Optical studies of thermal cycling and hysteresis effects in elastic order-disorder phase transformations. II. Cyanide-diluted and mixed alkali-metal cyanide crystals

Abstract

The order-disorder transformations and related hysteresis effects in various mixed alkali-metal halide cyanide crystals are studied by exploiting the light-scattering properties of their multi-domain ordered structures. These studies are performed on three cyanide-diluted systems, ${\mathrm{KCN}}_{\mathrm{x}}$:${\mathrm{KBr}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$, ${\mathrm{KCN}}_{\mathrm{x}}$:${\mathrm{KCl}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$, and ${\mathrm{RbCN}}_{\mathrm{x}}$:${\mathrm{RbBr}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$, and on two mixed alkali cyanide systems, ${\mathrm{NaCN}}_{\mathrm{x}}$:${\mathrm{KCN}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$ and ${\mathrm{KCN}}_{\mathrm{x}}$:${\mathrm{RbCN}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$. It is found that the amount of light scattering in some of these mixed crystals depends upon the prevailing crystal structure at particular temperatures and concentrations. This allows us to obtain phase boundaries for the (x,T) phase diagrams which, for the particular cases of the ${\mathrm{KCN}}_{\mathrm{x}}$:${\mathrm{KBr}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$ and ${\mathrm{KCN}}_{\mathrm{x}}$:${\mathrm{KCl}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$ mixed crystals, are in good agreement with independent results from neutron and x-ray diffraction studies.