Orientation domains in a monoclinic Mg–Al–O phase

Two types of Mg–Al–O structures were successfully synthesized under high temperature (above 1173 K). Transmission electron microscopy and group theory analysis reveal the existence of cubic MgAl₂O₄ and an unreported monoclinic MgAl_xO_y phase with four domain variants. The structural relationship between these two phases is discussed in detail. The results shed light on the structural investigation of Mg–Al–O oxides, which are important mineral components of the Earth's lower mantle as well as substrates for the epitaxial growth of semiconductor films. Monoclinic MgAl_xO_y nanowires with domain boundaries may also provide a possible high-strength candidate for industrial applications.