Thermoelectric power of superionic conductors

A technique for the calculation of the thermoelectric power in many-particle systems exhibiting hopping conduction is presented. It is shown that the combination of thermopower and conductivity data provides very useful information about the microscopic nature of the ion hopping process in solid electrolytes. There are two main qualitative features of the transport data. In most systems the heat of transport (determined from the thermopower) and the activation energy for conduction are nearly equal, and in systems exhibiting lattice gas order-disorder transitions, these parameters may change across the phase boundary. An extended polaron lattice gas model is presented which is consistent with these features of the data and which allows a determination of the relative strengths of static barrier and polaron effects on the hopping. The results of the model suggest that polaron coupling is relatively small in most materials except for those based on organic halides.