A composite body of the present invention includes a base and an oxide layer arranged on the base, the oxide layer containing more than 45% by volume of a perovskite-type oxide phase. The composite body may include a first member, a second member, and a joining portion that joins the first member and the second member, at least one of the first member and the second member serving as the base, and the joining portion serving as the oxide layer. The composite body may include the base and a covering portion that covers the whole or part of a surface of the base, the covering portion being formed of the oxide layer.

A composite body of the present invention includes a base and an oxide layer arranged on the base, the oxide layer containing more than 45% by volume of a perovskite-type oxide phase. The composite body may include a first member, a second member, and a joining portion that joins the first member and the second member, at least one of the first member and the second member serving as the base, and the joining portion serving as the oxide layer. The composite body may include the base and a covering portion that covers the whole or part of a surface of the base, the covering portion being formed of the oxide layer.

A fuel cell has an anode, a cathode, and a solid electrolyte layer. The cathode contains a main component containing a perovskite oxide which is expressed by the general formula ABO.sub.3 and includes at least one of La and Sr at the A site. The solid electrolyte layer is disposed between the anode and the cathode. The cathode includes an interface region that is within 5 m from a surface near to the solid electrolyte layer. The interface region contains a main phase containing the perovskite oxide, and a secondary phase containing strontium oxide. An occupied surface area ratio of the secondary phase in a cross section of the interface region is greater than or equal 0.05% and less than or equal to 3%.

A polycrystalline fused product based on brownmillerite, includes, for more than 95% of its weight, of the elements Ca, Sr, Fe, O, M and M, the contents of the elements being defined by the formula X.sub.yM.sub.zFe.sub.tM.sub.uO.sub.2.5, wherein the atomic indices are such that 0.76y1.10, z0.21, 0.48t1.15 and u0.52, 0.95y+z1.10, and 0.95t+u1.10, X being Ca or Sr or a mixture of Ca and Sr, M being an element chosen from the group formed by La, Ba and mixtures thereof, M being an element chosen from the group formed by Ti, Cu, Gd, Mn, Al, Sc, Ga, Mg, Ni, Zn, Pr, In, Co, and mixtures thereof, the sum of the atomic indices of Ti and Cu being less than or equal to 0.1.

An oxide ceramic expressed by the general formula Sr.sub.2-xBa.sub.xCo.sub.2-yMg.sub.yFe.sub.12-zAl.sub.zO.sub.22, where 0.7x1.3, 0<y0.8, and 0.8z1.2.

A ferrite composition is provided containing Ba, Co, and Ir and having a Z-type hexaferrite phase and a Y-type hexaferrite phase. The ferrite composition has the formula Ba.sub.3Co.sub.(2+x)Ir.sub.xFe.sub.(24-2x)O.sub.41 where x=0.05-0.20. The composition has equal or substantially equal values of permeability and permittivity while retaining low magnetic and dielectric loss factors. The composition is suitable for ultrahigh frequency applications such as high frequency and microwave antennas.

A hexagonal ferrite material includes a Y phase hexagonal ferrite material having the composition Sr.sub.2Co.sub.2Fe.sub.12O.sub.22 or Sr.sub.2-xNa.sub.xCo.sub.2-xSc.sub.xFe.sub.12O.sub.22, 0<x<2, doped with a trivalent element, a tetravalent element, and/or a transition metal.

Provided is a ferrite sintered magnet including a ferrite phase having a magnetoplumbite-type crystal structure. x, y, and m satisfy the following Equations (1), (2), and (3) when composition of the ferrite sintered magnet is represented by R.sub.1-xA.sub.xFe.sub.m-yCo.sub.y, where R denotes at least one kind of element selected from rare earth elements including Y and A denotes Ca or Ca and elements including at least one kind selected from Sr or Ba. The content of B in the ferrite sintered magnet is from 0.1% to 0.6% by mass in terms of B.sub.2O.sub.3.

0.2x0.8(1)

0.1y0.65(2)

3m<14(3)

A grain-oriented M-type hexagonal ferrite has the formula MeFe.sub.12O.sub.19, and a dopant effective to provide planar magnetic anisotropy and magnetization in a c-plane, or a cone anisotropy, in the hexagonal crystallographic structure wherein Me is Sr.sup.+, Ba.sup.2+ or Pb.sup.2+, and wherein greater than 30%, preferably greater than 80%, of c-axes of the ferrite grains are aligned perpendicular to the c-plane.

The present invention provides a ferrite sintered magnet comprising (1) main phase grains containing a ferrite having a hexagonal structure, (2) two-grain boundaries formed between two of the main phase grains, and (3) multi-grain boundaries surrounded by three or more of the main phase grains. The above ferrite sintered magnet comprises Ca, R, Sr, Fe and Co, with R being at least one element selected from the group consisting of rare earth elements and Bi, and comprising at least La. The number Nm of the above main phase grains and the number Ng of the above multi-grain boundaries in the cross section including the direction of the easy magnetization axis of the above ferrite sintered magnet satisfy the formula (1A):

50%Nm/(Nm+Ng)65%(1A).