Role of Strain in Surface Segregation of La 1-X SrxCo0.2Fe0.8O3

Strontium doped lanthanum cobalt ferrite (LSCF), a widely used cathode material in solid oxide fuel cells (SOFC), can have long-term stability issues that can adversely affect electrochemical performance. Heteroepitaxial thin films of La1-x SrxCo0.2Fe0.8O3 with varying Sr content (x = 0.4, 0.3, 0.2) were deposited on single crystal NdGaO3, SrTiO3 and GdScO3 substrates by pulsed laser deposition. The lattice mismatch between the films and the substrate led to different strains in the films. The extent of Sr-rich precipitate formation on the film surface was quantified using total reflection X-ray fluorescence (TXRF), and atomic force microscopy (AFM). The microstructure and the nature of the bonding of the surface Sr-rich phases were investigated by scanning/transmission electron microscopy (S/TEM) and hard x-ray photoelectron spectroscopy (HAXPES), respectively. The strain in the thin films was measured by high-resolution x-ray diffraction (HRXRD). The combined effects of the strontium content and strain on the extent of surface phase formation will be discussed.