Development of Dielectric Ceramics for Nickel Electrode Multilayer Capacitors

抄録

Calcium-doped BaTiO₃-based dielectrics have a high resistance to reduction. This can be explained by taking the following three factors into account: 1) decrease in conduction electron density caused by acceptor Ca ions at the Ti site, 2) low freezing temperature of the equilibrium reaction by Ca ions at the Ti site, and 3) large enthalpy change in the reduction reaction by Ca ions at the Ba site. Fine-grained BaTiO₃ ceramics can be prepared using the tetragonal BaTiO₃ powder using ultra-fine starting BaTiO₃ powder synthesized by hydrolysis method. The non-uniform distortion is caused in the grains during sintering, which is attributed to the surface tension and clamping stress from the thin grain boundary layer. This suppresses the tetragonality symmetry of the grains and provides the BaTiO₃ ceramics with a high dielectric constant, low loss, and flat capacitance temperature characteristics. The Ca-doped ultra-thin dielectric layer compatible with nickel electrode can realize the nickel electrode multilayer capacitors of large capacitance and large volumetric efficiency, which is competitive with the Ta and Al-electrolytic capacitors and as reliable as conventional precious metal electrode multilayer capacitors.