INVESTIGATION OF 3-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, ferroelec trics, and high-T-c superconductors are known to dominate their overal l bulk properties. The critical first step in a fundamental understand ing of how they control the properties of the material is a determinat ion 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 im ages are least sensitive to light elements, such as oxygen, the comple te three-dimensional boundary structure is particularly difficult to d etermine. Employing electron-energy-loss spectroscopy in a scanning tr ansmission-electron microscope, it is possible to obtain an oxygen K-e dge spectrum that contains information on the three-dimensional electr onic structure of the boundary. Using the multiple-scattering methodol ogy, originally developed for x-ray absorption near-edge structure, th is can be directly related to the local three-dimensional atomic struc ture. Contained in the spectrum is therefore all of the information ne eded 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.