Temperature dependence of ion irradiation damage in the pyrochlores La2Zr2O7and La2Hf2O7

Synthetic samples of the pyrochlores La 2 Zr 2 O 7 and La 2 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 2+ . 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 × 10 14 ions cm −2 ( dpa) for La 2 Zr 2 O 7 and 5.5 ± 0.7 × 10 14 ions cm −2 ( dpa) for La 2 Hf 2 O 7 . Non-linear least squares analysis of the dose–temperature curves gave values of the critical temperature ( T c ) of 339 ± 49 K for La 2 Zr 2 O 7 and 563 ± 10 K for La 2 Hf 2 O 7 . This analysis also gave values of the activation energy ( E a ) for thermal recovery of damage of 0.02 ± 0.01 and 0.05 ± 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 and x (48f) as well as the stopping powers, displacement energies, and defect energies of the materials.