Activation energy of ionic conductivity

Anderson OL, Stuart DA (1954) Calculation of activation energy of ionic conductivity in silica glasses by classical methods. J Am Ceram Soc 37 573-780... 

The concentrations of defects is controlled by a set of coupled equations, mass action laws and laws of conservation, as illustrated in section 11.1.2, and [D] is most often activated thermally. Consequently, the activation energy of ionic conductivity is the sum of two contributions, a transport term and a term reflecting the influence of temperature on the concentration of defects. A change of slope in a diagram Log (ctT)-1/T (see Figure 11.10) indicates a change in the defect regime. 

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

Chief among the interfacial properties of aqueous systems that suggest the occurrence of thermal anomalies are the following index of refraction, density, activation energy for ionic conductance, rates of surface reactions, surface tension, surface potentials, membrane potentials, heats of immersion, zeta potentials, rate of nucleation, viscous flow, ion activities, proton spin lattice relaxation times, optical rotation, ultrasonic velocity and absorption, sedimentation rates, coagulation rates, and dielectric properties. 

Figure 18 shows the influence of caustic concentration upon conductivity of the membrane. The decrease of conductivity with the increase in caustic concentration is ascribed to the decrease in mobility of sodium ions caused by the dehydration of the membrane. The increase of apparent activation energy for ionic conductance along with caustic concentration as is given in Table IE reflects the existance of increasing interaction between sodium ion and the fixed ion in the membrane. 

Extensive experiments have been carried out on the effect of impurity ions on the kinetics of decomposition, the optical properties, and the temperature dependence of ionic conductivity of several azides in an attempt to determine the nature and concentration of the species in the material. Torkar and colleagues studied the kinetics and conductivity of pure and doped sodium azide [97] and observed that cationic impurities and anionic vacancies speed up decomposition by acting as electron traps which facilitate the formation of nitrogen from N3. They also found that the activation energy for ionic conductivity was close to that for decomposition, implying a diffusion-controlled mechanism of decomposition. These results are qualitatively in accord with the microscopic observations of decomposition made by Secco [25] and Walker et al. [26]. 

The electrical properties of macromolecular semiconductors are generally characterized by the conductivity, the activation energy of the conductivity, the free radical concentration, and the thermal electromotive force (thermal emf). Since the polymers are usually in the form of amorphous powders, they are compressed into tablets. The contacts are either metal electrodes pressed into the surface or conductive pastes. The samples may not have any ionic conductivity (due to impurities) or surface conductivity and must be free of moisture, otherwise the conductivities will be too high. 

Hereby, B, A and Tq are material-dependent parameters. The parameter is proportional to the activation energy of ionic transport. In a system with a strict coupling between dynamic viscosity and conductivity, as described by the Stokes-Einstein equation, the parameter B in (8.8) is equal to the parameter B in (8.10). In a system with a higher probability for the motion of ionic charge carriers than for viscous flow events, as it can be found in case of cooperative proton transport mechanisms, the strict coupling between dynamic viscosity and conductivity does not hold [56-58]. In this case the parameter Bg in (8.10) will be smaller than B in (8.8). Combining (8.8) and (8.10) and considering the concentration dependence of cr, by introduction of the molar conductivity one will yield a fractional Walden rule (-product) as shown in (8.11). 

Calculations of the activation energies of ionic and electronic conduction for both cases, (i] full association and (ii] no association lead to the following ... 

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(

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