Single-crystal neutron-diffraction study of the orientational glass state of (NaCN)1−x(KCN)x

Abstract

Single crystals of (NaCN${)}_{1\mathrm{-}\mathit{x}}$(KCN${)}_{\mathit{x}}$ with concentrations x=0.19, 0.44, and 0.89 have been investigated by elastic neutron diffraction. The mixed crystals with x=0.19 and 0.44 exhibit a transition to an orientational glass state, while those with x=0.89 transform into a coexistence region of cubic and rhombohedral phases. Diffuse scattered intensities have been studied as a function of temperature T, phonon wave vector q, and momentum transfer Q. I(T,q,Q) provides insight into the character of the freezing process. From a detailed analysis of the structure factors, the orientational distribution of the CN molecules was determined. With increasing strength of random fields, 〈100〉 orientations are favored.