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Speciation and unusual reactivity in PuO2+x
Steven D Conradson1, Bruce D Begg, David L Clark
1Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA. conradson@lanl.gov
Inorganic Chemistry
|June 10, 2003
Summary
Excess oxygen in plutonium dioxide (PuO2+x) forms oxo groups, indicating a Pu(IV/V) mixture. Plutonium reactivity is influenced by nanoscale effects and free energy, differing from isolated complexes.
Area of Science:
- Materials Science
- Inorganic Chemistry
- Nuclear Chemistry
Background:
- Plutonium dioxide (PuO2+x) exhibits complex behavior due to excess oxygen.
- Understanding the structure and reactivity of PuO2+x is crucial for nuclear materials science.
Purpose of the Study:
- To investigate the nature of excess oxygen in PuO2+x using X-ray absorption fine structure (XAFS).
- To determine the oxidation state of plutonium and understand the structural implications of excess oxygen.
Main Methods:
- Pu L(3) X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy.
- Analysis of Pu-O and Pu-Pu pair distribution functions.
Main Results:
- Excess oxygen in PuO2+x exists as oxo groups with short Pu-O distances (1.83-1.91 Å).
- Spectroscopic data suggest a Pu(IV/V) oxidation state mixture, not Pu(IV/VI).
- Evidence of intrinsic hydrogenous species (H+/OH-/H2O) in high-fired materials, influencing Pu-O distribution.
Conclusions:
- The chemical properties of PuO2+x are governed by nanoscale cooperative phenomena and total free energy.
- Plutonium reactivity in this solid system differs significantly from isolated complexes.
- Equilibration with humid air increases oxo group concentration, highlighting environmental influences.