Conductive mode imaging of thermistor grain boundaries

PTC thermistors undergo a rapid increase in grain boundary resistivity, covering several orders of magnitude, at temperatures just above the Curie temperature, T-C, which is associated with a ferroelectric to paraelectric phase transformation. In this study, hot-stage conductive mode scanning electron microscopy has been used to investigate the characteristics of individual thermistor grain boundaries over a range of temperatures around T-C. Using the remote electron beam induced current (REBIC) configuration, imaging has revealed EBIC contrast consistent with the presence of negatively charged electrostatic grain boundary barriers for the first time in a commercial thermistor. Not all grain boundaries within the thermistor were found to be EBIC active and the EBIC contrast was only observed at temperatures above T-C. EBSP analysis of grain boundary crystallography indicated that the EBIC active grain boundaries were predominantly high angle. (C) 2003 Elsevier Ltd. All rights reserved.