One-dimensional quasicrystal in rapidly solidified alloys

The structure of quasicrystals

The aim of the present article is to give a review of the state-of-the-art on quasicrystal structure analysis. After a short discussion of the term “crystal” in chapter 1, the geometrical generation of quasilattices is touched in chapter 2. In the following the higher-dimensional description of 1d, 2d and 3d quasi-crystals is demonstrated in detail as well as the derivation of structure factor equations and symmetry relationships in the higher-dimensional space. Chapter 4 shows the experimental techniques and structure determination methods for the study of quasicrystals. The experimental results of structural studies performed with different tech-niques are critically reviewed in chapter 5. Some of the results of the literature research are that five years after the detection of the first quasicrystal not a single quantitative (in terms of a regular structure determination) analysis of its structure has been carried out, and that the famous Mackay-icosahedra do not play the important role as the basic structural building elements as one supposed before.

Twenty years of structure research on quasicrystals. Part I. Pentagonal, octagonal, decagonal and dodecagonal quasicrystals

Is quasicrystal structure analysis a never-ending story? Why is still not a single quasicrystal structure known with the same precision and reliability as structures of regular periodic crystals? What is the state-of-the-art of structure analysis of axial quasicrystals? The present comprehensive review summarizes the results of almost twenty years of structure analysis of axial quasicrystals and tries to answer these questions as far as possible. More than 2000 references have been screened for the most reliable structural models of pentagonal, octagonal, decagonal and dodecagonal quasicrystals. These models, mainly based on diffraction data and/or on bulk and surface microscopic images are critically discussed together with the limits and potentialities of the respective methods employed.

Investigation of transition from decagonal to vacancy ordered phase on replacement of Co by Cu in Al70Co15– x Cu x Ni15

The alloy with composition Al70Co15Ni15 forms one of the important quasicrystalline phase exhibiting formation of decagonal variants [1, 2]. In the present investigation, copper has been substituted in place of cobalt i.e. the phases corresponding to Al70Co15– x Cu x Ni15, have been investigated. It is found that when copper concentration reaches to a value of 10 atomic percent with the composition corresponding to Al70Co5Cu10Ni15, the decagonal phase starts yielding to give rise to vacancy ordered phase. When all cobalt is replaced by copper i.e. when the composition corresponds to Al70Cu15Ni15, the decagonal phase disappears and the only phase observed is the vacancy ordered phase. It can thus be said that copper substitution brings in decagonal to vacancy ordered (VOP) phase transition. It has also been observed that gradual increase in concentration of Cu in Al70Co15– x Cu x Ni15 leads to cellular to dendritic transition in morphology.