A configuration of the solid oxide fuel cell is formed of a unit cell including a fuel electrode, an electrolyte, and an air electrode and a connecting material which connects unit cells. Among them, a sealing material has different required conditions depending on an operating condition and a structure of the flat type solid oxide fuel cell so that the sealing material is the most important configuration.

Basic conditions of the sealing material required for a smooth operation of the solid oxide fuel cell are summarized as follows: First, the sealing material needs to be satisfactorily bonded to other components of the solid oxide fuel cell to be in physical contact therewith and a bonded part need not be weakened due to a thermal cycle which is given during an operation of the fuel cell. Second, the sealing material needs to have a low difference in coefficient of thermal expansion from other components so that even though a thermal cycle is given, the sealing material should not be broken due to thermal stress. Third, the sealing material need not be permeated into a porous electrode which is in contact with the sealing material. Fourth, the sealing material needs to be a stable material so that no chemical reaction with other components is caused at a fuel cell operating temperature. Fifth, the sealing material needs to be used without being chemically decomposed and evaporated under two extreme oxygen partial pressure conditions of the fuel and the oxidized gas. Finally, the sealing material needs to have high electrical resistivity at the fuel cell operating temperature, thereby maintaining electrical insulation.