Germanium and iron co-substituted SrCoO2.5+delta as oxygen permeable membrane
Abstract Germanium and iron co-doped SrCoO 2.5+ δ was investigated in terms of phase stability, oxygen permeability and electrical conductivity. The favorable high-temperature cubic structure of SrCoO 2.5+ 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 SrCo 0.8 Ge 0.2 O 2.5+ δ sample which showed a sharp decrease in oxygen permeability at temperature of ∼875 °C upon cooling, SrGe 0.1 Co 0.8 Fe 0.1 O 3− δ sample remained well-permeable to oxygen at lower temperatures down to at least 820 °C; an abrupt change in electrical conductivity in SrCo 0.8 Ge 0.2 O 2.5+ δ also occurred accompanying the phase transition. The oxygen permeation flux for SrGe 0.1 Co 0.8 Fe 0.1 O 3− 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.