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Title: Identification of NpO 2+x in the binary Np-O system

Abstract

In contrast to UO 2 and PuO 2, there is no consensus on the existence of mixed valence NpO 2+x, resulting in a gap between NpO 2 and Np 2O 5 (the highest binary oxide of Np) in the Np-O phase diagram. We now show NpO 2+x via Np L III Extended X-ray Absorption Fine Structure (EXAFS) spectra of three samples of NpO 2 that, analogous to U and Pu, exhibit multisite Np-O distributions with varying numbers of oxygen atoms at 1.87–1.91 Å. Furthermore this is supported by the diffraction pattern of the sample with the largest amount of this oxo-type species that can be refined with both the simple fluorite structure and a trigonal one related to α-U 4O 9. The implied Np(V)-bridging oxo moieties as well as possible indications of OH - found by detailed EXAFS analysis suggest that NpO 2+x more closely resembles PuO 2+x than UO 2+x. An additional common characteristic suggested by the EXAFS and X-Ray Diffraction (XRD) is the phase separation into NpO 2 and what would be previously unreported Np 4O 9(-δ), indicative of O clustering.

Authors:
 [1];  [2]; ORCiD logo [3];  [4];  [5];  [5];  [6]
  1. Synchrotron SOLEIL, Gif-sur-Yvette Cedex (France)
  2. Josef Stefan Institute, Ljubljana (Slovenia); Washington State Univ., Pullman, WA (United States)
  3. Chatenay-Malabry and CEA/DEN/DANS/DMN/SRMA/LA2M-LRC CARMEN, Gif-sur-Yvette (France)
  4. Devi Ahilya Vishwavidyalaya, Indore (India)
  5. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  6. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Chemical Sciences, Geosciences & Biosciences Division; USDOE
OSTI Identifier:
1510745
Alternate Identifier(s):
OSTI ID: 1396913
Grant/Contract Number:  
AC02-05CH11231
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Nuclear Materials
Additional Journal Information:
Journal Volume: 490; Journal Issue: C; Journal ID: ISSN 0022-3115
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE

Citation Formats

Tayal, Akhil, Conradson, Steven D., Baldinozzi, Gianguido, Namdeo, Sonu, Roberts, Kevin E., Allen, Patrick G., and Shuh, David K. Identification of NpO2+x in the binary Np-O system. United States: N. p., 2017. Web. doi:10.1016/j.jnucmat.2017.04.019.
Tayal, Akhil, Conradson, Steven D., Baldinozzi, Gianguido, Namdeo, Sonu, Roberts, Kevin E., Allen, Patrick G., & Shuh, David K. Identification of NpO2+x in the binary Np-O system. United States. doi:10.1016/j.jnucmat.2017.04.019.
Tayal, Akhil, Conradson, Steven D., Baldinozzi, Gianguido, Namdeo, Sonu, Roberts, Kevin E., Allen, Patrick G., and Shuh, David K. Fri . "Identification of NpO2+x in the binary Np-O system". United States. doi:10.1016/j.jnucmat.2017.04.019. https://www.osti.gov/servlets/purl/1510745.
@article{osti_1510745,
title = {Identification of NpO2+x in the binary Np-O system},
author = {Tayal, Akhil and Conradson, Steven D. and Baldinozzi, Gianguido and Namdeo, Sonu and Roberts, Kevin E. and Allen, Patrick G. and Shuh, David K.},
abstractNote = {In contrast to UO2 and PuO2, there is no consensus on the existence of mixed valence NpO2+x, resulting in a gap between NpO2 and Np2O5 (the highest binary oxide of Np) in the Np-O phase diagram. We now show NpO2+x via Np LIII Extended X-ray Absorption Fine Structure (EXAFS) spectra of three samples of NpO2 that, analogous to U and Pu, exhibit multisite Np-O distributions with varying numbers of oxygen atoms at 1.87–1.91 Å. Furthermore this is supported by the diffraction pattern of the sample with the largest amount of this oxo-type species that can be refined with both the simple fluorite structure and a trigonal one related to α-U4O9. The implied Np(V)-bridging oxo moieties as well as possible indications of OH- found by detailed EXAFS analysis suggest that NpO2+x more closely resembles PuO2+x than UO2+x. An additional common characteristic suggested by the EXAFS and X-Ray Diffraction (XRD) is the phase separation into NpO2 and what would be previously unreported Np4O9(-δ), indicative of O clustering.},
doi = {10.1016/j.jnucmat.2017.04.019},
journal = {Journal of Nuclear Materials},
number = C,
volume = 490,
place = {United States},
year = {2017},
month = {4}
}

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Figures / Tables:

Table S1 Table S1: EXAFS fitting results for ref. and ppt. samples. Parameters without error bars are kept constant. Here R, N and σ are bond distance, number of atoms and Debye-Waller factor, respectively.

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Figures/Tables have been extracted from DOE-funded journal article accepted manuscripts.