Phase stability of some actinides with brannerite structure at high pressures

Structure behavior of actinide brannerites ThTi2O6, Y0.5U0.5Ti1.5Nb0.5O6 and their analog oxide CeTi2O6 was studied at high pressure by using in situ x-ray diffraction, Raman scattering and infra-red absorption techniques, respectively. Brannerite structure was found to be not stable and started to become amorphous at pressures above 20 GPa. Some minor crystalline phase(s) due to phase decomposition was observed in all the three samples during pressurization. In addition, the observed bulk modulus indicated that the actinide-bearing brannerites are more compressible than their analog compound CeTi2O6, which may be related to the asymmetric 5f electron orbits of actinide elements.

Actinide-bearing compounds with brannerite structure and their analog CeTi2O6 are not stable at high pressure. They were amorphized after ∼20 GPa and a minor pressure-induced phase transition or decomposition process was always observed before amorphization.Figure optionsDownload as PowerPoint slideHighlights
► Phase stability of three brannerites CeTi2O6, ThTi2O6, and (U,Y)(Ti,Nb)2O6 at high pressures.
► Brannerite structure was not stable and became amorphous after ∼20 GPa.
► Actinide-bearing brannerites are easier compressed than their analog compound CeTi2O6.