Ba_(1-x)Sr_xCo_(1-y)Fe_yO_(3-δ) Perovskites Bulk and Thin Films: Phase Compositions and Electrical Conductivity

摘要

We report about the phase stability and the electric properties of the solid solutions in the Ba-Sr-Co-Fe-O system in which a new cathode material Ba_(0.5)Sr_(0.5)Co_(0.8)Fe_(0.2)O_(3-δ) is included. Powders were prepared by the solid state reaction method to synthesize the Ba_(1-x)Sr_xCo_(1-y)Fe_yO_(3-δ) (BSCF) compositions with 0.2 ≤ x ≤ 0.8 and 0.2 ≤ y ≤ 0.8 from raw materials of metal carbonates and oxides. Electric DC conductivity was measured on polycrystalline bulk samples. All the compounds showed semiconductivity from room temperature up to 500°C and a transition to metallic conductivity to higher temperatures. The compositions richer in Sr and Co show the highest electric conductivity as high as 250 S/cm around 470 °C, much higher than the previously reported single compound Ba_(0.5)Sr_(0.5)Co_(0.8)Fe_(0.2)O_(3-δ). Thin films of BSCF were deposited on MgO substrates by the pulsed laser deposition technique (PLD) and the electric conductivity was measured in plane and compared with bulk values. In order to elucidate the origin of different conductivity values for the different compositions and evaluate the oxygen non stoichiometry, the oxidation state of Co and Fe has been studied by XAS.