Low-Temperature Direct Synthesis of CeO₂–ZrO₂ Solid Solution Nanoparticles by a Hydrothermal Method

Well-crystallized CeO₂-ZrO₂ solid solution nanoparticles were successfully prepared by a hydrothermal method in a single step at 120 °C, for 6 h without any post heat treatment. The particle sizes of 6 ± 3 nm by surface area measurements are in good agreement with crystallite sizes of 6 ± 3 nm by X-ray diffraction. Transmission microscopy also confirmed the formation of crystals of 5-8 nm in the products. In the formation of the homogeneous solid solutions the complete oxidation of Ce³⁺ to Ce⁴⁺ in the precipitated gels seems to be one of the important steps. The solid solutions contained several wt % water, but it was expelled by calcining ≥600 °C. The heating of the samples brought about grain growths, but did not change the phases. The specific areas of 120-200 m²/g of as-prepared samples were decreased to 4-14 m²/g by heating at 900 °C for 4 h.