Effects of Al2O3 and/or CaO on properties of yttria stabilized zirconia electrolyte doped with multi-elements

Yttria stabilized zirconia (YSZ) has a high oxide ion conductivity at high temperatures. Some rare earth elements (e.g., Yb, Sc, Dy) with similar cation radii to Zr4+ can dissolve into ZrO2, increasing its vacancy concentration and crystal lattice distortion, and therefore enhancing its conductivity and lowering the activation energy. It is expected this material could be used as intermediate temperature electrolyte. In the present work, YSZ electrolyte materials doped by multi-elements (Sc2O3 or Dy2O3 and Yb2O3) were prepared by high temperature solid-state method. The high temperature conductivity was improved obviously, reaching 0.18 S/cm at 1000 °C, but the density and mechanical properties of sintered materials were not sufficiently high. It is found that sinterability and mechanical properties could be improved by inclusion of a small amount of Al2O3 and/or CaO into the multi-elements doped YSZ materials and our results proved it. The results showed density and bending strength of sintered bodies were enhanced by Al2O3 addition by 4.6% and 30%, respectively, while the conductivity did not degrade remarkably. But the degradation in bending strength and conductivity resulting from the CaO addition happened due to the second phase formed at the grain boundary. XRD patterns showed that all samples had cubic fluorite structure and crystalline lattice parameter was increased. SEM photographs obviously revealed the grain growth for the samples with CaO inclusion.