Probing heterogeneity in ptcr-BaTiO3 thermistors by local probe electrical measurements

Abstract

This paper reports on the conductive atomic force microscopy (C-AFM) characterisation, with high lateral resolution, a commercially available positive temperature coefficient of resistance (ptcr) BaTiO3-based thermistor. The sample has been investigated in the 25 to 250 °C temperature range, to study the conduction mechanisms below and above the ferroelectric-paraelectric transition around the Curie temperature (Tc ~ 130 °C). The combined effective thickness of the Schottky barrier regions associated with the grain-shell and grain boundary regions has been measured directly using C-AFM and is found to decrease from ~ 547(1) nm below Tc to 468(1) nm above Tc. The C-AFM results demonstrate the ptcr-effect is associated with both the grain boundaries and outer grain-shells of the ceramics. This confirms conventional Impedance Spectroscopy measurements that have been used to propose that the ptcr-effect is both a grain boundary and bulk phenomenon.