Ferroelectric transition in Co-I-Boracite under pressure

Abstract

The effect of hydrostatic pressure up to 103 atm has been measured on the ferroelectric phase transition temperature of Co3B7O13l. It was found that δTtr/δp = -11.1 × 10-3 deg/atm on cooling while δTtr/δp = -8.1 × 10-3 deg/atm on heating so that thermal hysteresis which reflects the 1st order nature of the transition increases with increasing pressure. Experimental data have been related to the thermodynamic theory developed by Dvor^ˆak which accounts for the fact that polarization is not the parameter of the transition in boracites. It is shown that the pressure dependence of the ideal transition temperature Ttr is governed by the interaction of stress with nonhomogeneous lattice modes and co-governed by the electrostrictive interaction. On the other hand, maximum thermal hysteresis. permittivity above Ttr and spontaneous polarization depend on pressure due to electrostriction only.