Uranium brannerite with Tb(III)/Dy(III) ions: Phase formation, structures, and crystallizations in glass

• Published in: Journal of the American Ceramic Society Vol. 102; no. 12; pp. 7699 - 7709
• Main Authors: Zhang, Yingjie, Wei, Tao, Zhang, Zhaoming, Kong, Linggen, Dayal, Pranesh, Gregg, Daniel J.
• Format: Journal Article
• Language: English
• Published: Columbus Wiley Subscription Services, Inc 01.12.2019
• Subjects: Argon; brannerite; Crystallization; crystals/crystallization; Diffuse reflectance spectroscopy; Dysprosium; Electron diffraction; Electron microscopy; Energy transmission; Glass; glass‐ceramics; Heat treatment; Microscopy; microstructure; nuclear waste; Phase equilibria; Phase transitions; Phases; Rutile; Sintering; Spectrum analysis; Terbium; Titanium dioxide; Uranium; uranium/uranium compounds
• ISSN: 0002-7820; 1551-2916
• DOI: 10.1111/jace.16657

Uranium brannerite phases with terbium(III) or dysprosium(III) ions have been investigated. The precursors with molar ratio of 0.5:0.5:2 (Ln: U: Ti with Ln = Tb or Dy) were prepared and calcined at 750°C in argon. Sintering the pelletized samples in argon at 1200°C led to the formation of pyrochlore phases with TiO2 rutile and U‐rich oxides while sintering in air led to the formation of brannerite phases with the nominal composition close to Ln0.5U0.5Ti2O6 together with trace amounts of TiO2 rutile and LnUO4. Incorporating an excess of TiO2 (20 wt%) and sintering at higher temperature (1300°C) resulted in no obvious change to the phase equilibrium. As designed, pentavalent uranium has been proven to be dominant in these brannerite phases with diffuse reflectance spectroscopy. The relationships between the cell parameters and the ionic radii of the A‐site cations have been explored and rationalized from the structure point of view for a range of titanate brannerite phases (ATi2O6). In addition, the crystallization of Ln0.5U0.5Ti2O6 brannerite in glass has been achieved via heat treatment at 1200°C and confirmed with X‐ray diffraction, scanning electron microscopy‐energy dispersive spectroscopy and transmission electron microscopy–selected area electron diffraction. The formation of uranium brannerite phases with terbium(III) or dysprosium(III) ions has been investigated. The crystallization of brannerite in glass via heat treatment at 1200°C has also been confirmed with XRD, SEM‐EDS and TEM‐SAED.