Aliovalent cation substitution in UO2: Electronic and local struc-tures of U1-yLayO2±x solid solutions


Aliovalent cation substitution in UO2: Electronic and local struc-tures of U1-yLayO2±x solid solutions

Prieur, D.; Martel, L.; Vigier, J.-F.; Scheinost, A. C.; Kvashnina, K. O.; Somers, J.; Martin, P. M.

For nuclear fuel related applications, the oxygen stoichiometry of mixed oxides U1-yMyO2±x is an essential property as it af-fects the fuel properties and may endanger the safe operation of nuclear reactors. A careful review of the open literature indicates that this parameter is difficult to assess properly and that the nature of the defects, i.e. oxygen vacancies or UV, in aliovalent cation – doped UO2 is still subject to controversy. To confirm the formation of UV, we have investigated the room temperature stable U1-yLayO2±x phase using several experimental methods (e.g. XRD, XANES and NMR) confirmed by theo-retical calculations. This paper presents the experimental proof of UV and its effect we identified in both electronic and local structure. We observe that UV is formed in quasi equimolar proportion as LaIII in U1-yLayO2±x (y=0.06; 0.11; 0.22) solid solu-tions. The fluorite structure is maintained despite the cationic substitution but the local structure is affected as variations of the interatomic distances are found. Therefore, we provide here the definitive proof that the substitution of UIV with LaIII is not accommodated by the creation of O vacancies as has often been assumed. The UO2 fluorite structure compensates the incorporation of an aliovalent cation by the formation of UV in quasi equimolar proportions

Keywords: UO2; Lanthanum; XANES; EXAFS; NMS

Related publications

Downloads

Permalink: https://www.hzdr.de/publications/Publ-26181
Publ.-Id: 26181