Dielectric anomalies of Pb0.7La0.2TiO3-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 Ca 2+ for Pb 2+ into A-site of Pb 0.7 La 0.2 TiO 3 with the required stoichiometry of Pb 0.7(1−x) Ca 0.7x La 0.2 TiO 3 (PCLT). The quantum ferroelectric relation that commonly applies to SrTiO 3 -based perovskites, T max α(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 SrTiO 3 , 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 CurieWeiss 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 microRaman spectroscopy.