Evaluating the phonon-phason coupling strength of an Al-Ni-Co decagonal quasicrystal

Abstract

Recently, a novel method was proposed to probe the phonon-phason coupling effect in quasicrystals, and it was applied to an Al-Pd-Mn icosahedral quasicrystal. In this study, the method was applied to an Al-Ni-Co decagonal quasicrystal with a periodic layered structure of a two-dimensional quasicrystal. We applied elastic phonon strain along a 2-fold (aperiodic) axis in the quasicrystal plane at high temperatures with active phasons. Then, the phason strain was induced to the quasicrystal, which was demonstrated by the phason momentum (G ⊥) dependences of the powder X-ray diffraction peak widths. In contrast, when we applied phonon strain along the 10-fold periodic axis, no appreciable phason strain was observed to be induced. These results present clear evidence on the presence of phonon-phason coupling in a decagonal quasicrystal. The shape and width of the powder X-ray diffraction peaks were calculated based on the generalized elasticity of quasicrystals. The absolute value of the phonon-phason coupling constant was evaluated by quantitatively comparing the calculated results with the measured diffraction peaks.