The role of SiO₂ in semiconducting BaTiO₃-based ceramics: Extension of the Jonker model and effect on the electrical properties

BaTiO₃-based ceramics with positive temperature coefficient of resistance (PTCR) recently gained in significance due to their application as cabin heaters in electrical vehicles. Although used as a sintering aid in BaTiO₃ ceramics for decades, the effect of SiO₂ on the electrical properties as well as the underlying physical mechanisms have not been investigated in detail. Here, we systematically study the influence of SiO₂ on PTCR properties, but also on the resistance development at temperatures below the PTC regime, which has hardly been given attention to so far. Using capacitance-voltage measurements, we determine temperature dependent grain boundary potential barrier parameters. By combining these results with x-ray diffraction measurements and resistance-temperature properties, we propose a model describing the resistance evolution throughout the whole temperature range from room-temperature up to the PTCR regime. Further, we show that electrical field strength increases with higher SiO₂ content, accompanied by a reduced voltage sensitivity of resistance.