facecentred

Facecentred, in crystallography often written as face-centered or face-centered cubic, refers to a type of crystal lattice where atoms occupy the corners of a cube and the centers of all six faces. The term is commonly used in American English as face-centered cubic (FCC) and is sometimes equated with the cubic close-packed (CCP) arrangement. The descriptor highlights the characteristic placement of atoms on the cube’s faces in addition to the corner positions.

A standard face-centered cubic unit cell contains four atoms: eight corner atoms contribute 1 atom in total (8 × 1/8), and the six face-centered atoms contribute 3 atoms (6 × 1/2). This arrangement yields a coordination number of 12, as each atom touches twelve neighbors. The packing efficiency of an FCC lattice is about 74%, making it one of the most densely packed crystal structures. The layers stack in an ABCABC sequence, giving rise to close packing along certain directions.

Materially, many metals crystallize in the FCC structure, including aluminum, copper, gold, silver, platinum, and nickel (at certain temperatures or phases). This structure imparts high ductility and good formability, owing to multiple slip systems that ease plastic deformation. FCC lattices contrast with body-centered cubic (BCC) and simple cubic (SC) structures in terms of packing density, number of nearest neighbors, and mechanical properties. In crystallography and materials science, the term facecentered is used interchangeably with face-centered, with the FCC designation commonly adopted in discussions of metal crystal structures.