Disordered Structure of Rb₂ZnCl₄ in the Normal Phase

Abstract

The crystal structure of Rb₂ZnCl₄ was determined at several temperatures in the normal phase by using X-ray reflection data collected by an automatic four-circle diffractometer. The β-K₂SO₄ type structure with large thermal amplitudes was obtained. The split-atom method reveals that the ZnCl₄ group lies with equal probability in two equilibrium arrangements. In addition to the disordered motion, softening of a rotational motion of the ZnCl₄ group is suggested from the temperature variation of thermal vibrations. The magnitude of the thermal amplitude gives an information about the mechanism of the phase transition in the β-K₂SO₄ type ferroelectrics.