Vitrification and structural differences between metal glass, quasicrystal, and Frank-Kasper phases

Journal of Structural Chemistry (Impact Factor: 0.51). 01/1996; 37(1):120-136. DOI: 10.1007/BF02578579


The concept of icosahedral short-range order is extended to metallic glass, quasicrystal, and Frank-Kasper phases. The cluster
model, together with the theory of local structural fluctuations, explains the static elasticity of glass, which distinguishes
glass from liquid. An elastic peak of the dynamic structural factor indicates the possibility of transverse mode propagation
in glass. As opposed to dislocations and disclinations in crystals, those in glass are artificially introduced defects, which
serve as easily perceptible structural models. Thermodynamic relaxation theory may only be used for limited groups of vitrifying
compounds the same applies to representation of vitrification as the second-order phase transition. The structure of real
quasicrystals may not be adequately represented by Penrose tiling even after its decoration. This is associated with packing
defects, inclusions of other phases, and chemical inhomogeneities. Quasicrystals have specific defects in an icosahedrally
coordinated network of bonds, which distinguish them from Frank-Kasper phases. Criteria for isolating physically realizable
Penrose tiling from all possible mosaics of this type are suggested. Structural distortions that transfer the diffraction
rings of quasicrystalline samples into ellipses are explicable even in a linear approximation for the stress field created
by a phason. The term “long-range order” seems to be wrong even for ordinary crystals. For quasicrystals, the notion of “rotational”
order is more pertinent.

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Available from: Alexander Galashev, Sep 10, 2014