Ionic sizes effect

It appears that for the layered Mn and Co oxides considered, ionic size effects do not play a significant role in the preference for octahedral or tetrahedral sites nor in the activation barrier to hops between the two. Consequently, size effects probably do not play a significant role in determining the mobility of Mn or Co through a ccp oxide framework. In contrast, the results indicate that valence and electronic structure are more decisive factors in the site preference of Mn or Co and hence in their propensity to migrate through a ccp oxide framework. This is consistent with the work of Goodenough that found valence to be an important determinant of the site preference of 3d TM ions in oxides. 

In LnSrNi04 (33), the a parameter decreases linearly with the size of the Ln ion, but there is an abrupt change in the c parameter and in the da ratio (Fig. 8c). Since the size of low-spin Ni3+ is comparable to that of Al3+, the markedly different behavior of LnSrNi04 compounds cannot be due to ionic size effects electronic factors seem to be important. A similar behavior is observed in LnSrFe04 and LnSrCr04 (34) as can be seen from Fig. 8. 

Another problem arises in the case of weak or moderate adsorption [46]. When the sign of the potential drop across the diffuse layer changes with solution composition or electrode charge density, there is a change in the nature of the predominant ion at the oHp. Since different ions have different sizes, the position of the oHp also changes. Ionic size effects are not considered in the GC model of the diffuse layer. Thus, use of the model based on equation (10.8.10) must consider the possibility that and K d vary with adsorbed charge density Oad for constant charge density 0 on the electrode [46]. 

Thus in the case of ions, measurements of this type are generally used to obtain values of the mobility and, through Stoke s law or related equations, an estimate of the effective ionic size. 

There is usually an ionic strength above which there is no more effect on hydrodynamic size or, worse yet, there are hydrophobic interactions of the polymer with the stationary phase. Thus, the optimum 1 is usually at the low 1 end of the plateau of size vs 1. This concentration will minimize ionic strength effects while also minimizing wear on the pump seals and pistons. 

The dominant features which control the stoichiometry of transition-metal complexes relate to the relative sizes of the metal ions and the ligands, rather than the niceties of electronic configuration. You will recall that the structures of simple ionic solids may be predicted with reasonable accuracy on the basis of radius-ratio rules in which the relative ionic sizes of the cations and anions in the lattice determine the structure adopted. Similar effects are important in determining coordination numbers in transition-metal compounds. In short, it is possible to pack more small ligands than large ligands about a metal ion of a given size. 

Chrambach this indicates that the effective protein size for gel filtration is larger than the effective size for gel electrophoresis. They concluded that this could not be accounted for by gel swelling, pH, or ionic strength effects. Biefer and Mason [36] found the constant a in Eq. (93) to be 0.93. They measured the conductance of cellulose acetate filter pads with porosities from 0.5 to 0.9 in solutions of 10 M KCl. 

On the contrary, a quite systematic behavior with the lanthanoid ion contraction is observed. A plot of the energy of CTI band versus the ionic radius at coordination number 8 of the Ln ions (16) indicates a linear decrease of this energy as the ionic radius increases. This is seen in Figure 3, and illustrates a bare size effect of the energy variation. The phenomenon is called "optical detection of the lanthanoid ion contraction by internal charge transfer absorption". 

For ions of the same charge, the ionic radius increases as you go down any column because the elements of higher atomic number have a greater number of electrons in a series of electronic shells progressively farther from the nucleus. The change in ionic size along a row in the chart just above shows the effect of attraction by protons in the nucleus. 

Some peculiarities of the described structure types can not be accounted for by the ionic aspects discussed so far. One may assume, that such peculiarities are connected with the electronic configurations of the ions concerned 231). Effects that depend on anomahes of the ionic sizes for special electronic configurations (e.g. maxima for high-spin or minima for low-spin d , see f. i. Blasse (36) Chadwick and Sharpe (63)) will be neglected, however, as well as the interesting questions connected with the stability of valency states (see f.i. Sheldon (279)). 

Instead, optical measurement was applied to clarify the formation mechanism of Agl nanoparticles in diluted suspensions. Figure 4.4.10A shows the absorption spectra of the 1-day aged suspension containing 3.33 X 10-4 M Ag+ and 6.67 X 10-4 M I- as a function of RSH concentration. When the content of RSH increased from 0 to 6.67 X I0-3 M (curves a-d), the absorption spectra of Agl particles blue-shifted, suggesting the quantum size effect. The relationship between the particle diameter, d (A), and the concentration of RSH, c (A/), was plotted in the inset, which shows the double-logarithmic linear line of d versus c. The aggregation number is found to be proportional to the cube of the size. The same relationship was reported on the formation of CdS nanoparticles (37). These correlations indicate that Agl and CdS have the same ionic nature and have the same reaction modules of thiols. 

This chapter deals mainly with quantum size effects in CD nanocrystalline films. However, another, quite separate property of such films is related to the large percentage of atoms located on the surface of the nanocrystals of these films, e.g. —50% for a crystal size of a few nm this is the effect of adsorption of molecular and ionic species on the nanocrystal surfaces. This aspect has been dealt with much less than has size quantization therefore, it constitutes only a very small part of this chapter, mainly Section 10.2.3, which discusses the effect of adsorbed water on CD CdSe films. Section 9.2.2.2 deals in somewhat more detail with this particular issue. 

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