Structural phase transition peculiarities in ion-molecular perchlorate crystals

Molecular relaxation processes are inspected in potassium and cesium perchlorates (KClO$_{4}$ и CsClO$_{4}$, respectively) via Raman spectroscopy. A first-order phase transition in KClO$_{4}$ and CsClO$_{4}$ crystal perchlorates is found to be extended. A pretransition region is also detected in KClO$_{4}$ and CsClO$_{4}$ systems, wherein the vibrational band widths are shown to remain almost unchanged, but abruptly increase at the phase transition point.