The preparation of fine-grained positive temperature coefficient resistance with superior electrical properties

The electrical characteristics of positive temperature coefficient resistance (PTCR effects) mainly come from the grain boundary. The useful way to enhance electrical characteristics of PTC ceramics is to decrease the grain size and add the number of grain boundary. In the paper, the grain size and PTCR effects of ceramics were investigated on the effects of the molar ratio of donor and acceptor, the sintering process and high-energy ball milling. The formulation of prepared ceramics were Ba0.8Sr0.2Ti1.01O3 + 0.03 mol% Mn(NO3)2 + x mol Y2O3 + 2 wt% SiO2. The grain size of these PTC ceramics was decreased to only 1–2 μm by adding Sr2+ and Y3+ to substitute the A-site barium ions, which were calcined at 1220 °C and sintered at 1300 °C after high-energy ball milling for powders. The prepared ceramics exhibited room temperature resistivity of 100 Ω cm, resistance rising rate more than 104 unit through the Curie temperature, and relative density between 75% and 90%.

► Synthetical methods are adopted to enhance the electrical properties of PTC ceramics.
► 1–2 μm fine-grained PTC ceramics with superior electrical properties are prepared.
► The physical mechanisms of the fine grain are studied in the discussion part.
► The modification mechanism of the multiple high donor-doped methods are discussed.
► The dynamics mechanism of grain growth in the sintering process are studied.