Comparison of ion-beam irradiation effects in X2YO4 compounds

The effects of 1.5 MeV Kr-ion irradiation on seven X2YO4 phases with the ol ivine (A(2)(VI)B(IV)O(4)), spinel (A(IV)B(2)(VI)O(4)), and phenakite struct ures have been investigated using in situ and high-resolution transmission electron microscopy (HRTEM) over a nide temperature range (20-873 K). At lo w temperatures (<200 K), the olivine and phenakite are susceptible to radia tion-induced amorphization with a critical amorphization dose of 0.2-0.5 di splacement per atom (dpa). The critical amorphization dose increases with i ncreasing irradiation temperature at varying rates for the various phases, resulting in a distinct critical amorphization temperature for each phase. For the Mg-Fe series of olivine, the susceptibility to amorphization at hig her temperatures (room temperature or above) increases with increasing Pe c ontent. Although the spinel phases are, in general, much more resistant to amorphization, a high-pressure metastable spinel phase, gamma-SiFe2O4, is e asily amorphized at doses <0.2 dpa at temperatures below 723 K, This phase decomposes after irradiation at 873 K. At 20 K, complete amorphization of t he FeCr2O4 spinel (chromite) is achieved at similar to 4 dpa, but no eviden ce of amorphization is observed in MgAl2O4 spinel after 5.4 dpa. The distin ct differences in the relative susceptibility of these phases to amorphizat ion are discussed in terms of the structural and chemical controls on the a morphization process.