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Abstract:
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).
