Raman Investigation of The Uranium Compounds U3O8, UF4, UH3 and UO3 under Pressure at Room Temperature Page: 3 of 18
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Raman investigation of the uranium compounds
U308, UF4, UH3 and U03 under pressure at room
temperature
M. J. Lipp, Zs. Jenei, J. Park Klepeis, W. J. Evans
High Pressure Physics Group
Condensed Matter & Materials Division
Lawrence Livermore National Laboratory
Dec 07, 2011
Introduction:
Our current state-of-the-art X-ray diffraction experiments are
primarily sensitive to the position of the uranium atom. While the
uranium - low-Z element bond (such as U-H or U-F) changes under
pressure and temperature the X-ray diffraction investigations do not
reveal information about the bonding or the stoichiometry.
Questions that can be answered by Raman spectroscopy are (i) whether
the bonding strength changes under pressure, as observed by either
blue- or red-shifted peaks of the Raman active bands in the spectrum
and (ii) whether the low-Z element will eventually be liberated and
leave the host lattice, i.e. do the fluorine, oxygen, or hydrogen
atoms form dimers after breaking the bond to the uranium atom.
Therefore Raman spectra were also collected in the range where those
decomposition products would appear. Raman is particularly well suited
to these types of investigations due to its sensitivity to trace
amounts of materials.
One challenge for Raman investigations of the uranium compounds is
that they are opaque to visible light. They absorb the incoming
radiation and quickly heat up to the point of decomposition. This has
been dealt with in the past by keeping the incoming laser power to
very low levels on the tens of milliWatt range consequently affecting
signal to noise. Recent modern investigations also used very small
laser spot sizes (micrometer range) but ran again into the problem of
heating and chemical sensitivity to the environment.
In the studies presented here (in contrast to all other studies that
were performed at ambient conditions only) we employ micro-Raman
spectroscopy of samples situated in a diamond anvil ceLL (DAC, see
Fig. 1). This increases the trustworthiness of the obtained data in
several key-aspects:1
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Lipp, M. J.; Jenei, Z.; Park-Klepeis, J. & Evans, W. J. Raman Investigation of The Uranium Compounds U3O8, UF4, UH3 and UO3 under Pressure at Room Temperature, report, December 15, 2011; Livermore, California. (https://digital.library.unt.edu/ark:/67531/metadc838025/m1/3/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.