In situ high temperature X-ray photoelectron spectroscopy study of barium strontium iron cobalt oxide

The surface chemistry of barium strontium iron cobalt oxide of nominal composition Ba0.5Sr0.5Co0.8Fe0.2O3−δ has been studied using X-ray photoelectron spectroscopy (XPS). Precursor powders were prepared by a wet chemical process and sintered into pellets at 1100 °C. Polished pellets were examined by XPS at ambient and elevated temperatures, and after in situ heat treatments at temperatures up to 800 °C. Curve fitting and analysis of the spectral peaks was carried out, and significant changes in surface composition were observed as a result of the thermal treatments. At intermediate temperatures (300–500 °C) there was a reduction in barium and strontium concentrations relative to cobalt and iron. At 800 °C the surface concentration of barium and strontium increased. The nature of the oxygen species present on the surface also changed with temperature. Initially carbonate was dominant, but its concentration decreased with increasing temperature and a (Ba,Sr)–O species appeared. A significant amount of cobalt was reduced to 2+ at a temperature of 300 °C but reoxidised on cooling.

► X-ray photoelectron spectroscopy study of Ba0.5Sr0.5Co0.8Fe0.2O3−δ membrane.
► In situ heating to measure effect of temperature on surface chemistry.
► Ba and Sr cations depleted at 300–500 °C, but return at 800 °C.
► Co is partially reduced to Co2+ at 300 °C, with reoxidation occurring on cooling.
► On heating, surface carbonate decreases, (Co,Fe)–O retained, (Ba,Sr)–O appears.