The lattice is usually distorted near impurities, crystal defects, and the crystal's surface. These parameters typically depend on the temperature, pressure (or, more generally, the local state of mechanical stress within the crystal), electric and magnetic fields, and its isotopic composition. The angles α, β, and γ are usually specified in degrees.Ī chemical substance in the solid state may form crystals in which the atoms, molecules, or ions are arranged in space according to one of a small finite number of possible crystal systems (lattice types), each with fairly well defined set of lattice parameters that are characteristic of the substance. Their SI unit is the meter, and they are traditionally specified in angstroms (Å) an angstrom being 0.1 nanometer (nm), or 100 picometres (pm). The three numbers represent the size of the unit cell, that is, the distance from a given atom to an identical atom in the same position and orientation in a neighboring cell (except for very simple crystal structures, this will not necessarily be disance to the nearest neighbor).
The crystal lattice parameters a, b, and c have the dimension of length.
A simple cubic crystal has only one lattice constant, the distance between atoms, but in general lattices in three dimensions have six lattice constants: the lengths a, b, and c of the three cell edges meeting at a vertex, and the angles α, β, and γ between those edges.
Unit cell definition using parallelepiped with lengths a, b, c and angles between the sides given by α, β, γ Ī lattice constant or lattice parameter is one of the physical dimensions and angles that determine the geometry of the unit cells in a crystal lattice, and is proportional to the distance between atoms in the crystal.
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