Precipitation of MgO·nAl₂O₃ in Mg-doped α-Al₂O₃ under electron irradiation

A number of nanoscale precipitates with random orientations were produced by electron irradiation of polycrystalline Mg-doped α-Al₂O₃. The precipitation behavior and microstructural changes were observed using in situ high-resolution transmission electron microscopy. A ring pattern corresponding to a polycrystalline fee structure was obtained from the region of these precipitates by selected-area diffraction, and they were identified as nonstoichiometric MgO·nAl₂O₃. It is believed that Al₂O₃ with MgO(ss) and/or MgO at the grain boundaries is effectively stabilized by the electron irradiation process, forming the fundamental structure of MgO·nAl₂O₃. The average size of the precipitates is about 10 nm.