Thermoelectric power in ionic and electronic mixed conductors

In order to study the thermoelectric property of the oxide ionic and electronic mixed conductor of 10 mol% CaO-doped CeO2 (CDC), a new type of thermocell was prepared, in which platinum electrodes were embedded in the tube-type sample to diminish the large temperature gradient over the electrodes due to the local heat radiation from heating furnace. Using this thermocell, reproducible data were obtained. The thermoelectric power measured in CDC under various oxygen atmospheres (Po-2) from 1.0 to about 10(-15) atm showed that the sign of Seebeck coefficients changed from minus to plus. This variation of Seebeck coefficients vs. Pot was well interpreted by considering that (1) the thermoelectric power could be a driving force to make actual and electrochemical oxygen transfer in the mixed conductor and (2) the electrode processes had limiting rates due to slow oxygen diffusion (or oxygen gas exhaustion at the cathode and evolution at the anode).