Quasicrystal

A solid with long-range order and sharp diffraction patterns but no periodic translational symmetry. Its atomic arrangement can exhibit rotational symmetries forbidden in periodic crystals.

Bragg diffraction: The coherent scattering of waves from regularly spaced structures, producing sharp peaks at specific angles. Sharp diffraction peaks expose quasicrystalline order despite the absence of periodic repetition.
Dan Shechtman: An Israeli materials scientist who discovered a metallic alloy with quasicrystalline diffraction in 1982. His observation launched the experimental study of quasicrystals.
Crystal structure: The arrangement of atoms or molecules in a solid, including its symmetries and spatial organization. Quasicrystals are crystal structures without translational periodicity.
Quasicrystalline coating: A surface layer containing quasicrystalline phases, used to modify friction, wear, or corrosion behavior. Coatings exploit quasicrystals' low friction and resistance to wear.
Periodic crystal: A solid whose atomic structure repeats exactly under translations along lattice directions. Periodic crystals have repeating unit cells; quasicrystals have sharp order without that repetition.
Fourier transform: A mathematical operation that expresses a signal or structure in terms of its spatial frequencies. It connects quasiperiodic atomic arrangements to the discrete diffraction peaks they produce.
Aluminum-manganese alloy: An alloy of aluminum and manganese in which Dan Shechtman first observed quasicrystalline diffraction. This was the material behind the initial discovery.
Translational symmetry: A symmetry in which shifting a structure by a fixed distance leaves it unchanged. Its absence distinguishes quasicrystals from periodic crystals.
Low-friction coating: A surface treatment designed to reduce resistance between contacting materials. Quasicrystalline coatings can provide low friction without conventional lubricants.
Glassy material: A noncrystalline solid whose disordered structure is frozen from a liquid-like state. Glasses lack the long-range order found in quasicrystals.

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