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Title: Vibrational properties of uranium fluorides

Abstract

Multiphase mixtures of the uranium fluoride compounds UFx with x = 3, 4, 4.5, 5, whose local U–F bonding geometry is conserved, may result from UF 6 reduction. One method for identifying multiphase mixtures is optical vibrational spectroscopy, but experimental Raman and IR spectra for UFx compounds are difficult to obtain. To supplement those experimental measurements, we use density functional perturbation theory (DFPT) with the on-site Coulomb correction (Hubbard + U) to calculate the phonon normal modes, their IR intensity, and their Raman activity for UF 3, UF 4, U 2F 9, and UF 5. In addition, we use neutron spectroscopy to measure the phonon density of states of the most stable UF 4. Our measurements on the Wide-Angular Range Chopper Spectrometer at the Spallation Neutron Source indicate that UF 4 has a broad phonon spectrum centered at about 30 meV, but modeling of this spectrum indicates significant multiphonon scattering is present. DFPT calculations for U 2F 9, which shares structural features with UF 4 and UF 5, suggest a dynamic instability and we speculate that previous crystallographic measurements of this compound were possible only in multiphase mixtures. Analysis of the detailed atomic motions of phonons in UF 5 indicatemore » that a series of high energy modes (between 69 and 75 meV) are described by motion of single-coordinated F atoms (bonded to only one U atom). These single-coordinated F atoms are unique to the UF 5 structure and those modes could be used to distinguish UF 5 in a multiphase mixture using optical spectroscopy.« less

Authors:
ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1564411
Alternate Identifier(s):
OSTI ID: 1542246
Grant/Contract Number:  
AC05-00OR22725
Resource Type:
Journal Article: Published Article
Journal Name:
Physica. B, Condensed Matter
Additional Journal Information:
Journal Volume: 570; Journal Issue: C; Journal ID: ISSN 0921-4526
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; Uranium; Phonons; Density functional theory; Inelastic neutron scattering; Lattice dynamics

Citation Formats

Miskowiec, Andrew J., Shields, Ashley E., Niedziela, Jennifer L., Cheng, Yongqiang, Taylor, Paul Allen, DelCul, Guillermo, Hunt, Rodney Dale, Spencer, Barry B., Langford, Jr., John, and Abernathy, Douglas L. Vibrational properties of uranium fluorides. United States: N. p., 2019. Web. doi:10.1016/j.physb.2019.06.049.
Miskowiec, Andrew J., Shields, Ashley E., Niedziela, Jennifer L., Cheng, Yongqiang, Taylor, Paul Allen, DelCul, Guillermo, Hunt, Rodney Dale, Spencer, Barry B., Langford, Jr., John, & Abernathy, Douglas L. Vibrational properties of uranium fluorides. United States. doi:10.1016/j.physb.2019.06.049.
Miskowiec, Andrew J., Shields, Ashley E., Niedziela, Jennifer L., Cheng, Yongqiang, Taylor, Paul Allen, DelCul, Guillermo, Hunt, Rodney Dale, Spencer, Barry B., Langford, Jr., John, and Abernathy, Douglas L. Mon . "Vibrational properties of uranium fluorides". United States. doi:10.1016/j.physb.2019.06.049.
@article{osti_1564411,
title = {Vibrational properties of uranium fluorides},
author = {Miskowiec, Andrew J. and Shields, Ashley E. and Niedziela, Jennifer L. and Cheng, Yongqiang and Taylor, Paul Allen and DelCul, Guillermo and Hunt, Rodney Dale and Spencer, Barry B. and Langford, Jr., John and Abernathy, Douglas L.},
abstractNote = {Multiphase mixtures of the uranium fluoride compounds UFx with x = 3, 4, 4.5, 5, whose local U–F bonding geometry is conserved, may result from UF6 reduction. One method for identifying multiphase mixtures is optical vibrational spectroscopy, but experimental Raman and IR spectra for UFx compounds are difficult to obtain. To supplement those experimental measurements, we use density functional perturbation theory (DFPT) with the on-site Coulomb correction (Hubbard + U) to calculate the phonon normal modes, their IR intensity, and their Raman activity for UF3, UF4, U2F9, and UF5. In addition, we use neutron spectroscopy to measure the phonon density of states of the most stable UF4. Our measurements on the Wide-Angular Range Chopper Spectrometer at the Spallation Neutron Source indicate that UF4 has a broad phonon spectrum centered at about 30 meV, but modeling of this spectrum indicates significant multiphonon scattering is present. DFPT calculations for U2F9, which shares structural features with UF4 and UF5, suggest a dynamic instability and we speculate that previous crystallographic measurements of this compound were possible only in multiphase mixtures. Analysis of the detailed atomic motions of phonons in UF5 indicate that a series of high energy modes (between 69 and 75 meV) are described by motion of single-coordinated F atoms (bonded to only one U atom). These single-coordinated F atoms are unique to the UF5 structure and those modes could be used to distinguish UF5 in a multiphase mixture using optical spectroscopy.},
doi = {10.1016/j.physb.2019.06.049},
journal = {Physica. B, Condensed Matter},
issn = {0921-4526},
number = C,
volume = 570,
place = {United States},
year = {2019},
month = {6}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1016/j.physb.2019.06.049

Figures / Tables:

Fig. 1 Fig. 1: Structure of (a) UF3 [2], (b) UF4 [4], (c) U2F9 [3], and (d) 1× 1×2 supercell of β-UF5 [5]. Crystal structure visualizations are produced with VESTA [18].

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