LOCAL STRUCTURE OF THE AgBr_1-xI_x ROCK-SALT TYPE SOLID-SOLUTION

Abstract
The local structure of the AgBr_1-xI_x rock-salt type solid-solution (0≤x≤0.4) was discussed on the basis of both EXAFS and single crystal X-ray diffraction. The cell dimensions increase linearly with increasing AgI content because of substitution of larger ion I^- for Br^-. The average distance Ag^-(Br,I) determined by X-ray diffraction increase apparently. However the interatomic distances between Ag and Br, which were determined by EXAFS on Ag K- and Br K-edge respectively, decrease with AgI content. The particular increase in temperature factor of Ag results from the displacements from the normal octahedral site owing to the fact that Br and I randomly occupy the normal site in the rock-salt type structure. Large shift of Ag K-edge was observed, indicating that the effective cation charge is lowered by replacing Br^- with I^-. Consequently, it should be expected that Ag in the solidsolution is attracted to Br^- which has larger effective anion charge than I^-.