Cubic superspace symmetry and inflation rules in metastable MgAl alloy

The diffraction properties of a quenched Al-Mg alloy which has been recentl y termed as a "cubic quasicrystal" are quantitatively reanalyzed. It is sho wn that the phase can be interpreted within the superspace formalism as an ordinary incommensurately modulated structure. The cubic six-dimensional su perspace group that describes its symmetry properties has been determined. The additional inflation symmetry features exhibited by the diffraction dia gram can be summed up by its invariance for the inflation factor (2 + root 3), but this property has its origin in the specific value of the modulus o f the modulation wave vectors, which is composition dependent. Other partic ular values of this modulus can give rise to similar scaling properties. Fu rther experiments are required to ellucidate if the mentioned inflation sym metry is a fortuitous situation in a composition dependent wave vector, or has indeed the physical significance which would allow to describe the syst em as a "cubic quasicrystal".