Structural stability of Nd2Zr2O7 pyrochlore ion-irradiated in a broad energy range

The phase transformations induced by electronic excitation (S_e) and ballistic processes (S_n) 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 S_e regime at high energy, results show that: (i) ion tracks are formed above a S_e 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 S_e, the deposited energy density and the recrystallization rate. For irradiations performed with low-energy ions in the S_n 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 S_e and non-amorphizable by S_n. 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.