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

Oxygen ionic conduction in the perovskite-type Sr0.97Ti0.60Fe0.40O3−δ 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−δ 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−δ 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 11.7×10−6 K−1 in the temperature range 300–720 K and 16.6×10−6 K−1 at 720–1070 K.