Radiation effects in corundum structure derivatives

The radiation response of α-Al₂O₃ (R3̄c), FeTiO₃ (R3̄), MgTiO₃ (R3̄), and LiTaO₃ (R3c) was investigated using 200 keV Ar²⁺ and 1 MeV Kr⁺ and a combination of Rutherford backscattering spectrometry and transmission electron microscopy. All of these materials have the corundum or a corundum-derivative crystal structure. This family of oxides is of interest due to the simple but significant differences in the structure of the cation sublattices in the different space groups. These materials are also of interest because of their range of melting temperatures, the range of melting temperatures of their oxide components, differences in bonding characteristics, and the complete solid solution between Fe-TiO₃ and MgTiO₃. Our results show that α-Al₂O₃ and MgTiO₃ are consistently more radiation tolerant than FeTiO₃ and that LiTaO₃ amorphizes substantially easier than the other three oxides. The greater stability of MgTiO₃ than Fe-TiO₃ appears to be analogous to the response of Mg-Fe silicates to ion irradiation and high pressure. A characteristic consistent with the radiation tolerance trend of the four oxides studied is a decreasing melting temperature of the component oxides. Thus, the lower stability of Fe-O octahedra in FeTiO₃ and Li-O octahedra in LiTaO₃ may adversely affect the radiation tolerance of these oxides.