Chemical diffusivity and ionic conductivity of GdBaCo2O5+δ

The transport properties of layered perovskite GdBaCo2O5+delta (GBCO), which has recently been proposed as a cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs), are investigated as a function of oxygen partial pressure (OPP) over the oxygen partial pressure range of 10(-4) <= pO(2) (atm) <= 0.21 at 1073 <= T(K) <= 1323. The increase in total conductivity with increasing temperature below the low-temperature, order-disorder transition indicates a semiconductor-type behaviour with an activation energy of 0.42 eV. When OPP is increased to air pressure at a fixed temperature, the total conductivity increases with an apparent slope (partial derivative log sigma/partial derivative log pO(2)) of 1/10 to 1/22. The maximum oxygen ion conductivity,as extracted from the oxygen permeation measurements,is around 0.01 S cm(-1) under the nitrogen condition, which strongly supports the potential for cathode application. The chemical diffusion coefficient((D) over tilde) and surface exchange coefficient (kappa) are also calculated from the d.c. conductivity relaxation measurement and the values are best fitted by the following two equations: (D) over tilde (cm(2) s(-1)) = 1.88 x 10(-2) exp (-0.77 eV/kT), kappa(cm s(-1)) = 1.37 x 10(0) exp (-0.86 eV/kT) (C) 2009 Elsevier B.V. All rights reserved.