Room-Temperature Cubic Ag2S1-2xSexTex with Promising Ductility and Thermoelectric Properties Enabled by Entropy Engineering

Since the discovery of superior ductility in semiconducting Ag2S at room temperature, Ag2S-based inorganics attract ever-increasing attention as ductile thermoelectrics (TEs) for flexible electronics, while the monoclinic to cubic structure transition near room temperature (approximate to 455 K for Ag2S) of these materials leads to instability of their structures and properties. In this work, single-phase cubic Ag2S1-2xSexTex (x = 0.13-0.33) samples are stabilized at room temperature via entropy engineering. In comparison with pure Ag2S, the random mixing of S, Se, and Te at the anion site results in increased configuration entropy, improved electrical conductivity, decreased lattice thermal conductivity, and thus significantly enhanced TE properties of cubic Ag2S1-2xSexTex samples. By further optimizing the carrier concentration through introducing Ag vacancies, the slightly Ag-deficient Ag1.98S0.34Se0.33Te0.33 sample achieves a power factor of 6.1 mu W cm(-1) K-2 and a dimensionless figure of merit zT of 0.4 at room temperature. In the measured temperature range of 300-500 K, this cubic sample with excellent ductility shows not only a record average zT value of 0.62 in ductile inorganics but also very stable TE properties, demonstrating the great potential of entropy engineering in the design of high-performance ductile TE inorganics.