Cubie Eu-doped Hafnia Ultrafine Particles Crystallized under Hydrothermal Conditions

Abstract

The crystallization of HfO₂-Eu₂0₃ amorphous co-precipitates was studied under hydrothermal conditions. The precipitates with the weight ratio of HfO₂: Eu₂O₃ = 80:20 and 70:30 co-precipitated by NH₄OH from the solution HfOCl₂ and EuCl₃ and dried at 90°C for 100 h, 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 10 MPa for 3 h. These products consist of non-aggregated, ultrafine, narrow-sized and single-crystalline particles of about 10 nm and 8 nm in size for 20 wt% and 30 wt% Eu₂O₂ samples, respectively. It was confirmed 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 2 wt% 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 cos Θ/λ vs sin Θ/λ).