AN INVESTIGATION OF ACCEPTOR-DOPED GRAIN-BOUNDARIES IN SRTIO3

Grain boundary (GB) doped SrTiO3 exhibits interesting electroceramic p henomena including varistor and barrier layer capacitor behaviour. We present here our investigation of GB acceptor-doped SrTiO3 using analy tical electron microscopy including electron holography. Mn was diffus ed into sintered polycrystalline SrTiO3 to attain GBs which are rich i n Mn. The presence and spatial extent of Mn at the GBs were analysed u sing x-ray emission spectroscopy (XES) and parallel electron energy lo ss spectroscopy (PEELS). The valence state of Mn was determined using PEELS to be predominantly +2. Finally, transmission high-energy electr on holography was utilized to directly image and quantify the electros tatic potential and associated space-charge across the GBs directly. T he holography results reveal a negatively charged GB with positive spa ce-charge, indicating that Mn with a valence of +2 resides as an accep tor dopant on the Ti site at the GB core. The barrier height and local charge density distribution, including the Debye length, of the doubl e Schottky barrier at the GB are derived from these holography results . This investigation demonstrates the usefulness of electron holograph y as a bulk-sensitive technique to probe the statics and dynamics of e lectrostatic field distribution and electrical charge across interface s in technologically useful materials, and the need to employ diverse analytical techniques for such an investigation.