Simultaneous Suppression of Phonon Transport and Carrier Concentration for Efficient Rhombohedral GeTe Thermoelectric

Superior electronic performance due to the highly degenerated Σ valence band (N_v∼12) makes rhombohedral GeTe a promising low-temperature (<600 K) thermoelectric candidate. Minimizing lattice thermal conductivity (κ_L) is an essential route for enhancing thermoelectric performance, but the temperature-dependent κ_L, corelated to T^-1, makes its reduction difficult at low temperature. In this work, a room-temperature κ_L of ≈0.55 W m^-1-K^-1, the lowest ever reported in GeTe-based thermoelectric, is realized in (Ge_{1- y}Sb_yTe)_{1- x}(Cu₈GeSe₆)_x, primarily due to strong phonon scattering induced by point defects and precipitates. Simultaneously, Cu₈GeSe₆-alloying effectively suppresses the precipitation of Ge, enabling the optimization of carrier concentration with the additional help of aliovalent Sb doping. As a result, an extraordinary peak zT of up to 2.3 and an average zT_avg. of ≈1.2 within 300-625 K are achieved, leading to a conversion efficiency of ≈9% at a temperature difference of 282 K. This work robustly demonstrates its potential as a promising component in thermoelectric generator utilizing low-grade waste heat.