Synergistic band convergence and endotaxial nanostructuring: Achieving ultralow lattice thermal conductivity and high figure of merit in eco-friendly SnTe

SnTe has emerged as an environmentally friendly alternative to PbTe for power generation application. Here, we achieve an ultralow lattice thermal conductivity and a high thermoelectric performance of SnTe via the synergy of valence band convergence and endotaxial nanostructuring. Low-content Ge and Sb alloying leads to band convergence in SnTe as supported by DFT calculations, thereby remarkably increasing Seebeck coefficient and power factor. We also propose a phase separation strategy to introduce endotaxial Cu2Te nanostructures to SnTe. Endotaxial Cu2Te nanoprecipitates cause the lattice thermal conductivity to reduce significantly. Sn0.92Ge0.04Sb0.04Te-5%Cu2Te exhibits an ultralow lattice thermal conductivity of 0.27 Wm(-1) K-1 at 873 K, which is not only lower than the amorphous limit of SnTe but also comparable with those of thermoelectric materials with complex crystal structures and strong anharmonicity. Consequently, a remarkably high figure of merit (ZT) of 1.5 at 873 K is achieved by synergistically optimizing the electrical and thermal transport properties of SnTe. Such remarkably high ZT is achieved by adopting a facile and controllable one-step process, nontoxic and low-content element doping. Low-content precious metal doping can effectively reduce the cost of thermoelectric modules and potentially expand their usefulness for various thermoelectric generator applications. The environmentally friendly material with high ZT and low cost can definitely accelerate the process of widespread use of thermoelectric modules.