Near-edge x-ray absorption fine-structure study of ion-beam-induced phase transformation in Gd{sub 2}(Ti{sub 1-y}Zr{sub y}){sub 2}O{sub 7}

• Published in: Journal of applied physics Vol. 97; no. 3
• Main Authors: Nachimuthu, P., Thevuthasan, S., Shutthanandan, V., Adams, E.M., Weber, W.J., Begg, B.D., Shuh, D.K., Lindle, D.W., Gullikson, E.M., Perera, R.C.C., Pacific Northwest National Laboratory, Richland, Washington 99352, Australian Nuclear Science and Technology Organization, Menai, New South Wales 2234, Lawrence Berkeley National Laboratory, Berkeley, California 94720, Department of Chemistry, University of Nevada, Las Vegas, Nevada 89154
• Format: Journal Article
• Language: English
• Published: United States 01.02.2005
• Subjects: ABSORPTION SPECTROSCOPY; BOND LENGTHS; CRYSTAL DEFECTS; FCC LATTICES; FINE STRUCTURE; FLUORESCENCE; FLUORITE; GADOLINIUM COMPOUNDS; GADOLINIUM IONS; GOLD IONS; INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; ION BEAMS; IRRADIATION; ORDER-DISORDER TRANSFORMATIONS; OXYGEN IONS; PYROCHLORE; TITANIUM COMPOUNDS; X-RAY SPECTROSCOPY; ZIRCONATES; ZIRCONIUM IONS; ZIRCONIUM OXIDES
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.1840097

The structural and electronic properties of Gd{sub 2}(Ti{sub 1-y}Zr{sub y}){sub 2}O{sub 7} (y=0-1) pyrochlores following a 2.0-MeV Au{sup 2+} ion-beam irradiation ({approx}5.0x10{sup 14} Au{sup 2+}/cm{sup 2}) have been investigated by Ti 2p and O 1s near-edge x-ray absorption fine structure (NEXAFS). The irradiation of Gd{sub 2}(Ti{sub 1-y}Zr{sub y}){sub 2}O{sub 7} leads to the phase transformation from the ordered pyrochlore structure (Fd3m) to the defect fluorite structure (Fm3m) regardless of Zr concentration. Irradiated Gd{sub 2}(Ti{sub 1-y}Zr{sub y}){sub 2}O{sub 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{sup 4+} in the irradiated Gd{sub 2}(Ti{sub 1-y}Zr{sub y}){sub 2}O{sub 7} with y{>=}0.75 determined by NEXAFS are the same as in the cubic fluorite-structured yttria-stabilized zirconia (Y-ZrO{sub 2}), thereby providing conclusive evidence for the phase transformation. The TiO{sub 6} octahedra present in Gd{sub 2}(Ti{sub 1-y}Zr{sub y}){sub 2}O{sub 7} are completely modified by ion-beam irradiation to TiO{sub 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{sub 2}Zr{sub 2}O{sub 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{sub 2}Ti{sub 2}O{sub 7}.