Thermoelectric Transport Performance in p-Type AgSbTe 2 -Based Materials through Entropy Engineering.

Being a major obstacle, Ag 2 Te has always been restricted in p-type AgSbTe 2 -based materials to improve their thermoelectric performance. This work reveals a stabilized AgSbTe 2 through Sn/Ge alloying as synthesized by melting, annealing, and hot press. Interestingly, addition of Sn/Ge in AgSbTe 2 extended the solubility limit up to ∼30% and hence suppressed Ag 2 Te in Ag (1- x ) Sn x Sb (1- y ) Ge y Te 2 compounds and led to enhanced electrical transport. Moreover, electrical and thermal transport properties of AgSbTe 2 have been greatly affected by the phase transition of Ag 2 Te near 425 K. However, high-entropy Ag 0.85 Sn 0.15 Sb 0.85 Ge 0.15 Te 2 compound results in a stabilized rock-salt structure and presents a high power factor of ∼10.8 μW cm -1 K -2 at 757 K. Besides, density functional theory reveals that available multivalence bands in Sn/Ge-doped AgSbTe 2 lead to reduction in energy offsets. Meanwhile, a variety of defects appear in the Ag 0.85 Sn 0.15 Sb 0.85 Ge 0.15 Te 2 sample due to entropy change, and thus lattice thermal conductivity decreases. Ultimately, a high figure of merit of ∼1.5 is attained at 757 K. This work demonstrates a roadmap for other group IV-VI materials so that the high-entropy approach may inhibit the impurity phases with extended solubility limit and result in high thermoelectric performance.