The evolution of structure and dielectric behavior of Pb(Sc0.5Ta0.5)O3 ceramics with various annealing times

Non-annealed and annealed Pb(Sc0.5Ta0.5)O3 ceramics were successfully prepared by using the traditional solid-state reaction method. The influence of annealing time on the structure and dielectric behavior was investigated. A pure-phase structure with a space group of Fm9m was obtained in all ceramics. As annealing time increased, both the degree of order and the ordered domain size increased. Superlattice reflection spots associated with B-site ordering arrangement were found in the long-time annealed ceramics by using selected area electron diffraction. The non-annealed sample exhibited clear relaxor ferroelectric behavior. Three unexpected peaks/jumps were observed in the dielectric-loss tangent curves of the annealed ceramics, in which each peak corresponded to a subtle dielectric change. X-ray powder diffraction analysis at −50, 10, and 50 °C performed on the 48-h annealed ceramics demonstrated that the degree of order and cell parameters barely changed. With increasing annealing time, the low-temperature dielectric transition weakened, the middle-temperature dielectric transition sharpened, and the transition temperature shifted toward high temperatures. At high temperatures, the dielectric transition increasingly strengthened with the increase in frequency. The unusual dielectric behavior was attributed to the inhomogeneous distribution of ordered and disordered regions in the ceramics. The low-temperature dielectric transition primarily originated from the disordered region, the middle-temperature dielectric transition was mainly attributed to the ordered region, and the dielectric transition at high temperatures was ascribed to the incommensurate structure that resulted from the intense competition of the ordered and disordered regions.