Temperature dependence of ion irradiation damage in the pyrochlores La2Zr2O7 and La2Hf2O7

Synthetic samples of the pyrochlores La2Zr2O7 and La2Hf2O7 were irradiated in situ in the intermediate voltage electron microscope (IVEM-Tandem Facility) at Argonne National Laboratory using 1.0 MeV Kr2+. Results of this study demonstrate that both pyrochlores pass through the crystalline-amorphous transformation albeit with significantly different critical amorphization dose curves. The critical dose values extrapolated to 0 K (D-c0) are 11 +/- 3 x 10(14) ions cm(-2) (similar to1.6 dpa) for La2Zr2O7 and 5.5 +/- 0.7 x 10(14) ions cm(-2) (similar to0.9 dpa) for La2Hf2O7. Non-linear least squares analysis of,the dose-temperature curves gave values of the critical temperature (T-c) of 339 +/- 49 K for La2Zr2O7 and 563 +/- 10 K for La2Hf2O7. This analysis also gave values of the activation energy (E-a) for thermal recovery of damage of 0.02 +/- 0.01 and 0.65 +/- 0.01 eV for the zirconium pyrochlore and the hafnium pyrochlore, respectively. These results demonstrate that there is a major difference in the dose-temperature response dependent upon the nature of the B-site cation of these two pyrochlores. Results are discussed in terms of the pyrochlore structural parameters r(A)/r(B) band x(48f) as well as the stopping powers, displacement energies, and defect energies of the materials.