Bascentrerad

Bascentrerad is a term used in crystallography to describe a type of lattice centering where lattice points occupy the corners of the unit cell and additional points lie at the centers of the two opposite faces that form the base of the cell. This centering is commonly referred to as base-centered and is indicated by the symbol C in Bravais-lattice notation.

In a bascentrerad orthorhombic cell, for example, the conventional lattice points are at (0,0,0) and at (1/2,1/2,0) in fractional coordinates, along with their equivalent positions. The presence of these extra lattice points alters the symmetry and the description of the lattice compared with a primitive cell of the same dimensions. Bascentrerad lattices are one of the centering options within the 14 Bravais lattices and can also occur in monoclinic systems.

Identification of bascentrerad structures typically involves X-ray or neutron diffraction, where the centering produces characteristic systematic absences in the diffraction pattern. These patterns help distinguish a bascentrerad lattice from primitive or other centered lattices and guide the selection of an appropriate unit cell and space group for structural refinement.

Relation to broader concepts: bascentrerad describes a specific way of placing lattice points within the unit cell and is part of the broader classification of Bravais lattices. It is especially common in certain orthorhombic and monoclinic lattices, where the base-centering can simplify the description of the crystal's symmetry or its packing.

See also: Bravais lattice, centering types, crystallography, X-ray diffraction.