LAUSR

DOI: 10.1002/aenm.201802116 TE material research has attracted intense interest over the past few decades.[1] The TE performance of a material is measured by zT = σS2T/κ, where T, σ, S, and κ are the absolute temperature, electrical conductivity, Seebeck coefficient, and total thermal conductivity, respectively. Typically, κ = κel + κph, where the κel and κph are the carrier and lattice thermal conductivity, respectively. Since σ, S, and κel are adversely interrelated whereas the κph is relatively independent of σ, S, and κel, the stride toward high zT is in line with a two-pronged strategy, coined by Slack as “electron-crystal phonon-glass” (ECPG):[2] i) decoupling σ, S, and κel through band structure engineering toward a high power factor (PF) = σS2;[3,4] and ii) suppressing the κph via all-scale hierarchical microstructures.[5–7] Rooted in the core effects of high entropy alloys (HEAs), entropy engineering enables a synergy of band structure engineering and multiscale hierarchical microstructures through high entropy alloying. HEAs typically refer to the solid solutions in which more than five principal elements each in 5–35% molar ratio compete for the same crystallographic site, yielding high entropy of mixing and a wider variety of exciting properties.[8] HEA is a subset of multielement-doped materials. Neither the doping process nor the resulting composition would differentiate a The core effects of high entropy alloys distinguish high entropy alloying from ordinary multielement doping, allowing for a synergy of band structure and microstructure engineering. Here, a systematic synthesis, structural, theoretical, and thermoelectric study of multi-principal-element-alloyed SnTe is reported. Toward high thermoelectric performance, the entropy of mixing needs to be high enough to make good use of the core effects, yet low enough to minimize the degradation of carrier mobility. It is demonstrated that high entropy of mixing extends the solubility limit of Mn while retaining the lattice symmetry, the enhanced Mn content elicits multiscale microstructures. The resulting ultralow lattice thermal conductivity of ≈0.32 W m−1 K−1 at 900 K in (Sn0.7Ge0.2Pb0.1)0.75Mn0.275Te is not only lower than the amorphous limit of SnTe but also comparable to those thermoelectric materials with complex crystal structures and strong anharmonicity. Co-alloying of (Sn,Ge,Pb,Mn) also enhances band convergence and band effective mass, yielding good power factors. Further tuning of the Sn excess yields a state-of-the-art zT ≈1.42 at 900 K in (Sn0.74Ge0.2Pb0.1)0.75Mn0.275Te. In view of the simple face-centeredcubic structure of SnTe-based alloys, these results attest to the efficacy of entropy engineering toward a new paradigm of high entropy thermoelecrics.