Brillouin Scattering at High Pressures
Pressure and temperature dependences of the Brillouin spectra for KCN and NaCN are shown for pressures of 0 to 7 kbar and temperatures of 178 K to 295 K for KCN and of 285 K to 340 K for NaCN. Dispersion of c44 and c’ = (c11 + c12 + 2c44)/2 and strong pressure dependence of To, the temperature where c44 would vanish, has been found for NaCN, whereas there is no dispersion for c44 and c’ and no pressure dependence of To in KCN. On the other hand it is shown for both substances that multiphonon interactions, which increase approaching the phase transition, are the dominant anharmonic effect for the zone center acoustic phonons. A review of current theories for the order-disorder transition of the CN--ion system is given.
KeywordsPhase Transition Temperature Pressure Dependence Elastic Dipole High Order Coefficient Brillouin Spectrum
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