EXAFS and Near Edge Structures in Mixed Valent SM_1−x Y _x S and the Energy Threshold Puzzle

Abstract

X-ray absorption can provide valuable information on mixed valence materials since it probes two important aspects of the intermediate valence problem. First, the white lines on the L_II and L_III (edges yield a simple and direct measurement of the valence in these materials. Second, the EXAFS can be used to determine possible lattice distortions about the mixed valent ion, thereby providing information on the nature of the electron-phonon coupling. An important step in analyzing the EXAFS data is the determination of the threshold energy, E₀, i.e., that photon energy for which the photo-ejected electron has zero kinetic energy and thus zero wavevector (k = 0). This threshold is expected to vary with the valence of the central atom since the atomic charge exerts a substantial effect on the binding energy of a core electron. Before addressing the threshold problem in the mixed valence materials, a summary of our results on the Sm L_III edge and EXAFS in Sm_1−xY_xS (x = 0, 0.2, 0.25) and SmP is presented.