Improvement in the Thermoelectric Figure-of-Merit of TAGS-85 by Rare Earth Additions

摘要

TAGS-85 is a well-known thermoelectric material based on germanium monotelluride that exhibits a second-order displacive transformation from a high-temperature cubic to a low-temperature rhombohedral polymorph. Recent efforts to improve the thermoelectric figure-of-merit through the addition of small amounts of the rare earth elements Ce and Yb have demonstrated a 25 percent increase in ZT at 700K in materials obtained by solidification from the melt. Preliminary analysis by x-ray diffraction of the chemically-modified alloy suggests a partial stabilization of the high-temperature cubic polymorph. ~(125)Te NMR studies confirm the incorporation of rare earth cations into the GeTe-based lattice. Solid state synthesis has been successfully applied to the processing of rare-earth-doped TAGS-85 and has resulted in a further increase in ZT beyond the levels initially observed in melt-solidified materials. This is believed to be due to improved homogeneity in the distribution of the lanthanide.