Faradaic efficiency and oxygen permeability of Sr0.97Ti0.60Fe0.40O3-δ perovskite

Oxygen ionic conduction in the perovskite-type Sr0.97Ti0.60Fe0.40O3-delta was studied using oxygen permeability, Faradaic efficiency and total electrical conductivity measurements at 973-1223 K. The ion transference numbers of the strontium titanate-ferrite in air vary from 0.005 to 0.08, decreasing with decreasing temperature. The electron-hole conductivity of the oxide is relatively low but exceeds the ionic conductivity. The activation energy for the electronic conductivity is 35+/-3 kJ/mol at 470-890 K and drops at higher temperatures. Studying the oxygen permeation through dense Sr0.97Ti0.60Fe0.40O3-delta ceramic membranes as a function of membrane thickness showed that at temperatures above 1170 K the permeation fluxes are limited by both bulk ionic conductivity and surface exchange rates. Depositing of porous layers of the same material or a mixture of platinum and praseodymium oxide onto the membrane feed-side surface leads to a significant increase in the oxygen permeability. Decreasing temperature results in increasing role of the bulk ionic transport in Sr0.97Ti0.60Fe0.40O3-delta as the permeation-determining factor. The oxygen permeation fluxes at 1073 K are limited predominantly by the oxygen ionic conductivity of the ceramics. The thermal expansion coefficients of the ceramic material in air were calculated from dilatometric data to be 11.7 x 10(-6) K-1 in the temperature range 300-720 K and 16.6 X 10(-6) K-1 at 720-1070 K. (C) 2000 Elsevier Science B.V. All rights reserved.