Acoustic, opto-acoustic, and thermal properties investigated around the phase transitions of NaCN and Na(CN)xCl1−xmixed crystals

The elastic and opto-acoustic properties of sodium cyanide crystals NaCN and sodium cyanide--sodium chloride mixed crystals Na(CN${)}_{\mathit{x}}$${\mathrm{Cl}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$ (1\ensuremath{\ge}x\ensuremath{\ge}0.63) were investigated below room temperature using high-resolution Brillouin spectroscopy. Employing special scattering techniques, we were able to measure the elastic behavior in both the high- and low-temperature phases. Changing from systems with high ${\mathrm{CN}}^{\mathrm{\ensuremath{-}}}$ concentrations, which undergo structural phase transitions of first order, to systems with low ${\mathrm{CN}}^{\mathrm{\ensuremath{-}}}$ concentrations, which show glass transitions, the discontinuities of the extremely soft shear stiffness of these cubic crystals gradually vanish. Using a space- and angular-resolving Brillouin technique, we report data on the inhomogeneity of the Czochralski-grown mixed crystals. The consequences of these inhomogeneities for the phase-transition behavior have been studied by thermal analyses. We try to describe our shear elastic stiffness data in the framework of current theoretical approaches.