Investigation of the Effect of Sb Doping on the Thermoelectric Properties of the Ge-based clathrates, Ba8Ga16+xSbxGe30-2x

We investigate the effect of Sb doping in the Ga-flux single crystalline samples Ba₈Ga _16+xSb_xGe_30-2x (x = 0.5 - 4) by measurements of electrical resistivity (rho) and thermoelectric power (TEP) in the temperature range of 4-300 K. Our results show that doping even very small amount of Sb (x = 0.5) has drastic effects on the electronic structure of the parent Ba₈Ga₁₆Ge₃₀ compound. The Sb-doping not only stabilizes the p-type transport properties but also improves the thermoelectric properties. TEP of Ba₈Ga_16.5Sb_0.5Ge₂₉ reaches a value of 212 muV/K at room temperature. However, the TEP of other alloys Ba₈Ga _16+xSb_xGe_30-2x with x up to 4 does not change much upon addition of more Sb content (217 muV/K for x = 4). An analysis of the temperature dependence of rho and TEP of the studied materials implies the presence of a variable-range hopping mechanism