Extended X-ray-absorption fine-structure studies of electron-lattice correlations in mixed-valence Sm0.75Y0.25S

X-ray absorption spectrum of the Sm LIII edge has been measured in mixed-valence Sm0.75Y0.25S. From analysis of the edge structure and extended x-ray absorption fine structure, the valence is determined and it is shown that the S neighbors of each Sm atom adopt an average distance rather than a dynamically distorted environment with two distances corresponding to the two valence states. From this it is concluded that the characteristic Sm 4f-band width is not greatly modified by polaron effects. © 1980 The American Physical Society.