The role of electronic affinity for dopants in thermoelectric transport properties of InTe

We investigate the anisotropy in thermoelectric transport properties of pristine and self-doped InTe after spark plasma sintering and ascribe the observed weak anisotropy to the lack in orientation preference of investigated specimens as characterized by the scanning electron microscope. Then, the effect of Cu/Na doping on the transport properties of InTe is discussed for comparison, which suggests Cu doping is more favorable for keeping decent carrier mobility than Na doping and In-deficiency. Such difference is qualitatively explained by the large electronic affinity of Cu as compared to Na, which can effectively weaken the Coulomb scattering for charge carriers. Finally, a maximum figure of merit zT of about 0.73 at 730 K is obtained for the compound with the nominal composition of In0.99Cu0.01Te, measured parallel to the pressing direction, which can be attributed to the enhanced carrier concentration and well-maintained mobility compared to the pristine specimen. Furthermore, the Cu-doped specimen shows a superior average zT about 0.34, more than 35% enhancement than that for both Na-doped and self-doped InTe compounds. Our results should provide a guidance for selecting dopants for thermoelectric materials that possess strong ionized-impurity scattering character.