Fluorite structure type example compounds

Transition metal difluorides are known mainly for first transition series elements, with palladium and silver difluorides from the second series, and no examples from the third. All these compounds have either the rutile structure, or, for chromium, copper, and silver, a distorted variant, which can be correlated with a Jahn-Teller distortion of the octahedral coordination of the ions. This rutile structure type is associated with smaller cations and, for comparison, although zinc difluoride has the same rutile structure, cadmium and mercury difluorides have the cubic fluorite structure with eight coordination of the cations (12). 

A majority of the important oxide ceramics fall into a few particular structure types. One omission from this review is the structure of silicates, which can be found in many ceramics [1, 26] or mineralogy [19, 20] texts. Silicate structures are composed of silicon-oxygen tetrahedral that form a variety of chain and network type structures depending on whether the tetrahedra share comers, edges, or faces. For most nonsilicate ceramics, the crystal structures are variations of either the face-centered cubic (FCC) lattice or a hexagonal close-packed (HCP) lattice with different cation and anion occupancies of the available sites [25]. Common structure names, examples of compounds with those structures, site occupancies, and coordination numbers are summarized in Tables 9 and 10 for FCC and HCP-based structures [13,25], The FCC-based structures are rock salt, fluorite, anti-fluorite, perovskite, and spinel. The HCP-based structures are wurtzite, rutile, and corundum. 

A study of a number of other compounds which are generally considered to be among the most completely ionic shows that cubic coordination is not confined to the alkali halides. It occurs, for example, in the fluorite structure in which many ionic MXa compounds crystallize. On the other hand the isolated [Tab s]3 group has the square antiprism arrangement (64) predicted by the simple theory. This underlines a point of great importance to the understanding of ionic crystal structures, namely, that the requirement that a structure can be extended indefinitely in space imposes severe restrictions on the types of coordination which are possible. Cubic coordination can be extended indefinitely, but it is not possible to form an extended... 

In the Y O iF + 2 system, compounds n = 4,5,6,7,8 have been confirmed, the structures of which can be understood in terms of the vernier structure, similar to structure model (II) (Fig. 2.36). Closely related compounds have also been observed in the Nb-Zr-O and Zr-N-F systems. Figure 2.37 shows the structure of ZriogNggFijg drawn in the same way as YjOgFg in Fig. 2.35. This structure is also an example of a vernier structure based on a Fluorite-type structure. A vernier structure with layer type [a] (as in Fig. 2.32) has been critically and systematically reviewed by Makovicky and Hyde. °... 

In addition to the binary nitrides described here, some ternary nitrides have been prepared, for example, Li5TiN3, Li7NbN4, and Li9CrNs, all with the fluorite type of structure (superstructures in most cases), and alkaline-earth compounds with Re, Os, Mo, or W(e.g. Sr9Re3Nio, CasMoNs). ... 

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