Thermoelectric properties of sintered clathrate compounds Sr8GaxGe46−x with various carrier concentrations

Abstract

Polycrystalline samples of Sr8GaxGe46−x clathrates with varied nominal Ga contents were prepared by powder metallurgy to produce n-type samples with carrier concentration n of 1.8×1020–1.1×1021cm−3. Their thermoelectric properties were measured in the temperature range from 300to900K. Their Seebeck coefficient and electrical conductivity were found to be typical for a heavily doped semiconductor, and varied systematically with their carrier concentration. The maximum value of the figure-of-merit ZT was 0.62 at 800K for n=5.6×1020cm−3. Other following properties were also measured or estimated, and their relationships with the thermoelectric properties are discussed. The band gap of the samples was estimated to be 0.4–0.5eV; their effective mass was an almost constant value of 3.1me at room temperature, and this value decreases with increasing temperature; and their electron Hall mobilities were 8–13cm2V−1s−1 at room temperature, increasing slightly with decreasing carrier concentration.