crystallography Crystallography is the branch of science devoted to the study of molecular and crystalline structure and properties. The word ''crystallography'' is derived from the Ancient Greek word (; "clear ice, rock-crystal"), and (; "to write"). In J ...

, an anti-structure is obtained from a salt structure by exchanging anion and cation positions. For instance,

calcium fluoride Calcium fluoride is the inorganic compound of the elements calcium and fluorine with the formula CaF2. It is a white solid that is practically insoluble in water. It occurs as the mineral fluorite (also called fluorspar), which is often deeply col ...

, CaF₂, crystallizes in a cubic motif called the

fluorite structure The fluorite structure refers to a common motif for compounds with the formula MX2. The X ions occupy the eight tetrahedral interstitial sites whereas M ions occupy the regular sites of a face-centered cubic In crystallography, the cubic (or is ...

. The same crystal structure is found in numerous ionic compounds with formula AB₂, such as ceria (CeO₂),

zirconia Zirconium dioxide (), sometimes known as zirconia (not to be confused with zirconium silicate or zircon), is a white crystalline oxide of zirconium. Its most naturally occurring form, with a monoclinic crystalline structure, is the mineral ba ...

(cubic ZrO₂),

uranium dioxide Uranium dioxide or uranium(IV) oxide (), also known as urania or uranous oxide, is an oxide of uranium, and is a black, radioactive, crystalline powder that naturally occurs in the mineral uraninite. It is used in nuclear fuel rods in nuclear reac ...

(UO₂). In the corresponding ''anti-structure'', called the antifluorite structure, anions and cations are swapped, such as beryllium carbide (Be₂C) or

lithium oxide Lithium oxide (Lithium, Oxygen, O) or lithia is an Inorganic compound, inorganic chemical compound. It is a white or pale yellow solid. Although not specifically important, many materials are assessed on the basis of their Li2O content. For examp ...

(Li₂O),

potassium sulfate Potassium sulfate (US) or potassium sulphate (UK), also called sulphate of potash (SOP), arcanite, or archaically potash of sulfur, is the inorganic compound with formula K2SO4, a white water-soluble solid. It is commonly used in fertilizers, prov ...

(K₂SO₄). Other anti-structures include: * anti- SnO₂: Ti₂N * anti- PbCl₂: Co₂P * anti- CdCl₂: Co₂N * anti- CdI₂: Cs₂O * anti- NbS₂: Hf₂S * anti- ReO₃: Cu₃N * anti- LaF₃: Cu₃P, Cu₃As

References

{{Reflist Crystallography