1. Field of the Invention
This invention relates to a dielectric ceramic composition for a temperature-compensating ceramic capacitor which has a high dielectric constant and in which the temperature coefficient of its capacity can be controlled within the range of .+-.30 ppm (10.sup.-6)/.degree.C. at temperatures within the range of -55.degree. to +125.degree. C. The invention also relates to a multilayer ceramic capacitor obtained by firing at relatively low temperatures a laminate of a layer of the above dielectric ceramic composition and an Ag-Pd alloy layer containing a major amount of silver.
2. Description of the Prior Art
Generally, a temperature-compensating ceramic capacitor having a high dielectric constant, particularly a commercial multilayer ceramic capacitor, is obtained by laminating a plurality of thin dielectric layers having an inner electrode formed on their surface so that the internal electrodes are alternately connected in series to electrodes for external connection, and firing the assembly. Laminated capacitors of this type require relatively high firing temperatures (at least 1240.degree. C.) in order to make them sufficiently compact and thus give a high dielectric constant. Hence, the electrodes must be made of a metal having a higher melting point than the firing temperature of the dielectric material, such as an expensive noble metal (e.g., platinum or palladium). The cost of the metallic material thus increases the total cost of capacitors of this type.
Attempts have therefore been made to obtain multilayer ceramic capacitors of low prices by lowering the firing temperature for the dielectric material and the internal electrodes, and using inexpensive Pd-Ag alloys particularly having a major amount of Ag instead of the expensive noble metals. It is known however that generally, the crystallinity of a dielectric decreases with decreasing firing temperature, and therefore, its dielectric constant decreases. When the firing is carried out at lower temperatures than the aforesaid firing temperature, sufficient electrical properties and temperature characteristics for a high dielectric ceramic capacitor cannot be obtained.
Japanese Laid-Open Patent Publication No. 170405/1982 states that by adding moderate amounts of ZnO and SiO.sub.2 to a composition comprising Nd.sub.2 TiO.sub.7, BaTiO.sub.3, TiO.sub.2, Bi.sub.2 O.sub.3 and Pb.sub.3 O.sub.4, the resulting composition can be fired at 1050.degree. to 1100.degree. C. to obtain a sintered body, and in the production of a laminated capacitor in which the baking of the internal electrodes and the firing of the ceramic composition must be simultaneously carried out, a low-melting inexpensive Ag-Pd alloy can be used as the internal electrodes. This prior technique, however, has the defect that the temperature coefficient of the electrostatic capacity is within a relatively broad range of +30 to -300 ppm/.degree.C., the insulation resistance is reduced, or the breakdown voltage is low and varies greatly.