Structural study of metastable tetragonal YSZ powders produced via a sol–gel route

Sol–gel yttria stabilized zirconia (YSZ) is investigated in this paper. The final aim is to process YSZ powders into stable slurries in order to prepare thick coatings for thermal barrier to be applied on hot turboengine components. In fact, this system is well-known for its excellent thermomechanical resistance at elevated temperatures but the relationship between these performances and the structural and microstructural characteristics of these materials is not fully understood. This paper reports a preliminary study concerning recent progress on the structural properties control of YSZ powders synthesized by sol–gel process and the main advantages of this process compared to conventional methods. As a first step towards this understanding, structural investigations of ZrO2 doped with various xmol%YO1.5 coatings, have been performed using X-ray diffraction, structural Rietveld refinement, Raman spectra analysis and transmission electron microscopy. The evolution of the crystallographic structure of YSZ powders after air annealing at various temperatures 1100 °C, 1200 °C and 1400 °C was studied to well understand the conditions of the formation of desired metastable tetragonal phase (t′). Then, this work should allow to correlate chemical and thermomechanical parameters as YSZ formulation and sol–gel elaboration conditions, temperature and t′ phase performances.