Ultramicroscopy 86 (2001) 303–318 Valence electron energy loss study of Fe-doped SrTiO 3 and a S13 boundary: electronic structure and dispersion forces K. van Benthem a, *, R.H. French b , W. Sigle a , C. Elsa¨sser a , M. Ru¨ hle a a Max-Planck-Institut fu ¨r, Metallforschung, Seestrabe 92, D-70174 Stuttgart, Germany b DuPont Corporation Central Research, E356-384, Exp. St., Wilmington DE 19880-0356, USA Received 14 July 2000; received in revised form 11 September 2000 Abstract Valence electron energy loss spectroscopy in a dedicated scanning transmission electron microscope has been used to obtain the interband transition strength of a S13 tilt grain boundary in SrTiO 3 .Inafirststeptheelectronicstructureof bulk SrTiO 3 has been analysed quantitatively by comparing VEELS spectra with vacuum ultraviolet spectra and with ab initio density of states calculations. The electronic structure of a near S13 grain boundary and the corresponding dispersion forces were then determined by spatially resolved VEELS. Also the effects of delocalization of the inelastic scattering processes were estimated and compared with results from the literature. # 2001 Elsevier Science B.V. All rights reserved. PACS: 82.80.P; 61.72.M; 78.20 Keywords: Electron energy-loss spectroscopy; VEELS; SrTiO 3 ; Grain boundary; Electronic structure; Delocalization; Interband transitions; Optical properties 1. Introduction Materials crystallizing in the perovskite struc- ture are used in applications such as oxygen sensors, actuators, capacitors or simply as sub- strates for thin film growth. Since polycrystalline material is used frequently, the influence of grain boundaries (GBs) on the material properties may be essential. As an example it is well known that GBs can reduce the ionic conductivity (e.g. [1–6]), especially in doped materials. This is often ascribed to the formation of space charge layers which compensate the charge of dopants or impurities segregated to the grain boundary thus leading to the formation of a double Schottky barrier (see e.g. [7]), whose space charge layer can have a spatial extent of several tens of nanometers. In addition, high-angle, or high S GB can exhibit substantial changes from the bulk material, with impurity and/or cation segregation or depletion at the boundary, changes in oxidation due to differences in the stoichiometry, and even changes in physical density because of linear or volumetric expansions of the material at the grain boundary. These types of phenomena are more often seen at *Corresponding author. Tel.: +49-711-2095-311; fax: +49- 711-2095-320. E-mail address: benthem@hrem.mpi-stuttgart.mpg.de (K. van Benthem). 0304-3991/01/$-see front matter # 2001 Elsevier Science B.V. All rights reserved. PII:S0304-3991(00)00121-2