EXAFS study of thermoelectric BiCuOSe: Effects of Cu vacancies

•The ZrCuSiAs-structured BiCuOSe is a promising thermoelectric material.•Its performance can be enhanced by introducing copper vacancies.•Temperature-dependent EXAFS is carried out for x=0 and 0.05 BiCu1−xOSe samples.•Cu vacancies are shown to make the lattice softer and lattice thermal conductivity lower.•In a local scale the nearest Cu–Se shell in x=0.05 sample displays higher static order.

Excellent thermoelectric performance has been reported for the ZrCuSiAs-type BiCuOSe derivatives; for these materials the transport properties can be effectively adjusted by chemical substitutions or by introducing Cu vacancies. In this work we compare stoichiometric BiCuSeO and its Cu-deficient derivative BiCu0.95SeO by utilizing temperature-dependent extended X-ray absorption fine structure (EXAFS) measurements. Such a local probe evidences that Cu vacancies make the lattice more ductile and susceptible to temperature variation.