Abstract: The mechanical strength of stabilized zirconia is improved without lowering the ion conductivity by providing a solid electrolyte comprising stabilized zirconia and a metal oxide dispersed within grains or grain boundaries of stabilized zirconia, the metal oxide having an average submicron particle size and stabilized zirconia having an average particle size larger than 1 micron, typically larger than 10 .mu.m or even 100 .mu.m.

Abstract: The present invention provides a solid electrolyte type of fuel cell of a planar type structure comprising a plurality of solid electrolyte plates, each being in the form of a flat plate and having a porous cathodic layer on one side and a porous anodic layer on the other side, which are laminated together through an interconnector plate provided in both its sides with grooves defining gas passages, wherein oxidizing agent and fuel gases are fed through said passages to the cathodic and anodic sides, thereby reducing the length of a current path running through regions of high resistance, increasing the degree of integration and improving reliability. By using heat-resistant parts for the interconnectors, cathodes and anodes, it is also possible to improve the resistance to oxidation and reduction as well as durability and obtain low resistance.