Relationship between Phason Strain and Approximant Crystal Structure in Co-Rich Al-Ni-Co Decagonal Phase

Abstract

Peak broadening and the peak positions of the Bragg reflections were studied with the high-resolution X-ray diffraction method for the decagonal Al_72.7Ni_8.5Co_18.8 quasicrystal. The full-widths at half-maximum (FWHM) of the Bragg reflections along the longitudinal direction (L), which is perpendicular to the periodic axis, have no Q_|| or Q_⊥ dependences. On the other hand, notable peak shifts from ideal Bragg peak positions with linear Q_⊥ dependence were observed. This means that the Al_72.7Ni_8.5Co_18.8 decagonal phase has linear phason strains. According to the absolute values of the linear phason strains, the transformation from the decagonal phase to an approximant crystal is discussed.