University of Illinois

Ferro Corporation

Sang M Park

David A Payne

Otto C Jahnke

A semiconducting internal boundary layer ceramic composition having a fine grain structure suitable for use in thin-layer multilayer capacitors is made in one step by firing a mixture comprising a major amount of finely divided strontium titanate, a minor amount of a compound containing either strontium or titanium, or an element functionally equivalent thereto, a minor amount of a semiconductor forming ingredient (dopant), the identity of which depends on whether the mixture is rich in strontium or in titanium, and a minor amount of a counterdopant selected from cuprous oxide or silver oxide. When the mixture is rich in titanium, the chemical doping agent used to produce semiconductivity is an oxide of a trivalent metal selected from bismuth, boron, iron, antimony, lanthanum and the rare earth and transition metals. When the mixture is rich in strontium, the dopant is an oxide of a pentavalent or hexavalent metal selected from tungsten (+6), niobium (+5), tantalum (+5), and molybdenum (+6).

Fine-grain semiconducting ceramic compositions

An improved polycrystalline semiconducting ceramic composition comprises an alkaline earth metal titanate doped with a hexavalent metal oxide such as (MO.sub.3)(Bi.sub.2 O.sub.3).sub.x where M is tungsten or molybdenum, and x ranges from 0 to 7, which is liquid phase sintered with lead germanate to produce internal insulating boundaries. The composition is fine grained and provides thin-layer, multi-layer capacitors that exhibit high dielectric constant values, low dissipation factors, and low temperature and voltage coefficients of capacitance.

Internal boundary layer ceramic compositions

An improved polycrystalline semiconducting ceramic composition can be produced from a novel powder which comprises a reduced alkaline earth metal titanate doped with a hexavalent metal oxide such as (MO.sub.3) (Bi.sub.2 O.sub.3).sub.x where M is tungsten or molybdenum, and x ranges from 0 to 7. This powder, which has a mean particle size on the order of less than 10 microns, may be liquid phase sintered with lead germanate to produce a ceramic composition having an extremely fine grain size. By reducing the earth metal titanate (either chemically or gaseously) prior to the liquid phase sintering with lead germanate, particle or grain size growth is substantially eliminated, and the grain size of the ceramic composition is similar to the original particle size of the earth metal titanate.

Reduced alkaline earth metal powders and process for producing same

Method of producing internal boundary layer ceramic compositions

Liquid phase sintering of a mixture comprising a major amount of barium titanate and a minor amount of a lead germanate composition at temperatures in the range of from about 750.degree. to about 1050.degree. C. provides a heterophasic ceramic body of high dielectric constant and strength, and low dissipation factor. Consequently, relatively inexpensive low melting point metals such as silver and copper can be utilized as electrodes in the fabrication of monolithic multi-layer capacitors.

Heterophasic ceramic composition

Liquid phase sintering of a mixture comprising a major amount of BaTiO.sub.3 and a minor amount of Pb.sub.5 Ge.sub.3 O.sub.11 at a temperature of 750.degree.-1050.degree. C. provides a heterophasic ceramic body of high dielectric constant and strength, and low dissipation factor. Consequently, relatively inexpensive low melting point metals such as silver and copper can be utilized as electrodes in the fabrication of monolithic multi-layer ceramic capacitors.

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Urbana, IL, United States of America

Sang M Park