Precursor behaviour of the ferroelastic phase transition in K ₂ZnCl₄

Linear birefringence and optical activity behaviours of K2ZnCl4 were studied between 100 K and 300 K. Birefringence deviation from linear thermo-optic behaviour and existence of unexpected optical gyration component were observed between 145 and 225 K, where a dielectric anomaly was also reported in the previous study. These phenomena can be ascribed to the precursor behaviour of the ferroelastic phase transition, that is, formation of ferroelastic nanodomains in the ferroelectric phase observed by previous x-ray scattering study.