Scanning transmission electron microscopy imaging of 180° ferroelectric domains and application to Ca0.28Ba0.72Nb2O6 single crystals

Understanding the configuration of ferroelectric domains and domain walls is critical for the fabrication and engineering of ferroelectric devices. Here, we demonstrate that scanning transmission electron microscopy (STEM) can be used to resolve a high density of 180° ferroelectric domains in Ca0.28Ba0.72Nb2O6 single crystals, previously studied by conventional transmission electron microscopy. We demonstrate the advantages of STEM for imaging in a specific set of diffraction conditions and deflection settings in conjunction with an angular dark-field detector. We specifically investigated the structure of a 180° domain wall at atomic resolution by aberration-corrected STEM under annular bright field and high angle annular dark field conditions. Our results suggest, based on observed cation displacements, that the 180° domain wall is a combination of Ising and/or Bloch-Néel types rather than pure Ising type, consistent with recent theoretical predictions.