Stoichiometry change

The description presented in this section applies to a gas mixture that is not undergoing chemical reactions. As long as reactions do not occur, the number of moles of each gas is determined by the amount of that substance initially present. When reactions occur, the numbers of moles of reactants and products change as predicted by the principles of stoichiometry. Changes in composition must be taken into account before the properties of the gas mixture can be computed. Gas stoichiometry is described in the next section. 

There are a number of ways this stoichiometry change can come about. Additional As atoms might be incorporated from the vapor and added to the crystal surface at both As and Ga sites ... 

Proton stoichiometries change as pH is altered and are influenced by oxo group... 

An interesting effect was observed by varying the pressure between 80 and 400 mTorr. At pressures of 180 mTorr and above, the deposition rate jumped from 600 to 2000 A/min. At the same time, resistivity rose as high as 4000 pi2-cm. The variation with pressure is shown in Figure 12. Apparently, the stoichiometry changed dramatically at pressures of 180 mTorr and higher. In fact, there is very little Ta in the film created at 400 mTorr (about 13%), so this is mostly a polysilicon film. 

We will successively discuss surface relaxation effects, changes of covalency in the outer layers, partial fillings of surface states and stoichiometry changes. 

Pyoverdin. Pyoverdin complexes of tetravalent actinides have been investigated due to the potential of this class of ligand to solubilize and sequester these metals (as they do for Fe ). At near-neutral pH pyoverdine forms a 1 1 Pu pyoverdine complex with Pu. The stoichiometry changes to 1 2 when excess ligand is present. Thorium(IV), U, and complexes have also been reported. Their optical absorbance spectroscopic properties, but no structural studies, are reported. The selectivity of pyoverdin for common actinides in the order Th > has been proposed. ... 

The global stoichiometry changes with operating conditions and feed composition kinetics and stoichiometry obtained from steady-state (chemostat) data cannot be used reliably over a wide range of conditions, unless fundamental models are employed. 

Admittedly, this idealized pathway for one specific surface can barely be able to represent the complex atomic rearrangements and stoichiometry changes one can expect more generally during this oxidation step. Still, it contains at least one aspect that appears quite crucial The effect of strain. As already pointed out before, oxygen incorporation will always lead to a substantial local expansion of the crystal lattice of late 4d TMs, and known bulk oxide structures of the latter are accordingly much more open compared to the... 

Stoichiometry changes affect E , e.g., in the reduction of a metal ion, M"+, in the presence of a complexing ligand, L. If a simple metal ion is reversibly reduced in the absence of L, the redox reaction is described by ... 

Case 1 the DC current is lower than Jiiml- The mass balance within a layer ofthe solid electrolyte near the cathode indicates that no stoichiometry change is obtained rather, only an oxide ions flux from the cathode to the anode is observed. This flux obeys the Faraday law (i.e., J = I/2F, and the cell functions as an oxygen pump (Figure 12.2). 

At higher temperatures (i.e., 1,000°C) and excess partial pressure of oxygen (i.e., 10 6to latm.), monoclinic zirconia contains completely ionized zirconium vacancies [26], At 1,000°C, zirconia is stoichiometric at a pressure of 10 16 atm. At this point, the concentration of oxygen vacancies is equal to twice the concentration of zirconium vacancies. As the partial pressure of oxygen increases, the stoichiometry changes such that for ZrO,+, with the S value defined by ... 

As Tc depends on the oxygen stoichiometry, changes that occur with reduction may provide the key to superconductivity in these materials. The most dramatic structural effect of oxygen removal is the loss of connectivity in the 1-D chains that run along the b axis. This may indicate that conductivity occurs along these chains. An alternate explanation (26)... 

To see what this means, we need a relationship between drii and d. We have already mentioned reaction increments in this chapter, although we didn t call them that. We said ( 14.2.4) that because reactant and product constituents are related by fixed stoichiometries, changes in their masses are related by (14.24),... 

Composition. Within those compositions with the same stoichiometry, R and D are identical, and F has the same chemical stucture and functionality, but with different molecular weights. Only the stoichiometry changes for the other compositions R, D, and F are the same. 

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