Fluorite structure

In solid state chemistry, the fluorite structure refers to a common motif for compounds with the formula MX₂.[1][2] The X ions occupy the eight tetrahedral interstitial sites whereas M ions occupy the regular sites of a face-centered cubic (FCC) structure. Many compounds, notably the common mineral fluorite (CaF₂), adopt this structure.

Magnesium compounds such as Mg₂X, where X can be one of the elements Si, Ge, Sn, or Pb, are said to have an antifluorite structure because the locations of the anions and cations are reversed relative to fluorite (an anti-structure); the anions occupy the FCC regular sites whereas the cations occupy the tetrahedral interstitial sites. Magnesium silicide, Mg₂Si, has a lattice parameter of 6.338 Å with magnesium cations occupying the tetrahedral interstitial sites, in which each silicide anion is surrounded by eight magnesium cations and each magnesium cation is surrounded by four silicide anions in a tetrahedral fashion.[3]

The fluorite structure of calcium fluoride CaF₂.[3]
The antifluorite structure of magnesium silicide Mg₂Si.[3]

Lattice constants for fluorite and antifluorite materials at 300 K[3]
Material	Lattice constant (Å)	Crystal structure
BaF₂	6.196	Fluorite (FCC)
β-PbF₂	5.94	Fluorite (FCC)
PuO₂	5.399	Fluorite (FCC)
SrF₂	5.7996	Fluorite (FCC)
UO₂	5.47065	Fluorite (FCC)
CaF₂	5.463	Fluorite (FCC)
ZrO₂	5.14	Fluorite (FCC)
K₂O	6.449	Antifluorite (FCC)
K₂S	7.406	Antifluorite (FCC)
Li₂O	4.61	Antifluorite (FCC)
Na₂O	5.55	Antifluorite (FCC)
Na₂S	6.54	Antifluorite (FCC)
Rb₂O	6.74	Antifluorite (FCC)
Mg₂Si	6.338	Antifluorite (FCC)

References

Holleman, Arnold Frederik; Wiberg, Egon (2001), Wiberg, Nils (ed.), Inorganic Chemistry, translated by Eagleson, Mary; Brewer, William, San Diego/Berlin: Academic Press/De Gruyter, ISBN 0-12-352651-5
Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
Rizescu, Costel; Rizescu, Mihaela (2018). Structure of Crystalline Solids, Imperfections and Defects in Crystals (First ed.). Parker, TX: Shutter Waves. ISBN 978-1-947641-17-4. Retrieved 29 January 2020.

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[1] Holleman, Arnold Frederik; Wiberg, Egon (2001), Wiberg, Nils (ed.), Inorganic Chemistry, translated by Eagleson, Mary; Brewer, William, San Diego/Berlin: Academic Press/De Gruyter, ISBN 0-12-352651-5

[2] Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.

[Costel-3] Rizescu, Costel; Rizescu, Mihaela (2018). Structure of Crystalline Solids, Imperfections and Defects in Crystals (First ed.). Parker, TX: Shutter Waves. ISBN 978-1-947641-17-4. Retrieved 29 January 2020.

Fluorite structure

See also

References