Optimization of the average figure-of-merit zT in medium-entropy GeTe-based materials via entropy engineering

Entropy engineering has emerged as an effective strategy for improving the figure-of-merit zT by decelerating the phonon transport while maintaining good electrical transport properties of thermoelectric materials. Herein, a high average zT of 1.54 and a maximum zT of 2.1 are achieved in the mid-entropy GeTe constructed by Ag, Sb, and Pb alloying. At room temperature, the mid-entropy GeTe tends to be a cubic structure. And the power factor is improved from 7.7 μW·cm⁻¹·K⁻² to 16.2 μW·cm⁻¹·K⁻² due to the large increase in effective mass and the optimized carrier concentration. The increasing disorder created by heavy and off-centering Ag, Sb, and Pb atoms induces strong mass/strain fluctuations and phonon scattering to decelerate the phonon transport in GeTe. A low lattice thermal conductivity is obtained in the medium-entropy GeTe-based material. Moreover, a GeTe-based thermoelectric cooler is fabricated with the cooling temperature difference of 66.6 K with the hot end fixed at 363 K. This work reveals the effectiveness of entropy engineering in improving the average zT in GeTe and shows potential application of GeTe as a thermoelectric cooler.