X-ray photoelectron spectroscopy of electronic ceramic materials

X-ray photoelectron spectroscopy (XPS) has been used to probe valency in substituted perovskite oxides of the general formula ABO3, including (La,Sr)CrO3, (Y,Ca)CrO3, and (Y,Ca)MnO3. When Sr was substituted for La or when Ca was substituted for Y in the chromite series, a second Cr 2p3/2 peak appeared 3-4 eV higher in binding energy than the principal peak, consistent with oxidation of Cr3+ to Cr4+ and with previously proposed conduction mechanisms involving a highly localized electron hole (small polaron). Similar substitutions in the manganite series gave no observable energy shifts in the Mn 2p peak and negligible satellite intensity. For the manganites, a highly localized electron hole on an Mn site does not appear to be formed. Rather, results indicate a higher degree of covalency than found in the chromites