Inversespinel

Inversespinel, commonly written as inverse spinel, refers to a cation distribution in a spinel oxide AB2O4 in which the arrangement of cations between tetrahedral and octahedral interstices differs from the normal spinel arrangement. In a normal spinel, A2+ cations occupy tetrahedral sites and B3+ cations occupy octahedral sites. In an inverse spinel, the B3+ cations occupy tetrahedral sites, while the A2+ cations and the remaining B3+ cations occupy the octahedral sites. This rearrangement changes the chemical and physical properties of the material.

The crystal structure of spinels consists of a close-packed array of oxide ions with two types of interstitial sites: tetrahedral (A) and octahedral (B). The classic representations use a site-occupancy notation: a normal spinel is written as (A)[B2]O4, while an inverse spinel is written as (B)[AB]O4. The degree of inversion, often described by an inversion parameter, indicates how far a given composition is from the normal arrangement and can vary with temperature, composition, and synthesis method.

Common examples and variability: magnetite, Fe3O4, is a well-known inverse spinel where Fe3+ occupies tetrahedral sites and Fe2+ and Fe3+ share octahedral sites. Other ferrites such as CoFe2O4 and NiFe2O4 often adopt inverse or partially inverse spinel structures, whereas ZnFe2O4 tends toward a normal spinel. The exact cation distribution significantly influences magnetic, electrical, and catalytic properties.

Applications and synthesis: inverse spinels are studied for their ferrimagnetic behavior, high magnetic anisotropy, and catalytic activity. They find use in magnetic storage materials, ferrofluids, biomedical imaging, catalysis, and energy-related applications. Synthesis methods include solid-state reactions, sol-gel processing, and hydrothermal routes, with characterization commonly using X-ray diffraction and spectroscopic techniques to determine cation distribution. See also spinel, normal spinel, ferrite, and superexchange.