Interspace of tetrahedron

Model of defect structure of wiistite. The defect structures of wiistite were well studied by many researchers and it is commonly considered that the basic unit of that is as shown in Fig. 3.6, and the defect cluster structure of that is as shown in Fig. 3.7. It will be seen from Fig. 3.7(a) that one of Fe + cation located in the interspace of tetrahedron is surrounded by four Fe + located in interstitial of octahedron. This structure is called as 4 1 defect clusters, 4 indicates the defect amount of cations and 1 indicates the interstitial amount of tetrahedron. The defect unit possesses five units with negative charges. It was proved for the existence of the mentioned defect structures by theoretical calculation in the works of Catlow, Grimes and Press. 

Nevertheless, in the structure of wiistite, for the reason of Fe + cations being defective, there still exist given amount of Fe + cations besides Fe + cations in order to preserve electric charge neutrality. These Fe + cations enter generally into the original empty interspace of tetrahedron. At the same time, if one of the vacancies of Fe + is formed in the lattice, then in order to maintain the electric charge neutrality, there must be two of Fe + transferring to be two of Fe +, one of which will enter into the tetrahedron interspace and leave behind an empty space in the octahedral interspace, while the another Fe + stays in octahedral interspace. For example, when X = 0.10 in Fei xO, then the structural formula can be written as ... 

In the crystal cell, there are 32 oxygen atoms located in the 43m, half of Fe + in the interspace of tetrahedron with 8a43m and the other half Fe + and 8 of Fe + in the interspace of octahedron with 16d3m. Software of Rietveld analysis is Rietica. In determining the parameters of oxygen, electron-cloud density determination is used after taking off the contribution of metal atoms on scattering. 

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. 

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