Influence of the Oxygen Content on the Electronic Transport Properties of SrxEu1-xTiO3-δ

The electronic transport properties of perovskite-type oxides with promising thermoelectric properties can be tuned by cationic substitutions as well as by creating oxygen vacancies. Here, two series of SrxEu1-xTiO3-delta (x = 0.00, 0.03, 0.25, 0.75, 0.97) samples with different oxygen stoichiometries are synthesized using various reductive atmospheres. Oxygen deficiencies in the series produced in highly reducing atmosphere are confirmed by thermogravimetric analysis. Electrical resistivity (rho) and Seebeck coefficient (S) data reflect the strong influence of the oxygen nonstoichiometry on the transport properties. Samples from the strongly reduced series possess up to 5 orders of magnitude lower electrical resistivities than samples from the less reduced series, confirming that oxygen vacancies act as electron donors in the former. Their Seebeck coefficients strongly decrease with the increase of the charge carrier concentration (lower rho). Pronounced S(T) peaks are observed, and are attributed to strong hybridization of the localized Eu 4f states with the delocalized Ti 3d states. The presence of optically active defect states is confirmed by UV-vis spectroscopy.