Effect of sintering conditions on microstructure and dielectric properties of CaCu₃Ti₄O₁₂ (CCTO) ceramics

The influence of sintering temperature and dwell time on the microstructure formation and dielectric properties of CaCu₃Ti₄O₁₂ ceramics was investigated. For sintering temperatures of 1050 and 1100 °C significant differences in the CaCu₃Ti₄O₁₂ ceramic microstructure and the segregation of a CuO_x-rich phase towards the grain boundary (GB) areas were observed with increasing dwell time. In addition to the formation of a semiconducting bulk and insulating grain boundary phase the segregated CuO_x forms an intergranular phase, and the effects of this phase on the dielectric properties are rather intriguing. At sintering temperature below 1050 °C only small amounts of CuO_x segregate, whereas sintering above 1050 °C (e.g., 1100 °C) leads to increased evaporation of the CuO_x. Therefore, the effects of the CuO_x-rich intergranular phase upon the dielectric properties are felt strongest in samples sintered at 1050 °C. Such effects are discussed in terms of microstructural variations due to liquid phase sintering behavior facilitated by the TiO₂-CuO_x-eutectic, which appears to be melted at high sintering temperature prior to evaporation of CuO_x at prolonged dwell times at the highest sintering temperatures (1100 °C).