Iron-stabilized nanocrystalline ZrO2 solid solutions: Synthesis by combustion and thermal stability

The synthesis of Fe³⁺-stabilized zirconia by the nitrate/urea combustion route was investigated. Using several characterization techniques, including X-ray diffraction, field-emission-gun scanning electron microscopy and notably Mössbauer spectroscopy, it was possible to determine the appropriate amount of urea that allows to obtain a totally stabilized Zr_0.9Fe_0.1O_1.95 solid solution. The nanocrystalline zirconia solid solution is mostly tetragonal, but the presence of the cubic phase could not be ruled out. An in-depth study of the thermal stability in air showed that the Fe³⁺ solubility in the stabilized solid solution starts to decrease at about 875 °C which results in the formation of hematite (possibly containing some Zr⁴⁺) at the surface of the zirconia grains and further provokes the progressive transformation into the monoclinic zirconia phase.