Beyond Substitution on the Role of Ce-Doping in Boosting Thermoelectric Performance of GeTe

Rare-earth (RE) doping shows extensive potential in boosting thermoelectric performance of GeTe-based materials, which are promising candidates for midtemperature thermoelectric applications. However, the low solubility of RE elements in GeTe limits their effectiveness in improving the thermoelectric dimensionless figure of merit (ZT). Here, we reveal that the influence of Ce doping in GeTe extends beyond atomic substitution. At low Ce concentrations, a minor amount of Ce can successfully substitute Ge in the GeTe matrix, forming Ce_Ge point defects, tuning the carrier concentration. At higher Ce doping levels, the formation of CeTe₂ precipitates introduces interfacial barrier scattering, further reducing the carrier concentration. Through Bi codoping, we achieve a high ZT of 2.0 in Ge_0.95Ce_0.01Bi_0.04Te. This study provides insight into the multifaceted effects of RE doping on the thermoelectric performance of GeTe-based materials.