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

Abstract

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.