Recent research and development on Quasicrystals † (original) (raw)

Some new structural and electronic characteristics of quasicrystals

Bulletin of Materials Science, 1999

The quasicrystals being based on quasiperiodic order other than crystal like periodic translational order and embodying self similarity, present unique condensed matter phases. In addition to their curious structural characteristics the paucity of translational periodicity leads to drastic deviations in their electronic behaviour as compared to crystalline counterparts. This paper describes and discusses some new developments in regard to structural and electronic aspects of quasicrystalline materials. In regard to the structural aspects, two comparatively newer features will be described. One of them relates to the observation of variable strain approximants (VSA) first found in Ti68Fe26NiSi5, qc alloys; the other relates to the structure of decagonal phases. The variable strain approximants correspond to qc phases exhibiting variable strain for the different diffraction spots for the same reciprocal lattice row (possessing linear shifts). The VSA is thought to result from variable...

Quasicrystals: A Matter of Definition

Foundations of Physics, 2003

It is argued that the prevailing definition of quasicrystals, requiring them to contain an axis of symmetry that is forbidden in periodic crystals, is inadequate. This definition is too restrictive in that it excludes an important and interesting collection of structures that exhibit all the well-known properties of quasicrystals without possessing any forbidden symmetries.

PERIODIC SURFACES IN THE DESCRIPTION OF QUASICRYSTALS

Le Journal de Physique Colloques, 1990

To give a full account of the atomic ordering in modulated crystals or in quasiclystals amounts to find suitable periodic surfaces living in a euclidean space of dimension higher than that of the physical 3 0 space. In a first part, I summarize the main features of quasiperiodic order and show that it is naturally described by the so-called section or cut method. Next, the problem of short range order will be raised :for quasicrystals, the solution consists in building surfacetin higher D whose intersections with the physical space (imbedded in RD as a vector subspace) provide the atomic sites. As an example, the "atomic surface" of the octagonal quasiperiodic tiling is analysed in more details in the last section.

Some remarks on quasi-crystal structure

Acta Crystallographica Section A Foundations of Crystallography, 1992

The Fourier transform of a skeletal delta function that characterizes the most striking features of experimental quasi-crystal diffraction patterns is evaluated. The result plays a role analogous to the Poisson summation formula for periodic delta functions that underlie classical crystallography. The real-space distribution can be interpreted in terms of a backbone comprising a system of intersecting equiangular spirals into which are inscribed (self-similar) gnomons of isosceles triangles with length-to-base ratio the golden mean r. In addition to the vertices of these triangles, there is an infinite number of other points that may tile space in two or three dimensions. Other mathematical formulae of relevance are briefly discussed.

An Overview of Quasicrystals, Their Types, Preparation Methods, Properties

2021

Quasicrystals, unlike crystals that contain regular and repetitive patterns, are composed of regular patterns that are not repetitive. Moreover, the symmetry of quasicrystals in crystals is impossible. For example, ordinary crystals can have triple symmetries from the repetition of a triangle or quadruple symmetries from the repetition of a cube. Quasicrystals are a special type of real crystals that are artificially formed only in laboratories, under certain conditions and temperatures, and it is not possible to form them like the earth. Evidence suggests that quasicrystals can form naturally under conditions contrary to astrophysical laws and remain stable for long periods. Quasicrystals are a group of new materials with unique mechanical, physical, and chemical properties. Among the known properties of these materials are low adhesion and friction, high resistance to corrosion, very high hardness, electrical insulation at low temperatures, and light absorption. Quasicrystals are ...