The high-energy nature of grain boundaries makes them a common source of undesirable phase transformations in polycrystalline materials. In both metals and ceramics, such grain-boundary-induced phase transformation can be a frequent cause of performance degradation. Here, we identify a new stabilization mechanism that involves inhibiting phase transformations of perovskite materials by deliberately introducing nanoparticles at the grain boundaries. The nanoparticles act as "roadblocks" that limit the diffusion of metal ions along the grain boundaries and inhibit heterogeneous nucleation and new phase formation. Ba0.5Sr0.5Co0.8Fe0.2O3-δ, a high-performance oxygen permeation and fuel cell cathode material whose commercial application has so far been impeded by phase instability, is used as an example to illustrate the inhibition action of nanoparticles toward the phase transformation. We obtain stable oxygen permeation flux at 600 °C with an unprecedented 10-1000 times increase in performance compared to previous investigations. This grain boundary stabilization method could potentially be extended to other systems that suffer from performance degradation due to a grain-boundary-initiated heterogeneous nucleation phase transformations.
Keywords: Grain boundaries; nanoparticles; oxygen permeation; perovskite membrane; phase transformation.