure-defining unit is the same and it involves a distorted polyhedron of “SbS7” fragment of ∼7Å diameter. The similarity of local structure between the glassy and crystalline phases accounts for the facile crystallization rate in this system. [Copyright &y& Elsevier]