Realizing high thermoelectric performance in GeTe through decreasing the phase transition temperature via entropy engineering

Abstract

Entropy engineering is one of the powerful approaches to suppress phase transitions. GeTe has a very high thermoelectric performance at relatively high temperatures, but the low structure symmetry and phase transition in the low temperature range limits its performance stability for power generation applications. Therefore, the optimized electrical transport properties of GeTe in a low temperature range are expected for improving the structural symmetry via suppressing phase transition. Herein, the phase transition temperature for GeTe was successfully decreased by introducing high entropy via continuously multiple doping; the phase transition temperature is correspondingly reduced from 660 K to 523 K. The Seebeck coefficient was enhanced by the improved structural symmetry through enhancing band effective mass while the carrier concentration is maintained in an optimum range. A record-high power factor of ∼23 μW cm⁻¹ K⁻² was obtained at 300 K in the highest entropy sample. We found that the increased configurational entropy obtained by continuous, multiple doping produces short-range disordered microstructures, which lead to an ultralow lattice thermal conductivity of ∼0.4 W m⁻¹ K⁻¹. Combining the record high power factor and low thermal conductivity, a maximum ZT value of ∼2.1 at 800 K was achieved for the highest entropy species Ge_0.84In_0.01Pb_0.1Sb_0.05Te_0.997I_0.003. This study provides an effective path to enhance thermoelectric performances via introducing entropy engineering.