Effects of ZnO and CeO2 additions on the microstructure and dielectric properties of Mn-modified (Bi0.5Na0.5)0.88Ca0.12TiO3 ceramics

The effects of ZnO and CeO2 on the microstructure and dielectric temperature characteristics of the Mn-modified (Bi0.5Na0.5)0.88Ca0.12TiO3 ceramics were investigated to develop temperature-stable dielectric ceramics. By adding 1–2 wt% ZnO, the overall dielectric constant increased. With further increasing the amount of ZnO, the dielectric constant at temperatures lower than 25 °C decreased, whereas the dielectric constant at temperatures higher than 75 °C increased. The temperature characteristic of capacitance became flatter when more than 4 wt% ZnO was doped. By adding CeO2, the dielectric constant decreased and a flat temperature characteristic of permittivity was obtained. X-ray diffraction analysis revealed that the perovskite BNT phase formed for all the compositions and the secondary phases Zn2TiO4 and Bi2Ti2O7 occurred, respectively when ZnO and CeO2 was added. Scanning electron microscope indicated that an inhomogeneous microstructure comprising fine and rectangle grains was observed in the ZnO-free sample. ZnO less than 2 wt% could inhibit the grain growth and decrease long grains. However, the grain growth was promoted as more than 8 wt% ZnO was added. The dielectric loss with different contents of ZnO and CeO2 were characterized as the function of temperatures for potential use at high temperature. The dielectric loss at 25 °C was independent of the amounts of ZnO and CeO2. However, the dielectric loss at 250 °C decreased by adding 1 wt% ZnO and then increased with increasing ZnO. This system is considered to be a potential material for high-temperature capacitors.