Dielectric and thermal studies of the phase transitions in Cr-Cl boracite

Abstract

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 (e=ϵ_r=8.5- 13) and discontinuity at the onset of the phase transitions at T₁, and T₂, which are characterized by improper nature. Above T₁ e=ϵ_r ' 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 discussedis.