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|Title:||Charge Distribution and Local Structure and Speciation in the UO2+x and PuO2+x Binary Oxides for x <0.25.|
|Authors:||CONRADSON S.d.; BEGG B.d.; CLARK D.l.; DEN AUWER C.; DING M.; DORHOUT P.k.; ESPINOSA-FALLER J.; GORDON P.; HAIRE R.g.; HESS N.j.; HESS R.f.; WEBSTER KEOAGH D.; LANDER Gerard; MANARA DARIO; MORALES L.a.; NEU M.p.; PAVIET-HARTMANN P.; REBIZANT JEAN; RONDINELLA VINCENZO; RUNDE W.; DREW TAIT C.; KIRK VEIRS D.; VILLELLA P.m.; WASTIN FRANCK|
|Citation:||JOURNAL OF SOLID STATE CHEMISTRY vol. 178 p. 521-535|
|Publisher:||ELSEVIER SCI LTD|
|JRC Publication N°:||JRC30033|
|Type:||Articles in Journals|
|Abstract:||The local structure and chemical speciation of the mixed valence, fluorite based oxides UO2+x (0.00pxp0.20) and PuO2+x PuO2+xy(OH)2y 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 (1.75A) 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 x 1:4 0:25 endpoint, also displays (1) oxo groups at longer 1.9A distances consistent with Pu(V+d), (2) a multisite Pu O distribution even when x 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.|
|JRC Institute:||Institute for Transuranium Elements|
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