Ternary metal oxides with spinel

Ternary Metal Oxides with Spinel Structure... 

One of the difficulties with the classical solid-state reaction is that mechanical mixing methods are relatively ineffective in bringing the solid reactants in contact with one another. Diffusion lengths, on an atomic scale, are still enormous and the temperatures required may preclude the formation of phases that might be stable at intermediate temperatures. One method, called a precursor method, involves the formation of a mixed-metal salt of a volatile organic oxyanion such as oxalate by wet chemical methods, which result in mixing essentially on the atomic level. The salt is then ignited at relatively low temperatures to form the mixed-metal oxide. The method has been applied successffilly to the preparation of a number of ternary transition metal oxides with the spinel structure. ... 

Recall that we can take vertical slices of the ternary phase diagrams, as well as isothermal (horizontal) slices. If we take, for example, a slice that begins at the tenarite composition (CuO) and extends across to the hematite composition (Fc203), we would end up with a pseudobinary phase diagram, which, when plotted on the appropriate temperature-composition axes, would look like Figure 2.22. Note that the compound CuFc204 is present, here labeled as spinel (see Section 1.2.2.3), but there is much more phase and temperature information available to us. This is, in fact, how many metal oxide phase diagrams are presented. The most stable forms of the... 

Surprisingly many spinel-type chalcogenides form with copper as an A element. In a ternary representative Cu should be divalent in order to satisfy the valence rules. The spinel structure, however, shows no Jahn-Teller distortions contrary to the oxides. Assuming the cation-anion bonds to be saturated, the metallic properties must be due either to a metallic de band of Cu2+ or to the simultaneous presence of T4+ and T3+. 

Some ternary and mixed-valency oxides have the spinel structure where metal ions occupy a proportion of tetrahedral and octahedral holes in a cubic close-packed lattice. Examples include M304 with M=Mn,... 

Some ternary and mixed-valency oxides have the spinel structure where metal ions occupy a proportion of tetrahedral and octahedral holes in a cubic close-packed lattice (see Topic G5). Examples include M304 with M=Mn, Fe, Co. The distribution of M2+ and M3+ ions between the tetrahedral and octahedral sites shows the influence of ligand field stabilization energies (see Topic H2). In Fe304, Fe2+ (3d6) has an octahedral preference whereas Fe3+ (3d5) has none, and this... 

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