Cubic superspace symmetry and inflation rules in metastable MgAl alloy
Departamento de Física de la Materia Condensada, Facultad de Ciencias, Universidad del País
Vasco, Apdo 644, 48080 Bilbao, Spain
Accepted: 23 September 1998
Published online: 15 January 1999
The diffraction properties of a quenched Al-Mg alloy which has been recently termed as a "cubic quasicrystal" are quantitatively reanalyzed. It is shown that the phase can be interpreted within the superspace formalism as an ordinary incommensurately modulated structure. The cubic six-dimensional superspace group that describes its symmetry properties has been determined. The additional inflation symmetry features exhibited by the diffraction diagram can be summed up by its invariance for the inflation factor , but this property has its origin in the specific value of the modulus of the modulation wave vectors, which is composition dependent. Other particular values of this modulus can give rise to similar scaling properties. Further experiments are required to ellucidate if the mentioned inflation symmetry is a fortuitous situation in a composition dependent wave vector, or has indeed the physical significance which would allow to describe the system as a "cubic quasicrystal".
PACS: 61.44.Fw – Incommensurate crystals / 61.44.-n – Semi-periodic solids / 61 – Structure of solids and liquids; crystallography
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 1999