Residual strains and dielectric properties of Pb0.7La0.2TiO3-based perovskites

A correlation between the local structural distortions and dielectric behaviors of Pb_0.7La_0.2TiO₃ (PLT-A20) was developed on the basis of XRD residual strain analyses. It was observed that A-site iso-valent substitutions with various ionic sizes, i.e. Ba²⁺ and Sr²⁺, generate tensile and compressive lattice mismatch strains, which are balanced delicately by the long-range Coulombic forces and short-range repulsions, leading to a breakdown in dipolar long-range order. Thus, both dielectric transition from normal ferroelectric to relaxor and enhancement in diffuse phase transition (DPT) are observed by increasing the level of Ba²⁺ and Sr²⁺ substitution in PLT-A20, respectively.