Microstructure and phase transformation of zirconia-based ternary oxides for thermal barrier coating applications

Five dopant oxides, Sc2O3, Yb2O3, CeO2, Ta2O5, and Nb2O5, were incorporated into 7YSZ to create ternary zirconia-based oxides with varying oxygen vacancies and substitutional defects. These ternary oxides were consolidated using a high-temperature sintering process. The resulting bulk oxides were subjected to microstructural study using scanning electron microscopy (SEM), X-ray diffraction (XRD), and differential scanning calorimetry (DSC). The results show that the microstructures of the ternary zirconia-based oxides are determined by the amount of oxygen vacancies in the system, the dopant cation radius, and atomic mass. Increasing the number of oxygen vacancies in the lattice by the addition of trivalent dopant as well as the use of larger cations promotes the stabilization of the high-temperature cubic phase. The tetravalent cation, on the other hand, has the effect of retaining tetragonal phase to room temperature without the influence of oxygen vacancy. The addition of pentavalent oxide leads to the formation of monoclinic phase upon cooling.