Mixed oxygen ionic and electronic conduction in CaFe0.2Ti0.8O3-δ:a combined oxygen permeation and electrical conductivity study

摘要

A combined oxygen permeation and electricalconductivity study on CaFe0.2Ti0.8O3-δ was conductedin the temperature range of 1100-850℃, aiming atclarifying the oxygen transport mechanism. The oxideshows appreciated oxygen permeability at elevatedtemperature. An oxygen permeation flux of 6.37 X 108 molcm-2 s -1 was observed at 1 100℃ by applying an oxygenpartial pressure difference to a 0.84-mm thick disk-shaped sample (Po2(h) = 0.209 and Po2(l) = 0.004 atm).The apparent activation energy for oxygen permeationremained almost unchanged ( 170 kJ/mol) with thevariation of the sample thickness in the range of 2.5-0.8mm. This indicates that the oxygen permeation kineticsis controlled by the transport of charge carriers in thebulk of sample, and can by promoted by further reductionof the thickness. In combination with electricalconductivity measurements, the partial conductivitiesof oxygen ions and electron holes, σ1and σe, weredetermined. The value of σ1 is comparable to that forσe at the high temperature of 1 100℃, but the latterbecame dominant at reduced temperature. This is due tothe much higher activation energy associated with thetransport of oxygen ions (179-4-6 kJ/mol) than that forelectron holes (22-i-2 kJ/mol). It becomes clear thatincreasing the partial conductivity of oxygen ions inthe oxide should lead to the improvement of the oxygenpermeability of the oxide.