Thermodynamics of charge carriers weak electrolyte theory

5 Thermodynamics of charge carriers weak electrolyte theory 

As suggested in Fig. 4.3 the charge carrier formation in step (a) may be compared to a dissociation leading to the following equilibrium 

In a medium with a relatively low dielectric constant like a glass, the dissociation constant is expected to be small, and the thermodynamic ionic activities proportional to their concentrations. An approximate expression for (4.12) is then 

Many fast ion conducting glasses contain several salts of the same alkali metal to optimise the conductivity. The expression for the charge carrier concentration in terms of the thermodynamic activities of all the 

Such a chemical approach which links ionic conductivity with thermodynamic characteristics of the dissociating species was initially proposed by Ravaine and Souquet (1977). Since it simply extends to glasses the theory of electrolytic dissociation proposed a century ago by Arrhenius for liquid ionic solutions, this approach is currently called the weak electrolyte theory. The weak electrolyte approach allows, for a glass in which the ionic conductivity is mainly dominated by an MY salt, a simple relationship between the cationic conductivity a+, the electrical mobility u+ of the charge carrier, the dissociation constant and the thermodynamic activity of the salt with a partial molar free energy AG y with respect to an arbitrary reference state  

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