The Phase Transition of Crystalline Potassium Thiocyanate, KSCN. I. Thermal and Infrared Studies

Abstract

Abstract The phase transition of the potassium thiocyanate crystal at ca. 140°C has been studied by thermal and infrared methods. The transition is of a higher-order type, accompanied by an entropy change of 1.30±0.05 e. u., which is nearly equal to R ln 2. The infrared band due to the in-plane bending vibration of a thiocyanate ion shifts to lower frequencies in the course of the phase transition. From these results, it has been concluded that the phase transition is connected with the dynamical disordering of the direction of thiocyanate ions in crystal, a disordering which is mainly brought about by the frequent excitation of the out-of-plane torsional oscillation and the flipping motion.