Multilayer ceramic capacitors with CaCu3Ti4O12 dielectric

The nonferroelectric high-permittivity material CaCu₃Ti₄O₁₂, being a naturally formed internal barrier layer capacitor, was utilized for preparation of slurries for tape casting and fabrication of multilayer ceramic capacitors. Screen printed silver or silver-palladium electrodes were co-fired with ceramic green sheets at 940°C. The dielectric properties of the CaCu₃Ti₄O₁₂-based multilayer capacitors were studied in a wide frequency range of 0.1 Hz-2 MHz and in the temperature range from -55 to 400°C. The dominant response which is recorded at low frequency range and at temperatures above 150°C is related to grain boundaries. The dielectric response at low temperatures and/or high frequencies is attributed to grains. SEM and EDS studies showed heterogeneous microstructure and composition of ceramic layers. Large grains have composition close to stoichiometric CCTO, while smaller grains and grain boundaries regions are enriched in oxygen and depleted in copper. The fabricated multilayer capacitors exhibit low sintering temperature suitable for use of cheap electrodes, good compatibility of ceramic layers with the applied commercial conductive pastes, high specific capacitance and a relatively low temperature coefficient of capacitance.