Thermoelectric properties of TlSbTe2 doped with In and Yb

p-type TlSbTe2 and its In- and Yb-doped variants were prepared by hot pressing of the elements in the stoichiometric ratios, and their thermoelectric properties were determined after verifying the purity of the samples by powder X-ray diffraction. Theoretically, TlSbTe2 is an intrinsic semiconductor possessing a narrow band gap; however, the as-prepared TlSbTe2 exhibited relatively high electrical conductivity, decreasing with ascending temperature, which provides evidence for the presence of p-type extrinsic charge carriers (holes) along with the positive Seebeck coefficient. Doping In onto the Tl site inserts more electrons, thereby decreasing the hole concentration; as a result, the electrical and thermal conductivity decreased and the Seebeck coefficient increased. The best thermoelectric performance of In-doped TlSbTe2 was achieved at 625 K, with a figure of merit (zT) of 0.77. The overall best zT was improved to 0.85 at 620 K with the sample of nominal composition Tl0.98SbYb0.02Te2. An anisotropy test was implemented by comparing the electrical conductivity and Seebeck coefficient measured on the prismatic bars cut parallel and vertical to the pressing direction. The results indicate basically isotropic behavior in polycrystalline TlSbTe2 along these two orthogonal directions.