Effect of Strontium-Doped Lanthanum Vanadate on Crystal Structure, Conductivity and Vanadium Valence State of a La_1−xSr_xVO₃Anode in a Reducing Environment

La_1−xSr_xVO₃(where x = 0, 0.1, 0.3, 0.5, 0.7, and 1) exhibits a transition from an antiferromagnetic insulator to a paramagnetic metallic conductor and has been synthesized as a potential anode material for solid oxide fuel cells (SOFCs). La_1−xSr_xVO₃was synthesized by a solid-state reaction process followed by heat treatment under a reducing atmosphere (Ar:80/H₂:20). X-ray diffraction (XRD) results indicate that LaVO₃was substituted with various amounts of Sr²⁺in the cation sublattice. Pure LaVO₃shows an orthorhombic structure. After Sr²⁺substitution, a more symmetrical cubic perovskite structure was obtained because the tolerance factor is close to 1. The valence state of the vanadium ions of the La_1−xSr_xVO₃was further verified by x-ray photoelectron spectroscopy (XPS). According to the XPS results, when the lanthanum ion was substituted by a strontium ion, the negatively charged defect, Sr_La’, was compensated for by changing the valence of vanadium from a trivalent to a tetravalent or pentavalent state. The dependence of conduction behavior of La_1−xSr_xVO₃on the amount of Sr addition is discussed in terms of the hopping process with super/double exchange interaction and a charge transfer mechanism.