Crystallinity

Crystallinity is the degree to which a solid’s atoms, ions, or molecules form ordered, repeating structures. It ranges from fully crystalline through partially crystalline to amorphous material.

Crystal structure: The repeating arrangement of atoms, ions, or molecules in a crystalline solid. Crystallinity describes how much of a solid possesses this repeating arrangement.
Crystal lattice: An idealized periodic array of points representing the translational symmetry of a crystal. A lattice provides the repeating framework used to describe crystalline order.
Polymer crystallinity: The fraction of a polymer that forms ordered crystalline regions rather than amorphous regions. Polymer crystallinity affects stiffness, density, melting behavior, and permeability.
Short-range order: Structural order extending over only a few neighboring atoms or molecules. A material can have local order without the long-range periodicity associated with crystallinity.
Nucleation: The formation of initial stable clusters from which a new phase can grow. Crystalline order often begins when stable nuclei form during cooling or deposition.
Unit cell: The smallest volume element that, repeated by translation, generates a crystal lattice. Repeating unit cells produce the long-range order measured as crystallinity.
Crystallization of metals: The formation of crystalline grains as molten metal solidifies or a metal recrystallizes. Processing controls grain structure and crystalline order in metallic materials.
Liquid crystal: A phase that flows like a liquid while retaining some orientational or positional order. Its partial order differs from the three-dimensional periodic structure of ordinary crystals.
Crystal growth: The enlargement of an ordered solid as atoms, ions, or molecules join its crystal lattice. Growth extends ordered regions and can increase a material’s crystalline fraction.
Crystallographic defect: A deviation from perfect periodic order in a crystal, such as a vacancy or dislocation. Defects disrupt local order without necessarily eliminating a material’s crystallinity.

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