Developement of High Oxide Ion Conductors Based on Stabilized Zirconia

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Oxide ion conductivity and mechanical properties of Sc_2O_3-ZrO_2 system have been studied in view point of an application to solid oxide fuel cells. The scandia doped zirconia system showed the hightest oxide ion conductivity in the zirconia system. The solid solution with low content of Sc_2O_3 as 8mole% showed a significant conductivity degradation with annealing at 1000ﾟC.On the other hand, bno conductivity change was observed in the samples with higher content of Sc_2O_3 as 11 and 12 mole%. The phase change by annealing has been examined with help of XRD and Raman scattering technique. The bending strength of the sintered samples was measured at room temperature and higher temperatures. The scandia doped zirconia showed almost same bending strength to that of yttria doped zirconia.Moreover, the phase relation and electrical conductivity of the (ZrO_2)_<0.89>(Sc_2O_3)_x(Y_2O_3)_<0.11-x> and (ZrO_2)_<0.89>(Sc_2O_3)_x(Yb_2O_3)_<0.11-x> system have been examined as a function of x. The latter system had slightly higher conductivity than the former system. (ZrO_2)_<0.89>(Sc_2O_3)_<0.11> has the rhombohedral structure at room temperature, which is transformed to cubic structure at 580ﾟC.The substitution of Yb^<3+> or Y^<3+> for Sc^<3+> in (ZrO_2)_<0.89>(Sc_2O_3)_<0.11> stabilized at the high temperature cubic phase to room temperature. These system exhibited no conductivity degradation by annealing at 1000ﾟC.