Nanoscale structural oscillations in perovskite oxides induced by oxygen evolution

Understanding the interaction between water and oxides is critical for many technological applications, including energy storage, surface wetting/self-cleaning, photocatalysis and sensors. Here, we report observations of strong structural oscillations of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ (BSCF) in the presence of both H₂O vapour and electron irradiation using environmental transmission electron microscopy. These oscillations are related to the formation and collapse of gaseous bubbles. Electron energy-loss spectroscopy provides direct evidence of O₂ formation in these bubbles due to the incorporation of H₂O into BSCF. SrCoO_3-δ was found to exhibit small oscillations, while none were observed for La_0.5Sr_0.5CoO_3-δ and LaCoO₃. The structural oscillations of BSCF can be attributed to the fact that its oxygen 2p-band centre is close to the Fermi level, which leads to a low energy penalty for oxygen vacancy formation, high ion mobility, and high water uptake. This work provides surprising insights into the interaction between water and oxides under electron-beam irradiation.