Electrical conductivity and thermopower of lead titanate crystals

The temperature dependences of the thermopower ?? and volume conductivity ?? _V of lead titanate crystals have been studied in the temperature range 400?C550 K, in which there are anomalies of the permittivity ? that are not related to the phase transition. It has been found that, in this temperature range, the thermopower ?? has a maximum and changes sign in many crystals; in this case, ?? _V decreases. It has been assumed that the anomalies of ?? and ?? _V , which correlate with anomalies of ?, are caused by thermal activation of electron traps, which leads to compensation of the p-type conductivity. The concentrations of free charge carriers and their drift mobility in the paraphase near the Curie point have been determined. These data indicate that the possibility exists of occurring the total internal screening of the bound charge P _s .