Structure Analysis of the Phase Transition in KSCN

Abstract

Crystal structures of KSCN are investigated with an X-ray diffraction method at several temperatures in the orthorhombic and the tetragonal phases. The nature of the order-disorder transition for SCN⁻ ions is confirmed above and below the transition temperature. Thermal motion of K⁺ ions shows a high anharmonicity in the a-b plane of the tetragonal unit cell. The spontaneous displacement of K⁺ in the orthorhombic phase correlates to the order parameter of SCN⁻. It is suggested that the phase transition is explained by the orientation-phonon coupling system.