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Abstract: Raman spectra of synthetic non-substituted and U/Np/Pu- substituted thorutite (ThTi2O6) samples were collected. Factor group analysis was used to analyse the possible vibration modes. Theoretical simulations based on density functional theory (DFT) were performed on both CeTi2O6 and ThTi2O6. All possible vibrational modes for thorutite have been identified and assigned to the measured spectra. The presence and the effect of higher valence of U in thorutite has been discussed and the U–O bond lengths have been calculated by using the measured wavenumbers of ν 1 (UO2)2+ symmetric stretching vibrations. The presence of U6+ in uranyl form can be inferred from the wavenumbers of U–O vibrations. Corresponding Np–O and Pu–O vibrations were not observed in the Raman spectra. Thus the presence of Np6+ and Pu6+ in the studied samples was not established. [Copyright &y& Elsevier]

Abstract: Raman spectra of a well-characterized natural brannerite and some synthetic brannerite samples have been collected and analysed. For the first time, all 12 theoretical Raman vibrational modes of CeTi2O6 with brannerite structure have been positively identified by using quantum chemical calculations based on density functional theory (DFT) and assigned to the spectra. For synthetic samples with Y or Ca substitution on the U site and Fe substitution on the Ti site, Y–O, Fe–O and U–O vibrational modes are tentatively assigned. The U–O bond lengths for the uranyl (UO2)2+ groups, have been calculated by using the measured wavenumbers of ν 1 (UO2)2+ symmetric stretching vibrations and compared with the published U–O bond lengths of a natural brannerite. [Copyright &y& Elsevier]