Ionic charge carriers

This situation appears to be different when microwave conductivity measurements are used in parallel with electrochemical measurements. As Fig. 1 shows, there is a marked parallelism between electrochemical processes and microwave conductivity mechanisms. In both cases electrical fields interact with electronic or ionic charge carriers as well as dipoles. In electrochemical processes, it is a static or low-frequency electrical field that is moving electrical charge carriers or orienting dipoles. In a micro-wave measurement, the electric field of the microwave interacts with... 

Figure 1. Drawing showing how static electrical fields and microwave fields interact with the same electronic or ionic charge carriers and electrical dipoles.

The type of conductance exhibited by the oxide and its value are structure sensitive. The oxide is essentially an ionic conductor. One could maintain that it has a relatively high concentration of low-mobility ionic charge carriers. As far as electronic conductance is concerned although pure alumina is an insulator with a band gap of 8 to 9 eV, one has to bear in mind that when it is produced anodically as a thin film adhering firmly to the metal, an entirely different electronic situation may arise [cf. Section V(2)]. 

As already stated, when metal electrodes are used in electrochemical reactions and one speaks of a limiting diffusion current, one is referring to ionic charge carriers... 

There is still another type of internal solid state reaction which we will discuss and it is electrochemical in nature. It occurs when an electrical current flows through a mixed conductor in which the point defect disorder changes in such a way that the transference of electronic charge carriers predominates in one part of the crystal, while the transference of ionic charge carriers predominates in another part of it. Obviously, in the transition zone (junction) a (electrochemical) solid state reaction must occur. It leads to an internal decomposition of the matrix crystal if the driving force (electric field) is sufficiently high. The immobile ionic component is internally precipitated, whereas the mobile ionic component is carried away in the form of electrically charged point defects from the internal reaction zone to one of the electrodes. 

Many important phenomena in solid state ionics, such as ionic conduction, gas permeation through dense solids, solid state reactions, high temperature corrosion, or sintering of polycrystals, involve mobile ionic charge carriers. In most crystalline... 

In the case of electrical transport across and along space charge layers at grain boundaries, there is usually no fundamental difference between electronic and ionic charge carriers. At electrodes, however, electrons and ions behave completely differ-... 

In the simplest and most important cases, two general reasons responsible for ion mobility in solids are (i) the presence of ions or groups of ions with a relatively weak bonding with respect to the neighborhood, and (ii) the existence of a network of positions available for ion jumps. These factors may be quantitatively expressed in terms of ionic -> charge carrier - concentration, and their - diffusion coefficient. 

The type and concentration of defects in solids determine or, at least, affect the transport properties. For instance, the -> ion conductivity in a crystal bulk is usually proportional to the -> concentration of -> ionic charge carriers, namely vacancies or interstitials (see also -> Nernst-Einstein equation). Clustering of the point defects may impede transport. The concentration and -> mobility of ionic charge carriers in the vicinity of extended defects may differ from ideal due to space-charge effects (see also - space charge region). 

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. 

The ionic charge carriers in ionic crystals are the point defects.1 2 23,24 They represent the ionic excitations in the same way as H30+ and OH-ions are the ionic excitations in water (see Fig. 1). They represent the chemical excitation upon the perfect crystallographic structure in the same way as conduction electrons and holes represent electronic excitations upon the perfect valence situation. The fact that the perfect structure, i.e., ground structure, of ionic solids is composed of charged ions, does not mean that it is ionically conductive. In AgCl regular silver and chloride ions sit in deep Coulomb wells and are hence immobile. The occurrence of ionic conductivity requires ions in interstitial sites, which are mobile, or vacant sites in which neighbors can hop. Hence a superionic dissociation is necessary, as, e.g. established by the Frenkel reaction ... 

Figure 18. In the same way as the concentration of protonic charge carriers characterizes die acidity (basicity) of water and in the same way as the electronic charge carriers characterize the redox activity, the concentration of elementary ionic charge carriers, that is of point defects, measure the acidity (basicity) of ionic solids, while associates constitute internal acids and bases. The definition of acidity/basicity from the (electrochemical potential of the exchangeable ion, and, hence, of the defects leads to a generalized and thermodynamically firm acid-base concept that also allows to link acid-base scales of different solids.77 (In order to match the decadic scale the levels are normalized by In 10.) (Reprinted from J. Maier, Acid-Base Centers and Acid-Base Scales in Ionic Solids. Chem. Eur. J. 7, 4762-4770. Copyright 2001 with permission from WILEY-VCH Verlag GmbH.)...

The principal function of a separator in a Li-ion battery is to keep the positive and negative electrodes apart. This is needed to prevent electrical short circuits and at the same time allow for rapid transport of ionic charge carriers that are critical to complete the... 

The other parameter, C2, has been used for the fg determination of the crosslinked DGEBA network. Miyamoto and Shibayama [ 118,124] calculated the fractional free-volume of the DGEBA network using the C2 parameter based on the ionic conduction. The DC conduction measurement is the method investigating the same kind of moving unit, the ionic charge carrier, both in the un-crosslinked oligomer and in the crosslinked network. Table 12 summarizes the fg values that are obtained from the DC conduction measurement for three... 

Mobility Difference Between Chain Segment, Dipole, and Ionic Charge Carrier... 

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