Direct evidence for grain boundary potential barrier breakdown via in situelectron holography

Static and dynamic grain boundary potential barrier effects are directly ob served at high spatial resolution for a varistor of model structure and che mistry. Grain boundary mechanisms for nonlinear electrical behavior are inv estigated for Nb-doped SrTiO3 bicrystals by in situ high-resolution electro n holography under applied current coupled with electrical measurements. Fo r the static case, holography reveals a positive grain boundary barrier of about 0.45 V, which is indicative of positive grain boundary charge adjoine d by negative space charge regions. Under high applied current, in situ hol ography records the breakdown of this grain boundary barrier in accord with the macroscopic varistor effect, which is reflected in bulk I-V experiment s.