Rational approximant structures and phason strain in icosahedral quasicrystals

The degeneracy of the reciprocal space with respect to the icosahedral symmetry has been demonstrated by experimental diffraction patterns obtained from rapidly solidified Al-Mn-Si, Mg-Al-Ag, Mg-Al-Zn alloys. The distortion in diffraction patterns has been attributed to rational approximant (RA) structures. The distorted pattern obtained from Mg-Al-Zn system has been indexed based on 3/2 RA structure. The shift parameter has been quantified and shown to vary linearly with the pseudospace counterpart of the corresponding quasicrystalline reciprocal vector, which is the characteristic feature of phason strain