Quasicrystals definition

Having particularly in view intermetallic substances (crystals, quasicrystals) a critical discussion by Steurer (2005) on several questions concerning clusters (definition, stability, etc.) is especially interesting (see also 4.4.4.8). 

The discovery of quasicrystals has led to a paradigm change in crystallography, expressed even in a new definition of what is a crystal by... 

A quasicrystal (QC) is a type of solid that is well-ordered but not periodic. QCs are often associated with classically forbidden rotational symmetries, although strictly speaking, this is not necessary [1]. The discovery of QCs led to a refinement of the definition of a crystal as any soHd with an essentially discrete diffraction pattern. [2]. This transferred the definition of the concept from real to reciprocal space and in doing so broadened the scope of the term to encompass both periodic and quasiperiodic materials. Thus a QC is a nonperiodic crystalline material. 

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