High-frequency dielectric study of the dynamics of (KBr)1−x (KCN) x mixed crystals

Dielectric measurements have been performed at 1 and 10 GHz in (KBr)_1–x (KCN) _x mixed crystals for cyanide concentrationsx=0.25 andx=0.50 in the temperature rangeT=1.7–150 K. The maxima of the real and imaginary parts of the dielectric constant falls into the Arrhenius straight lines obtained at lower frequencies. These dipolar lines cross over the so-called quadrupolar (acoustic) lines, in contradiction with theoretical predictions on the nature of the freezing. We also present a qualitative model which reinterprets the dipolar and quadrupolar freezings in terms of an individual and a collective processes.Associated with the Centre National de la Recherche Scientifique