Kidejärjestys

Kidejärjestys, often translated as crystal order, refers to the regular, repeating arrangement of atoms, ions or molecules in a crystal. This arrangement is defined by two components: the lattice, a periodic array of points in space, and the basis (motif), the set of atoms attached to each lattice point. Together they generate the crystal structure.

The smallest repeating unit is the unit cell, whose geometry is described by the lattice parameters a, b, c and angles alpha, beta, gamma. The full crystal can be built by translating the unit cell in space. Crystallography classifies crystals into seven crystal systems and fourteen Bravais lattices according to lattice symmetry (cubic, tetragonal, orthorhombic, monoclinic, triclinic, hexagonal and rhombohedral systems).

Crystals exhibit long-range order: a consistent arrangement over many unit cells, along with characteristic rotational or reflection symmetries captured in space groups. This order contrasts with amorphous solids, where long-range periodicity is absent and only short-range order exists.

The kidejärjestys can be determined experimentally using diffraction techniques such as X-ray crystallography, electron diffraction, or neutron diffraction, which reveal the arrangement of atoms and the symmetry of the structure.

The crystal order influences many material properties, including mechanical strength and cleavage, optical behavior, electronic structure, thermal conductivity, and diffusion. It is a central concept in mineralogy, materials science, chemistry, and solid-state physics.