Non-stoichiometric composition

Assigning oxidation states of —2 to oxygen, + 3 to yttrium and + 2 to barium, one would obtain an oxidation state 7/3 for copper when jc = 0. The non-integer oxidation state of copper is interpreted as if 2/3 of the ions are present as Cu2+ and 1/3 as Cu3 +. This mixed-valent composition seems to be determinant for the occurrence of superconductivity. In fact, as noted in Table 1, all the superconducting ceramic oxides contain Cu in a non-stoichiometric composition. 

The typical liquid clathrate is characterized by (a) a low viscosity relative to that of a neat ionic liquid, (b) immiscibility with excess aromatic solvents, and (c) non-stoichiometric compositions. The formation of air- and water-stable liquid clath-rates has been reported for the compositions consisting of aromatic hydrocarbons (e.g., benzene, toluene, and xylenes) and common salts of [AMIM] cation with the anions PF, [Tf2N] , BFJ, and Cl 91). 

A sulfuric acid solution of the oxide (25-75% solution) can be reduced with tin, copper, zinc, and other reducing agents forming a blue solution of molybdenum blue which are hydrous oxides of non-stoichiometric compositions (see Molybdenum Blue). Reduction with atomic hydrogen under carefully controlled conditions yields colloidal dispersion of compounds that have probable compositions Mo204(OH)2 and Mo40io(OH)2. Reduction with lithium aluminum hydride yields a red compound of probable composition MosOtIOEOs. Molybdenum(Vl) oxide suspension in water also can be reduced to molybdenum blue by hydriodic acid, hydrazine, sulfur dioxide, and other reductants. 

In general, an increase in conversion increases Tg and series prepared with non-stoichiometric compositions, the minimum value of fracture energy is obtained when the stoichiometric ratio of both functionalities is used (Morgan et al., 1984 Won et al., 1990), as expected (maximum values of both Tg and [Pg.385]

Polymeric compounds with limited Si-Si units in which the polymeric character is due to other bond systems, have been described. Another series of polymeric compounds exists, in which the Si-Si bonds themselves are responsible for the polymeric state. The extreme case, when all four valencies of a silicon atom are bonded with Si atoms, produces metallic silicon with a diamond structure. Compounds of the type (SiX2) or (SiX) result when some valencies of each silicon atom are occupied by other atoms or groups. Only polymeric compounds (SiXj,) withy from 2 to 1 exist SiX3 yields disilanes, and compounds withy between 3 and 2 yield limited chains. The possible stoichiometric compositions SiX2 and SiX are sometimes found, but a non-stoichio-metric composition is more common, which is understandable in view of the irregular framework of the Si-Si structure. The formation of regular or irregular Si-Si structures of stoichiometric or non-stoichiometric composition will depend on the procedures used in preparation. 

Under the above conditions, the use of the non-stoichiometric composition peculiar to sulfides and the use of a monosulfide which can form lower sulfides by the thermal decomposition were considered. 

These results in Figure 2 were obtained with iron sulfide used as an example of a non-stoichiometric composition and were obtained repeatedly in both cycles. 

In order to understand the characteristics of chalcopyrite, which has a wide range of non-stoichiometric compositions similar to iron sulfide and is a double sulfide, an exeriment with a copper concentrate was carried out. 

Based on the identification by X-ray diffraction and observation by micrography, the variation was found to be within the non-stoichiometric composition of chalcopyrite in the normal pressure cycle. Despite the decomposition into bornite(Cu FeS ) and pyrrhotite during the reduced pressure cycle, the chalcopyrite was found to be completely restored to its original chalcopyrite form by the succeeding sulfurization. 

The alkali-metal X and Y zeolites react with alkali metal vapour to form coloured products of non-stoichiometric compositions containing the paramagnetic centres Na + and Na . The Na + centres are stable up to 500°C and they react reversibly with gases with oxygen they form Oj radicals. 

Basic chromium(lll) salts with non-stoichiometric compositions are used in tanning, particularly oligomers of basic chromium(III) sulfate with the approximate composition Cr(OH)S04. Basic chromium sulfates are marketed as liquids or as a spray-dried powder. 

This study attempts to identify the experimental parameters required to achieve the full-colored emission under accelerated electrons (cathode ray tube) and ultraviolet light excitations for ZnGa204 phosphor with graded and non-stoichiometric composition. 

Bismuth nitrate pentahydrate (Bi(N03)3-5H20) is found as lustrous hygroscopic crystals and smells like nitric acid. It is readily decomposed by water to subnitrate BiO(N03), but dissolves without decomposition in water containing nitric acid. It is soluble in organic solvents such as acetone, acetic acid and glycerol, but practically insoluble in ethanol and ethyl acetate. By heating above 590°C, it is converted to bismuth oxide. Bismuth subnitrate is a white, odorless and tasteless powder of non-stoichiometric composition its properties and composition vary considerably depending on... 

Another similarity between Monterey and Stevens dolomites is their excess Ca, typical of Tertiary dolomite compositions. Apparently these non-stoichiometric compositions are retained in San Joaquin dolomites at temperatures at least as high as 100°C (their present burial condition). Stevens dolomites are generally much richer in Fe than Monterey dolomites, possibly owing to the alteration of Fe-bearing minerals in the Stevens sandstones. 

Of course, the "ideal three-phase model begins to break down for good chemical reasons for very thin compound films such as Si02, which are formed from the substrate, as there is, by definition, always an interphasial region of non-stoichiometric composition. Nevertheless, progress has been... 

There are some cases where a non- stoichiometric composition will be obtained even though the compound is congruently- melting. An example of such a phase - system is shown in 4.2.47., given on the next page. 

Although hydrogen can react with transition metals to form compounds such as UH3 and FeHg, most of the interstitial hydrides have variable compositions (often called non-stoichiometric compositions) with formulas such as LaH2 76 and VHose- The compositions of the nonstoichiometric hydrides vary with the length of exposure of the metal to hydrogen gas. 

In this case, the composition of the solid phase is represented by AB (non-stoichiometric composition), and the system is determined by fixing both temperature T and composition x. The vapor pressure of each component Pi is a function of T and x. 

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