Evidence for a new non-ferroelectric phase transition in (Pb_1-xCa_x)TiO₃ Ceramics for 0.60 ≤ x ≤ 0.90

Abstract

Results of low temperature dielectric measurements on the mixed (Pb_1-xCa_x)TiO₃ system are presented to show that the strong dielectric anomaly observed for compositions with x < 0.60 is replaced by a very weak dielectric anomaly for x ≥ 0.60. The temperature dependence of the unit cell parameters, as obtained by Rietveld analysis of the neutron powder diffraction data, shows change of slope at the dielectric anomaly temperature. The observed dielectric peak for x ≥ 0.60 is shown to be due to a thermodynamic phase transition and not due to a relaxor or dipole glass type transition. Absence of hysteresis loop below the transition temperature reveals that this new phase transition is of non-ferroelectric type. Curie-Weiss fit to the dielectric constant gives negative Curie temperature which points towards an antiferroelectric transition.