nichtkristallinen

Nichtkristallinen, in English non-crystalline (amorphous), refers to materials that lack a long-range periodic arrangement of atoms. Unlike crystals, amorphous materials do not have translational symmetry; they may exhibit short-range order but no long-range order. This category includes glasses, amorphous polymers, and some metallic glasses.

Formation and structure: Non-crystalline materials form when a liquid cools so rapidly that atoms cannot rearrange into a crystal lattice, or when deposition and processing conditions suppress crystallization. The resulting atomic network is disordered, though it often preserves local bonding or short-range order. They do not have a sharp melting point; many undergo a glass transition at a finite temperature where properties change gradually.

Properties: They are typically isotropic and can be optically transparent or opaque. Mechanical properties vary: polymers and metallic glasses can be strong yet brittle, while some amorphous materials exhibit excellent toughness. Thermal properties differ from crystalline solids, including lacking a well-defined melting point.

Examples and applications: Common examples include window glass (silica-based), fused silica, amorphous silicon used in thin-film solar cells, and many polymers in their amorphous state. Amorphous metals (metallic glasses) are used for specialty components due to high strength and elasticity.

Characterization and terminology: X-ray or neutron diffraction yields broad halos rather than sharp Bragg reflections, indicating lack of long-range order. Differential scanning calorimetry reveals a glass transition. Microscopy and spectroscopy assess local structure and bonding. The term non-crystalline (nichtkristallinen) is used across materials science to distinguish these materials from crystalline solids and includes glasses, polymers, and amorphous alloys.