Influence of Alumina Dopant and Environment on the Electrical Properties of Calcium Copper Titanate Ceramics

Calcium copper titanate (CaCu3Ti4O12; CCTO) ceramics are useful as capacitor dielectrics for many applications. In this study the effect of doping with alumina and testing atmospheres in air and dry N2 on the stability and reproducibility of electrical and dielectric properties of CCTO-xAl2O3 system, where x = 0, 0.5, and 4 wt.% as a function of temperature are investigated. Solid-state synthesis route is used to fabricate the pure and doped CCTO samples sintered at 1080 °C and 1100 °C for 5 h in air. Stable and reproducible dielectric properties are obtained only by switching the measuring atmosphere from air to dry N2. Increased space charge accumulation at the grain boundaries leading to large dielectric constant (ε′) and tan δ are measured in air. Much lower tan δ values of 0.021–0.020 are obtained with a large ε′ (8,815–11,090) at low frequencies (500–800 Hz) in N2 at 23 °C for 0.5 wt.% alumina in both samples sintered at 1080 °C and 1100 °C. These results clearly demonstrate that testing environment can dominate the dielectric properties of pure and alumina-doped CCTO at low frequencies unless measured in dry nitrogen atmosphere to achieve intrinsic behavior useful for applications as capacitors.