Pearson symbol: cF12, prototype: CaF2.The calcium fluoride (CaF2)
structure, more commonly known as the fluorite structure, has itspositive ions forming the fcc substructure and usually larger negative ions occupying tetrahedral interstices in this substructure. This is shown in Fig. 104a for CaF2. Each F− anion is placed in the center of a tetrahedral interstice and has
4 NNs (see also Fig. 105a). In Fig. 104b, we show the cubic unit cell for the CaF2 structure with the anions in its vertices. We can see in this figure that
Table 21 Lattice constants (in Angstroms) obtained under normal conditions for
compounds of Be-VI and TM-VI type that crystallize in the zinc blende structure.
O S Se Te Po
Be BeS (4.8624) BeSe (5.1477) BeTe (5.6225) BePo (5.838)
Mn β-MnS (5.601) β-MnSe (5.902) α-MnTe (6.338)
Zn ZnO (4.63) β-ZnS (5.4109) ZnSe (5.6676) β-ZnTe (6.1037) ZnPo (6.309)
Cd β-CdS (5.8304) CdSe (6.077) CdTe (6.4809) CdPo (6.665)
Hg β-HgS (5.8537) α-HgSe (6.0854) α-HgTe (6.453)
Table 22 Lattice constants (in Angstroms) obtained under normal conditions for
compounds of TM-VII type that crystallize in the zinc blende structure.
F Cl Br I
Cu CuF (4.255) γ-CuCl (5.4202) γ-CuBr (5.6955) γ-CuI (6.05844)
the anions define 8 small cubes with cations in their centers, Ca2+ cation, contrary to the anion,
In addition to CaF structure. They are listed at t
compounds that crystallize in this structure, we can mention hydrides, silicides, oxides, and fluorides of some TMs (mainly RE metals and actinides) and also lead difluoride
dioxide in the alpha phase (
obtained under normal conditions for the compounds specified above, are listed in Table 23. This table allows to identify quickly which metals form compounds within a given group of hydrides, silicides, oxides, fluoride chlorides (see columns of the table) and also allows to see how many compounds with the fluorite struc
rows of the table).
Figure 104 Cubic unit cells for the CaF cations in (a) and F− anions in
Figure 105 (a) Regular tetrahedron defined by the
defined by the NNs of the Ca
the anions define 8 small cubes with cations in their centers, therefore , contrary to the anion, has 8 NNs, what is shown in Fig. 105b. In addition to CaF2, other II-VII compounds crystallize in the fluorite
structure. They are listed at the top of Table 23. Among other examples of compounds that crystallize in this structure, we can mention hydrides, silicides, oxides, and fluorides of some TMs (mainly RE metals and actinides) and also lead difluoride in the beta phase (β-PbF2) and poloniu
dioxide in the alpha phase (α-PoO2). The experimental lattice constants,
obtained under normal conditions for the compounds specified above, are listed in Table 23. This table allows to identify quickly which metals form compounds within a given group of hydrides, silicides, oxides, fluoride chlorides (see columns of the table) and also allows to see how many compounds with the fluorite structure can be formed by a given metal (see
Cubic unit cells for the CaF2 structure. In the cube vertices are placed anions in (b).
Regular tetrahedron defined by the NNs of the F− anion in CaF 2. the Ca2+ cation in CaF2.
therefore each s, what is shown in Fig. 105b. VII compounds crystallize in the fluorite he top of Table 23. Among other examples of compounds that crystallize in this structure, we can mention hydrides, silicides, oxides, and fluorides of some TMs (mainly RE metals and ) and polonium The experimental lattice constants, obtained under normal conditions for the compounds specified above, are listed in Table 23. This table allows to identify quickly which metals form compounds within a given group of hydrides, silicides, oxides, fluorides, or chlorides (see columns of the table) and also allows to see how many ure can be formed by a given metal (see structure. In the cube vertices are placed Ca2+
When the ionic positions are reversed, and the anions and cations occupy the Ca2+ and F− positions, respectively, we obtain the anti-fluorite structure, which will be considered below.
Table 23 Lattice parameters (in Angstroms) obtained under normal conditions for II-VII
compounds and hydrides, silicides, oxides, and fluorides of some TMs, all of them crystallizing in the fluorite structure. In addition, the data for β-PbF2 and α-PoO2 are included. H Si O F Cl Ca CaF2 (5.46295) Sr SrF2 (5.7996) SrCl2 (6.9767) Ba BaF2 (6.1964) Ra RaF2 (6.368) Sc ScH2 (4.78315) Co CoSi2 (5.365) Ni NiSi2 (5.406) Y YH2 (5.207) Zr ZrO2 (5.09) Nb NbH2 (4.566) Cd CdF2 (5.393) Pt PtH2 (5.517) Hg HgF2 (5.5373) Ce CeH2 (5.581) CeO2 (5.413) Pr PrH2 (5.516) PrO2 (5.392) Nd NdH2 (5.4678) Sm SmH2 (5.3773) Eu EuF2 (5.796) Gd GdH2 (5.303) Tb TbH2 (5.246) TbO2 (5.213) Dy DyH2 (5.2049) Ho HoH2 (5.165) Er ErH2 (5.1279) Tm TmH2 (5.0915) Lu LuH2 (5.0330) Th ThO2 (5.5997) Pa PaO2 (5.505) U UO2 (5.470) Np NpO2 (5.4341) Pu PuO2 (5.39819) Am AmO2 (5.3746) Cm CmO2 (5.368) Pb β-PbF2 (5.9463) Po α-PoO2 (5.637)
4.2. Anti-Fluorite Structure Pearson symbol:
the anions are in a fcc
interstices present in the anion
cations have a coordination number 4. Fig for the anti-fluorite structure with the cations in that figure that the 8
cube that represents one eight of the cubic unit cell. an anion are shown in Figs. 107a and 107b, respectively.
In the anti-fluorite structure crystallize some alkali metals with elements from column VI of the periodic table
selenides, and tellurides. They all are listed in Table 2 some II-III and II
crystallize in the anti
Figure 106 Cubic unit cells of Li
cube vertices are placed O
Figure 107 (a) Regular tetrahedron defined by the
defined by the NNs of the
luorite Structure
Pearson symbol: cF12, prototype: Li2O.In the anti-fluorite structure,
fcc arrangement and the cations occupy all the tetrahedral interstices present in the anion substructure. This is shown in Fig. 106a. The cations have a coordination number 4. Figure 106b shows the cubic unit cell fluorite structure with the cations at the vertices. We can observe in that figure that the 8 NNs of an anion are placed at the vertices of a small cube that represents one eight of the cubic unit cell. The NNs of a cation and an anion are shown in Figs. 107a and 107b, respectively.
fluorite structure crystallize some alkali metals with elements from column VI of the periodic table, forming metal oxides, sulfides, selenides, and tellurides. They all are listed in Table 24. In Table 25
III and II-IV compounds, and also phosphides of TM crystallize in the anti-fluorite structure.
Cubic unit cells of Li2O which crystallizes in the anti-fluorite structure. In the cube vertices are placed O2− anions in (a) and Li+ cations in (b).
Regular tetrahedron defined by the NNs of the Li+ cation in Li 2O. the O2− anion in Li2O.
fluorite structure, arrangement and the cations occupy all the tetrahedral . This is shown in Fig. 106a. The 106b shows the cubic unit cell the vertices. We can observe the vertices of a small of a cation and fluorite structure crystallize some alkali metals with elements forming metal oxides, sulfides, 5 we list TMs that
fluorite structure. In the