Crystal structure and transport properties of Ba8Ge43□3

Abstract

The single phase clathrate-I Ba₈Ge₄₃□₃ (space group Iad (no. 230), a = 21.307(1) Å) was synthesized by quenching the melt between cold steel plates. Specimens for physical property measurements were characterized by microstructure analysis and X-ray diffraction on polycrystalline samples as well as single crystals. Transport properties including thermopower, electrical resistivity, thermal conductivity and specific heat were investigated in a temperature range of 2–673 K. The electrical resistivity exhibits a metal-like temperature dependence below 300 K turning into a semiconductor-like behaviour above 300 K. The analysis of the specific heat at low temperature indicates a finite density of states at the Fermi level, thus corroborating the metallic character below 300 K. The temperature dependence of the specific heat was modelled assuming Einstein-like localized vibrations of Ba atoms inside the cages of the Ge framework. A conventional crystal-like behaviour of the thermal conductivity with a low lattice contribution (κ_l(300 K) = 2.7 W m⁻¹ K⁻¹) has been evidenced.