Praseodymium Telluride: A High-Temperature, High-ZT Thermoelectric Material

Refractory rare-earth tellurides with the Th3P4 structure type have attracted considerable interest as high-performance thermoelectric materials since the 1980s due to their high dimensionless figure of merit (ZT). Extensive work has been conducted on La3−xTe4 with peak ZT values greater than 1.1 at 1,273 K. The high ZT of La3-xTe4 is in part due to a large peak in the density of states near the Fermi level from the La 5d states. Here, we revisit Pr3−xTe4, for which our electronic structure calculations predict a favorable modification of the density of states by the introduction of praseodymium's 4f electrons. This was experimentally verified by preparing Pr3−xTe4 samples with varying Pr vacancy concentrations using a mechanochemical synthesis approach. The thermoelectric properties were measured and a ZT of 1.7 at 1,200 K was achieved with Pr2.74Te4. The 50% improvement in peak ZT compared with La3−xTe4 resulted from an increased effective mass, improved Seebeck coefficient, and lower thermal conductivity.