The Clathrate Ba8-xSi46 Revisited: Preparation Routes, Electrical and Thermal Transport Properties

The clathrate-I Ba8-xSi46 was manufactured from BaSi2 and a-Si by high-pressure high-temperature synthesis at 5 GPa and 900 degrees C and by redox reaction from Ba4Li2Si6. The transport properties were measured on specimens from the high-pressure high-temperature synthesis. The composition of the Ba8-xSi46 phase [space group Pm (3) over bar n, a = 10.3051(1)angstrom] corresponds to x = 0.8(2) according to the refined lattice parameter, the value determined from full-profile refinement of powder X-ray diffraction data amounts to x = 0.73(1), and the chemical analysis results in x = 1.0(1), yielding the average composition Ba7.2(2)Si46. The electrical transport properties of the phase with x = 0.8 were determined in the temperature range 2-300 K using a polycrystalline bulk specimen. The material is a metallic conductor with rho(300 K) = 3.3 mu Omega m and S(300 K) = -6.8 mu V K-1. The thermal conductivity shows a relatively large -for an intermetallic clathrate value of about 8 W.K-1 m(-1).