CONDUCTIVITY AND SEEBECK MEASUREMENTS ON STRONTIUM FERRATES

The Seebeck coefficient of nine strontium ferrate ceramics with the no minal compositions: SrFeyO3-x (where y = 0.909, 0.952, 1, 1.05, 1.10), and NazSr1-zFeO3-x and LazSr1-zFeO3-x, (where z=0.05, 0.1) were measu red in air from 300-1000 degrees C. The deficiency in oxygen stoichiom etry, x, adjusts itself in air from approximately 0.15 to 0.35 in this temperature range. Most of the materials have reasonably high electro nic conductivities, and some samples of lanthanum-doped ferrate reache d conductivities of 50-90 S/cm at 25 degrees C. The total spread in co nductivity between the 9 samples was 4 decades at 25 degrees C. Negati ve temperature coefficients for the total conductivity were observed a bove 5-600 degrees C. The thermopowers (-5 to +120 mu V/K) show simila r (strong) temperature dependencies for all materials and increase wit h increasing temperature. The temperature dependency of conductivity a nd thermopower can be explained by the strong variation of oxygen cont ent (hole concentration decreases with increasing temperature). A simp le defect model for SrFeO3-x at high P-O2 was consistent with the obse rved oxygen partial pressure dependence of the conductivity at 800 deg rees C.