Raman spectroscopy of plutonium dioxide and related materials

Evidence to support the Raman assignments of the 1LO (578 cm−1) and 2LO (1158 cm−1) lattice vibrations for PuO2 material is presented. The T2g signal is established at 476 ± 2 cm−1 in agreement with literature values. An increase of the 1LO band and an increase of the unit cell lattice parameter with ageing in our samples are found not to be a consequence of PuO2+x formation but rather a result of simple lattice defects due to radiation damage. The Raman spectrum of AnO2(OH)2⋅xH2O (An = Np, Pu) and laser induced decomposition products suggest that the transition to AnO2 involves Np2O5 for neptunium but no such analogue could be detected for Pu. The presence of a band around 1150 ± 10 cm−1 for a range of MO2 fluorite structures (CeO2, ThO2, UO2, NpO2 and PuO2) suggests that this band is not derived from crystal field electronic f–f transitions as proposed previously and supports recent suggestions that it is the first overtone of the 1LO lattice vibration. The spectrum of PuO2 is taken across a wide wavenumber range (200–4000 cm−1) and additional signals (2116 and 2611 cm−1) not previously reported have been observed but are not yet assigned with confidence.