Transport properties and thermal expansion of Sr(0.97)Ti(1-x)Fe(x)O3-delta(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 - de lta membranes is limited by both bulk ionic conduction and surface exchange rates. Prolonged stabilization under oxygen chemical potential gradients s uggests formation of ordered microdomains in the perovskite lattice. The ac tivation energy for the ionic conductivity, evaluated from oxygen permeatio n and Faradaic efficiency data, is nearly independent of iron content, vary ing in the range 97 - 104 kJ/mol. Thermal expansion coefficients of Sr0.97T i1 - 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 temper atures. In comparison with the Sr(Ti, Co)O3 - delta system, strontium titan ates ferrites possess somewhat poorer transport properties, but lower therm al expansion. (C) 2001 Academic Press.