Other Spinel Oxides

X-ray photoelectron spectroscopic (XPS) analysis has shown that the surface modification indeed suppresses the formation of thick SEI layers and thereby improves the rate capability [89]. 

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The diverse structural, electronic and magnetic properties of Fe304 have attracted interest to other spinel oxides. LiMn204 is a geometrically frustrated compound with a spinel structure. The magnetisation and... 

Titanium IV) oxide, T1O2. See titanium dioxide. Dissolves in concentrated alkali hydroxides to give titanates. Mixed metal oxides, many of commercial importance, are formed by TiOj. CaTiOj is perovskite. BaTiOa, per-ovskite related structure, is piezoelectric and is used in transducers in ultrasonic apparatus and gramophone pickups and also as a polishing compound. Other mixed oxides have the il-menite structure (e.g. FeTiOj) and the spinel structure (e.g. MgjTiO ). 

The structures of ternary oxides such as spinels, perovskites, pyrochlores, layered cuprates (high-7 c superconductors), and other lamellar oxides are fascinating subjects by themselves and are beyond the scope of the present discussion. 

Also, other metal oxide coatings are possible, for example, electrochemically deposited manganese dioxide. Moreover, further electrocatalytically active oxides are research objectives, for example, oxides with spinel structure such as CoMu204 [36]. 

Although the thermal decomposition of Zn-Cr-C03-LDHs has, therefore, been studied in detail, a specific characterisation of the actual spinel oxides obtained from the LDHs, separated from the mixed oxide phase, has not been reported either for Zn-Cr-LDHs or for other cation combinations. Although the structure of the spinel oxides formed from LDHs has been reported occasionally, the effect of separating the spinel phases from the whole thermal decomposition product in the properties of the spinel oxide has not been evaluated. Here we report on the properties of the spinel oxides produced by the thermal decomposition of a Zn-Cr-C03-LDH. For comparison, spinel oxides phases were synthesised by the two other methods described above, and treated in a similar way to those obtained by LDH decomposition. 

Materials obtained from the LDH show a reduction in SSA with the temperature as reported in the literature. This reduction can be attributed to the crystallisation of the material [15,17]. However, post-treatment with mineral acid was an increase in the SSA for all temperatures. It is possible to attribute this increase to two combined effects, which can both increase the porosity of the materials, as well as yield more active adsorption sites (i) the elimination of ZnO and (ii) the elimination Zn(II) cations occupying octahedral sites in the spinel oxide structure. Even though the SSA had varied sensibly, the average pore size (APS) remained fairly constant with temperature. Acid treatment increases the APS value for all temperature tested, although the effect was very small (Figure 5b). Comparison of the materials obtained by the different synthesis methods showed that spinel oxides obtained from the LDH presented greater SSA values than those obtained by other methods, principally after the posttreatment with mineral acid. On other hand, the treatment with acid had little influence on the textural properties of the spinel oxides obtained by the other methods. 

Most spinels contain small quantities of other metal oxides as modifiers to alter hue without affecting crystal structure. To illustrate this point, the most common form of pigment green 26 also contains zinc the most common form of pigment green 50 also contains nickel and zinc and the most common form of pigment black 30 also contains manganese. 

Numerous important mixed oxide phases are formed by the combination of aluminum oxide and one or more other metal oxides. The foremost of these from an industrial viewpoint are spinels, jS-aluminas, and tricalcium aluminate, an important constituent of Portland cement. 

There are a few catalytic applications in which other mixed oxide structures are cited. Among them are pyrochlore compounds such as La2Zr207, spinels such as AB2O4, and lanthanum beta aluminates, all of them with well-defined crystalline structures. There are also a few examples of oxide solid solutions made up of a rare-earth oxide and a transition-metal oxide. 

The following subdivisions will be considered (i) binary oxides (ii) spinel oxides (iii) other ternary oxides (iv) iron(IV) oxides (v) chalcogenides (vi) silicate minerals and (vii) lunar samples. 

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