title: Speciation and unusual reactivity in PuO2+x.
abstract: Pu L(3) XAFS measurements show that the excess oxygen in single phase PuO(2+)(x)() occurs as oxo groups with Pu-O distances of 1.83-1.91 A. This distance and the energy of the edge (via comparison with a large number of related compounds) are more consistent with a Pu(IV/V) than a Pu(IV/VI) mixture. Analogous to Pu(IV) colloids, although the Pu-Pu pair distribution remains single site even when it shows substantial disorder, the Pu-O distribution can display a number of additional shells at specific distances up to 3.4 A even in high fired materials when no oxo groups are present, implying intrinsic H(+)/OH(-)(/H(2)O). The number of oxo atoms increases when samples are equilibrated with humid air at ambient temperature, indicating that the Pu reactivity in this solid system differs notably from that of isolated complexes and demonstrating the importance of nanoscale cooperative phenomena and total free energy in determining its chemical properties.
authors.affiliation: Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA. conradson@lanl.gov
authors.forename: Steven D
authors.initials: SD
authors.lastname: Conradson
authors.forename: Bruce D
authors.initials: BD
authors.lastname: Begg
authors.forename: David L
authors.initials: DL
authors.lastname: Clark
authors.forename: Christophe
authors.initials: C
authors.lastname: Den Auwer
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Espinosa-Faller
authors.forename: Pamela L
authors.initials: PL
authors.lastname: Gordon
authors.forename: Nancy J
authors.initials: NJ
authors.lastname: Hess
authors.forename: Ryan
authors.initials: R
authors.lastname: Hess
authors.forename: D Webster
authors.initials: DW
authors.lastname: Keogh
authors.forename: Luis A
authors.initials: LA
authors.lastname: Morales
authors.forename: Mary P
authors.initials: MP
authors.lastname: Neu
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Runde
authors.forename: C Drew
authors.initials: CD
authors.lastname: Tait
authors.forename: D Kirk
authors.initials: DK
authors.lastname: Veirs
authors.forename: Phillip M
authors.initials: PM
authors.lastname: Villella