Crosssover from normal ferroelectrics to relaxor - spontaneous relaxor to normal ferroelectric transition at the crossover compositions

Spontaneous relaxor to normal ferroelectric transitions have been reported in a number of lead based relaxor systems,but not in all relaxors. It is unclear about its necessary condition, and about its origin. We systematically studied two representative relaxor systems, PZT based La doped PbZr_0.65Ti_0.35O₃ and BT based system xLa doped Ba_0.75Ca_0.25TiO₃, by dielectric, ferroelectric and XRD measurements and find that in both systems, spontaneous relaxor to normal ferroelectric transitions occur at the crossover composition regime. It is thus concluded that spontaneous relaxor to normal ferroelectric transition is a general effect occurring at the crossover regime between normal ferroelectric and relaxor. Finally a phenomenological interpretation for the origin of spontaneous transition at the crossover composition is provided.