Diffusion phase transition and impedance spectroscopy of Bi2O3/CuO co-doped BCZT lead-free ceramics

Perovskite type (Ba_0.85Ca_0.15?2x Bi_2x )(Zr_0.1Ti_0.9?x Cu _x )O₃ lead-free ceramics were prepared via a conventional solid-state reaction method. The phase structure, dielectric, ferroelectric properties and complex impedance were investigated in detail. XRD and dielectric measurements determined that single orthorhombic phase displayed in (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ at room temperature. With the introduction of Bi₂O₃/CuO, the phase structure exhibited the mixture of orthorhombic and tetragonal phases, and then turned to single tetragonal phase. In contrast to the sharp dielectric transition of (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ ceramics, a broad dielectric peak coupled with a slight decrease in Curie temperature was observed in (Ba_0.85Ca_0.15?2x Bi_2x )(Zr_0.1Ti_0.9?x Cu _x )O₃ ceramics with increasing x. The observed diffuse phase transition behavior was further confirmed by a couple of measurements with polarization loops and polarization current density curves. The structural and the composition fluctuations induced by ions doping should be responsible for the diffuse phase transition behavior. Furthermore, physical mechanisms of the conduction and relaxation processes were revealed by using impedance spectroscopy analyses. It was concluded that the conduction and relaxation processes were thermally activated, which was closely linked with the singly and doubly ionized oxygen vacancies.