Cubic Eu‐doped Hafnia Ultrafine Particles crystallized under hydrothermal conditions

The crystallization of HfO₂–Eu₂O₃ 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% Eu₂O₃ 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).