DOE PAGES title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Identification of NpO2+x in the binary Np-O system

Journal Article · · Journal of Nuclear Materials
 [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)

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.

Research Organization:
Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences, and Biosciences Division
Grant/Contract Number:
AC02-05CH11231
OSTI ID:
1510745
Alternate ID(s):
OSTI ID: 1396913
Journal Information:
Journal of Nuclear Materials, Vol. 490, Issue C; ISSN 0022-3115
Publisher:
ElsevierCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 2 works
Citation information provided by
Web of Science

Figures / Tables (4)