On the Anisotropy of Quasicrystal Structures (original) (raw)

Elastic and anelastic behaviour of icosahedral quasicrystals

1987

A theory is developed, based on theoretical-group analysis, which describes the linear, reversible, time-dependent response of an icosahedral quasicrystal, containing point defects, to stress the field known as anelastic relaxation. We obtain also anelastic relaxation relationships for the practical Young, shear and Poisson moduli.

Recent research and development on Quasicrystals †

AIMS Materials Science, 2017

Quasicrystals are a kind of unique materials and characterized by the discrete diffraction patterns which cannot be indexed with the conventional three indices but require additional ones [1,2]. They occur in almost every type of solid including organic and inorganic compounds, minerals, metals and alloys, macromolecules and oxides [3,4,5]. It is convenient to describe their structures in higher dimensional space, a conceptual environment, in which threedimensional periodic crystals recover their periodicities [6]. The inconvenience of visualization due to extra dimensions is compensated by the mathematical elegance achieved through recovering periodicity. Studies of quasicrystalline structures have greatly enriched our understanding of the physics and chemistry of atomic orders, and have opened up new perspectives for correlating structure with the properties of complex materials. The ICQ13 conference was attended by 134 participants from all over the world including two participants from India, T.P. Yadav (Banaras Hindu University-Varanasi)

From texture to volume an investigation in quasi-crystalline systems

The relation between texture, pattern and massing is a fundamental question in architecture. Classical architecture, as Leon Battista Alberti states in "De re aedificatoria" (Book VI, Chapter 2), is developed through massing and structure first; texture is added afterwards to give the bold massing and structure beauty. Only the ornamentation adds pulcritudo to the raw structure and massing. Rather than starting with a volume and applying texture afterwards, the Digital Girih project started with textural operations that informed the overall volume later. The stereometric, top-down methodology is questioned through the bottom-up methodology of the Girih project. Girih lines of traditional Islamic patterns were used as a starting point. The aspect of 3-dimensionality was developed analogue as well as digital, using the deformability of different materials at various scales and digital construction techniques as parameters. The flexibility within the Girih rules allowed the system to adapt to different tasks and situations and to react to different conditions between 2-and 3-dimensionality. The project in that way explored a bottom-up process of form generation. This paper will describe the process of the project and explain the necessity of digital tools, such as Grasshopper and Rhino, and fabrication tools, such as laser cutter and CNC fabrication technology, that were essential for this process.

Time-resolved structural investigation of quasicrystal surfaces

2000

The atomic structure of quasicrystal^i s neither periodic, as in crystals, nor ran¬ dom, as in an amorphous material, by contrast, it is aperiodic. The aperiodicity explicitly includes a long-range order like in crystals but with a wider formalism of translational symmetry. In the icosahedral quasicrystal, twofold-, thrcefoldand fivefold-symmetry elements are observed in the near-surface region using a real-space imaging technique based on secondary-electron emission. rLTre observed icosahedral point-group symmetry implies the presence of atomic clusters within the analyzed region of the solid. At the same time, the surface produces pro¬ nounced Kikuchi lines, typical for well-defined ciystallographic planes. In the following, a model which reconciles this dual structural nature of quasicrystals is presented. This model is constructed from an icosahedral seed followed by a concentric symmetry-preserving growth to form the macroscopic solid. The same positions for the atoms can also be obtained by stacking planes along the symme¬ try axes of an icosahedron. The spacing between the planes follows the Fibonacci sequence, atoms are placed at the points oi intersection of the planes. Peculiarities of the structure such as steps on the suifaoe or the interpretation of the Kikuchi lines are discussed in the light of this model. werden. Die Unterlage bestimmt aber m beiden Fallen ihre Ausrichtung; im Falle der kubischen Struktur ergeben sich zwei äquivalente Orientierungen. Entweder ist eine [110] oder L3lT Achse parallel zu einei funfzähligen Rotationsachse des Quasikristalles. Die zchnzahlige Rotationsachse des quasiki istallincn Films ist im¬ mer parallel zur* funfzähligen Rotationsachse der Unterlage, welche zugleich auch die Oberflächcnnormale bildet Das vorgeschlagene Modell bietet auch eine In¬ terpretation zui Ait der Phaseugrenzcn an. Die anfängliche chemische Zusam¬ mensetzung und demzufolge die anfänglich ikosaedrische Struktur kann entweder durch Erwärmen und somit Segregation oder durch Ablagerung der dezimierten Elemente zurückgewonnen werden ]

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 ...

Tetracoordinated quasicrystals

Physical review. B, Condensed matter, 1991

Current model networks for amorphous Ge contain five-membered rings and pentagonal dodecahedra to explain why in the radial distribution function the third peak of the diamond structure is missing. By presenting an algorithm based on a decoration of the three-dimensional Penrose quasilattice, we prove that this local pentagonal symmetry can be extended globally to an icosahedral quasicrystalline tetracoordinated network. Its structural elements and topological properties coincide with previous hand-built models of random networks. Thus it is suitable for simulating bulk properties of amorphous semiconductors.