STRUCTURAL RELAXATION IN AN EQUILIBRIUM QUASI-CRYSTAL

The presence of additional hydrodynamic modes, associated with the flu ctuations in incommensurate, or phason degrees of freedom, is a distin ctive dynamical feature of quasicrystals. The phason dynamics can give rise to a novel form of atomic transport, which is expected to be muc h faster than the conventional vacancy-driven diffusion in crystals an d amorphous solids. In this paper, a computer simulation is reported u tilizing a realistic 3D model of an axial stacked dodecagonal quasicry stal, which is found to exhibit a high rate of phason flips as well as the related atomic diffusion. The tagged particle dynamics, explored through the simulated incoherent intermediate scattering function, F-s (Q, t), are found to display, in the alpha-relaxation time window, a p ronounced stretching of relaxation times. This can be successfully app roximated by the Kohlrausch function, revealing an anomalously small v alue of the stretching exponent, beta = 0.47, which is analyzed in ter ms of modes involved.