Raman scattering from phonons and electronic excitations in UO 2 with different oxygen isotopes

Comparison of the phonons and electronic excitations of UO 2 with different oxygen isotopes ( 16 O, 18 O), two purely electronic excitations at 4162 and 5778 cm −1 have been evidenced by their limited shift, when 16 O is replaced by 18 O. The bands observed at 570, 1144 and 2300 cm −1 in U 16 O 2 shift to 545, 1091 and 2190 cm −1 for U 18 O 2 . The wavenumbers and the isotope shifts of these bands exhibit multiple relationships. It supports the assignments of the 1LO (~570 cm −1 ) and 2LO (~1144 cm −1 ) phonons for U 16 O 2 . Both bands exhibit marked decrease for increasing O/U ratio. The observed phenomenon is regarded as a good estimation of the stoichiometry of a uranium oxide. In addition, by analyzing the intensity ratios of the 2LO to 1LO phonons for various UO 2 samples, the 2LO band is assigned to the Fröhlich interaction. Defect‐induced and/or deformation potential mechanisms play a dominant role for the 1LO band. Copyright © 2015 John Wiley & Sons, Ltd.