Ion Irradiation of Ternary Pyrochlore Oxides

Polycrystalline synthetic samples of Y2Ti2-xSnxO7 with x = 0.4, 0.8, 1.2, and 1.6, together with Nd2Zr2O7, Nd2Zr1.2Ti0.8O7, and La(1.6)y(0.4)Hf(2)O(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 Sri content oil the pyrochlore B site. Nonlinear least-squares analysis of the fluence-temperature curves gave critical temperatures (T-c) of 666 +/- 4, 335 +/- 12, and 25 +/- 15 K for the Y2Ti2-xSnxO7 samples with v = 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 x 10(15) ions cm(-2) and remains crystalline to 5 x 10(15) ions cm(-2) at, 50 K. Additionally, the critical fluence-temperature response curves were determined for Nd2Zr1.2Ti0.8O7 and La1.6Y0.4Hf2O7, and we obtained T-c values of 685 +/- 53 K and 473 +/- 52 K, respectively, for these pyrochlores. Nd2Zr2O7 did not become amorphous after a fluence of 2.5 x 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 similar to 135 K. The observed Tc results are discussed with respect to the predicted Tc 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 Y2Ti2-xSnxO7 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.