Preparation of Porous BaTiO3 PTC Thermistors by Adding Graphite Porosifiers

Using an ordinary ceramic processing technique, a new method of preparing porous BaTiO₃, PTC thermistors is introduced. Adding proper graphite powders into calcined BaTiO₃, powder can increase porosity and enhance the PTC effect of the sintered sample. When the graphite addition is about 1.0 wt%, the resisivity of samples from low-purity raw materials decreases to 20 Σ·cm at room temperature, while the PTC resistivity ratio is over 10⁵ and 1–2 orders higher than that of samples without the porosifier. The porosifier has increased the reproducibility of resistivity from 60% up to 90%. In addition, the porous thermistor has a fast response to overcurrent and shows some improvement in heat resistance. With the aid of the Heywang model and the Kuwabara conclusion, the influence of graphite on grain surfaces is discussed. The experimental results show that this method is a useful technique to prepare good PTC thermistors from low-purity raw materials.