PNNL

Abstract

Gd2(Ti2-xZrx)O7 samples with 0 = x = 1.5 were single-phase and pyrochlore structured after sintering at 1600oC in air. The Gd2Zr2O7 (x=2) end member was predominantly fluorite-structured. Raman spectroscopy indicated that the level of short-range fluorite-like disorder in the unirradiated Gd2(Ti2-xZrx)O7 samples increased significantly as Zr was substituted for Ti, despite the retention of a long-range pyrochlore structure for samples with 0 = x = 1.5. Glancing-incidence X-ray diffraction indicated that pyrochlores with an ionic radii ratio rA/rB = 1.52 (x=1.5) were transformed into a radiation resistant fluorite-structure after irradiation at room temperature with 2 MeV Au2+ to a fluence of 5 ions/nm2. As the ionic radii ratio of the pyrochlore increased beyond rA/rB > 1.52, the fluorite structure became increasingly unstable with respect to the amorphous state under identical irradiation conditions.