Microstructure and electrical properties of (1−x)[0.8Bi0.5Na0.5TiO3-0.2Bi0.5K0.5TiO3]-xBiCoO3 lead-free ceramics

The (1−x)[0.8Bi0.5Na0.5TiO3-0.2Bi0.5K0.5TiO3]-xBiCoO3 (x = 0, 0.02, 0.05, abbreviated as BNKT, BNKT-002Co, BNKT-005Co, respectively) lead-free ferroelectric ceramics were prepared via the solid state reaction method. The phase structure, microstructure, dielectric, ferroelectric, pyroelectric, and piezoelectric properties of the ceramics were investigated comparatively by using a combination of characterization techniques. All the samples exhibit typical X-ray diffraction peaks of ABO3 perovskite structure. The doping of BiCoO3 causes a decrease in lattice parameters and an increase in grain size of the ceramics. The Raman spectroscopy results suggest a lattice distortion due to the doping. It is found that BNKT-002Co and BNKT-005Co have higher depolarization temperatures compared with BNKT. The Curie-Weiss law and modified Curie-Weiss law explored a diffuse phase transition character for all the samples. The results of ultraviolet-visible diffuse reflectance suggests that BiCoO3-doped ceramics possess higher defect concentration. The impedance analysis shows a temperature dependent relaxation behavior, and the activation energy for the electrical responses varies with the change of BiCoO3 amount. The ferroelectric and piezoelectric properties of the ceramics decrease due to the doping of BiCoO3. Based on the results of the Rayleigh analysis, it was suggested that the differences in the electrical properties among the ceramics are closely related to the change in oxygen vacancy concentration.