Anomalous Debye-Waller factor associated with an order-disorder transformation in an Al72Ni20Co8 decagonal quasicrystal

order-disorder transformation in a single decagonal quasicrystal of Al72Ni2OCo8 is studied in detail. In X-ray diffraction, the anomalous attenuation of intensities of Bragg reflections was found around the transformation temperature, T-c. The intensity attenuation at high temperature is explained by the anomalous Debye-Waller factor in thermal lattice dynamics. In particular, the intensity ratio above T-c and below T-c depends on \G(parallel to)\(2) values. In addition, the intensity ratio between room temperature and high temperature shows \G(perpendicular to)\(2) dependence. The results correspond to the in situ observation of a local vibrational anomaly related to an atomic flip by electron microscopy [Abe et al.: Nature 421 (2003) 347]. By X-ray diffraction, dynamic fluctuations as observed in electron microscopy are also realized even on a macroscopic scale at high temperature.