Diffusion in quasicrystals

Quasicrystalline phases represent interesting states between amorphous and crystalline phase with unusual physical and mechanical properties. The diffusion mechanism in such aperiodic structures is very interesting subject and the knowledge of the diffusion in the quasicrystals is also important to understand various processes occurring in the materials. In this paper recent development of diffusion in the icosahedral and decagonal quasicrystalline materials is presented. Most of the diffusion measurements have been carried out in the icosahedral quasicrystals. In icosahedral Al-Pd-Mn quasicrystals the temperature dependence is described by the Arrhenius equation. The pre-exponential factor D sub 0 and the activation energy Q are not significantly different from those in the crystalline materials. Thus, it is suggested that diffusion takes place via a vacancy mechanism, which was also supported by activation volume measurements and positron lifetime spectroscopy. No indication was found to support the phason-assisted diffusion mechanism. In i-AlPdMn quasicrystals, self- and impurity diffusion can be classified into two groups; the non-transition metal elements, Zn, Ge and In are relatively fast diffusors, while the transition metal elements such as Mn, Fe, Co, Ni, Cr and Pd are slow diffusors with high values of D sub 0 and Q. Two kinds of the diffusors may diffuse via vacancies at different atomic sites of the constituents. In the decagonal Al-Ni-Co quasicrystals, anisotropic diffusion behaviour was observed. Co atoms in the periodic direction diffuse faster in the aperiodic direction.