SPACE-CHARGE DISTRIBUTION ACROSS INTERNAL INTERFACES IN ELECTROCERAMICS USING ELECTRON HOLOGRAPHY .1. PRISTINE GRAIN-BOUNDARIES

The role and importance of interface charge and the associated space-c harge in governing the electrical activity of interfaces are well appr eciated, and have been the focus of a large number of investigations. Despite a considerable progress in this area, the direct determination of the sign, magnitude of the interface charge, and the space-charge potential associated with the interface double-Schottky barrier has re mained elusive. We propose electron holography as a bulk sensitive too l with subnanometer resolution to obtain direct real-space evidence of space-charge, as well as determine the electrical activity of individ ual grain boundaires (GBs) in electroceramics. Part I of this investig ation is focused on the theory and practice of electron holography of interfaces, in the context of pristine (undoped) GBs in SrTiO3. We sho w that pristine GBs exhibit very little electron phase change, and tha t the phase change is associated with a reduction in the mean inner po tential and with any residual charge, both present by the virtue of th e GB. This investigation forms the basis for the electron holography i nvestigation of doped (charged) GBs in Part II. It is shown that quant itative information about the magnitude, sign, and spatial extent of e lectrical potential and charge, as well as defect densities across ind ividual GBs in electroceramics, can be obtained using transmission ele ctron holography.