Lattice Distortions, Orientational Correlations and Lattice Relaxation in (KBr)1-x(KCN)x

The coherent elastic diffuse scattering of thermal neutrons from (KBr)1-x(KCN)x single crystals with x = 0.07, 0.17 and 0.32, which strongly increases below the (orientational) freezing temperature, is described as Huang diffuse scattering caused by the lattice distortions around the CN- defects in the KBr matrix. A quantitative analysis reveals that at the lowest temperatures the CN- ions are frozen preferably in [111] directions with some also in [100]. The orientational pair correlation function of the CN- shows parallel (or antiparallel) alignment. At temperatures above the freezing temperature relaxation-time effects of the distortion field, due to the rapid reorientation of the defect, are apparent.