Electron concentrations, solid electrolytes

It is important to realize that the migration in an electric field depends on the magnitude of the concentration of the charged species, whereas the diffusion process depends only on the concentration gradient, but not on the concentration itself. Accordingly, the mobility rather than the concentration of electrons and holes has to be small in practically useful solid electrolytes. This has been confirmed for several compounds which have been investigated in this regard so far [13]. 

Improvement of the ionic current by fast transport in the electrodes. High electronic mobility and low electronic concentration favor fast chemical diffusion in electrodes by building up high internal electric fields [14]. This effect enhances the diffusion of ions toward and away from the solid electrolyte and allows the establishment of high current densities for the battery. 

Figure 13. Voltage relaxation method for the determination of the diffusion coefficients (mobilities) of electrons and holes in solid electrolytes. The various possibilities for calculating the diffusion coefficients and from the behavior over short (t L2 /De ) and long (/ L2 /Dc ll ) times are indicated cc h is the concentration of the electrons and holes respectively, q is the elementary charge, k is the Boltzmann constant and T is the absolute temperature.

Figure 14. Charge-transfer technique for measurement of the concentration of electrons or holes in solid electrolytes. Two samples of different length are polarized by the same voltage.

Liquid-solid contact Liquid-liquid contact Statistical distribution due to ion concentration fluctuations Double layer (zeta potential) disruption Volta potential (for electron conducting materials) Electrolytic (galvanic) potential (for ionic systems)... 

The net result is the formation of a dense and uniform metal oxide layer in which the deposition rate is controlled by the diffusion rate of ionic species and the concentration of electronic charge carriers. This procedure is used to fabricate the solid electrolyte yttria stabilized zirconia (YSZ). 

This technique can be even applied if the conditions (ii), (iii), and (iv) are not observed. In the latter case, however, regression analysis of the I-U dependencies requires to define explicit relationships between chemical potentials of all components, their concentrations, and mobilities. In practice, experimental problems are often observed due to leakages, non-negligible -> polarization of reversible electrodes, indefinite contact area between solid electrolyte and electronic filter, formation of depletion layers and/or phase decomposition of the electrolyte. 

Solid electrolyte — is a class of solid materials, where the predominant charge carriers are -> ions. This term is commonly used for -> conducting solids with ion -> transport number equal to or higher than 0.99 (see also -> electrolytic domain). Such a requirement can only be satisfied if the -> concentration and -> mobility of ionic -> charge carriers (usually -> vacancies or interstitials) both are relatively high, whilst the content of -> electronic defects is low. See also -> superionics, -> defects in solids, - diffusion, and -> Nernst-Einstein equation. 

Often this term is used for - solid electrolytes and/or for solids with structural disorder (see -> defects in solids), although all these designations are not synonyms. The high concentration of defects, necessary for fast ionic conduction, may be induced by external factors such as - doping, electromagnetic forces, radiation, etc. Creation of these defects may lead to the generation of - electron - charge carriers and, thus, induce electronic - conductivity. 

Theoretical modeling for redox processes in ion insertion solids predicts that, in the presence of a sufficiently high concentration of electrolyte, the voltammetric response of electroactive centers attached to porous materials will be similar, in the case of reversible electron transfer processes, to that displayed by species in solution (Lovric et al., 1998). Figure 2.7 shows the square-wave voltammetry (SQWV)... 

Inchemical sensors, solid electrolytes functionastransducersbyprovidingarelationship between chemical species and electrons, so that an electrical signal corresponding to the concentration of a particular chemical species is produced. This signal can be either a voltage or current, depending on the configuration in which the solid electrolyte is used. 

Therefore, the oxygen concentration on the metal-electrolyte interface is constantly decreasing in time at i=const mode. This fact consequently stipulates the development of an electronic conductivity in the electrochemical cell. Moreover, the prolonged and deep purification of the liquid metal from oxygen is possible only at ti > 0.99 in [/ = const mode of the pump, that is, without influence of an electronic conductivity. As a result, it is more preferable to use the solid electrolyte oxygen pumps in the potentiostatic modes. 

The relative oxygen concentration in Equation (4.128) can be expressed by using the electrophysical parameters of the pump at the initial moment Tq and at the moment T when an electronic conductivity appears in the solid electrolyte. The purification time can then be calculated for the obtained correlation ... 

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