Thermoelectric properties of BiCuSeO with bismuth and oxygen vacancies

Introducing vacancies in oxychalcogenides is an effective paradigm for the improvement of thermoelectric properties by reducing thermal conductivity through phonon scattering as well as by decreasing electrical resistivity via incorporation of holes through vacancies. In this paper, we present thermoelectric properties of Bi1−x CuSeO1−y with y = 0 for x = 0, 0.04, and y = 0.02 for x = 0.04, 0.08, 0.12. X-ray diffraction studies reveal BiCuSeO as the main phase with trace amounts of Cu1.8Se in Bi0.92CuSeO0.98 and Bi0.88CuSeO0.98. The impurity phases of Cu1.8Se in Bi0.92CuSeO0.98 and Bi0.88CuSeO0.98 could be due to the presence of vacancies. The electrical resistivity of Bi0.96CuSeO0.98 is lower than BiCuSeO, but higher than Bi0.96CuSeO, since Bi vacancies produce holes that are partially compensated by O vacancies. Electrical resistivity decreases with an increase in Bi vacancy content for y = 0.02. The Seebeck coefficient of samples shows that the similar trend as in electrical resistivity, following Mott's formula. Total and lattice thermal conductivity of Bi0.96CuSeO is higher than BiCuSeO as well as Bi0.96CuSeO0.98. This increases with further increase in bismuth vacancy. Introduction of vacancies (Bi and O) in BiCuOSe lead to higher thermal conductivities and lower Seebeck coefficients, and result in adverse effect on zT.