Anomalies of dielectric properties of cs2hgci4 crystals in the vicinity of phase transitions

A short review of the published experimental data on various physical properties and some new results of the measurement of dielectric and electromechanical properties of Cs₂HgCI₄ crystals in a wide temperature range are presented. The crystal is shown to reveal anomalies at seven temperatures associated with structural phase transitions and hence to have eight phases. In two temperature regions there exists a small spontaneous polarization and the anomalous dielectric permittivity is a nonlinear function of the electric biasing field. Within the phase followed by the first polar phase on cooling the crystal, the effects of thermal, electrical and mechanical memory, specific for incommensurate phases, are observable.