Raman spectroscopic study of the uranyl titanate mineral betafite (Ca,U)₂(Ti,Nb)₂O₆(OH): effect of metamictization

Abstract

Raman spectra of the uranyl titanate mineral betafite were obtained and related to the mineral structure. A comparison is made with the spectra of uranyl oxyhydroxide hydrates. Observed bands are attributed to the (UO 2 ) 2+ stretching and bending vibrations, U-OH bending vibrations and H 2 O and (OH) − stretching, bending and libration modes. U-O bond lengths in uranyls and O − H · · · O bond lengths are calculated from the wavenumbers assigned to the stretching vibrations. Raman bands of betafite are comparable with those of the uranyl oxyhydroxides. The mineral betafite is metamict as is evidenced by the intensity of the UO stretching and bending modes being of lower intensity than expected and by bands that are significantly broader.

Synthesis and characterisation of the uranium pyrochlore betafite [(Ca,U)2(Ti,Nb,Ta)2O7]

“…The intense peak at 542 cm −1 and shoulder at 620 cm −1 was also described in by Frost et al [15] as elongation of U 3 O bonding and Ti O bonding respectively. The peak intensities of the aforementioned peaks were all similar to what was reported in Frost [15].…”

“…The intense peak at 542 cm −1 and shoulder at 620 cm −1 was also described in by Frost et al [15] as elongation of U 3 O bonding and Ti O bonding respectively. The peak intensities of the aforementioned peaks were all similar to what was reported in Frost [15]. McConnell et al [30] showed Raman bands of Nb O in Nb 2 O 5 occurring at 704 cm −1 , this is consistent with observed bands in the synthetic betafite spectrum.…”

“…at 220 and 294 cm −1 were shown to be due to O U O bonding when a comparison was made between Frost [15] and the acquired spectrum. The intense peak at 542 cm −1 and shoulder at 620 cm −1 was also described in by Frost et al [15] as elongation of U 3 O bonding and Ti O bonding respectively.…”

“…Their results also provided evidence showing the chemical distinction between betafite and the related mineral groups pyrochlore and microlite. Other aspects of betafite that have been investigated include the temperature at which amorphous/metamict betafite can be recrystallised [14]; the X-ray diffraction patterns of naturally occurring betafites [12]; and the types of functional groups present in betafite (using Raman spectroscopy analysis [15].…”

Chemical and microstructural characterisation studies on natural and heat treated brannerite samples

“…4a and b. In previous work, the brannerite Raman spectrum has been thoroughly analysed between 100 cm À1 and 1100 cm À1 , with the vibration modes fitted by Raman data from known uranyl titanate minerals holfertite, davidite and betafite and from known uranyl oxyhydroxide minerals (Frost et al, 2009;Frost andReddy, 2010, 2011;Frost, 2011). As well, the RRUFF™ Project online database (http://rruff.info/) also contains reference spectra for a natural (RRUFF ID: R060613) and heated (RRUFF ID: R080091) brannerite sample sourced from Crockers Well.…”