Ionic displacements

Today, the term solid electrolyte or fast ionic conductor or, sometimes, superionic conductor is used to describe solid materials whose conductivity is wholly due to ionic displacement. Mixed conductors exhibit both ionic and electronic conductivity. Solid electrolytes range from hard, refractory materials, such as 8 mol% Y2C>3-stabilized Zr02(YSZ) or sodium fT-AbCb (NaAluOn), to soft proton-exchange polymeric membranes such as Du Pont s Nafion and include compounds that are stoichiometric (Agl), non-stoichiometric (sodium J3"-A12C>3) or doped (YSZ). The preparation, properties, and some applications of solid electrolytes have been discussed in a number of books2 5 and reviews.6,7 The main commercial application of solid electrolytes is in gas sensors.8,9 Another emerging application is in solid oxide fuel cells.4,5,1, n... 

Considerable practical importance attaches to the fact that the data in Table 6.11 refer to electrode potentials which are thermodynamically reversible. There are electrode processes which are highly irreversible so that the order of ionic displacement indicated by the electromotive series becomes distorted. One condition under which this situation arises is when the dissolving metal passes into the solution as a complex anion, which dissociates to a very small extent and maintains a very low concentration of metallic cations in the solution. This mechanism explains why copper metal dissolves in potassium cyanide solution with the evolution of hydrogen. The copper in the solution is present almost entirely as cuprocyanide anions [Cu(CN)4]3, the dissociation of which by the process... 

ZnS(llO) surface consists of parallel zigzag chains with equal numbers of zinc and sulphur ions (see Fig. 9.12(a)). It is a charge neutral surface. Relaxation of the ZnS (110) surface has been performed using GGA with CASTER Some pioneering works show that there is a negligible displacement of ions below the second and third atomic layer. Therefore, in relaxation calculation, only the atoms on the first layer of the surface are allowed to move. The surface structure and ionic displacement vectors for the (110) surface are shown in Fig. 9.12(b). Ionic displacements due to surface relaxation are presented in Table 9.5. 

Figure 9.12 The model of ZnS (110) surface and schematic relaxation of surface (a) ZnS (110) surface (b) Ionic displacement vectors in surface relaxation...

Table 9.5 The ZnS (110) surface ionic displacements due to surface relaxation...

Table 9.7 Ionic displacements of the doped ZnS (110) surface due to stuface relaxation...

Fig. 4.7 is an attempt to illustrate an ionic displacement for an interstitial pair by a VTF mechanism along a macromolecular chain. The... 

Standard Green s function techniques are used in the following [46] to describe the dynamics of the protons and the ionic displacements. The equations of motions for the retarded Green s functions [[A (q) S (q))) are obtained from the Hamiltonian Eq. 1 where the operator A denotes 0p, 0k> u or... 

Values of s and s" are calculated using equations in which the contributions of dipolar effects, ionic displacements, and electrode polarization effects are additive. If conduction effects predominate, i.e., when neither interfacial effects nor dipolar effects are significant, the loss factor is given by (Kranbuehl et al., 1986) ... 

Figure 2.38 illustrates that in the case of an ionic solid the optical mode of the lattice vibration resonates at an angular frequency, co0, in the region of 1013Hz. In the frequency range from approximately 109-10nHz dielectric dispersion theory shows the contribution to permittivity from the ionic displacement to be nearly constant and the losses to rise with frequency according to... 

Among the 32 classes of single-crystal materials, 11 possess a centre of symmetry and are non-polar. For these an applied stress results in symmetrical ionic displacements so that there is no net change in dipole moment. The other 21... 

Metal complexes of E fragments that contain E-H bonds may be deproto-nated by strong bases. The E atoms in these complexes are often highly negatively charged and consequently very basic. When these complexes are subjected to reactions involving the ionic displacement strategy, the site of reaction is often at E as exemplified in Eqs. (27)282 and (28).282... 

Ionic Displacement. Electromotive Series. When a strip of zinc is placed in a solution of copper sulphate, it is noticed that a spongy deposit of copper metal soon appears on the surface of the zinc, and that the solution loses its blue color. Then if the solution is tested for the presence of copper and zinc ions by adding ammonium sulphide, it is found that this reagent gives a white precipitate. This test shows that copper ions are now absent and that zinc ions are present because we know ammonium sulphide will precipitate black copper sulphide from a solution of copper ions, and white zinc sulphide from a solution of zinc ions. Since ordinary pieces of metal are not charged, it is obvious that the reaction consists in a transfer of the positive charges of the copper ions to the zinc atoms, or, more strictly, of negative electrons from the zinc atoms to the copper ions ... 

