Temperature- and composition-dependent valence mixing of Sm in cation-and anion-substituted SmS observed by X-ray photoemission spectroscopy

We have determined the interconfiguration mixing ratios (Sm+3/Sm+2) of 1.4 and 4.1 for Sm0.81Y0.19S and SmAs0.18S0.82 at 295 K from their x-ray photoemission spectra. These ratios are observed to decrease reversibly by a factor of 2 at 110 K. The agreement of these results with valences deduced from lattice-constant measurements is direct evidence that configuration mixing is responsible for the anomalous temperature- and composition-dependence of the lattice constant. © 1974 The American Physical Society.