Crystal chemistry of spinels

The examples of minerals affected by Jahn-Teller distortions that are listed in table 6.1 demonstrate that the concept of ionic radius is not a rigorous atomic property when applied to crystal structures containing the Cr2+, Mn3+ and Cu2+ ions. Other consequences of Jahn-Teller distortions in mineral structures are discussed in 6.8.3.2 and elsewhere (Strens, 1966a Walsh et al., 1974). 

N = normal spinel I = inverse spinel 0 = no prediction - = no data = tetragonally distorted. 

Sources of data [1] Dunn, McClure Pearson (1965), p. 86 [2] Hill, Craig Gibbs (1979) [3] Lenglet, Guillamet, D Huysser, Durr J0rgensen (1986) [4] Navrotsky Kleppa (1967). 

One of the unusual features of spinel crystal chemistry is that some transition metals form normal spinels and others inverse. The spinel-types are summarized in table 6.2. The site occupancy patterns were considered to be anomalous until they were explained by crystal field theory (McClure, 1957 Dunitz andOrgel, 1957). 

Measurements of absorption spectra of oxides, glasses and hydrates of transition metal ions have enabled crystal field stabilization energies (CFSE s) in tetrahedral and octahedral coordinations to be estimated in oxide structures (see table 2.5). The difference between the octahedral and tetrahedral CFSE is called the octahedral site preference energy (OSPE), and values are summarized in table 6.3. The OSPE s may be regarded as a measure of the affinity of a transition metal ion for an octahedral coordination site in an oxide structure such as spinel. Trivalent cations with high OSPE s are predicted to occupy octahedral sites in spinels and to form normal spinels. Thus, Cr3, Mn3, V3+ 

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Crystal chemistry of spinels. A classic example showing that transition metal ions display distinct site preferences in oxides stems from studies of spinel crystal chemistry. The spinel structure contains tetrahedral and octahedral sites normal and inverse forms exist in which divalent and trivalent ions, respectively, fill the tetrahedral sites. The type of spinel formed by a cation is related to its octahedral site preference energy (OSPE), or difference between crystal field stabilization energies in octahedral and tetrahedral coordinations in an oxide structure. Trivalent and divalent cations with large site preference energies (e.g., Cr3 and Ni2+) tend to form normal and inverse spinels, respectively. The type of spinel adopted by cations with zero CFSE (e.g., Fe3+ and Mn2+) is controlled by the preferences of the second cation in the structure. 

See also Iron entries hydration, 5 477-478 in Portland cement, 5 467 in Portland cement clinker, 5 473t classification of, 11 55-58 crystal chemistry of, 11 59-71 defined, 11 55 energy losses in, 11 64-66 physical properties of, 11 59-71 processing of, 11 71-75 properties of spinel and M-type,... 

Figure 48 The structure of fi-alumina shown as a packing of spinel layers. The alkali metal ions, which are not shown, are to be found in the empty positions between the spinel sheets (Reproduced by permission from Crystallography and Crystal Chemistry of Materials with Layered Structures , ed. F. Levy, Reidel, Dordrecht, Holland, 1976, p. 127)...

Harrison RJ, Putnis A (1999a) The magnetic properties and crystal chemistry of oxide spinel solid solutions. Surveys Geophys 19 461-520... 

Watanabe, A., Yamamura, H., Moriyoshi, Y. Shirasaki, S. (1982). Crystal chemistry of the spinel-type ferrite series LijM FCgOn (M = Ti, Sn ", Ge, Si ). In Ferrites Proceedings of the Third International Conference. Eds. H. Watanabe, S. lida and M. Sugimoto. Center for Academic Publications, Tokyo, pp. 170-3. 

S. Lucchesi and A. Della Giusta. Crystal chemistry of highly disordered Mg-Al natural spinel. Mineralogy and petrology, 59 91-99, 1997. 

Carbonin, S., F. Martignano, G. Menegazzo and A. dal Negro (2002). X-Ray Single-Crystal Study of Spinels In Situ Heating . Physics and Chemistry of Minerals 29 503-514. 

The octahedral site preference energy parameter listed in table 6.3, applied originally to spinel crystal chemistry, has had a profound influence in transition metal geochemistry following its introduction into earth science literature in 1964 (Bums and Fyfe, 1964 Curtis, 1964). The use of such site preference energies to explain distribution coefficients of transition metal ions in coexisting minerals and phenocryst/melt systems are described in 7.6, 7.8 and 8.5.3. 

Beale AM, Sankar G. Understanding the crystallization of nanosized cobalt aluminate spinel from ion-exchanged zeolites using combined in situ QEXAFS/XRD. Chemistry of Materials. 2005 18(2) 263-272. 

Figure 63 Crystal structures of the spinel structure materials, X-Mn02, LiMn204, and Li2Mu204, in a polyhedral representation. The light colored polyhedra are the Li ions and the dark polyhedra the Mn ions. (Ref. 110. Reproduced by permission of Royal Society of Chemistry)...

Blasse G (1964) Crystal chemistry and some magnetic properties of mixed metal oxides with spinel stracture. Philips Res Rep Supp 3 1-139... 

The chemistry of the alumina precursor used for fiber spinning varies with synthesis technique. This chemistry is maintained throughout the pyrolysis process and affects the nature of the crystals formed at higher temperatures. For instance, the presence of the AI13 complex leads to highly ordered spinel structures, whereas the presence of 5-coordinated Al species in solution produces poorly ordered crystals (Wood et al., 1990). 

Fig. 10 Decomposition of N2O by bulk and mesoporous NiMn20x samples as a function of reaction temperature show an enhanced behaviour when the mesostructured materials are employed. Not only this, but the crystal structure of the resulting materials can lead to increases in behaviour, with the haematite phase showing higher conversion rates than the spinel phase. 2011 Royal Society of Chemistry.

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