Influence of Te substitution on the structural and electronic properties of thermoelectric BiCuSeO

We report on the influence of tellurium substitution on the structural and electronic properties of the thermoelectric oxychalcogenide BiCuSeO. Our results show that a complete solid solution exists between the two end members BiCuSeO and BiCuTeO. However, a complex evolution of the properties has been observed, with both a monotonous evolution of the structural and electrical parameters between Te = 0.5 and Te = 1, and a structural anomaly between Te = 0.1 and Te = 0.5. This structural anomaly correlates with an evolution from a metallic-like electrical resistivity to a semiconducting behaviour with the opening of a small gap in the electronic structure, and it is essentially suppressed with hole doping performed by the partial substitution of Bi³⁺ by Sr ²⁺. Lastly, our thermoelectric measurements evidence a large increase of the thermoelectric power factor for large Te fractions, which decrease upon hole doping.