High-Pressure Brillouin Scattering Study of the Order-Disorder Transition in KCN

Abstract

Pressure and temperature dependences of the Brillouin spectra for KCN are shown for pressures of 0 to 7 kbar and temperatures of 178 to 295 K. It is shown that multiphonon interactions are the dominant anharmonic effect, and it is suggested that the phase transition at 168 K comes from a ferroelastic ordering of C${\mathrm{N}}^{\ensuremath{-}}$ dipoles strongly coupled anharmonically to the phonons.