Successive Phase Transitions in Cs₂CdBr₄

Abstract

X-ray and dielectric measurements were made on Cs₂CdBr₄ (CCB) crystals, and optical observation was also made. CCB undergoes successive phase transitions at T₁=−21°C, T₂=−36°C and T₃=−65°C. The space groups in all phases have been determined: I: Pnam, II: P_1ss^Pnam, III: P2₁/n and IV: P\bar1. The space group for the incommensurate II-phase is determined on the basis of four-dimensional space group concept. Temperature dependence of the position and the intensity of satellite reflections in the incommensurate phase was measured. Rotation of optical indicatrix was found in III- and IV-phases and its temperature dependence was measured. Ferroelastic activities in III- and IV-phases were found.