Dielectric and thermal studies of the phase transitions in cr-cl boracite

The antiferro-/paraelectric (42m/43m at T1=264 K) and ferro-/antiferroelectric (mm2/42m at T2≈160 K) phase transitions of Cl-Cl boracite have been studied by dielectric and thermal analysis. The permittivity of both ferroic phases shows small and weakly temperature dependent values (er-8. 5–13) and discontinuity at the onset of the phase transitions at T1 and T2, which are characterized by improper nature. Above T1 er decreases with increasing temperature, referring to the Curie-Weiss law. Microcalorimetry shows the revelant enthalpy changes: ΔH1 = 1. 98 kJ. mole-1 at T1; ΔH2=0. 03 kJ. mole-1 at T2. The effect of the hydrostatic pressure on the phase transition temperature is discussed.