Tetrahedral interspace

But this structure is unstable and usually accompanied with the defects of metal ions. As a consequence, there would be certain amounts of Fe + cations to maintain the charge-neutrality. These Fe + cations often enter into the original unoccupied tetrahedral interspaces. For example, when the defect concentration of metal ions is X, the wiistite could be expressed as Fei j 0, where x < 1. And if x = 0.1, according to the principle of charge-neutrality, then ... 

There are two types of interspace present amongst the cube Octahedral interspace (B site) and tetrahedral interspace (A site), as shown in Fig. 3.62. The 32 of oxygen ions constitute the interspace of both 64 tetrahedrons and 32 octahedrons. In a crystal of Fe304, eight Fe + and eight Fe + ions occupy the octahedral interspace, while the another eight Fe + ions occupy the tetrahedral interspace, namely, Fe3+ (Fe2+ Fe3+) O4. 

As previously described, FeO is an oxygen excessive (Fe defect) non-stoichiometric iron oxide (Fei xO), which shows the rock-salt type face center cubic structure (fee). The unit cell of Fei xO are constituted from four Fei xO molecules, where there are eight tetrahedral interspaces A site) and four octahedral interspaces B sites) with 0 closely packing onto NaCl-type cubic lattices. 

The prism caps of Pb coordination prisms are fairly well commensurable with the dimensions of square pyramids of As, Sb and Bi, the latter (or the groups BSg) are in turn commensurable with the coordination octahedra around Pb, Mn, In, Fe, Ag, (Hg), etc., or with tetrahedral and trigonal coordinations of primarily Ag and Cu. The latter may fill interspaces in the above arrays or form polyhedral arrangements of their own, with only subdued amounts of prismatic, pyramidal or octahedral cations present. 

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