The high dielectric constant of barium titanate-based materials make them suitable materials for multilayer ceramic capacitors, commonly referred to as "MLC's". MLC's comprise alternating layers of dielectric and electrical conductor materials. Examples of MLC's are disclosed in U.S. Pat. Nos. 3,612,963 and 4,435,738. Palladium, silver, palladium-silver alloys and nickel are common electrical conductor materials used in MLC's. The dielectric layers of an MLC are usually prepared from a high solids dispersion, known in the art as a "slip". Such slips typically comprise powdered barium titanate-based material and a polymeric binder in an aqueous or non-aqueous solvent. Films of binder-stabilized powder made by casting or coating with a slip are dried to provide a "green" layer of ceramic dielectric. Green layers are coated with conductor materials in a pattern and are then stacked to provide a laminate of alternating layers of green ceramic dielectric and conductor. The stacks are diced into MLC-sized cubes which are heated to burn off organic materials such as binder and dispersant and then fired to sinter the particles of barium titanate-based material to form a capacitor structure with laminated, dense ceramic dielectric and conductor layers. Sintering temperatures are typically in the range of 1000 to 1500.degree. C. During sintering increased ceramic dielectric density is achieved as a result of the fusion and consolidation of the particles to form grains. Even with the use of grain growth inhibitors, ceramic grain size in an MLC dielectric layer is typically larger, e.g. by a factor of 3 to 5, than the size of the original primary particles. Moreover, not all porosity is removed during the sintering process. Typically, 2 to 10% porosity remains in MLC dielectric layers. These pores, or hole defects, in the dielectric layer, tend to be larger in larger grain size ceramics. Certain critical capacitor properties such as break down voltage and DC leakage are influenced by dielectric thickness, grain size and pore defects. For instance, it is believed that effective dielectric layers need to be several, e.g. at least 3 to 5, grains thick. Because a defect in any one of the layers of an MLC can be fatal to its performance, MLC's are manufactured with a sufficient thickness of dielectric layer to effectively reduce the impact of ceramic defects which can be caused by random large grains or pores, adversely affect the properties of the MLC.
With the market demand for miniaturization in the design of electronic devices there is a need in the MLC industry for ceramic materials that will allow thinner dielectric layers without incurring the catastrophic effects of large grain and pore size relative to dielectric thickness.
Barium titanate powders produced by prior art processes, e.g. calcination or hydrothermal processes, have large particles and/or strongly-agglomerated fine particles of a size substantially larger than 1 .mu.m and that such particles and agglomerates are not readily amenable to the production of MLC's with fine grained, ultrathin dielectric layers, e.g. less than 4-5 .mu.m. Thus, it would represent an advance in the art to provide a barium titanate-based material that would be suitable for making MLC's with thinner dielectric ceramic layers, e.g. less than 4 .mu.m, with acceptable or exceptional electrical properties including DC leakage and breakdown voltage without the need for extended milling.