Role of Strain in Surface Segregation of La _1-X Sr_xCo_0.2Fe_0.8O₃

Abstract

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 La 1- x Sr x Co 0.2 Fe 0.8 O 3 with varying Sr content ( x = 0.4, 0.3, 0.2) were deposited on single crystal NdGaO 3 , SrTiO 3 and GdScO 3 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.