Multiple Valence Bands Convergence and Localized Lattice Engineering Lead to Superhigh Thermoelectric Figure of Merit in MnTe

MnTe has been considered a promising candidate for lead-free mid-temperature range thermoelectric clean energy conversions. However, the widespread use of this technology is constrained by the relatively low-cost performance of materials. Developing environmentally friendly thermoelectrics with high performance and earth-abundant elements is thus an urgent task. MnTe is a candidate, yet a peak ZT of 1.4 achieved so far is less satisfactory. Here, a remarkably high ZT of 1.6 at 873 K in MnTe system is realized by facilitating multiple valence band convergence and localized lattice engineering. It is demonstrated that Sb-Ge incorporation promotes the convergence of multiple electronic valence bands in MnTe. Simultaneously, the carrier concentration can be optimized by Sb-Ge-S alloying, which significantly enhances the power factor. Simultaneously, MnS nanorods combined with dislocations and lattice distortions lead to strong phonon scattering, resulting in a markedly low lattice thermal conductivity(kappa(lat)) of 0.54 W m K-1, quite close to the amorphous limit. As a consequence, extraordinary thermoelectric performance is achieved by decoupling electron and phonon transport. The vast increase in ZT promotes MnTe as an emerging Pb-free thermoelectric compound for a wide range of applications in waste heat recovery and power generation.