LOCAL STRUCTURE OF THE AgBr1-xIx ROCK-SALT TYPE SOLID-SOLUTION

The local structure of the AgBr1-xIx 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-