Discrete nature of the orientational glass ordering inNa1−xKxCN

Abstract

The local orientational ordering of the ${\mathrm{CN}}^{\mathrm{\ensuremath{-}}}$ molecular ions in strongly substitutionally disordered ${\mathrm{Na}}_{1\ensuremath{-}x}{\mathrm{K}}_{x}\mathrm{CN}$ crystals is investigated via ${}^{14}\mathrm{N}$ quadrupole-perturbed NMR line-shape measurements. At low temperatures these systems represent order-disorder-type three-state orientational glasses with the ${\mathrm{CN}\mathrm{}}^{\mathrm{\ensuremath{-}}}$ molecular axes oriented essentially along the cubic crystal axes. The temperature dependence of the orientational glass order parameter is determined and shown to fit nicely to a recently developed three-state random-bond--random-field model of orientational glasses.