| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2016) | |
| Thin Films | Monday Sessions |
| Session TF-MoM |
| Session: | Advances/Innovation in Synthesis & Characterization |
| Presenter: | Dean Miller, Argonne National Laboratory, USA |
| Authors: | D.J. Miller, Argonne National Laboratory, USA J.G. Wen, Argonne National Laboratory, USA X. Wu, Temple University, USA |
| Correspondent: | Click to Email |
Artificially structured perovskite superlattices offer rich opportunities for novel ferroelectricity. We have developed a new high-resolution TEM imaging technique that allows the direct observation of A-site associated oxygen octahedral rotations in perovskite oxide superlattices that reveals the underlying mechanisms of enhance ferroelectricity in complex heterostructures. By combining the amplitude-contrast high-resolution electron microscopy and DFT calculations, we show that a highly polar CaTiO3 phase with a BiFeO3-like structure can be stabilized in (CaTiO3)n/(BaTiO3)n superlatice. Amplitude contrast imaging (ACI) relies on both spherical and chromatic aberration correction for TEM imaging. Under ACI conditions, atomic resolution channeling contrast can be realized, allowing one to obtain directly interpretable high-resolution electron microscopic images with discrimination between light and heavy atomic columns. Using this imaging approach, we were able to image the atomic structure in a BaTiO3/CaTiO3 superlattice with high spatial accuracy and discrimination between Ba and Ca columns, providing direct visualization of the Ca and Ba associated oxygen octahedral rotations. Combined with the first-principles calculations, we found that a highly polar metastable “interface phase” of CaTiO3 with a structure of BiFeO3 is stabilized by the mechanical and electrical boundary conditions of the BaTiO3/CaTiO3 superlattice. Under this new mechanism, a large number of perovskites with the CaTiO3 type structure will become good candidates for novel highly-polar multiferroic materials.