Phase evolution from Ln2Ti2O7 (Ln=Y and Gd) pyrochlores to brannerites in glass with uranium incorporation.

Ln₂Ti₂O₇ (Ln=Y and Gd) pyrochlore glass-ceramics have been fabricated successfully via internal crystallization. Subsequently, the phase evolution from Ln₂Ti₂O₇ pyrochlores to Ln_0.5U_0.5Ti₂O₆ brannerites in glass with uranium (U) substitutions on the Ln-site of Ln₂Ti₂O₇ has been investigated using X-ray diffraction, scanning electron microscope-electron dispersive spectroscopy, transmission electron microscopy, Raman and diffuse reflectance spectroscopy. Combined characterization by XRD, SEM- EDS and TEM SAED confirms the structures and phase evolution while Raman spectroscopy reveals characteristic vibration modes for both pyrochlore and brannerite. In addition, DRS of the U⁵⁺ ion has been used to probe the phase evolution, with the corresponding f- f transition band of ² F_7/2 energy level significantly shifting to longer wavenumbers due to the local coordination environment changing from eightfold coordination in pyrochlore to sixfold coordination in brannerite. [ABSTRACT FROM AUTHOR]