Dynamic and Static Disorder of Alkali Halide Solid Solutions studied by Temperature-dependent Extended X-Ray-Absorption Fine Structure

Abstract

Interatomic potential of ionic bonds in alkali halide solid solutions has been studied by temperature dependent EXAFS (extended X-ray absorption fine structure). As a typical ionic bond in alkali halide solid solutions, K–Br bond of KCl 0.8 Br 0.2 and KBr 0.2 I 0.8 solid solutions have been focused. The K–Br bond was contracted for KCl 0.8 Br 0.2 , while it was elongated for KBr 0.2 I 0.8 , as compared to that in KBr. The longer K–Br bond was softer and less anharmonic than the shorter K–Br bond. We could explain this bond length dependence of the force constants in terms of the interatomic potential of the K–Br bond. The static disorder also increased with the K–Br bond length.