Synthesis, structure and electrochemical performance of double perovskite oxide Sr2Fe1-xTixNbO6-δ as SOFC electrode

A new series of double perovskite oxides Sr2Fe1-xTixNbO6-δ (x = 0, 0.05 & 0.1) were prepared by traditional solid state reaction method and characterized by X-ray diffraction, scanning electron microscope (SEM), energy dispersive x-ray (EDX), ac impedance and dc four point using Van Der Pauw method. The samples were sintered at 1200 °C for 12 h in air to get single phase. Rietveld refinement shows that all composition crystallizes in tetragonal symmetry in the space group I4/m. The lattice parameter were related to the ideal single perovskite ap as a ≈ b ≈ √2ap, and c ≈ 2ap. Scanning electron microscope shows increase in porosity with increase of Ti content. Sr2Fe1-xTixNbO6-δ/YSZ shows a good interface with no lamination problem between the two materials. EDX shows that the element contents of the materials synthesized in this study close to the nominal stoichiometry. Chemical compatibility studies with YSZ electrolyte shows no reaction with the anode. A symmetrical cell with the configuration of Sr2Fe1-xTixNbO6-δ|YSZ|Sr2Fe1-xTixNbO6-δ (x = 0.05 & 0.1) shows the lowest polarization resistance of 49.80 Ω cm2 and the highest ac conductivity of 3.57 × 10−3 S cm−1 in dry H2/Ar for x = 0.1. The activation energy was found to be 1.20 eV which is almost similar to Sr2FeNbO6-δ as reported in literature. The dc conductivity measurement was highest for SFTN0.1 at 750 °C in dry 5% H2/Ar with a value of 1.17 S cm−1.