halitetype

Halitetype is a crystallographic term used to describe the rock-salt or halite-type crystal structure, a common archetype for binary ionic compounds with 1:1 stoichiometry. In this arrangement, the anions form a face-centered cubic (fcc) lattice, and the cations occupy all octahedral interstices, giving each ion six nearest neighbors. The structure is typically described by the space group Fm-3m and contains four formula units per unit cell.

Key characteristics include octahedral coordination for both ion types and a close-packed anion framework. The lattice parameter a is related to ionic radii by approximately a ≈ 2(r_cation + r_anion) for many halite-type materials, though deviations occur with highly mismatched sizes. Halitetype is distinguished from other 1:1 structures, such as the zinc blende (sphalerite) type, in which ions have tetrahedral coordination instead of octahedral.

Occurrences and examples: A wide range of ionic compounds crystallize in halite-type form, including NaCl, KCl, MgO, CaS, and PbS. The structure is favored for compounds with relatively similar ionic sizes and strong ionic bonding. Under high pressure or temperature changes, some materials may transform to different structural types, but the halite-type form remains a fundamental reference archetype in crystallography and materials science.

Applications: Halitetype serves as a standard classification in crystal-structure databases and materials screening, aiding comparisons of ionic radii, coordination, and bonding characteristics across compounds.

See also: Rock-salt structure, Crystal structure, Ionic compound, Octahedral coordination.