High thermoelectric figure-of-merit in Sb2Te3/Ag2Te bulk composites as Pb-free p-type thermoelectric materials

We investigated the thermoelectric properties of Sb2Te3/Ag2Te (ST/AT) composites with ST/AT molar ratios of 1/1, 2/1, 4/1, 8/1, 16/1, and 32/1. The extrinsic composites, synthesized by wet ball milling of two separate powders of Sb2Te3 and Ag2Te, can be differentiated from the intrinsic composites by high temperature phase separation because of the low temperature synthesis process. The thermoelectric properties of the composites show a systematic behaviour of decreased electrical and thermal conductivities with increasing Ag2Te dispersion concentration. The composite with ST/AT ratio = 1/1 exhibits an extremely low lattice thermal conductivity with a high power factor over a wide temperature range, resulting in a high ZT value of 1.5 at 700 K, which is a significantly enhanced value of ZT compared with those of other Pb-free p-type chalcogenide thermoelectric materials.