Dielectric relaxor behavior of A-site complex ferroelectrics of Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3–BiFeO3

A new Bi-based lead-free ferroelectric with A-site complex perovskite structure, (1−x−y)Bi0.5Na0.5TiO3–xBi0.5K0.5TiO3–yBiFeO3, was fabricated by a conventional solid-state reaction method and the diffuse phase transition and relaxor characteristics were investigated. The XRD analysis shows that the ceramics system possesses a pure perovskite phase. There are two abnormal dielectric peaks and a dielectric loss peak with the increasing temperature in εr–Tεr–T curves. Obvious dielectric frequency dependence occurs near the low abnormal peak, but the temperature of high abnormal peak keeps almost constant as the measuring frequency increases. The theory that relaxor ferroelectrics are divided into intrinsic relaxor ferroelectrics and extrinsic relaxor ferroelectrics is put forward. It is found that dielectric relaxor of the ceramics at low abnormal peak comes from the polarization of space charges and dipolar defects by the εr–Tεr–T curves between poled samples and unpoled samples.