The conductivity degradation of yttria stabilized zirconia(YSZ) due to the phase transformation from cubic phase to tetragonal phase is one of the issue in solid oxide fuel cells [1,2]. The phase transformation is enhanced by the reduction of nickel oxide which dissolved into YSZ electrolyte when making an anode-support-type-cells. The correlation of conductivity degradation and phase transformation ratio and dependence on oxygen profile in electrolyte for the area of tetragonal formation region about the 1 mol % nickel doped 8mol% yttria stabilized zirconia (Ni-YSZ) at 1173K were reported in our previous studies [2,3,4]. In this study, in order to investigate the factor of temperature for this phase transformation phenomena in nickel doped YSZ electrolyte, conductivity degradation behaviors were measured at various conditions. Even at around 750oC which similar to operating temperature of industrial SOFCs, the tetragonal formation was slightly observed at the area where the reduction of nickel oxide was occurred after over 500h measurement. The time constant for the conductivity degradation due to the tetragonal formation is well fitted on the Arrhenius type plot. This results show the strong temperature dependence for phase transformation. This is an important factor for rapid evaluation of durability of SOFCs.
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