Abstract

Oxygen permeation and faradaic efficiency measurements of perovskite solid solutions Sr_0.97Ti_{1 − x − y}Fe_xMg_yO_{3 − δ} (x = 0.20–0.40; y = 0–0.10) at 973–1223 K showed that the oxygen transport at membrane thicknesses below 2 mm is limited by both bulk ionic conductivity and the surface exchange kinetics. Incorporation of either iron or magnesium into the B sublattice of strontium titanate results in greater p-type electronic and oxygen ionic conductivities. For Sr_0.97(Ti,Fe)O_{3 − δ} solid solutions, the role of the surface exchange as the permeation-determining factor decreases with reducing temperature. In contrast, the limiting effect of the interphase exchange on oxygen transport through Sr_0.97Ti_0.70Fe_0.20Mg_0.10O_{3 − δ} membranes is observed to be significant within the studied temperature range, suggesting that doping with magnesium leads to higher ionic conductivity and lower surface exchange rates in comparison with Sr_0.97Ti_0.60Fe_0.40O_{3 − δ} perovskite which exhibit similar permeation fluxes. The ion transference numbers of the solid solutions in air, estimated from the oxygen permeation and faradaic efficiency results, do not exceed 0.14. TGA/DTA results demonstrated the stability of the perovskite phases in CO₂-containing atmospheres at temperatures above 770 K. The effect of the surface exchange limitations on the faradaic efficiency results is analysed.