NaCltype

NaCl-type structure, also called the rock-salt or B1 structure, is a common crystal arrangement for binary ionic compounds. In this structure, the anions form a face-centered cubic (fcc) lattice, and the cations occupy all octahedral voids, yielding two interpenetrating fcc sublattices. Each ion is six-coordinate, surrounded by six oppositely charged neighbors (coordination number 6). The crystal belongs to the space group Fm-3m (225) and typically contains four formula units per unit cell (Z = 4). The nearest neighbor distance is a/2, with the lattice parameter a related to the ionic radii by a ≈ 2(r+ + r−) in an idealized ionic model; actual materials may deviate due to covalency and polarizability.

Stability of the NaCl-type arrangement depends on the size ratio of the ions, generally requiring radii that support sixfold coordination. The structure is favored when the ions are of comparable sizes and bonding is predominantly ionic. It is widely observed in many compounds, including NaCl, KCl, LiF, MgO, and CaS, among others.

In materials science and mineralogy, the NaCl-type description serves as a standard reference for classifying crystalline phases and modeling properties such as diffusion and defect behavior. The structure can accommodate substitutions or vacancies and remains a foundational reference for comparing other rock-salt–type materials. It is distinct from other cubic binary structures, such as the CsCl-type, which features different coordination and lattice arrangements.