p-type electron transport in La_1-xSr_xFeO _3-δ at high temperatures

Electrical conductivity, thermopower and oxygen content were measured for La_1-xSr_xFeO_3-δ (x=0.2, 0.5, 0.9) within the oxygen partial pressure range 10^-4-0.5 atm and at temperatures 750-950°C. The dominating charge carriers under these experimental conditions are electron holes. The results of oxygen nonstoichiometry measurements are used to estimate the concentration of holes and to analyze data on conductivity and thermopower. The changes in thermopower are described by the model assuming that the number of sites accessible for migration of holes is independent on oxygen content. The mobility of electron holes is calculated, and it is found to be virtually independent on temperature in the compositions with x<0.5 while compositions with x>0.5 exhibit thermally activated mobility and mobility values about 0.1 cm² V ^-1 s^-1 or smaller. It is suggested that the main contribution to the composition dependent variations in electron hole mobility are associated with Coulomb interactions at small x's, whereas at high degrees of doping the mobility of holes is most strongly affected by the increasing amount of oxygen vacancies.