Stabilization and transformation of the phases in nanostructured zirconia prepared by wet chemical synthesis route

Nanostructured yttrium stabilized zirconia powders with yttria concentrations between 0.0 and 10.0 mol % were prepared via an aqueous chemical synthesis route. This synthesis involved the spray atomization of the aqueous solution mixture of zirconyl chloride and yttrium chloride into a reaction vessel that contained a diluted ammonium hydroxide, followed by ultrasonication, separation and heat treatment. These powders were characterized using SEM, TEM, XRD, and chemical analysis. The crystalline structure was refined using the Rietveld technique. At temperatures below 200 °C, the powders were amorphous solid solutions with an structure independent of yttria concentration, where yttrium atoms occupied the zirconium positions in the zirconyl group, e.g., (Zr_4(1-x)Y_4x (OH)₈(OH₂)₁₆)^{(8-4x) +}. Annealing the sample at 400 °C, the amorphous phases crystallized into monoclinic, tetragonal or cubic nanocrystalline zirconia, depending on yttria concentration, where the non-doped samples had a mixture of monoclinic and tetragonal phases.