Local and nanoscale structure and speciation in the PuO2+x-y(OH)2y.zH2O system.
Pu L(3) X-ray absorption fine structure spectra from 24 samples of PuO(2+x) (and two related Pu-substituted oxides), prepared by a variety of methods, demonstrate that (1) although the Pu sublattice remains the ordered part of the Pu distribution, the nearest-neighbor O atoms even at x = 0 are found in a multisite distribution with Pu-O distances consistent with the stable incorporation of OH(-) (and possibly H(2)O and H(+)) into the PuO(2) lattice; (2) the excess O from oxidation is found at Pu-O distances <1.9 A, consistent with the multiply bound "oxo"-type ligands found in molecular complexes of Pu(V) and Pu(VI); (3) the Pu associated with these oxo groups is most likely Pu(V), so that the excess O probably occurs as PuO(2)(+) moieties that are aperiodically distributed through the lattice; and (4) the collective interactions between these defect sites most likely cause them to cluster so as give nanoscale heterogeneity in the form of domains that may have unusual reactivity, observed as sequential oxidation by H(2)O at ambient conditions. The most accurate description of PuO(2) is therefore actually PuO(2+x-y)(OH)(2)(y).zH(2)O, with pure, ordered, homogeneous PuO(2) attained only when H(2)O is rigorously excluded and the O activity is relatively low.
Conradson
Steven D
SD
Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA. conradson@lanl.gov
Begg
Bruce D
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Clark
David L
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den Auwer
Christophe
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Ding
Mei
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Dorhout
Peter K
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Espinosa-Faller
Francisco J
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Gordon
Pamela L
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Haire
Richard G
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Hess
Ryan F
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D Webster
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Morales
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Patricia
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Runde
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Tait
C Drew
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Phillip M
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