Experimental approach and atomistic simulations to investigate the radiation tolerance of complex oxides: Application to the amorphization of pyrochlores

摘要

Both experimental approach and atomistic simulations are performed in order to investigate the influence of the composition of pyrochlores on their radiation tolerance. Therefore, Gd_2Ti_2O_7 and Gd_2Zr_2O_7 were irradiated with 4 MeV Au and 92 MeV Xe ions in order to study the structural changes induced by low and high-energy irradiations. XRD results show that, for both irradiations, the structural modifications are strongly dependent on the sample composition: Cd_2Ti_2O_7 is readily amorphized, whereas Gd_2-Zr_2O_7 is transformed into a radiation-resistant anion-deficient fluorite structure. Using atomistic simulations with new interatomic potentials derived from the SMTB-Q model, the lattice properties and the defect formation energies were calculated in Gd_2Ti_2O_7 and Gd_2Zr_2O_7. Calculations show that titanates have a more covalent character than zirconates. Moreover, in Gd_2Ti_2O_7 the formation of cation antisite defects leads to strong local distortions around Ti-defects and to a decrease of the Ti coordination number, which are not observed in Gd_2Zr2O_7. Thus, the radiation resistance is related to the defect stability: the accumulation of structural distortions around Ti-defects could drive the Gd_2Ti_2O_7 amorphization induced by irradiation.