Effect of In additions on the thermoelectric properties of the type-I clathrate compound Ba8Ga16Ge30

The thermoelectric properties of quaternary type-I clathrate compounds, Ba8Ga16−xInxGe30 (x=0–9), have been investigated as a function of In content and temperature. The substitution of In atoms for Ga atoms leads to a decrease in electrical resistivity, as well as a decrease in thermal conductivity. The decrease in electrical resisitivity is explained in terms of the In occupancy behavior in the 6c sites, whereas the decrease in thermal conductivity in terms of the increased extent of the rattling motion of Ba atoms due to the increased lattice constant. As a result, the value of thermoelectric dimensionless figure of merit (ZT) of Ba8Ga16Ge30 is improved by In substitutions from 0.49 to 1.03 at 670°C when x=6.