Structure, dielectric, ferroelectric and diffuse phase transition properties of the Ce, Ca hybrid doped BaTiO₃ ceramics

Lead-free relaxor/diffuse ferroelectrics have attracted continued interest due to their unusual properties about broad maximum in temperature dependence of the dielectric permittivity and thin, narrow hysteresis loops. In this work, the diffuse behavior is studied in the Ce, Ca hybrid doped BaTiO₃ ceramics (denoted as BT-8Ce-xCa, x = 10, 15, 20, 25 mol%) prepared by a conventional solid-state reaction. Pure perovskite phase structure can be observed in all the samples. Dense ceramics are successfully prepared and the grain size changes little with the increase of Ca content. The dielectric measurements show diffuse phase transition behaviors for all the samples, which are identified by a fit of the phenomenological equation with the character parameter ξ for all the samples is about 1.80, the diffuse parameter Δ increases from 80.5 to 97.1, showing stronger diffuse behavior with more Ca content. As the Ca content increases, the Curie temperature (T_c) decreases. The decreased T_c and diffuse phase transition are discussed from the role of Ca, Ce dopants. In addition, the diffuse ferroelectric properties of these ceramics are verified through the hysteresis loops changing to constricted loops with decreased P_r at low temperature which leads to larger P_max-P_r and larger energy storage density. This phenomenon is analyzed based on a field induced transition from diffuse ferroelectrics to normal ferroelectrics.