Nondestructive depth-resolved chemical state analysis of (La,Sr)MnO3 film under high temperature

Fluorescence yield (FY) X‐ray absorption spectroscopic experiments with a grazing‐ exit geometry for detection of emitted fluorescence were carried out. The observed XAFS spectra provide the information about depth‐resolved chemical state in the surface layer of film materials through the take‐off angle dependence of the escape depth of the fluorescent X‐ray emitted from the sample. For La1−xSrxMnO3 films which are the oxygen electrode materials of a solid‐oxide fuel cell (SOFC), the Mn K XANES spectra were measured using undulator radiation at BL37XU in SPring‐8 synchrotron radiation facility. The results of the conventional FY‐XAS indicated differences due to distortion of MnO6 caused by different temperature, oxygen partial pressure p(O2) and voltage loading conditions in the spectrum profiles. From the results of the angle‐resolved measurements at 973 K in air, a depth‐dependent variation of the Mn K XANES profile in surface region of the film was observed. Though such depth‐dependence was also measured in case of lower p(O2) or voltage loading conditions at the same temperature, the absorbance proportion of absorbing bands contributing the change was different among the split 1s −>4p transition bands. These results indicate a difference in surface region caused by a difference between the surface and the inside of the film in the chemical potential of oxygen. Copyright © 2010 John Wiley & Sons, Ltd.