Partial conductivities and Onsager transport coefficient matrix of BaCo0.70Fe0.22Nb0.08O3−δ

Abstract

BaCo0.70Fe0.22Nb0.08O3 − δ (BCFN) is known to be one of state-of-the-art materials for oxygen permeation membranes, but its partial conductivities governing the oxygen permeability are still yet to be characterized. We have established, by an electrochemical polarization method under the ion-blocking condition, the Onsager transport coefficient matrix Lmn such that Jm = −Lmn∇ηn, where Jm and ∇ηn are the flux and electrochemical potential gradients of charge carriers (m, n = oxide ions O2 −, holes h+), respectively, and thereby derived its partial ionic and electronic conductivities as functions of oxygen activity in the range of − 5 < logaO2 < 0 at 750 °C, 850 °C, and 950 °C, respectively. It has been found that the oxide ionic conductivity is on the order of 1 S/cm with the ionic transference number of the order of 0.1; furthermore, the cross coefficient Lmn(m ≠ n) or ion–electron interference upon their transfer is appreciable in the entire ranges examined. The oxygen permeation flux is finally calculated as a function of the sweep-side oxygen activity at the three temperatures and compared with the experimental values available.