Amorphous

Amorphous describes a material whose internal structure lacks long-range periodic order. In contrast to crystalline solids, whose atoms occupy repeating lattice positions, amorphous materials have only short-range order, with atomic arrangements that become irregular beyond a few nanometers. This absence of long-range order leads to properties that can differ markedly from crystalline counterparts, such as the absence of sharp, well-defined diffraction peaks and, in many cases, isotropic behavior in mechanical and thermal responses.

Amorphous solids include glasses, some polymers, gels, and certain metallic alloys known as metallic glasses. Glasses, such as silica glass, are typically formed by rapid cooling from the melt, which prevents crystal nucleation and growth. Some polymers are entirely amorphous, while others are semicrystalline. Amorphous silicon and amorphous carbon are important in electronics and materials science; metallic glasses are used for their strength and elasticity.

Key properties include the lack of a true melting point; instead, a glass transition temperature marks the transition from a rubbery, viscous state to a rigid glass. They are usually isotropic and can be transparent or opaque, depending on composition and processing. They may devitrify—crystallize—upon heating, which alters properties.

Characterization methods include X-ray diffraction, which shows broad halos rather than sharp peaks, and differential scanning calorimetry (DSC), which detects the glass transition. Common formation methods include rapid quenching from the melt, vapor deposition, and sputtering.

Applications span consumer glass for bottles and windows, optical components and coatings, thin-film electronics such as amorphous silicon in solar cells, and specialized metallic glasses used in structural components and sporting goods.