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Quasicrystals are formed in a couple of Al-based ternary systems with decagonal AlCoNi being the best studied phase. Decagonal quasicrystals that have been successfully grown as cm3-size single crystals [1] may be structurally described as periodically stacked quasiperiodic atomic planes. Some phases in the Al-Co-Ni system as well as in related ternaries with chemical composition close to that of the parent quasicrystalline phase consist of the same type of large icosahedral clusters and the same periodicity of stacking of the planes with similar structure motifs, but are periodic in all three directions. They are called approximants to quasicrystals or complex metallic phases because sometimes they have very large lattice parameters and hundreds or even thousands of atoms per unit cell. Comparing these two types of crystals, quasicrystals may be considered as the ultimate case of complex metallic phases with a unit cell of infinite dimensions. They allow comparative studies as to judge whether some unusual properties of quasicrystals arise from the lack of periodicity or from the clusters that are common to all these phases. Using the Czochralski method we have grown decagonal AlCoNi and AlCoCu quasicrystals and various complex metallic phases of the Al13TM4 type (TM: transition metal) that are approximants to their parent quasicrystals: monoclinic Al13(Co,Ni)4, orthorhombic Al13Co4, monoclinic Al13Fe4 and its ternary extensions Al13(Fe,Cr)4 and Al13(Fe,Ni)4. Since all these phases cannot be crystallized from congruent melts but only at temperatures below their peritectic reactions, Czochralski growth was done from Al-rich solutions. Permanently decreasing liquidus temperatures during the experiment and extremely low pulling rates in the range of 100 μm/h are some of the consequences. Nevertheless, cm3-size single crystals were successfully grown [2] that are large enough for surface science studies and for a number of investigations of the physical properties of these complex phases. Based on these approximants as well as on the decagonal AlCoNi and AlCoCu quasicrystals, some morphological features that could be observed during growth will be compared and physical properties will be presented that may help to understand the similarities and the differences between these phases. The large icosahedral clusters seem to be the dominant feature as well as the same periodicity of stacking that can be found in all these structures in individual directions. But, certainly it is too early to totally ignore some influence due to threedimensional periodicity or quasicrystallinity.

Growth of Al-based quasicrystals and other complex metallic phases