Ionic conductivity activation energy

For most ionic conductors, the conductivity activation energy ( ) may be consid-... 

A number of studies have also shown that the ionic conductivity of stabilized zirconia depends on the size of acceptors the conductivity tends to be highest with a minimization of the conductivity activation energy for those acceptors whose ionic radius closely matches that of host cation... 

Figure 1. Temperature dependence of ionic conductivity of microcrystalline acceptor stabilized zirconia. Data taken from [1-4], Solid lines represent the result of fitting the model (Eq.5) to experimental results [8], The insert is the dependence of the conductivity activation energy as a function of acceptor radius.

In Figure 14.3 the conductivity of various fluoride-ion solid electrolytes with tysonite-and fluorite-like structures is presented as a function of the ionic transfer activation energy (Ea). It can be seen that a suitable fluoride solid electrolyte with optimal properties for any applications could be chosen or its targeted search could be carried out. 

Figure 14.3 Conductivity of various fluorine and oxygen conductors as a function of the ionic transfer activation energy. (Reprinted with permission from [2]. (1 -fluorite-likephases, 2-tysonite-Uke phases). Copyright (2007) Pleiades Publishing Inc.)...

For an ion to move through the lattice, there must be an empty equivalent vacancy or interstitial site available, and it must possess sufficient energy to overcome the potential barrier between the two sites. Ionic conductivity, or the transport of charge by mobile ions, is a diffusion and activated process. From Fick s Law, J = —D dn/dx), for diffusion of a species in a concentration gradient, the diffusion coefficient D is given by... 

At temperatures above or near the eutectic temperature of the polymer phase, CSEi values are typically in the range of 0.1-2 pFcm-2 [5], However, for stiff CPEs or below this temperature, CSEI can be as low as 0.001 pFcm 2 (Fig. 16). When a CPE is cooled from 100 °C to 50 °C, the CSE1 falls by a factor of 2-3, and on reheating to 100 °C it returns to its previous value. This is an indication of void formation at the Li/CPE interface. As a result, the apparent energy of activation for ionic conduction in the SEI cannot be calculated from Arrhenius plots of 1// sei but rather from Arrhenius plots of 7SE)... 

Electrical conductivity measurements revealed that ionic conductivity of Ag-starch nanocomposites increased as a function of temperature (Fig.l7) which is an indication of a thermally activated conduction mechanism [40]. This behavior is attributed to increase of charge carrier (Ag+ ions) energy with rise in temperature. It is also foimd to increase with increasing concentration of Ag ion precursor (inset of Fig.l7). This potentiality can lead to development of novel biosensors for biotechnological applications such as DNA detection. 

The temperature dependence of the conductivity can be described by the classical Arrhenius equation a = a"cxp(-E7RT), where E is the activation energy for the conduction process. According to the Arrhenius equation the lna versus 1/T plot should be linear. However, in numerous ionic liquids a non-linearity of the Arrhenius plot has been reported in such a case the temperature dependence of the conductivity can be expressed by the Vogel-Tammann-Fuller (VTF) relationship a = a°cxp -B/(T-T0), ... 

Figure 6.5 Arrhenius plots of ln(

The activation energy for ionic conductivity is derived from a plot of ... 

Estimate the activation energy for ionic conductivity in the Lu2Ti207 phase illustrated in Figure 6.5b. 

It has been noted that the conductivity and activation energy can be correlated with the ionic radius of the dopant ions, with a minimum in activation energy occurring for those dopants whose radius most closely matches that of Ce4+. Kilner et al. [83] suggested that it would be more appropriate to evaluate the relative ion mismatch of dopant and host by comparing the cubic lattice parameter of the relevant rare-earth oxide. Kim [84] extended this approach by a systematic analysis of the effect of dopant ionic radius upon the relevant host lattice and gave the following empirical relation between the lattice constant of doped-ceria solid solutions and the ionic radius of the dopants. 

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