Ion irradiation of ternary pyrochlore oxides

Polycrystalline synthetic samples of Y ₂Ti _2-xSn _xO ₇ with x = 0.4, 0.8, 1.2, and 1.6, together with Nd ₂Zr ₂O ₇, Nd ₂Zr ₁₂Ti _0.8O ₇, and La _1.6Y _0.4Hf ₂O ₇, were irradiated in situ in the intermediate voltage electron microscope (IVEM)-Tandem Facility at Argonne National Laboratory using 1.0 MeV Kr ions at temperatures of 50 to 650 K. Determination of the critical amorphization fluence (F _c) as a function of temperature has revealed a dramatic increase in radiation tolerance with increasing Sn content on the pyrochlore B site. Nonlinear least-squares analysis of the fluence-temperature curves gave critical temperatures (T _c) of 666 ± 4, 335 ± 12, and 251 ± 51 K for the Y ₂Ti _2-xSn _xO ₇ samples with x = 0.4, 0.8, and 1.2, respectively. The sample with x = 1.6 appears to disorder to a defect fluorite structure at a fluence below 1.25 × 10 ⁵ ions cm ^-2 and remains crystalline to 5 × 10 ¹⁵ ions cm ^-2 at 50 K. Additionally, the critical fluence-temperature response curves were determined for Nd ₂Zr _1.2Ti _0.8O ₇ and La _1.6Y _0.4Hf ₂O ₇, and we obtained T _c values of 685 ± 53 K and 473 ± 52 K, respectively, for these pyrochlores. Nd ₂Zr ₂O ₇ did not become amorphous after a fluence of 2.5 × 10 ¹⁵ ions cm ^-2 at 50 K, but there is evidence that it may amorphize at a higher fluence, with an estimated T _c of ∼135 K. The observed T _c results are discussed with respect to the predicted T _c values based upon a previously published empirical model (Lumpkin, G. R.; Pruneda, M.; Rios, S.; Smith, K. L.; Trachenko, K.; Whittle, K. R.; Zaluzec, N. J. J. Solid State Chem. 2007, 180, 1512). In the Y ₂Ti _2-xSn _xO ₇ pyrochlores, T _c appears to be linear with respect to composition, and is linear with respect to r _A/R _B and x(48f) for all samples investigated herein.