Direct imaging of the core-shell effect in positive temperature coefficient of resistance-BaTiO3 ceramics

A conductive atomic force microscopy (C-AFM) study on a positive temperature coefficient of resistance (ptcr) BaTiO3 thermistor is reported. The method provides imaging of the dielectric properties with a lateral resolution on the nanometer scale. Measurements were carried out in the temperature range of 25-250 C to study the conduction mechanisms below and above the ferroelectric-paraelectric transition at similar to 130 C. The effective thickness of the barrier regions associated with the grain-shell and grain boundaries is similar to 450-550 nm and is similar to 10% of the volume fraction of the grains. The C-AFM results therefore confirm previous impedance spectroscopy studies that show the ptcr-effect to be associated with both the grain boundaries and outer grain-shells of individual grains.