XRD, XANES, and Electrical Conductivity Analysis of La- and Zr-Doped Ba_0.5Sr_0.5Fe_0.9Cu_0.1O_3-δ Suitable for IT-SOFC Cathodes

Lanthanum- and zirconium-doped perovskite Ba_0.5Sr_0.5Fe_0.9Cu_0.1O_3-δ ceramics, i.e., LaBa_0.5Sr_0.5Fe_1.8Cu_0.2O6_-δ (LBSFC) and Ba_0.5Sr_0.5Fe_0.85Cu_0.1Zr_0.05O_3-δ (BSFCZ), were synthesized and characterized. The characterizations include x-ray diffraction, scanning electron microscopy, x-ray near-edge absorption spectroscopy of the Fe K-edge and Cu K-edge, iodometric titration, and electrical conductivity measurements. The structure of BSFCZ was pseudo-cubic single perovskite, whereas LBSFC was orthorhombic double perovskite. It was also discovered that the iron and copper in the octahedron-site has a mixed oxidation state with iron having 3+/4+ and copper 2+/3+. The ratio of Fe³⁺/Fe⁴⁺ was found to be 59/41 for LBSFC and 75/25 for BSFCZ. Similarly, copper has a mixed Cu²⁺/Cu³⁺ = 24/76 for BSFCZ and 44/56 for LBSFC. The unit cell symmetry, the presence of La³⁺, and the formation of Fe⁴⁺/Cu³⁺ are thought to be responsible for the improvement in the electrical conductivity and performance of the LBSFC. In contrast, the Zr^4- stabilized perovskite structure was unfavorable for electrical conductivity. The electrical performance of the LBSFC achieved a maximum conductivity σ = 150 S/cm^-1 at 500°C.