Low-temperature sintering of CaCu3Ti4O12 ceramics in N2 atmosphere for dual-function capacitor-varistor properties

Due to the elevated sintering temperature, CaCu 3 Ti 4 O 12 ceramics are unsuitable for co-firing with copper electrodes, which has notable advantages including low production cost, high conductivity and broad high-frequency applicability. Therefore, the sintering of CaCu 3 Ti 4 O 12 ceramics should be conducted at temperatures below 1083 °C (the melting point of Cu) and under protecting atmosphere to prevent the oxidation of Cu. In this paper, CaCu 3 Ti 4 O 12 ceramics were sintered at only 1000 °C in high-purity N 2 , then reoxidized at 800 °C in air to restore their electrical properties. Among them, Ge 4+ -Ni 2+ co-doped CaCu 3 Ti 4 O 12 ceramics exhibited significantly increased grain-boundary resistivity, resulting in substantially decreased dielectric loss (about 0.055 at 1 kHz), while still remaining a large dielectric constant of 9.4 × 10 3 . Additionally, the nonlinear coefficient and breakdown strength field were also improved to values of 3.3 and 1360 V/cm, respectively. The results provide a promising candidate material for multilayer capacitor-varistor devices with Cu internal electrode.