No 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.

Owing to the quasiperiodic order, one independent term in the elasticity of quasicrystals (phonon-phason coupling) is characteristic of quasicrystals. It is not seen in conventional crystals and has continued to be a significant subject in the research field of quasicrystals.Recently, a novel method was applied to a Mackay-type Al-Pd-Mn icosahedral quasicrystal to prove the existence of phonon-phason coupling and to evaluate its strength based on the elasticity of quasicrystals. This study applied the method to a Tsai-type Ag-In-Yb icosahedral system to evaluate its phonon-phason coupling strength. We applied phonon strain to the quasicrystal at a temperature with active phason, and the induction of phason strain was successfully detected and evaluated using powder X-ray diffraction. We evaluated the phonon-phason coupling elastic constant of the Ag-In-Yb icosahedral quasicrystal to be 0.17 ± 0.04 GPa by quantitatively comparing the measured induced phason strain with our calculation results.