Analysis of oxygen transport and stoichiometry in mixed-conducting SrFeCo0.5Ox by conductivity and thermogravimetric analysis

The conductivity and weight changes of SrFeCo0.5Ox in various different oxygen partial pressures (p(o2)) were measured simultaneously by the four-point de method and a thermogravimetric analysis apparatus, respectively. The apparent oxygen diffusion coefficients were derived from the weight and conductivity relaxation experiments by abruptly changing the p(o2) in the surrounding atmosphere and monitoring the change of weight and conductivity as functions of relaxation time. At 950 degrees C in air, the obtained apparent oxygen diffusion coefficient of SrFeCo0.5Ox is approximate to 1 x 10(-6) cm(2)s(-1). Conductivity increases while the weight decreases with increasing temperature within our experimental p(o2) range (1 greater than or equal to p(o2) greater than or equal to 10(-18) atm), and the activation energy decreases while conductivity increases with increasing p(o2). The p(o2)-dependent conducting behavior can be understood by considering the trivalent-to-divalent transition of transition metal ions in the sample. The oxygen stoichiometry of SrFeCo0.5Ox in air is x = 3 at 950 degrees C.