Activation energy, for conductance

The values of the conductivity due to Na+ ions in a glass are given in the following table, (a) Estimate the activation energy for conductivity. The conductivity at 700 K is 0.00316 S m-1. (b) Estimate the value of the diffusion coefficient Da at this temperature if the concentration of Na+ ions is 7.2 x 1027 m-3. (c) Using the data in Chapter 5, Question 5, calculate the Haven ratio at this temperature. 

The activation energy for conduction, is the major factor controlling the ionic mobility, u. The Arrhenius expression for conductivity is either... 

In such a compound, a mbced Fe " " valence is only introduced through impurities and/or oxygen vacancies. Upon reduction, the mobile electrons become trapped at oxygen vacancies the activation energies for conduction are 0.48 eV in the ferrimagnetic domain and 0.57 eV in the paramagnetic domain . ... 

An alternative model considers the carriers to be localized on individual molecules, and that charge transfer occurs by the carrier hopping between these localized centres. The hopping process involves the charge carrier overcoming a potential energy barrier and thus involves an activation energy for conduction.7 The temperature dependence of this conductivity may depend on the dimensionality of the system.8... 

When the activation energies for conduction are computed from the log A versus 1/Tplots, it is seen (Table 5.26) that they are a little lower than the activation energies for viscous flow and self-diffusion, i.e.,... 

Much better stability was reported for AsFg-doped polyacetylene coated with poly(p-xylylene) (26), which is an excellent barrier toward oxygen and water. Samples having conductivities of 260 S/cm were coated by vacuum deposition thus, the initial concentration of oxygen in the sample was low. After 24 h in air, a conductivity loss of 10% was observed for treated films, whereas the conductivity of uncoated control samples decreased by a factor of 3. After 1 month, the coated samples had a conductivity of 150 S/cm, whereas that of the control was only 11 S/cm. From isothermal aging studies, the poly(p-xylylene) coating was found to increase the first-order activation energy for conductivity loss by 2.4 Kcal/mol, from 17.2 to 14.8. These data... 

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