NOVELTY - A single cell comprises first solid electrolytes (10), a fuel electrode (12), an air electrode (14), and an intermediate layer (16). The first solid electrolyte has an oxide ion conductivity at 800degreesC of greater than or equal to 0.015 S/cm and a bending strength of greater than or equal to 600 MPa. The fuel electrode is bonded to one side of the first solid electrolyte. The fuel electrode comprises a cermet of catalyst and a second solid electrolyte having an oxide ion conductivity at 800degreesC of greater than or equal to 0.08 S/cm. The air electrode is bonded to the other side of the first solid electrolyte.    USE - The single cell is used for a low operating temperature solid oxide fuel cell for distributed power source, or cogenerative system.    ADVANTAGE - The cell provides improved performance under disadvantageous conditions for a single cell, i.e. low temperature operation, particularly 600-900degreesC. The cell has good adhesion to a separator with low current collecting loss. The cell maintains permeability of electrodes.    DETAILED DESCRIPTION - An air electrode comprises a compound of a first perovskite type oxide with a third solid electrolyte. The intermediate layer comprises a fourth solid electrolyte interposed between the air electrode and the first solid electrolyte. The first perovskite type oxide is one or more perovskite type transition metal oxide(s), e.g. lanthanum strontium cobalt iron oxide, praseodymium strontium manganese oxide, or lanthanum strontium cobalt oxide. The third solid electrolyte is a mixed solid electrolyte. The mixed solid electrolyte comprises yttria-stabilized zirconia containing yttrium oxide (8-10 mol.%), scandia-stabilized zirconia containing scandium oxide (9-12 mol.%), or a ceria-based solid solution containing gadolinium oxide, yttrium oxide, and/or samarium oxide (10-35 mol.%). The cell includes a fuel electrode contact layer (18) and an air electrode contact layer (20).    DESCRIPTION OF DRAWING(S) - The figure shows a schematic diagram of the cell structure of a three-layered cell.    Six-layered cell (6A)    First solid electrolytes (10)    Fuel electrode (12)    Air electrode (14)    Intermediate layer (16)    Fuel electrode contact layer (18)    Air electrode contact layer (20)