(1) In order to improve the long-term reliability of cofired multilayers, the elevation of cofired temperature and optimization of composition and synthesis process of cathode for the elevated temperature were effective. The elevation of cofiring temperature decreased the power densities of cofired multilayers. On the contrary, the degradation rate of terminal voltage of the multilayers cofired at higher temperature was superior to that of the multilayers cofired at lower temperature.

(2) By minimizing the mismatch of sintering shrinkage profiles of anode, cathode and electrolyte materials, we achieved to fabricate the good flatness of multilayers with surface area of 225 and 400cm2. Due to the increase in current collecting resitivity, the maximum power densities of large size multilayers deteriorated. But, polarization characteristics of these large size multilayers were almost equal to those of multilayers with surface area of 150cm2.

(3) The multiple cell stacks were fabricated with cofired multilayers and Ni-Cr alloy or LaCrOj interconnects. The maximum power of 5x4 multiple cell stack (5 planes of cells in series. 4 cells in parallel in each planes, 400cm2 effective electrode area of each cell planes) were 465W (0.23W cm'2) and 472W (0.24Wcm"2), respectively (Uf=40%). The degradation rate of terminal voltage of the stack with ceramics interconnects was lower than that of the stack alloy interconnects.

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