Synthesis and characterization of vacancy-doped neodymium telluride for thermoelectric applications.

Thermoelectric materials exhibit a voltage under an applied thermal gradient and are the heart of radioisotope thermoelectric generators (RTGs), which are the main power system for space missions such as I, II, and the Mars rover. However, materials currently in use enable only modest thermal-to-electrical conversion efficiencies near 6.5% at the system level, warranting the development of material systems with improved thermoelectric performance. Previous work has demonstrated large thermoelectric figures of merit for lanthanum telluride (La Te), a high-temperature -type material, achieving a peak value of 1.1 at 1275 K at an optimum cation vacancy concentration. Here we present an investigation of the thermoelectric properties of neodymium telluride (Nd Te), another rare-earth telluride with a similar structure to La Te. Density functional theory (DFT) calculations predicted a significant increase in the Seebeck coefficient over La Te at equivalent vacancy concentrations due to an increased density of states (DOS) near the Fermi level from the 4f electrons of Nd. The high temperature electrical resistivity, Seebeck coefficient, and thermal conductivity were measured for Nd Te at various carrier concentrations. These measurements were compared to La Te in order to elucidate the impact of the four 4f electrons of Nd on the transport properties of Nd Te. A of 1.2 was achieved at 1273 K for Nd.Te, which is a 10% improvement over that of La.Te.