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 Ba0.5 Sr0.5 Co0.8 Fe0.2 O3-δ (BSCF) in the presence of both H2 O 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 H2 O into BSCF. SrCoO3-δ was found to exhibit small oscillations, while none were observed for La0.5 Sr0.5 CoO3-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.