Unique Semi-Coherent Nanostructure Advancing Thermoelectrics of N-Type PbSe

Introducing nanostructures into bulk thermoelectric materials is an effective strategy for reducing lattice thermal conductivity (kappa(lat)). However, large numbers of hanging bonds emerge on account of lattice mismatch usually at the interfaces between nanostructures and matrix, thereby significantly deteriorating carrier mobility (mu (H)) and seriously limiting thermoelectric performance. Here, utilizing the cointroduction of Gd-Cu2Te into n-type PbSe as a paradigm, the zT could be greatly improved. The conduction band flattening caused by Gd doping can successfully compensate for the small Seebeck coefficient in n-type PbSe, thus achieving extraordinary electrical performance. Further advanced electron microscopy and X-ray absorption fine structure spectra directly demonstrate that most of the Cu forms nanoscale Cu2Se precipitates, especially a unique semi-coherent interface between the PbSe matrix and the Cu2Se nanoprecipitate is observed for the first time. Such nanoprecipitate accompanied by the semi-coherent interface not only ensures higher mu (H) as an excellent charge transfer mediator but also collectively scatters the heat-carrying phonons over a wide frequency range to obtain the ultralow kappa(lat), resulting in the prominent improvement of the ratio mu (H)/kappa(lat). The present finding represents an important step forward in electron-phonon decoupling via constructing semi-coherent nanostructure and interface engineering, which should be applicable for other thermoelectric materials.