Rashba effect and point-defect engineering synergistically improve the thermoelectric performance of the entropy-stabilized Sn0.8Ge0.2Te0.8Se0.2 alloy

Abstract

High-entropy alloys (HEAs) extend the phase composition and thus enlarge the space for optimizing the performance of structural materials, catalysts, thermoelectrics, etc. To date, researchers have constructed SnTe-based HEAs mainly by alloying at the Sn cationic sublattice, leaving the anionic site untouched, which hinders performance optimization by exploring new phase compositions and band structures. Herein, we report that Sn_1−yGe_yTe_0.80Se_0.20 alloys can be stabilized by increasing the Ge content to larger than 5% (y > 5%), as a result of the entropy stabilization effect. Meanwhile, heavily co-alloying Ge and Se in SnTe breaks the inversion symmetry by lattice distortion, inducing the Rashba effect to split the L band and align multiple valence bands at valence band maximum (VBM). Additionally, introducing Sb and vacancies at the Sn site of Sn_0.8Ge_0.2Te_0.8Se_0.2 has enabled a high zT value of 1.3 at 823 K, which is comparable to those of cation-disordered SnTe-based high-entropy samples. This work reassures the choice of heavily alloying Se in SnTe-based materials and paves the way to design new SnTe-based high-entropy thermoelectric materials with multiple elements at both anionic and cationic sites.