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Neptunium Substitution into the Structure of Alpha-U3O8

Published online by Cambridge University Press:  11 February 2011

Robert J. Finch  and
A. Jeremy Kropf
Robert J. Finch
Affiliation:
Chemical Technology Division, Argonne National Laboratory, Argonne, IL 60439. finch@cmt.anl.gov
A. Jeremy Kropf
Affiliation:
Chemical Technology Division, Argonne National Laboratory, Argonne, IL 60439. finch@cmt.anl.gov
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Abstract

We synthesized powder samples of NpxU3-xO8 with x between 0 and 0.33. Analyses of solids by x-ray absorption spectroscopy indicate that Np occupies U sites and is predominantly tetravalent. Lattice parameters vary smoothly as a function of Np concentration. The a and b parameters (parallel to structural sheets in U3O8) depend strongly on Np concentration below x = 0.3; however, extrapolation of a least-squares fit up to x = 1 (the maximum value of x if Np is tetravalent) suggests little expected change in a or b for values of x greater than approximately 0.5. The c cell parameter (perpendicular to the plane of the sheets) shows relatively small dependence on Np concentration for all values of x. The a and b cell parameters vary in a complementary fashion, such that the a-b plane and unit-cell volumes remain nearly constant for small x (below ∼0.2). The projected volume increase at higher x may be accommodated by expansion along c; the maximum volume expansion for NpxU3-xO8 is projected to be less than 0.2% up to x = 1. Our results demonstrate that NpxU3-xO8 forms a homogeneous solid solution up to (at least) x = 0.33, and that a complete solid solution may exist between α-U3O8 and NpU2O8; however, the structure of NpU2O8 may resemble that of β-U3O8.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 757: Symposium II – Scientific Basis for Nuclear Waste Management XXVI , 2002 , II3.3
Copyright
Copyright © Materials Research Society 2003

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References

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