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

Abstract

Abstract 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 TiO 2 rutile and U‐rich oxides while sintering in air led to the formation of brannerite phases with the nominal composition close to Ln 0.5 U 0.5 Ti 2 O 6 together with trace amounts of TiO 2 rutile and LnUO 4 . Incorporating an excess of TiO 2 (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 (ATi 2 O 6 ). In addition, the crystallization of Ln 0.5 U 0.5 Ti 2 O 6 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.