Phase compositions, structures and properties of scandia-stabilized zirconia solid solution crystals co-doped with yttria or ytterbia and grown by directional melt crystallization

The effect of co-doping an impurity on the transport parameters and cubic phase stabilization of ZrO2-Sc2O3-based solid solutions has been compared for Y2O3 and Yb2O3 dopants. Solid solution crystals of (ZrO2)(1-x-y)(Sc2O3)(x)(Yb2O3)(y) and (ZrO2)(1-x-y)(Sc2O3)(x)(Y2O3)(y) (x = 0.08-0.10, y = 0.01, 0.02) were grown by directional melt crystallization in a cold crucible. Co-doping of the (ZrO2)(1-x)(Sc2O3)(x) crystals (x = 0.08-0.10) with 2 mol% Y2O3 or Yb2O3 for all experimental compositions produced transparent homogeneous single crystals of the t '' phase or the cubic phase. For co-doping of the scandia-stabilized zirconia crystals with 1 mol% Y2O3 or Yb2O3, the stabilization of the high-temperature phases depended on the Sc2O3 content in the solid solutions. For co-doping of the solid solutions with 1 mol% Y2O3 or Yb2O3, the conductivity of the crystals increased with the Sc2O3 concentration. For co-doping of the crystals with 2 mol% Y2O3 or Yb2O3, the conductivity decreased with the Sc2O3 concentration. At scandia concentrations of 9-10 mol%, the high-temperature conductivity of the crystals co-doped with ytterbia were higher compared to those with yttria co-doping. The (ZrO2)(0.9)(Sc2O3)(0.09)(Yb2O3)(0.01) crystals had the highest conductivity over the entire experimental temperature range.