X-Ray Diffraction Study of Phason Strain Field in Oriented Icosahedral Al-Mn

We have produced large-area (some square centimeters), crystallographically oriented icosahedralphase material by implanting Mn ions directly into single-crystal Al substrates. High-resolution x-ray measurements of the positions and line shapes of the quasicrystal diffraction peaks reveal systematic deviations from perfect icosahedral symmetry. A quantitative analysis of the data shows that the samples contain a simple form of phason strain field which depends on the kinetics of grain formation. The results rule out the icosatwin model proposed by Pauling.