Germanium and iron co-substituted SrCoO2.5+δ as oxygen permeable membrane

Germanium and iron co-doped SrCoO2.5+δ was investigated in terms of phase stability, oxygen permeability and electrical conductivity. The favorable high-temperature cubic structure of SrCoO2.5+δ was stabilized to lower temperatures by co-doping Ge (10 mol%) and Fe (10 mol%) that substituted for Co, which however could not be achieved by doping Ge (20 mol%) alone. In contrast to SrCo0.8Ge0.2O2.5+δ sample which showed a sharp decrease in oxygen permeability at temperature of ∼875 °C upon cooling, SrGe0.1Co0.8Fe0.1O3−δ sample remained well-permeable to oxygen at lower temperatures down to at least 820 °C; an abrupt change in electrical conductivity in SrCo0.8Ge0.2O2.5+δ also occurred accompanying the phase transition. The oxygen permeation flux for SrGe0.1Co0.8Fe0.1O3−δ increased significantly with the decrease of the membrane thickness, indicating the transport of oxygen ions in the bulk of the membrane as the rate-limiting step.