Local atomic structure of a zirconia-based americium transmutation fuel

(Zr,Y,Am)O2 with 6 and 19 mol% Am were prepared by infiltration of americium in porous yttria-stabilised zirconia (YSZ) beads. Samples were sintered at 1600 °C in Ar/H2 to yield Am(III). By annealing them at 1000 °C in flowing air, the Am is oxidised to Am(IV). Both Am(III) and Am(IV) samples exhibit the presence of a single (Zr,Y,Am)O2 phase with fluorite structure. The local atomic structure around the Zr, Y, and Am atoms is determined by EXAFS analysis. The Zr–O bond distance decreases from 2.15 to 2.12 Å with increasing Am(III) content, whereas the Y–O bond distance is independent of Am content and oxidation state. The Am(III)–O bond distance is 2.37 Å for both Am concentrations, while oxidation to Am(IV) decreases the Am(IV)–O distance to 2.28 Å, with a simultaneous expansion of the environment around the Zr atoms. The Am–O bond distances are contracted compared with the compounds Am2Zr2O7 and AmO2 and the distances expected from the ionic radii.