Thermoelectric Transport Performance in p-Type AgSbTe₂-Based Materials through Entropy Engineering

Being a major obstacle, Ag₂Te has always been restricted in p-type AgSbTe₂-based materials to improve their thermoelectric performance. This work reveals a stabilized AgSbTe₂ through Sn/Ge alloying as synthesized by melting, annealing, and hot press. Interestingly, addition of Sn/Ge in AgSbTe₂ extended the solubility limit up to ∼30% and hence suppressed Ag₂Te in Ag_(1-SnSb_(1-GeTe₂ compounds and led to enhanced electrical transport. Moreover, electrical and thermal transport properties of AgSbTe₂ have been greatly affected by the phase transition of Ag₂Te near 425 K. However, high-entropy Ag_0.85Sn_0.15Sb_0.85Ge_0.15Te₂ 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 AgSbTe₂ lead to reduction in energy offsets. Meanwhile, a variety of defects appear in the Ag_0.85Sn_0.15Sb_0.85Ge_0.15Te₂ 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.