Epitaxial growth and enhanced conductivity of an IT-SOFC cathode based on a complex perovskite superstructure with six distinct cation sites

Abstract

Epitaxial thin films of the 10 layer cubic perovskite superstructure Ba_1.7Ca_2.4Y_0.9Fe₅O₁₃ were grown by pulsed laser deposition, retaining the six distinct cation sites found in the bulk material. Growth on single crystal strontium titanate (STO) (0 0 1) substrates changes the observed symmetry from orthorhombic to tetragonal and orients the layer stacking direction of the superstructure normal to the substrate plane. The material is a candidate cathode for solid oxide fuel cells (SOFCs) and in the intermediate temperature (IT) region at 600 °C we measure the in-plane AC conductivity of the thin film as 30 S cm⁻¹, significantly enhanced over 3.5 S cm⁻¹ found for the polycrystalline form. This is assigned to reduction of the grain boundary density and alignment of the planes predicted to have the highest electronic and ionic conductivities. High resolution electron microscopy measurements demonstrate the atomic site ordering producing the superstructure and reveal defects associated with stacking faults in the ordering sequence.