Dielectric behavior associated with the synergetic microstructure and oxygen vacancies in CaCu₃Ti₄O₁₂ ceramics

CaCu₃Ti₄O₁₂ (CCTO) ceramics has been successfully fabricated by sol–gel processing. The microstructure of CCTO ceramics sintered at 1050 °C exhibits the inhomogeneity with the large grain in the order of several tens of micrometers separated by the nano-scale small grain in the grain boundary. And with the sintered temperatures increasing to 1075 °C, the small grain in the grain boundary gradually grows up, accompanied by the emergence of secondary phase Cu_xO. The temperature dependence of dielectric properties has been demonstrated that with the emergence of secondary phase, the dielectric constant for the ceramics sintered at 1075 °C is inferior to the one of the ceramics sintered at 1050 °C from room temperature to 250 °C. Defect model related to the contribution of the second ionized oxygen vacancies in the grain boundary are proposed, supported by the thermal activation theory.