Investigation into the extremely low thermal conductivity in Ba heavily doped BiCuSeO

Heavily doped Bi0.875Ba0.125CuSeO alloys were found to exhibit the highest ever ZT value in oxygenous thermoelectric systems, attributed to the extremely low thermal conductivity. In this report, we investigated the microstructural reason of the thermal conductivity in Ba- heavily doped BiCuSeO through scanning transmission electron microscopy (STEM). We found a large amount of nano-scale BaSeO3 precipitates dispersed widely in BiCuSeO matrix grains; besides, for the first time, we provide visual evidence of Ba substituting Bi atoms in Bi-O layers. Combined with DFT calculations, we conclude that intrinsic lattice vibration anharmonicity, together with Ba-Bi alloying and excess BaSeO3 precipitation, is responsible for the observed low lattice thermal conductivity in experiments. (C) 2016 Elsevier Ltd. All rights reserved.