Carrier density enhancement in semiconducting NaSn and CsPb

The electrical conductivity and thermoelectric power S data have been measured in two semiconductors that undergo a solid-state transformation to a dynamically disordered phase about 100°C below the melting point. At the transition, for NaSn is reduced while that for CsPb exhibits a dramatic rise. For both semiconductors, S is reduced in magnitude and changes sign at the transition. These results are consistent with a model which explicitly allows for the interactions between mobile ions and electrons and which provides a unified explanation of the transport properties of these compounds and other fast ion conductors with appreciable electronic conductivity.