Evidence to support the Ra
man assign
ments of the 1LO (578 c
m?1) and 2LO (1158 c
m?1) lattice vibrations for PuO
2 material is presented. The T
2g signal is established at 476 ¡À 2 c
m?1 in agree
ment 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+m>xm> formation but rather a result of simple lattice defects due to radiation damage. The Raman spectrum of AnO2(OH)2?m>xm>H2O (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 ¡À 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 m>fm>-m>fm> 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.
