Unusual dielectric relaxation of the mixed crystal (KBr)1−x(KCN)xat low temperatures and at low defect concentrations

For a study of the transition from a crystalline system with isolated defects to an orientational glass with the typical low-temperature anomalies of glasses we have investigated the complex dielectric constant of (KBr${)}_{1\mathrm{-}\mathrm{x}}$(KCN${)}_{\mathrm{x}}$ below 1 K for 0.05≤x≤0.12. For x<0.1 we have observed an unusual relaxation behavior with rates increasing on cooling. This effect can be explained with a relaxation within the system of ${\mathrm{CN}}^{\mathrm{-}}$ dipoles. At higher concentration this relaxation mechanism loses importance and the dielectric properties approach those of a structural glass.