Nondestructive depth-resolved chemical state analysis of (La,Sr)MnO ₃ 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 La_1-xSr_xMnO₃ 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.