CaF2 structure

The CaF2 structure can be regarded as a network of three-dimensionally linked, edgesharing FCa4 tetrahedra (cf. Fig. 17.3 b). 

Figure 9 Crystal structure of the oxide sulfate Na60(S04)2 The [ONa6] octahedra and SO f tetrahedra are arranged like Ca2+ and F ions in the CaF2 structure type.

Figure 7.8. Projections on the (001) and (110) planes ofthe cP4-AuCu3, cF12-CaF2 structures and the hexagonal (c/a = 0.80) hP6-CaCu5 structure.

The most studied non-stoichiometric system in actinide CaF2-structured compounds is the An-0 system all actinide dioxides (with the exception of Th02) present large departures from stoichiometry. Since uranium and plutonium dioxides (and their solid solutions) are employed as fuels in nuclear reactors, a very large effort has been dedicated to the study of their physical and physico-chemical properties. All these properties are affected by the oxygen composition of the compound. 

Fluorite (CaF2) structure (Fig. 4-14)- Comparison of the fluorite structure (Fig. 4.14) with Fig. 4.12 shows that fluorite can be described as an fee array of Ca2+ with F ions in all the tetrahedral holes (forming a simple cubic sublattice of fluorides). In this case, the Ca2+ and F sites are not interchangeable. This is to be expected, since we have twice as many F as Ca2+ as noted earlier, there are indeed twice as many T-holes as lattice atoms. The coordination numbers of Ca2+ and F are eight and four, respectively. Other solids with this structure include the nuclear fuel UO2. 

Compounds with the Li20 structure are shown in Table 6.3. Those with the CaF2 structure are shown in Table 6.4. 

CaF2 structure, and while Mg2Si is almost an insulator, Mg2Pb is a good metallic conductor. 

F. d Heurle, S. Petersson, L. Stolt, B. Stritzker. Diffusion in intermetallic compounds with CaF2 structure A marker study of the formation of NiSi2 thin films // J.Appl.Phys - 1982.- V.53, No.8.- P.5678-5681. 

In the fluorite (CaF2) structure both sets of tetrahedral positions are occupied and the octahedral sites are empty. 

KLaF and K2UFg have the CaF2 structure (p. 150) with random arrangement of metal ions in the positions. BaUFg and BaThFg have the random lanthanum fluoride lattice (LaFg has the ReOg structure see p. 485). 

E3J7 We are removing only every second Cs cation from the CsCl structure. This means that while coordination around Cf drops for one-half (from eight to four), the coordination around Cs remains the same (eight). This corresponds to the CaF2 structure (each F" is surrounded by four Ca, whereas each Ca has eight closest F" neighbours). 

Figure 7.13 The fluorite (CaF2) structure as an array of edge-shared CsFg cubes...

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