A phason strain in an Al–Cu–Fe icosahedral quasicrystal

The peak profiles and peak positions for an icosahedral Al–Cu–Fe single quasicrystal were measured using a high-resolution four-circle X-ray diffractometer. Notable peak shifts from the ideal Bragg positions with Q⊥ dependence were observed only for the reflections on the five-fold axis. This means that the specimen has the linear phason strain along the five-fold direction. The amplitude of this linear phason strain is estimated as −0.0543 by using matrix elements for Ih to D5d deformation. This value corresponds to the phase transformation from the icosahedral phase to the pentagonal phase. Furthermore, two-dimensional intensity distributions around the Bragg reflections on the two-, three- and five-fold axes are well interpreted with this deformation scheme.