The effect of processing on the giant dielectric properties of CaCu3Ti4O12

The effect of processing on the dielectric properties of CaCu3Ti4O12 (CCTO) was researched. CaCu3Ti4O12 was prepared using conventional ceramic solid state reaction processing techniques. Powders mixed via mortar and pestle yielded CCTO with a room temperature permittivity of 11,700 and a loss of 0.047, which is similar to reported values in the literature. However, attrition-milled powders led to CCTO with permittivities close to 100,000 which are in the same range reported for single crystal CCTO. Increasing sintering temperature in the range from 990 to 1050 °C led to an increase in both the dielectric constant (714 to 82,450) and loss (0.014 to 0.98). Increasing sintering times also led to substantial improvements in permittivity. Grain size and density differences were not large enough to account for the enhancement in dielectric constant. The colossal effective dielectric constant of close to one million at room temperature was measured after annealing in flowing argon at 1000 °C. Based on the observations, it is believed that the primary factor affecting dielectric behavior is the development of internal defects. It appeared that higher defect concentration within the ‘core’ of a grain results in higher conductivity of the core and therefore, higher effective dielectric constant but also higher loss. The correlation between grain size and dielectric constant was also observed.