Abstract
We report an electron and X-ray diffraction study of commensurately modulated states corresponding to the high-temperature equilibrium states in the Mg-Al system. The aluminium contents (49–54 at. %) and temperatures (425–445°C) of interest here are located within the large γ-phase domain of the Mg-Al phase diagram. The present work is focused on the indexation of these three-dimensionally modulated states which are required to be reliable to combine electron and X-ray diffraction information. We finally obtain an indexation in terms of a P-type cubic lattice for the mean lattice and an F-type cubic lattice for the modulation. In this indexation scheme, the stable crystalline phases γ-Mg17Al12 and β-Mg2Al3 appear as lock-in states characterized by the rational values 1/3 and 3/8 respectively.