From these experiments it is seen that both iodine and oxygen are more active than sulphur. The reactions are quite certainly ionic displacements although it is rather complicated to represent them in intersecting ionic equations. 

The multiplication of the e s by /S s creates an effective dielectric response that includes ionic displacement. Double-layer screening of zero-frequency fluctuations is through the exponential e 2An . The formal resemblance to retardation screening comes clear here and in subsequent similar factors. 

The use of grey binary numbers (where one mutation would always imply a small ionic displacement, rather than the possibility of an ion moving half the way across the unit cell) for the DNA representation of the unknown coordinates towards the end of a GA run. 

The inherent plausibility of metastable bridged carbonium ions as intermediates is supported by two independent types of observation. One is the extensive rearrangements which can occur in allylic systems under conditions in which ionic displacement reactions are possible. A second is the existence of stable bridged compounds, including, in the case of boron compounds, pentavalent atoms. Thus diborane and substituted diboranes have stable bridged structures. 

Figure 3.88. Schematic representation of the polarization of a particle with a Stem layer only. The distribution of the cation concentration and the potential in the Stem layer are sketched. Arrows Indicate ionic displacements upon polarization.

Another recent addition to the fluorous biphase toolbox is the discovery of fluorous phase transfer catalysts for halide substitution reactions in aqueous-fluorous systems.This class of reactions is academically intriguing, as an ionic displacement reaction has taken place in one of the least polar solvents known. They make use of fluorous phosphonium salts under biphasic conditions but can also make use of non-fluorous phosphonium salts in a triphasic system. Further information and reactions using such systems will no doubt be reported in the next few years. 

For the alternative mechanism, in which chlorine would become attached to the molecule while the hydrogen was being displaced, they could make no prediction, except that formation of an optically inactive product would be highly unlikely there was certainly no reason to expect that back side attack (on the face opposite the hydrogen) would take place to exactly the same extent as front-side attack. (In ionic displacements, attack is generally back-side.)... 

After the force constants and amplitudes of the ionic displacements are found, it is possible to draw the potential energy surface of the excited electronic state. In the harmonic approximation, this energy is described by the following expression ... 

In Lesson 6-2,1 mentioned that displacement reactions are a bit misleading at times. Sometimes, a product that is shown on the product side of the equation does not really appear in the physical chemical reaction. The reason for this has to do with the solubility of ionic substances in water. If a particular product is soluble, it will stay dissolved in the aqueous solution. If a product is insoluble, it will appear as a solid precipitate in the test vessel. It is important to know which products stay dissolved in the water, so we can make proper identification of the precipitates that do form as the result of the chemical reactions. Ionic equations are more realistic representations of these reactions that take place in aqueous solution. Ionic equations show the individual ions that exist in solution. When we take an ionic displacement reaction and remove the information that is misleading, we produce a net ionic equation. 

The interaction between a free electron in a metal and the ionic displacements u is frequently given by the deformable potential approximation (E.g.92), p. 128). If the potential felt by the electron in position r is V 0) without the lattice being distorted, then upon distortion of the lattice to an extent of u(r), the potential experienced by the electron is y(r-u). Another approximation views the potential as the sum of separate ionic potentials based on the instantaneous positions X(k) + u(k) of each ion... 

The normal excitation mode interchanges energy in its transitions similar to the electromagnetic radiation between molecule bands, leading to the emission or absorption of photons that are named phonons. This species is the quanta for the ionic displacement in the metal lattice that normally characterizes the classic sonic wave. The value nks is the normal mode of the wave vector k in its branch s for the //-dim excited state. Taking the particle point of view, we can say that we have nks phonons of the. r-type with a k wave vector. 

Figure 2-2. A non-linear optical material, ammonium dihydrogen phosphate, displaying second-harmonic generation, the frequency doubling of light (infrared to blue). The origin of this physical phenomenon is entirely dependent on ionic displacement or molecular charge-transfer (see color plate...

Bulk rutile shows a high dielectric constant and low-fiequency ( soft ) phonons, but how is this manifest at the surface An FP study finds a soft, anisotropic and anharmonic surface mode (0.15 A ionic displacements at room temperature), which could accoimt for some of the discrepancy between SXRD and zero-temperature FP structures [60]. More generally, this illustrates that many oxide surfaces can be expected to show vibrational anisotropy [40], complicating the use of FP to provide quantitative predictions of structure at a given temperature. 

Figure 4.7 Histograms of ionic displacements of I and Ag+ ions in the superionic a-phase Agl. The largest of the Ag+ displacements exceed twice the cube edge lattice...

In this case, there are two types of ionic displacements ... 

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