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

Abstract The phase transformations induced by electronic excitation ( S e ) and ballistic processes ( S n ) in Nd 2 Zr 2 O 7 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 Nd 2 Zr 2 O 7 exhibits an unusual behaviour since this compound is amorphizable by S e and non-amorphizable by S n . Annealing of totally amorphized Nd 2 Zr 2 O 7 samples reveals strong differences in the recovery processes with other pyrochlore materials that are related to their different chemical compositions.