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US 4,266,265 AGranted
Ceramic capacitor and method for making the same
AssigneeSprague Electric Company
InventorGaleb H. Maher
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AssigneeSprague Electric Company
InventorGaleb H. Maher
Estimating the term…
High-cadmium silicates, namely 2CdO.SiO.sub.2, 5CdO.2SiO.sub.2 and 3CdO.SiO.sub.2, are employed as the flux in a dielectric ceramic precursor mixture. The characteristic melting temperature of these fluxes is greater than the maximum ceramic firing temperature employed in the present method. Nevertheless, liquid phase sintering is achieved when such cations as the alkaline earth metals or lead from the high firing ceramic precursors diffuses into the flux, displacing some of the cadmium and reducing the melting temperature of the flux below that of the firing temperature. Some of the cadmium from the flux is drawn into the grains to replace the lost barium and lead. Escape of cadmium into the atmosphere is thereby substantially prevented. This method is particularly effective when the dielectric ceramic is a barium lead titanate zirconate and when the amount of the flux is kept very small. Even more particularly, unusually smooth capacitance versus temperature characteristics and high room-temperature dielectric-constants are realized for solid solutions of barium titanate with from 8-15 mole percent lead zirconate.
A method for making a ceramic capacitor comprising:
A ceramic capacitor comprising a dielectric ceramic body and two spaced electrodes in contact with said body, said body consisting essentially of a granular crystalline phase and an intergranular silicate phase, said granular phase consisting essentially of from 92 to 84 mole percent BaTiO.sub.3 and from 8 to 15 mole percent PbZrO.sub.3 wherein from 0.4 to 3 mole percent of said Ba and Pb are replaced by cadmium cations, the atomic ratio of the total number of Cd atoms to the total number of Si atoms in said body being from 2:1 to 3:1.
A ceramic capacitor comprising a dielectric ceramic body and two spaced electrodes in contact with said body, said body consisting essentially of a granular crystalline phase and an intergranular silicate phase, said granular phase consisting essentially of from 92 to 84 mole percent BaTiO.sub.3 and from 8 to 15 mole percent PbZrO.sub.3 wherein from 0.4 to 3 mole percent of said Ba and Pb are replaced by cadmium cations, the atomic ratio of the total number of Cd atoms to the total number of Si atoms in said body being from 2.1 to 3:1, said body having been formed from a mixture of a high-temperature-firing ceramic powder and a cadmium silicate powder selected from CdO.SiO.sub.2, 2CdO.SiO.sub.2, 5CdO.2SiO.sub.2, 3CdO.SiO.sub.2 and combinations thereof and said body having been fired at a temperature less than the melting temperature of said cadmium silicate.
Dependencies are inferred from the claim text.