Dielectric anomalies of Pb0.7La0.2TiO 3-based perovskite

Abstract

Dielectric transitions from normal ferroelectric to relaxor-like and then to quantum paraelectric-like behaviour were observed by substituting 10 to 60% of Ca2+ for Pb2+ into A-site of Pb0.7La 0.2TiO3 with the required stoichiometry of Pb 0.7(1-x)Ca0.7x La0.2TiO3 (PCLT). The quantum ferroelectric relation that commonly applies to SrTiO3-based perovskites, T maxα (X - X c )1/2, fails to describe the observed dielectric anomalies in PCLT, whereby the transition temperature vanishes with a finite slope. Quantum ferroelectric behaviour that exhibits a sharp dielectric peak but violates the Curie-Weiss law was not observed throughout the composition range studied. Unlike the typical quantum paraelectric SrTiO3, the quantum paraelectric-like behaviour observed for PCLT with x = 0.55 and 0.60 exhibit negative transition temperatures, as shown by the fittings to both the Curie-Weiss and Barrett's relations. Thermal hysteresis was surprisingly observed in substituted PCLT with x = 0.30 and 0.40 that exhibit frequency dispersive relaxation. To establish a correlation between the dielectric anomalies and structural parameters, analyses on global and local perovskite lattices were carried out using X-ray diffraction technique and micro-Raman spectroscopy. © Springer Science + Business Media, LLC 2006.