Ion Irradiation of Ternary Pyrochlore Oxides.

Polycrystalline synthetic samples of Y2Ti2−xSnxO7with x= 0.4, 0.8, 1.2, and 1.6, together with Nd2Zr2O7, Nd2Zr1.2Ti0.8O7, and La1.6Y0.4Hf2O7, 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 (Fc) 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 (Tc) of 666 ± 4, 335 ± 12, and 251 ± 51 K for the Y2Ti2−xSnxO7samples 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 × 1015ions cm−2and remains crystalline to 5 × 1015ions cm−2at 50 K. Additionally, the critical fluence-temperature response curves were determined for Nd2Zr1.2Ti0.8O7and La1.6Y0.4Hf2O7, and we obtained Tcvalues of 685 ± 53 K and 473 ± 52 K, respectively, for these pyrochlores. Nd2Zr2O7did not become amorphous after a fluence of 2.5 × 1015ions cm−2at 50 K, but there is evidence that it may amorphize at a higher fluence, with an estimated Tcof ∼135 K. The observed Tcresults are discussed with respect to the predicted Tcvalues 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−xSnxO7pyrochlores, Tcappears to be linear with respect to composition, and is linear with respect to rA/rBand x(48f) for all samples investigated herein. [ABSTRACT FROM AUTHOR]