Raman and Infrared Spectra of Non-Stoichiometry Uranium Oxides
Both of Raman and infrared spectra of seven non-stoichiometry and threestoichiometry uranium oxidesincluding UO2, U3O7 and UO2+x
(0x0.66), are presented and discussed. The spectra of UO2+x
in the stoichiometry
range, U3O7 to U3O8, were first obtained and reported. Three typical peaks were observed at 445, 578 and 1 150 cm-1 in the Raman spectrum of uranium dioxide. The intensities of the peaks at 578 and 1 151 cm-1 decrease quickly
with increasing x value of UO2+x
, and while x=0.19, the two peaks disappear. Such peaks can therefore be considered as a fin-gerprint of the quasi-perfect UO2 fluorite structure. The peak at 445 cm-1 tends to weaken, broaden and shift to
higher wavenumber in more oxidised samples. When x=0.32, this peak is shifted to the 459 cm-1 and a weak peak at about 630 cm-1 appears. The two new peaks are typical of the tetragonal U3O7. While x≥0.39, the peak at 459 cm-1
further splits into separate components. Two peaks at 235 and 754 cm-1 appear for UO2.39 and are visible with increased intensity as the oxygen-uranium ratio is increased. And the Raman spectra of UO2+x
are gradually close to U3O8
in the α-phase, which has an orthorhombic unit cell. But several strongest features of theα-U3O8 specturm at 333, 397, 483 and 805 cm-1 are still not outstanding even in UO2.60. The main feature of the UO2 infrared spectrum
shows a very broad and strong adsorption band at 400570 cm-1 and another feature is a weak adsorption peak at about 700 cm-1. The 400570 cm-1 band undergoes a progressive splitting into two new peaks at 421 and 515 cm-1 through increasing incorporation
of oxygen into UO2. The weak peak at about 700 cm-1 disappears and a new weak peak appears at about 645 cm-1. The three new peaks are the infrared absorption features of U3O7. An absorption peak at 744 cm-1 which is the strongest
feature ofα-U3O8 infrared spectrum appears for UO2.39 and is visible with increased intensity in more oxidised samples. The peak at about 645 cm-1 still exists and 515 cm-1 peak has no further splitting into two new peaks at 485
and 535 cm-1 which also are the infrared absorption features of U3O8 in UO2.60. This indicates that UO2.60 is still in the transition period between tetragonal and orthorhombic phase of uranium oxide. A sequence of phase transitions occurs
through increasing x value of UO2+x
with different Raman and infrared features.It is easy to identify different uranium oxides by comparing of relative intensities and locations of their characteristic peaks.
Keywords: Infrared spectroscopy; Raman spectroscopy; Uranium oxide
Document Type: Research Article
Publication date: 15 February 2014
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