Spinel superstructures

The other ternary oxides also occur as spinel superstructures such as CaFe204 (ferrite) or potassium iron oxides which contain the spinel structure as a building block. These complex structures of the beta alumina type consist of the formal composition (K2O x 11 Fc203) and can be described as a layer structure with unit cells of spinel linked by layers of potassium ions octahedrally coordinated to the (4 -h 4) oxygen ions of two adjacent spinel units. 

The 6 modification has also frequently been used in adsorption studies. The 5 phase may be regarded as a superstructure of three Al203-spinel cells containing an integer number of aluminum ions (111). 

Indium Sulfide. The indium sulfide (In2S3) possesses a high temperature modification which has a defect spinel structure, and a low temperature modification which is a superstructure of the spinel structure (16, 18, 19, 21). Several MIn2S4 compounds have the spinel structure (17) and we observed the existence... 

In the synthesis of y-Fe203, careful oxidation of magnetite in a spinel lattice to a superstructure of crystallizing ferrimagnetic y-Fe203 (maghemite) under well-defined conditions is necessary ... 

The 5 and 6 phases formed at intermediate temperatures are both highly crystalline phases, the former with a superstructure of the spinel type and the latter with the 3-Ga203 structure mentioned in the section on Oxides M2O3 . 

Cation vacancies and interstitials, (111) twins and stacking faults, grain boundaries, microstrains, misfit dislocation network at C03O4/C0O interface Dislocations and (100) stacking faults intergrowth of e and P phases. Cations vacancies and superstructure (110) stacking faults and twins Clusters of point defects (110) twins surface steps, dislocations, spinel microinclusions, planar defects stabilized by impurities. 

Current issues on refractory monolithics include no-cement castables, self-flow and free-flow mixes [64], and special compositions such as spinel-based [65], placement techniques [66], new applications (i.e., crown superstructures for glass melters [67]), characterization [68, 69], and basic castables [70, 71]. Specialized publications have compiled and reproduced most of the most important topics [i.e, 72-74], which include the following ... 

Among the wide variety of the phases formed by the thermal decomposition of aluminum hydroxides we shall consider only alumina forms which derive from pseudoboehmite, boehmite and bayerite. Information about these structures is rather poor. With the exception of the spinel form (t -, y-), the species are mainly characterized by the dimensions of the unit cell and by some indications on their crystallographic system [20]. The structure of y-AbOs was considered as a tetragonal distorted spinel lattice (a superstructure with one unit cell parameter tripled in the case of 8-AI2O3) and is depicted by the formula A18/3 [ ] 1/3 O4, where [ ] is a cation vacancy. This formula is consistant with the constraints of stoichiometry and electrical neutrality. It is difficult to know the exact distribution of the cations in the octahedral or tetrahedral sites despite an abundance of work on this subject [21-23]. The 0-phase, isomorphous with... 

Fig. 163. (Cr2Sj),-j(In2S3)j. (a) Lattice constant vs. composition for samples quenched from 1000 °C. Arrows indicate the occurrence of the superstructure reflections 2 1 ordering of A (double arrow) or 1 1 ordering (single arrow) (A = tetrahedral sites), (b) Lattice constant of spinel phases in samples quenched from temperature Tq for several compositions. Arrows indicate the occurrence of the superstructure reflections (200) and (420) [71 Lot 3].

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