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

Oxygen ionic conduction in the perovskite-type Sr0.97Ti0.60Fe0.40O3-delta w as studied using oxygen permeability, Faradaic efficiency and total electri cal conductivity measurements at 973-1223 K. The ion transference numbers o f the strontium titanate-ferrite in air vary from 0.005 to 0.08, decreasing with decreasing temperature. The electron-hole conductivity of the oxide i s 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 sho wed that at temperatures above 1170 K the permeation fluxes are limited by both bulk ionic conductivity and surface exchange rates. Depositing of poro us layers of the same material or a mixture of platinum and praseodymium ox ide 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 pre dominantly by the oxygen ionic conductivity of the ceramics. The thermal ex pansion coefficients of the ceramic material in air were calculated from di latometric 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 rig hts reserved.