Structure of CaF2 and related compounds

The stmcture of fluorite, CaF2, may be regarded as being composed of cubic closest packed Ca2+ cations with all the tetrahedral interstices occupied by F-anions, as shown in Fig. 10.1.6. The stoichiometric formula is consistent with the fact that the number of tetrahedral holes is twice that of the number of closest packed atoms. 

Some compounds, such as Na20 and K2S, have the inverse fluorite (or antifluorite) structure, which is a ccp structure of anions with all the tetrahedral interstices occupied by cations. 

Many inorganic compounds have the fluorite and inverse fluorite structures (a) all halides of the larger divalent cations except two fluorides in this class (b) oxides and sulfides of univalent ions (c) oxides of large quadrivalent cations and (d) some intermetallic compounds. Table 10.1.5 lists some compounds of the fluorite and inverse fluorite types and their a parameters. 

The fluorite structure may also be regarded as being composed of a simple cubic packing of anions, and the number of cubic holes is the same as the 

The structure of Li3Bi is formed by a ccp of Bi atoms with the Li atoms occupying all the tetrahedral and octahedral holes. 

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