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Pu L3 x-ray absorption fine structure spectra demonstrate that although the Pu sublattice remains the ordered part of the Pu distribution, the nearest-neighbor O atoms even at x=o are found in a multisite distribution with Pu-O distances consistent with the stable incorporation of OH- into the PuO2 lattice.

A study investigates disorder in Gd2[Ti(sub1-y)Zr(sub y)](sub 2)O(sub 7) pyrochlores, for y = 0.0-1.0, by Ti 2p and O 1s near-edge X-ray absorption fine structure spectroscopy. Ti(super 4+) ions are found to occupy octahedral sites in Gd2Ti2O7 with a tetragonal distortion induced by vacant oxygen sites.

Pu L3 W-ray near edge absorption spectra for Pu(0-VII) for more than 60 chalcogenides, chlorides, hydrates, hydroxides, nitrates, carbonates, oxy-hydroxides and other compounds both as solids and in solution are reported.

Research has been conducted on PuO (sub)2+x. The authors report that the number of oxo atoms increases when the samples are equilibrated with humid air, and indicate that Pu reactivity in this system differes from that of isolated complexes.

Abstract: The local structure and chemical speciation of the mixed valence, fluorite-based oxides UO2+ x (0.00⩽x⩽0.20) and PuO2+ x /PuO2+ x−y (OH)2 y ·zH2O have been determined by U/Pu LIII XAFS spectroscopy. The U spectra indicate (1) that the O atoms are incorporated as oxo groups at short (1.75Å) U–O distances consistent with U(VI) concomitant with a large range of U displacements that reduce the apparent number of U neighbors and (2) that the UO2 fraction remains intact implying that these O defects interact to form clusters and give the heterogeneous structure consistent with the diffraction patterns. The PuO2+ x system, which does not show a separate phase at its endpoint, also displays (1) oxo groups at longer 1.9Å distances consistent with Pu(V+δ), (2) a multisite Pu–O distribution even when is close to zero indicative of the formation of stable species with H2O and its hydrolysis products with O2−, and (3) a highly disordered, spectroscopically invisible Pu–Pu component. The structure and bonding in AnO2+ x are therefore more complicated than have previously been assumed and show both similarities but also distinct differences among the different elements. [Copyright &y& Elsevier]

Studies the behavior of uranium (U) in zirconolite, CaZrTi2O7, which is an important constituent of synroc. Study of U in a range of atmospheres; Related pyrochlore-structured titanate phase; Processing atmosphere of solid materials to immobilize multivalent waste ions such as actinides.

Trivalent Pu can be incorporated in the silicate apatite structure to form Ca[sub 2]Pu[sub 8](SiO[sub 4])[sub 6]O[sub 2] by sintering under reducing conditions, while the incorporation of tetravalent Pu in the Ca/rare earth sites in oxidizing or neutral conditions is limited to only 0.6 formula units (f.u.). The d-spacings and intensities of the X-ray pattern of hexagonally structured Ca[sub 2]Pus(SiO[sub 4])[sub 6]O[sub 2] after firing at 1250°C are given, and the a and c lattice parameters are 0.9561[sub 1] and 0.7028[sub 1] nm, respectively. The respective solid solubility limits of U and Hf in Ca[sub 2]Gd[sub 8-x](U/Hf)[sub x](SiO[sub 4])[sub 6]O[sub 2] apatite samples were 0.3 and 0.2 f.u. [ABSTRACT FROM AUTHOR]

Pu L[sub 3] XAFS measurements show that the excess oxygen in single phase PuO[sub 2+x] occurs as oxo groups with Pu-O distances of 1.831.91 Å. 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 Å even in high fired materials when no oxo groups are present, implying intrinsic H[sup +]/OH[sup -](/H[sub 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. [ABSTRACT FROM AUTHOR]

Abstract: Diffuse reflectance spectra at room temperature have been collected on polycrystalline perovskite (CaTiO3), zirconolite (CaZrTi2O7) and thorutite (ThTi2O6) samples doped with Np. The Np species give rise to a number of broad, unresolved intraconfigurational f–f electronic transition bands in the near-infrared and visible spectral regions. Both Np3+ and Np4+ can substitute in the Ca site of perovskite by the appropriate choice of charge compensation and sintering atmosphere. No detectable spectral differences were observed when Np4+ was targeted towards either the Ca or Zr sites in zirconolite. Np4+ but not Np5+ can be incorporated in the Th site of thorutite by sintering in air. Even in the most dilute [≤0.03 formula units (f.u.)] Np4+ samples of the different titanates studied, there was only very approximate agreement with the Kubelka–Munk law. [Copyright &y& Elsevier]

Highlights: [•] The incorporation of neptunium (Np) and plutonium (Pu) in thorutite (ThTi2O6) has been studied. [•] The effect of Np/Pu doping on the unit cell parameter changes has been discussed from the structure point of view. [•] The effect of Y as charge compensator to encourage the formation of higher valences of Np and Pu has been explored. [•] The resulting Np/Pu doped thorutite samples have been characterised by using XRD, SEM and DRS. [ABSTRACT FROM AUTHOR]

Disorder in Gd2(Ti(1-y)Zry)2O7 pyrochlores, for y = 0.0-1.0, is investigated by Ti 2p and O 1s near-edge X-ray absorption fine structure spectroscopy. Ti(4+) ions are found to occupy octahedral sites in Gd2Ti2O7 with a tetragonal distortion induced by vacant oxygen sites. As Zr substitutes for Ti, the tetragonal distortion decreases, and Zr coordination increases from 6 to 8. The migration of oxygen ions from 48f or 8b sites to vacant 8a sites compensate for the increased Zr coordination, thereby reducing the number of vacant 8a sites, which further reduces the tetragonal distortion and introduces more disorder around Ti. This is evidence for simultaneous cation disorder with anion migration.

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.