Effects of ZnO and CeO₂ additions on the microstructure and dielectric properties of Mn-modified (Bi_0.5Na_0.5)_0.88Ca_0.12TiO₃ ceramics

The effects of ZnO and CeO₂ on the microstructure and dielectric temperature characteristics of the Mn-modified (Bi_0.5Na_0.5)_0.88Ca_0.12TiO₃ 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.