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

Abstract 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.