SEM-based techniques are shown to be powerful tools for thedetermination of grain boundary electrical activity in zinc oxidevaristors and barium titanate PTC thermistors. Commercial thermistormaterial was studied by in situ heating above the Curie temperature.Conductive model (restive) contrast clearly showed grain boundarieswith differing degrees of PTC effect. The different behaviour ofstrongly active and inactive interfaces was compared with thedifferences in grain boundary crystallography determined by electronbackscattering patterns, and discussed in terms of the coincidencesite lattice model.
展开▼
