Heavy-ion irradiation effects on structures and acid dissolution of pyrochlores

The temperature dependence of the critical dose for amorphization, using 0.6 MeV Bi+ ions, for A2Ti2O7 pyrochlores, in which A=Y, Sm, Gd and Lu, exhibits no significant effect of A-site ion mass or size. The room temperature dose for amorphization was found to be ∼0.18 dpa in each case. After irradiation with 2 MeV Au2+ ions glancing-incidence X-ray diffraction (XRD) revealed that each pyrochlore underwent an irradiation-induced structural transformation to fluorite in conjunction with amorphization. The effect of amorphization on the dissolution rates of fully dense pyrochlores, at 90°C and pH 2 (nitric acid) varied from a factor of 10 to 15 increase for Gd2Ti2O7 to none for Y2Ti2O7. Significant differences were observed in the A-site dissolution rates from the crystalline pyrochlores, indicating differences in the manner in which the A-site cations are incorporated into the pyrochlore structure. These indications were supported by Raman spectroscopy.