Transport properties and thermal expansion of Sr0.97Ti1-xFexO3-δ (x=0.2-0.8)

Increasing iron concentration in perovskite-type solid solutions Sr0.97Ti1 - xFexO3 - delta (x = 0.2 - 0.8) was found to decrease the unit cell volume and to increase the partial ionic and electronic conductivities as well as the thermal expansion. The oxygen permeation through Sr-0.97(Ti,Fe)O3 - delta membranes is limited by both bulk ionic conduction and surface exchange rates. Prolonged stabilization under oxygen chemical potential gradients suggests formation of ordered microdomains in the perovskite lattice. The activation energy for the ionic conductivity, evaluated from oxygen permeation and Faradaic efficiency data, is nearly independent of iron content, varying in the range 97 - 104 kJ/mol. Thermal expansion coefficients of Sr0.97Ti1 - xFexO3 - delta (x = 0.4 - 0.8) vary from (11.7 - 13.8) x 10(-6) K-1 at temperatures of 300 - 720 K to (16.6 - 27.0) x 10(-6) K-1 at higher temperatures. In comparison with the Sr(Ti, Co)O3 - delta system, strontium titanates ferrites possess somewhat poorer transport properties, but lower thermal expansion. (C) 2001 Academic Press.