Dielectric behaviours of Pb1-3x/2LaxTio3 (PLT-A)-based ferroelectrics derived from mechanical activation

Abstract

Dielectric behaviours of Pb1-3x/2LaxTiO3 (PLT-A)-based perovskites derived from mechanical activation at room temperature were investigated systematically by post-sinter annealing in either oxygen or nitrogen and X-ray diffraction (XRD) strain analyses. The dramatic changes in dielectric behaviours of PLT-A upon post-sinter annealing were attributed to space charge polarization manifested by the surface effect and types of defect structures. Further, the dielectric transitions from ferroelectric to relaxor and even to quantum paraelectric-like behaviour were observed by substituting Ca2+, Sr2+ and Ba2+ into A-site of Pb0.7La0.2TiO3, as a result of the size mismatch strains. Indeed, the quantum paraelectric-like behaviour observed in Pb0.35Ca0.35La0.2TiO3 exhibited a temperature independent relative permittivity up to ~200 K, where quantum mechanical fluctuation could not be significant. Failing to elucidate these transitions with various classical ferroelectric models, a new approach that correlates the dielectric behaviours and the local structural distortions was taken on the basis of XRD triaxial strain analyses.