Yksikkökide

Yksikkökide, known in English as the unit cell, is the smallest repeating unit of a crystal lattice that, when translated through space, recreates the entire crystal structure. It is defined by three lattice vectors a, b, c and the interaxial angles α, β, γ.

In crystallography, the unit cell is a fundamental element used to describe the arrangement of atoms in a crystal. The lattice itself represents the periodic array of points, while the basis (or motif) attached to each lattice point specifies the actual atoms or ions. The full crystal is generated by translating the basis through all lattice vectors.

There are 14 Bravais lattices that classify possible lattice point arrangements in three-dimensional space. A unit cell can be primitive, containing exactly one lattice point, or conventional, which may contain more than one lattice point to reflect the symmetry of the lattice. The number of lattice points per cell is denoted Z; for a primitive cell Z = 1, for a body-centered cell Z = 2, and for a face-centered cell Z = 4, among other possibilities.

Atoms within the unit cell are often described by fractional coordinates relative to the cell edges, which can then be converted to Cartesian coordinates if needed. The geometry and symmetry of the unit cell determine many properties of the crystal, including its diffraction pattern, density, and mechanical behavior.

In practice, the concept of the yksikkökide is central to crystallography, solid-state chemistry, and materials science. It provides a compact description of structure, supports indexing in X-ray and electron diffraction, and serves as the basis for calculating structural parameters and interpreting crystal symmetries.