Structural stability of Nd2Zr2O7 pyrochlore ion-irradiated in a broad energy range
Résumé
The phase transformations induced by electronic excitation (Se) and ballistic processes (Sn) in Nd2Zr2O7 pyrochlores irradiated with heavy ions in three domains of energy (∼1 GeV, ∼100 MeV and a few MeV) were investigated by X-ray diffraction, Raman spectroscopy and transmission electron microscopy. In the Se regime at high energy, results show that: (i) ion tracks are formed above a Se threshold of 12.5 keV nm−1; (ii) both pyrochlore → anion-deficient fluorite phase transition and amorphization occur; (iii) total amorphization is always observed at the highest fluences; (iv) the internal structure (amount of amorphous phase vs. its anion-deficient fluorite counterpart) and the diameter of tracks depend on many parameters such as Se, the deposited energy density and the recrystallization rate. For irradiations performed with low-energy ions in the Sn regime, only the anion-deficient fluorite phase is formed up to a dose of 40 dpa. Thus Nd2Zr2O7 exhibits an unusual behaviour since this compound is amorphizable by Se and non-amorphizable by Sn. Annealing of totally amorphized Nd2Zr2O7 samples reveals strong differences in the recovery processes with other pyrochlore materials that are related to their different chemical compositions.