Oxygen stoichiometry, electrical conductivity, and thermopower measurements of BSCF (Ba0.5Sr0.5CoxFe1-xO3-δ, 0≤x≤0.8) in air

The DC electrical conductivity and Seebeck coefficient of sintered BSCF ceramics (Ba0.5Sr0.5CoxFe1-xO3-delta, 0 <= x <= 0.8) were simultaneously measured from 200 to 900 degrees C in air. Oxygen stoichiometry (3-delta) was determined from iodometry at room temperature and thermogravimetry analysis to 900 degrees C. The electrical conductivity was thermally activated at low temperatures, exhibiting a maximum of 32 +/- 4 S/cm at similar to 350 degrees C and then decreasing with increasing temperature above 400 degrees C. The Seebeck coefficient ranged from a minimum of 37 +/- 10 mu V/K for all compositions at -300 degrees C to 150 mu V/K for x=0 and 67 mu V/K for x = 0.8 at 900 degrees C. Oxygen stoichiometry ranged from 2.65 for x=0 and 2.54 for x=0.8 at 100 degrees C to 2.55 for x=0 and 2.36 for x = 0.8 at 900 degrees C. A simple p-type polaron hopping model, assuming negligible contribution from n-type or ionic carriers, was used to extract the carrier concentration and mobilities from the measured data. The calculated mobilities were <0.1 cm(2)/V-s, supporting the p-type polaron hopping model. For a given composition, the activation energy for conduction below similar to 350 degrees C was identical to that of the carrier mobility, ranging from 0.2 eV for x=0 to 0.6 eV for x=0.8. Above 350 degrees C, the activation energy for carrier mobility decreased dramatically, ranging from 0.05 eV for x= 0.2 to 0.1 eV for x= 0.8. Unlike the carrier mobilities of the x >= 0.2 samples, the carrier mobility for the x=0 sample did not appear to be thermally activated above 350 degrees C (C) 2010 Elsevier B.V. All rights reserved.