Surface-limited ionic transport in perovskites Sr-0.97(Ti,Fe,Mg)O3-delta

Oxygen permeation and faradaic efficiency measurements of perovskite solid solutions Sr0.97Ti1-x-yFexMgyO3-delta (x = 0.20-0.40; y = 0-0.10) at 973-12 23 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 stronti um titanate results in greater p-type electronic and oxygen ionic conductiv ities. For Sr-0.97(Ti,Fe)O3-delta solid solutions, the role of the surface exchange as the permeation-determining factor decreases with reducing tempe rature. In contrast, the limiting effect of the interphase exchange on oxyg en transport through Sr0.97Ti0.70Fe0.20Mg0.10O3-delta membranes is observed to be significant within the studied temperature range, suggesting that do ping with magnesium leads to higher ionic conductivity and lower surface ex change rates in comparison with Sr0.97Ti0.60Fe0.40O3-delta perovskite which exhibit similar permeation fluxes. The ion transference numbers of the sol id solutions in air, estimated from the oxygen permeation and faradaic effi ciency results, do not exceed 0.14. TGA/DTA results demonstrated the stabil ity 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.