Stoichiometric solids

The various types of point defect found in pure or almost pure stoichiometric solids are summarized in Figure 1.17. It is not easy to imagine the three-dimensional consequences of the presence of any of these defects from two-dimensional diagrams, but it is important to remember that the real structure of the crystal surrounding a defect can be important. If it is at all possible, try to consult or build crystal models. This will reveal that it is easier to create vacancies at some atom sites than others, and that it is easier to introduce interstitials into the more open parts of the structure. 

The antibacterial sulfonamide phthalazole 268 is obtained free of imide and bisamide side products (that occur upon reaction in solution or in the melt) if stoichiometric solid-state milling of the reactants 266 and 267 is performed for the acylation [95] (Scheme 38). Numerous solid arylamines and heterocyclic amines react correspondingly with phthalic anhydride upon stoichiometric milling and provide 100% yield without any workup requirement [22]. 

Elemental composition, A1 10.11% and Br 89.89% A1 analyzed by AA spectrophotometry or colorimetric methods Br analyzed by iodometric titration or ion chromatography and then calculated stoichiometrically solid may be dissolved in an organic solvent and determined by GC/MS, identified by mass ions (AlBr3 )n where n is 2, 4 and 6. 

The thermodynamic functions of non-stoichiometric solids at very high deviations from stoichiometry are strongly affected by defect clusters and molecularities. The detailed theoretical description of the interactions between defects and the lattice as well... 

Note that aZn(s) = 1 since zinc is a pure substance. A more complex relationship is required if one component is a non-stoichiometric solid which can exist over a range of compositions. E % is known as the standard electrode potential of zinc. 

The existence of a stoichiometric solid silver hydride remains doubtful, but evidence has been obtained for a gaseous silver hydride (AgH).383,384 Silver hydride species have been postulated in the reaction mechanism of oxidations involving gaseous hydrogen with silver salts present as catalysts.385... 

The influence of steric factors was thoroughly studied in the reaction of Ln(btsa)3 with the alcohol tritox-H. While the reaction takes place with larger lanthanides like neodymium to yield the homoleptic alkoxide complexes (Eq. 18) [264], the analogous reaction does not work with smaller metals like yttrium and thulium (Eq. 19). However, variation of the reaction conditions to a stoichiometric solid reaction yielded a fully exchanged product along with an unexpected and unusual silylamine degradation [265] (Eq. 20). This degradation reaction seems to be sterically forced and points out N-Si bond disruptions and C-Si bond formations under mild conditions [114]. 

It was a long-standing puzzle in the 1930s that intense color was seen in crystals and solutions of weak stoichiometric (1 1) complexes (benzene (1) with iodine (I2), or naphthalene (2) with trinitrobenzene (TNB, 7)) and other similar systems. This intense color formed when the components are mixed in solution, and cocrystallized as stoichiometric solid-state complexes. These solutions and crystals showed, almost unchanged, the full optical absorption spectrum of the neutral components, plus an extra broad, intense absorption band with little or no vibrational structure one seemed to get something (color) for nothing (no change in other properties). 

The major products from most metal oxalate decompositions can be predicted from thermodynamic data [46,47] (Chapter 2). Interpretation of observations must allow for the possibility that the identifiable sohd phases may not be those initially formed, but arise as stable products of a secondary process. Secondary reactions may involve adsorption-desorption steps at the surfaces of finely-divided, reactive and perhaps non-stoichiometric solids. The composition of product gases may also vary within the mass of reactant, through chemical interactions between primary products. 

The titanium-oxygen system is particularly complex among the binary metal-oxygen systems. It exhibits many stoichiometric and widely non-stoichiometric solid phases as well as two gaseous compounds, TiO(g) and Ti02(g). The complexity explains the large number of investigations carried out... 

Point (microscopic) defects in contrast from the macroscopic are compatible with the atomic distances between the neighboring atoms. The initial cause of appearance of the point defects in the first place is the local energy fluctuations, owing to the temperature fluctuations. Point defects can be divided into Frenkel defects and Schottky defects, and these often occur in ionic crystals. The former are due to misplacement of ions and vacancies. Charges are balanced in the whole crystal despite the presence of interstitial or extra ions and vacancies. If an atom leaves its site in the lattice (thereby creating a vacancy) and then moves to the surface of the crystal, it becomes a Schottky defect. On the other hand, an atom that vacates its position in the lattice and transfers to an interstitial position in the crystal is known as a Frenkel defect. The formation of a Frenkel defect therefore produces two defects within the lattice—a vacancy and the interstitial defect—while the formation of a Schottky defect leaves only one defect within the lattice, that is, a vacancy. Aside from the formation of Schottky and Frenkel defects, there is a third mechanism by which an intrinsic point defect may be formed, that is, the movement of a surface atom into an interstitial site. Considering the electroneutrality condition for the stoichiometric solid solution, the ratio of mole parts of the anion and cation vacancies is simply defined by the valence of atoms (ions). Therefore, for solid solution M X, the ratio of the anion vacancies is equal to mJn. 

In the same way, a 100% La-Y sample was obtained by stoichiometric solid-state ion exchange when the starting zeolite was a 100% exchanged NH -Y and a ratio La/Al =... 

Note that each case corresponds to the influence of a reacting external factor on a stoichiometric solid, which contains Intrinsic defects. These factors produce additional defects because of nonstoichiometry and charge-compensation. The defect produced is enclosed in bradcets in Table 2-2. 

The appearance of superconductivity and the magnitude of the superconducting transition temperature are also closely coimected with the composition of these non-stoichiometric solids, which all exhibit considerable variation in oxygen content. The superconducting transition temperature is also affected by external factors such as pressure and crystal elastic strain. 

Room temperature crystal structures of RGaOs and stoichiometric solid solutions Patterns of consistence... 

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