Microstructural evolution and dielectric properties of SiO2-doped CaCu3Ti4O12 ceramics

The abnormal grain growth (AGG) behavior of undoped and SiO2-doped CaCu3Ti4O12 (CCTO) ceramics were investigated. With the addition of 2 wt.% SiO2, the AGG-triggering temperature decreased from 1100 to 1060 °C, and the temperature for obtaining a uniform and coarse microstructure decreased from 1140 to 1100 °C. The lowering of the AGG temperature by SiO2 addition was attributed to the formation of a CuO-SiO2-rich intergranular phase at lower temperature. The apparent dielectric permittivity of coarse SiO2-doped CCTO ceramics was ∼10 times higher than that of fine SiO2-doped CCTO ceramics at the frequency of 103–105 Hz. The doping of SiO2 to CCTO ceramics provides an efficient route of improving the dielectric properties via grain coarsening. The correlation between the microstructure and apparent permittivity suggests the presence of a barrier layer near the grain boundary.