Entropy engineering enhances the thermoelectric performance and microhardness of (GeTe)1−x(AgSb0.5Bi0.5Te2)x

Abstract

As an endogenous material genetic property, entropy is an emerging fingerprint factor in the material genome. By designing multicomponent thermoelectric materials with high configuration entropy, the lattice thermal conductivity can be significantly reduced via severe lattice distortion, and the Seebeck coefficient can be improved by enhancing the crystal symmetry. However, high entropy also causes the deterioration of carrier mobility, restraining the improvement of the dimensionless figure of merit zT. Herein, we design the (GeTe)1−x(AgSb0.5Bi0.5Te2)x, aka TABGS alloys, via replacing half of the Sb by Bi in the well-known (GeTe)1−x-(AgSbTe2)x, aka TAGS alloys, to attest the efficacy of entropy engineering. In view of the low carrier mean free path of TAGS alloys approaching to the Mott-Ioffe-Regel limit, further Bi substitution and increased configuration entropy cannot impair the carrier mobility any longer. In addition, the suppressed rhombohedral-cubic phase transition via high configuration entropy and the reduced carrier concentration contribute to the substantially improved Seebeck coefficient. Furthermore, the elicited multiscale microstructures and the decreased sound velocity upon AgSb0.5Bi0.5Te2 alloying effectively restrain the lattice thermal conductivity. As a result, (GeTe)0.80(AgSb0.5Bi0.5Te2)0.20 achieves a high zT of 1.60 at 723 K and an average zTave of 1.23 from 300 to 773 K. Meantime, its room-temperature Vickers hardness reaches 2.21 GPa due to solid solution hardening. These results highlight the efficacy of entropy engineering in enhancing the thermoelectric performance, especially for numerous materials with intrinsically low carrier mobility.