High Thermoelectric Performance in Phonon-Glass Electron-Crystal Like AgSbTe2

Abstract

Achieving glass-like ultra-low thermal conductivity in crystalline solids with high electrical conductivity, a crucial requirement for high-performance thermoelectric energy conversion, continues to be a formidable challenge. A careful balance between electrical and thermal transport is essential for optimizing the thermoelectric performance of a material. Despite this inherent trade-off, the experimental realization of an ideal thermoelectric material with a “phonon-glass electron-crystal” (PGEC) nature has rarely been achieved. Here, we have demonstrated PGEC-like AgSbTe2 by tuning the atomic disorder upon Yb doping, which resulted in an outstanding thermoelectric performance with figure of merit, zT∼2.4 at 573 K. Yb-doping induced enhanced atomic ordering decreases the overlap between the hole and phonon mean free paths and consequently leads to a PGEC-like transport behaviour in AgSbTe2. We observed a two-fold increase in electrical mobility while keeping the position of the Fermi level (EF) nearly unchanged, which significantly increased the electrical conductivity and corroborates the enhanced crystalline nature of the AgSbTe2 lattice upon Yb doping for electrical transport. The cation-ordered domains, on the other hand, lead to the formation of nanoscale superstructures (∼ 2 to 4 nm) that strongly scatter heat carrying phonons, resulting in a temperature-independent glass-like thermal conductivity. Furthermore, we have achieved a promising output power density of 388 mWcm−2 in a 4-leg device fabricated using 4 mol% Yb-doped AgSbTe2 as the p-type analogue. Our strategy paves the way for realizing high thermoelectric performance in various disordered crystals by making them amorphous to phonons while favoring crystal-like electrical transport.