Temperature-Dependent XAFS Study on AgBr1-xIx Solid Solution

Abstract

Local structures of rock salt type AgBr1-xIx solid solutions with x varying from 0.07 to 0.4, substances interesting from both viewpoints of crystal structure and excellent properties as a photographic material, have been investigated by EXAFS analysis of three sets of spectra, i.e., I K-edge, Br K-edge and Ag K edge, at various temperature from 10K to room temperature. The Br-Ag and I-Ag interatomic distances in the solid solution were different from each other and deviated from the average Ag-(Br,I), or virtual crystal, distance determined from X-ray diffraction at any temperature. The iodide content x dependence of I-Ag and Br-Ag interatomic distances changed with temperature. At low temperature the I-Ag and Br-Ag distances increased with increasing the iodide content, whereas at room temperature they did not exhibit significant change with composition. This suggested that the bonding nature of the AgBr1-xIx solid solution is rather ionic at low temperature, while it is rather covalent at room temperature.