Phase stability and thermal conductivity of ytterbia and yttria co-doped zirconia

Rare earth oxides doping has been extensively investigated as one of the effective methods to lower thermal conductivity of 4.55 mol% Y₂O₃ stabilized ZrO₂ (YSZ) thermal barrier coatings (TBCs). In the present work, 5–6 mol% Yb₂O₃ and Y₂O₃ co-doped ZrO₂ ceramics were synthesized by solid reaction sintering at 1600 °C. The phase stability of the samples after heat treatment at 1500 °C was investigated. Yb₂O₃ and Y₂O₃ co-doped zirconia, especially when Yb₂O₃/Y₂O₃≥1, contained less monoclinic phase than single Yb₂O₃ or Y₂O₃ phase doped zirconia, indicating that co-doped zirconia was more stable at high temperature than YSZ. The thermal conductivity of the 3 mol% Yb₂O₃+3 mol% Y₂O₃ co-doped ZrO₂ was 1.8 W m^?1 K^?1 at 1000 °C, which was more than 20% lower than that of YSZ.