Structure, high temperature transport, and thermal properties of Ba8GaxSi46−x (x=10 and 16) clathrates prepared by the arc melting method

Abstract

Ba 8 Ga 10 Si 36 and Ba8Ga16Si30 clathrates were prepared by the arc melting method and characterized for their structure, transport, and thermal properties by x-ray diffraction, electron probe microanalysis, electrical resistivity, and thermal conductivity measurements. The Rietveld refinement results gave the total occupancy of Ga/Si equal to 3.49/2.01, 0.99/14.01, and 5.51/17.99 for Ba8Ga10Si36 and 3.99/2.01, 1.99/14.01, and 10.01/13.99 for Ba8Ga16Si30, respectively, for 6c, 16i, and 24k sites. From the refined isotropic thermal displacement parameters, Debye temperature, average velocity of sound, lattice thermal conductivity, and Einstein temperature values were estimated. The calculated lattice thermal conductivity values were in agreement with room temperature experimental values of 1.128 and 1.071 W m−1 K−1, respectively, for two clathrates. The temperature variation of (300–850 K) electrical resistivity of Ba8Ga16Si30 showed metallic like behavior, whereas that of Ba8Ga10Si36 showed semiconducting behavior. The semiconducting nature was due to vacancies in the framework sites. High temperature thermal conductivity above Debye temperature was explained with anharmonic approximation.