Valence fluctuation in Sm 1−xEu xS system: An X-ray absorption spectroscopic study

Abstract

Sm 1− x Eu x S ( x = 0.10 to 0.85) alloys have been investigated using XANES (X-ray absorption near-edge structure) technique to examine the question of intermediate valence of Sm and Eu. SmL III absorption edge data point to the intermediate valence of Sm, and the Sm valence data clearly exhibits a continoous valence transition of Sm with increasing Eu content. On the other hand, the single peaked white lines at the L III edge of Eu indicate a purely divalent ground state of Eu in the alloys throughout the range. Sm valence data shows an agreement with the earlier X-ray absorption studies and the theoretical calculations for low concentrations of Sm while the high Sm concentration data tends to differ from them, showing an unmistakeble intermediate valence (IV) state, contrary to the earlier findings. XRD data indicates a 1% volume change of the unit cell for x = 0.1 to 0.85, isostructurally. The present investigation raises some important questions regarding the mechanism of valence fluctuation in this system that still remain to be answered.