Near-edge x-ray absorption fine-structure study of ion-beam-induced phase transformation in Gd2(Ti1-yZry)2O7 -: art. no. 033518

The structural and electronic properties of Gd-2(Ti1-yZry)(2)O-7 (y=0-1) pyrochlores following a 2.0-MeV Au2+ ion-beam irradiation (similar to5.0x10(14) Au2+/cm(2)) have been investigated by Ti 2p and O 1s near-edge x-ray absorption fine structure (NEXAFS). The irradiation of Gd-2(Ti1-yZry)(2)O-7 leads to the phase transformation from the ordered pyrochlore structure (Fd3m) to the defect fluorite structure (Fm3m) regardless of Zr concentration. Irradiated Gd-2(Ti1-yZry)(2)O-7 with yless than or equal to0.5 are amorphous, although significant short-range order is present. Contrasting to this behavior, compositions with ygreater than or equal to0.75 retain crystallinity in the defect fluorite structure following irradiation. The local structures of Zr4+ in the irradiated Gd-2(Ti1-yZry)(2)O-7 with ygreater than or equal to0.75 determined by NEXAFS are the same as in the cubic fluorite-structured yttria-stabilized zirconia (Y-ZrO2), thereby providing conclusive evidence for the phase transformation. The TiO6 octahedra present in Gd-2(Ti1-yZry)(2)O-7 are completely modified by ion-beam irradiation to TiOx polyhedra, and the Ti coordination is increased to eight with longer Ti-O bond distances. The similarity between cation sites and the degree of disorder in Gd2Zr2O7 facilitate the rearrangement and relaxation of Gd, Zr, and O ions/defects. This inhibits amorphization during the ion-beam-induced phase transition to the radiation-resistant defect fluorite structure, which is in contrast to the ordered Gd2Ti2O7. (C) 2005 American Institute of Physics.