Nickel arsenide structure example compounds

A closely analogous state of affairs is seen in the systems NiTe2-NiTe and TiTe2-TiTe, in which the AB2 compound has the cadmium iodide structure and the AB compound that of nickel arsenide. In both of these structures the B atoms are arranged as in hexagonal close-packing, but in other respects the relationship between them is precisely the same as that between the cadmium chloride and sodium chloride structures, so that solid solution can take place by the same mechanism. Examples such as this, and many others which could be quoted, emphasize that solid solution is in no sense a satisfactory criterion for isomorphism, and that substances may form solid solution even if their structures are formally quite different. 

The nickel arsenide (NiAs) structure (Figure 2.20) is an important hep example in this case, the cations form the backbone lattice, and the larger anions occupy both octahedral sites. This structure, also associated with metal chalocogenides such as CoSe, NiTe, CoxNii xAs, FeS, NiSe, PtSbxBii x, and PdxNii xSb are only adopted for weakly ionic compounds. Since the octahedral sites are extremely close to one another, purely ionic compounds would be much too unstable due to strong anion-anion repulsions. 

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