Highly defective spinel structure

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... 

The chemistry of alumina is more complex. There are several modifications of the defect spinel structure adopted. Al iminium ions reside in both octahedral and tetrahedral sites, and these are in different relationships in these various phases [1,3,7]. This provides a substantial range of potential surface sites, and indeed five hydroxyl types have been classified according to their 0-H stretching frequencies. Some hydroxyl content is present after treatment at temperatures below 1200 C, and the strength and quantity of their acidity is highly dependent upon the pretreatment temperature. Surface oxide or hydroxyl groups can act as electron transfer reagents to an acceptor such as TONE [8]. However, the reactivity of dehydrated aluminas is not primarily due to Br nsted acidity, but to the Lewis acid sites at exposed aluminium ions. 

Complex lithium halide spinels (Kanno, Takeda and Yamamoto, 1982 Lutz, Schmidt and Haeuseler, 1981), based on Li2CdCl4 and Li2MgCl4 have remarkably high Li ion conductivity for close packed structures. Fig. 2.11. These are complicated materials however, they have essentially inverse spinel structures but may exist also in various distorted forms. Some of them undergo a phase transition to defect rock salt structures at high temperatures some are non-stoichiometric. 

When or-Fe203 was used as the positive electrode in high-temperature lithium cells, the introduction of a small amount of lithium into the corundum-type structure caused the hexagonal-close-packed oxygen array to shear irreversibly to cubic-close packing which generated a defect /-Li FCjOj (spinel-type) structure. Further lithiation resulted in the formation of LiFe,Ojj thereafter, the reaction followed the same sequence as that shown in reactions (4), (5) and (6) [100]. The stability of the spinel structures at elevated temperatures, as well as the ability of the cubic close-packed oxygen array to accommodate lithium at the expense of... 

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