A MgF.sub.2—CaF.sub.2 binary system sintered body for a radiation moderator having a compact polycrystalline structure excellent in radiation moderation performance, especially neutron moderation performance, comprises MgF.sub.2 containing CaF.sub.2 from 0.2% by weight to 90% by weight inclusive, having a bulk density of 2.96 g/cm.sup.3 or more, and a bending strength of 15 MPa or more and a Vickers hardness of 90 or more as regards mechanical strengths.

There is provided a dielectric ceramic composition including a base powder, wherein the base powder includes: a first major component represented by BaTiO.sub.3, a second major component represented by (Na, K)NbO.sub.3, and a third major component represented by (Bi, Na)TiO.sub.3. The base powder is represented by xBaTiO.sub.3-y(Na, K)NbO.sub.3-z(Bi, Na)TiO.sub.3, where x+y+z=1, and x, y, and z are represented by mol, and x, y and z satisfy 0.5≦x≦0.97, 0.01≦y≦0.48, and 0.02≦z≦0.2, respectively. In certain embodiments, the base powder is be represented by xBaTiO.sub.3-y(Na.sub.0.5K.sub.0.5)NbO.sub.3-z(Bi.sub.0.5Na.sub.0.5)TiO.sub.3.

A method for producing a multilayer ceramic capacitor that includes preparing a dielectric ceramic material by mixing a perovskite compound, a Re compound, a Mn compound, a Mg compound, and a Si compound. The perovskite compound contains Ba and Ti and has 1.2×10.sup.15 or more and 4.5×10.sup.15 or less Ba vacancies per gram. Re in the Re compound is at least one element selected from Y, Gd, Tb, Dy, Ho, Er, and Yb. Green sheets containing the dielectric ceramic material are then formed. Inner electrode patterns are then formed on some of the green sheets. An unsintered capacitor body is then formed by stacking the green sheets, some of which have the inner electrode patterns formed thereon. Sintering of the unsintered capacitor body is then conducted.

A preparation method of a SiC porous ceramic material and porous ceramic material manufactured by using the method, comprising: mixing a SiC aggregate, a sintering aid (zirconium oxide), a pore-forming agent (activated carbon) and a polymer binder with a reinforcing agent (SiC whiskers) according to a certain proportion, and obtaining a porous ceramic material via forming, drying and high-temperature sintering. The porous ceramic material has a high strength, a high porosity, a good thermal shock resistance and a low sintering temperature, and can server as a filter material of high-temperature flue gas and a carrier material in vehicle exhaust purification.

A dielectric ceramic composition has good characteristics even under the high electric field intensity, and particularly good IR characteristic and the high temperature accelerated lifetime. The dielectric ceramic composition has a main component having a perovskite type compound shown by a compositional formula (Ba.sub.1-x-ySr.sub.xCa.sub.y).sub.m(Ti.sub.1-zZr.sub.z)O.sub.3, a first sub component having oxides of a rare earth element R, a second sub component as a sintering agent, wherein the dielectric particles has dielectric particles having high diffusion rate of the rare earth element, preferably of a complete solid solution particle, and when a concentration of Ti atom in the diffusion phase is 100 atom %, then an average concentration of the rare earth element R in the diffusion phase is 5 atom % or more, and an average concentration of Zr in the diffusion phase is 10 atom % or more.

The invention relates to a ceramic material, comprising lead zirconate titanate, which additionally contains K and optionally Cu. The ceramic material can be used in an electroceramic component, for example a piezoelectric actuator. The invention also relates to methods for producing the ceramic material and the electronic component.

A cordierite-based sintered body according to the present invention contains cordierite as a main component and silicon nitride or silicon carbide. The cordierite-based sintered body preferably has a thermal expansion coefficient less than 2.4 ppm; ° C. at 40° C. to 400° C., an open porosity of 0.5% or less, and an average grain size of 1 μm or less.

A sintered Ni ferrite body having a composition comprising, calculated as oxide, 47.0-48.3% by mol of Fe.sub.2O.sub.3, 14.5% or more and less than 25% by mol of ZnO, 8.2-10.0% by mol of CuO, and more than 0.6% and 2.5% or less by mol of CoO, the balance being NiO and inevitable impurities, and having an average crystal grain size of more than 2.5 μm and less than 5.5 μm.

A dielectric composition containing a complex oxide represented by the formula of xAO-yBO-zC.sub.2O.sub.5 as the main component, wherein A represents at least one element selected from the group including Ba, Ca and Sr, B represents Mg, and C represents at least one element selected from the group including Nb and Ta, and x, y and z meet the following conditions, x+y+z=1.000, 0.198≦x≦0.375, 0.389≦y≦0.625, and x/3≦z≦x/3+1/9.

A dielectric composition containing a complex oxide represented by the formula of xAO-yBO-zC.sub.2O.sub.5 as the main component, wherein A represents at least one element selected from the group including Ba, Ca and Sr, B represents Mg, and C represents at least one element selected from the group including Nb and Ta, and x, y and z meet the following conditions, x+y+z=1.000, 0.000<x≦0.281, 0.625≦y<1.000, and 0.000<z≦0.375.