Thermoelectric power of mixed electronic-ionic conductors III. Case of calcium titanate

The primary purpose of the present work is the determination of the thermopower component related to electronic charge carriers for undoped calcium titanate. The second purpose of this work is establishment of the relationship between this thermopower component and the electronic component of electrical conductivity. An essential part of the present study includes the determination of the thermopower components corresponding to different charge carriers (electrons, electron holes and ions). The determination procedures are based on the following three models: Symmetrical model. This model assumes consistency between thermopower and electrical conuctivity in terms of the n-p transition (this model assumes that minimum of electrical conductivity corresponds to the electronic component of the thermopower equal zero). It was shown that this model does not apply for CaTiO ₃. The Heikes model. This model is based on Heikes formula and also hopping mechanism of the transport of electrons. It was shown that thermopower of CaTiO ₃ cannot be described by this model and, consequently, thermopower vs. electrical conductivity cannot be considered within the Jonker formalism. General model. This model is based on a general thermopower equation for mixed conductors without any simplifying assumptions. Application of this model indicates that the electronic component of thermopower is not consistent with the minimum of electrical conductivity.