Investigation of three-dimensional grain-boundary structures in oxides through multiple-scattering analysis of spatially resolved electron-energy-loss spectra

Grain boundaries in oxide materials such as electroceramics, ferroelectrics, and high-T-c superconductors are known to dominate their overall bulk properties. The critical first step in a fundamental understanding of how they control the properties of the material is a determination of the atomic structure of the boundary. While this determination has traditionally been performed by transmission-electron microscopy, the images that are generated are only a two-dimensional projection of the atomic columns in the grain-boundary core. In addition, as the images are least sensitive to light elements, such as oxygen, the complete three-dimensional boundary structure is particularly difficult to determine. Employing electron-energy-loss spectroscopy in a scanning transmission-electron microscope, it is possible to obtain an oxygen K-edge spectrum that contains information on the three-dimensional electronic structure of the boundary. Using the multiple-scattering methodology, originally developed for x-ray absorption near-edge structure, this can be directly related to the local three-dimensional atomic structure. Contained in the spectrum is therefore all of the information needed to investigate the atomic scale structure-property relationships at grain boundaries. The application of the technique is demonstrated here for the 25 degrees [001] symmetric tilt boundary in SrTiO3.