Effects of TiO2 doping on the defect chemistry and thermo-physical properties of Yb2O3 stabilized ZrO2

Yb2O3 stabilized ZrO2 (YbSZ) doped with different TiO2 contents were produced, and their phase structure, thermal conductivities and thermal expansion coefficients were investigated. A new solid-solution model is proposed, i.e. Ti4+ would take the interstitial sites when its content is below a critical value (≤2.5 mol%) and then substitute for Zr4+. The abnormal lattice volume and thermo-physical properties of 2.5 mol% TiO2 doped YbSZ, and the positive effects of TiO2 doping on the thermal conductivity at moderate doping level are consistent with the new defect model. However, monoclinic phase is formed when the TiO2 content reaches to 10 mol% and its content increases with doping content, which have negative influence on the thermo-physical properties. Considering the comprehensive properties, 10 mol% TiO2 doped YbSZ is considered as a promising thermal barrier coating ceramic.