The structural and electronic properties of Gd 2(Ti 1-yZr y) 2O 7 (y=0-1) pyrochlores following a 2.0-MeV Au 2+ ion-beam irradiation (∼5.0×10 14 Au 2+/cm 2) have been investigated by Ti 2p and O 1s near-edge x-ray absorption fine structure (NEXAFS). The irradiation of Gd 2(Ti 1-yZr y) 2O 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(Ti 1-yZr y) 2O 7 with y<0.5 are amorphous, although significant short-range order is present. Contrasting to this behavior, compositions with y>0.75 retain crystallinity in the defect fluorite structure following irradiation. The local structures of Zr 4+ in the irradiated Gd 2(Ti 1-yZr y) 2O 7 with y>0.75 determined by NEXAFS are the same as in the cubic fluorite-structured yttria-stabilized zirconia (Y-ZrO 2), thereby providing conclusive evidence for the phase transformation. The TiO 6 octahedra present in Gd 2(Ti 1-yZr y) 2O 7 are completely modified by ion-beam irradiation to TiO x 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 Gd 2Zr 2O 7 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 Gd 2Ti 2O 7.
ASJC Scopus subject areas
- Physics and Astronomy (miscellaneous)
- Physics and Astronomy(all)