The intermediate valence state in rare earth compounds; bulk and surface manifestations

Abstract X-ray photoelectron spectroscopy (XPS) has made significant contributions to our understanding of the interconfiguration fluctuation (ICF) phenomenon in rare earth solid. ICF behavior has been found in compounds of most of the rare earths which exhibit more than one stable valence state, i.e., Ce, Sm, Eu, Tm and Yb. XPS generally leads to conclusions consistent with those from other measurements. However, it has recently been shown that certain materials which have a stable trivalent state in the bulk undergo a transition to an ICF state at the surface, and that others which have an ICF state in the bulk may have a stable divalent surface.