Sintering, microstructure and electrical properties of 0.4(Bi0.5K0.5)TiO3-0.6BiFeO3 lead-free piezoelectric ceramics

The effect of sintering temperature on the densification, microstructure and structure of 0.4(Bi0.5K0.5)TiO3-0.6BiFeO3 lead-free piezoelectric ceramics is assessed. The 0.4(Bi0.5K0.5)TiO3-0.6BiFeO3 powders were prepared by using the mixed-oxide method and were sintered at temperatures of 1000, 1050 and 1100 °C for 1 to 5 hrs. Unlike earlier work, the sintered samples showed high densities even when sintered at 1000 °C. X-ray diffraction revealed that the sintered samples shared the same rhombohedral structure as BiFeO3. With increasing sintering temperature, the rhombohedral distortion of the unit cell decreased. In addition to the relaxor-like broad peak around 400 °C, a low-temperature dielectric peak was found at temperatures below 190 °C by employing a low-frequency sweep down to 10 mHz. The DC conductivity of the 0.4(Bi0.5K0.5)TiO3-0.6BiFeO3 sample exhibited three temperature regions with activation energy values of 0.56 eV (T > 500°C), 0.72 eV (400°C < T <200°C) and 0.81 eV (T < 190°C). The characteristic transitions in the conductivity could be related to the Néel temperature (370°C) and the conductivity anomaly observed at ca. 190°C in BiFeO3.