Preparation of Cubic Hf_1-xEu_xO_2-x/2 (x=0.230, 0.339) Ultrafine Crystalline Particles by Hydrothermal Crystallization

Abstract

The crystallization of HfO₂-Eu₂O₃ amorphous co-precipitates was studied under hydrothermal conditions. The precipitates with the weight ratios of HfO₂:Eu₂O₃=80:20 and 70:30, coprecipitated by NH₄OH from the solution of HfOCl₂ and EuCl₃, and dried at 90°C for 100h yielded a single phase cubic solid solution Hf_1-xEu_xO_2-x/2 (x=0.230 and 0.339) with a fluorite lattice by hydrothermal treatment at 300°C under 10MPa for 3h. These products consist of non-aggregated, ultrafine, narrow-sized and single-crystalline particles of about 10nm and 8nm in size for 20wt% and 30wt% Eu₂O₃ samples, respectively. It was comfirmed by the TEM observation, X-ray diffraction and specific surface area measurement by BET method which gave almost the same particle size. The maximum compositional fluctuation in the products was less than 2wt% by energy dispersive spectroscopy for each particle and by precise X-ray profile analysis of all the diffraction lines of the cubic phase using a Williamson-Hall plotting (β cosθ/λ vs sinθ/λ).