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Crystal Clear
Published in Sharon Ann Holgate, Understanding Solid State Physics, 2021
There is a lot of interest in these unusual materials, not only because of the nature of their structure, but also because they have some useful properties. For example, quasicrystals have good wear-resistance, hardness, and low-friction surfaces, which makes them ideal for coating things like machine parts and the heads of electric razors. In aviation, their low thermal conductivity (see Table 5.3) allows quasicrystals to be used for coating the blades of aircraft turbine engines which require a thermal barrier. The additional non-stick quality of quasicrystals enables a more down-to-earth use too, namely coating non-stick kitchen pans.
Artificial Particles: “Man-Made Atoms” or “Meta-Atoms”
Published in Tie Jun Cui, Wen Xuan Tang, Xin Mi Yang, Zhong Lei Mei, Wei Xiang Jiang, Metamaterials, 2017
Tie Jun Cui, Wen Xuan Tang, Xin Mi Yang, Zhong Lei Mei, Wei Xiang Jiang
As is well known, a crystal is a solid natural material whose constituents, such as atoms, molecules, or ions, are arranged periodically. The crystal lattice extends in all directions, and results in homogeneous property of the solid. A crystal can be either isotropic or anisotropic in different directions. In contrast, a noncrystal is a solid in which the atoms inside it form a random arrangement; whereas a quasicrystal is a solid in the ordered state between crystalline and noncrystalline. The quasicrystal consists of arrays of atoms that are ordered but not strictly periodic. Therefore, a quasicrystal is inhomogeneous, either isotropic or anisotropic. The man-made metamaterials can be classified in a similar way. When the artificial particles, the electrically resonant particles and/or the magnetically resonant particles, are arranged periodically, they form a metamaterial termed as the “super crystal.” When they are arranged randomly, they form a metamaterial termed as the “super noncrystal.” When they are arranged quasiperiodically, varying in a specific manner, they form a metamaterial termed as the “super quasicrystal.”
Photonic Quasicrystals: Basics and Examples
Published in Filippo Capolino, Theory and Phenomena of Metamaterials, 2017
Alessandro Della Villa, Vincenzo Galdi, Filippo Capolino, Stefan Enoch, Gérard Tayeb
Although the above extrema of the “order” scale seem to be well characterized, the “gray zone” in between, which encompasses a broad range of hierarchical order types (from “quasiperiodic” to “quasirandom”), turns out to be still largely unexplored. Although the concept of aperiodicity has traditionally been tied to the concept of amorphousness, the discovery, in 1984, of “quasicrystals” [1,2] has significantly changed this view. Quasicrystals are metallic alloys whose x-ray diffraction spectra exhibit bright spots (typical of crystals), yet display unusual rotational symmetries (e.g., 10-fold) that are known to be incompatible with spatial periodicity. This apparent puzzle and the growing awareness of the important role played by aperiodic order in solid-state physics have motivated the study of aperiodic structures from a different perspective, in many fields of science and technology.
Les vertus des défauts: The scientific works of the late Mr Maurice Kleman analysed, discussed and placed in historical context, with particular stress on dislocation, disclination and other manner of local material disbehaviour
Published in Liquid Crystals Reviews, 2022
In later work in this general area Maurice turned his attention to quasicrystals [174–178], see also the reviews [166,179]. Quasicrystals were discovered by Schechtman et al. [180]; for this work Schechtman received the 2011 Nobel Prize in Chemistry. They were so labelled by Levine and Steinhardt [181]. These materials exhibit local symmetries which appear, at least according to previous ideas in solid state physics, incompatible with the tiling of space, and thus impossible. Examples of such symmetries are pentagonal in two dimensions, and icosahedral in three dimensions. Such solids do exhibit sharp crystal-like spots in X-ray or neutron scattering. Thus, interestingly and anomalously, they are crystalline in reciprocal space, but apparently ‘amorphous’ in real space.
Stability of three-dimensional icosahedral quasicrystals in multi-component systems
Published in Philosophical Magazine, 2020
Quasicrystals [1] are a class of important ordered materials possessing quasiperiodic positional order and long-range orientational order between periodic crystals and amorphous materials. The mathematical description of quasicrystals can track back to the work done independently by Meyer [2] and Penrose [3] in early 1970. The first quasicrystal, actually a three-dimensional (3D) icosahedral quasicrystal (IQC), was discovered by Shechtman in a rapidly quenched Al-Mn alloy until 1982 [4]. Since the first discovery of quasicrystals, the quasiperiodic long-range order has been found in a large number of metallic alloys [5–7] and also in a host of soft-matter systems [8,9]. Among these discoveries, icosahedral symmetric quasicrystals are the most frequently found, concretely in more than hundred different metallic alloys [7,10]. However, the thermodynamic stability of quasicrystals in multi-component systems, including IQCs, remains a challenge [11,12], mainly due to the lack of appropriate theoretical models and high-precision numerical methods.
The effect of phason defects on the radiation-induced swelling of quasicrystalline materials
Published in Radiation Effects and Defects in Solids, 2018
Galina N. Lavrova, Anatoliy A. Turkin, Alexander S. Bakai
Quasicrystals are some of the most intriguing materials discovered 30 years ago. Unlike crystals with periodic structures, quasicrystals lack translational symmetry and possess non-crystallographic long-range rotational invariance. The exact structure of quasicrystals is still a subject of debates despite extensive research in this area. Similar to crystalline materials, real quasicrystals have defects such as PD (vacancies and interstitials), dislocations, grain boundaries, etc. There are also defects specific for quasicrystals which are called phasons (1). They were described in the density-wave picture as additional hydrodynamic (long-wavelength) modes besides phonon modes present in conventional crystals (2). Phasons appear in a variety of physical forms related to different atomic displacements, such as phason mode, phason-shift, phason-strain, phason-hop, phason-flips, phason-fluctuations, etc. (3). Such localized atomic rearrangements can be represented as linear superpositions of phason modes of different wavevectors, similar to the representation of an atomic vibration as a superposition of phonons. Mompiou (4) and Feuerbacher (5) noted that the formation and movement of a dislocation in a quasicrystal is accompanied by a so-called phason fault, i.e. a planar agglomeration of individual phasons, chemical and structural PD. Likewise, the dislocation moving in a conventional crystal induces the formation of a stacking fault. We will be following this notion of a phason to describe the kinetics of defects in a quasicrystal.