Quasicrystals Structure, properties and applications

Discovered in 1984 by Daniel Shechtman, quasicrystals are among the most important developments in solid-state physics and chemistry in recent decades. They are intermetallic compounds characterized by a long-range order incompatible with the translational periodicity of crystals. They exhibit rotational symmetries prohibited by the rules of classical crystallography. The discovery of these aperiodic materials overturned the foundations of crystallography, demonstrating that periodic repetition of the same unit cell is not the only way to build a long-range ordered structure. Its importance has been recognized by the award of the 2011 Nobel Prize in Chemistry to its discoverer.

This discovery led to a major research effort in the field of intermetallics to discover new quasicrystalline phases in binary or ternary phase diagrams, and to synthesize them in the purest forms. Numerous large-mesh crystalline compounds have also been discovered. They are called approximates, because their chemical composition is close to that of the parent quasicrystalline phase, and they possess a similar local order. Structural models have been proposed to describe quite precisely where the atoms are. It is possible to describe them as an assembly of highly symmetrical aggregates, found in both quasicrystals and their approximants. This structural complexity gives rise to physical and chemical properties very different from those of their constituents. They are, for example, poor conductors of electricity and heat, despite being obtained from metallic elements such as aluminum and transition metals.

This article describes the main families of quasicrystals discovered to date, and the different ways in which they can be synthesized. It also discusses the main physical and chemical properties, from electronic to surface properties. Emphasis is placed on the use properties of these materials, such as friction, adhesion and wetting. Finally, the main applications for which these materials are being considered or are already in use are described at the end of the article. For example, quasicrystals can be used as new materials for coatings or surface deposits, to take advantage of their surface properties. They are also used as reinforcement particles in solid composites, both metal-matrix and polymer-matrix. They are also used in the composition of new materials for additive manufacturing, to produce functional composite parts with new or improved properties in polymer or metal matrix. Other high-potential technological applications, such as anti-counterfeiting materials and catalysis, are also described.

A table of acronyms is provided at the end of the article.