Preparation And Properties Of BaTiO₃-based PTCR Fine-grained Ceramics

PTCR thermistor must develop towards multilayer, chip type, low room temperature resistance to meet miniaturization, chip type, low loss of electronic device. To prepare high-performance multilayer PTCR, there are two key points: first, preparing fine-grained ceramic to ensure strong PTC effect and high resisting electrical strength with the decrease of size; second, lowering sintering temperature and improving the formulation of electrode paste to prevent oxidation of inner electrode. This paper mainly studied on preparing of fine-grained ceramic powders and forming of chip PTCR ceramics.The influence of content of donor element, content of acceptor element, presintering temperature and sintering temperature on grain size were systemically studied to find that PTCR ceramic with raw materials synthesized by solid phase method could semiconduct at about 1280℃and the average grain size was less than 2μm. In order to lower the sintering temperature of ceramic, BaTiO₃ powders were synthesized by sol-gel method. The average particle size can be 37 nm. The PTCR ceramic prepared by nanometer BaTiO₃ powders could semiconduct at about 1240℃and the average grain size was less than 2μm. BaTiO₃ powder prepared by sol-gel method was more suitable for multilayer chip PTCR components than that prepared by solid phase method. Tape casting has been the main technology to prepare multilayer chip PTCR components. Green tape made from nanometer BaTiO₃ powder was prepared by organic tape casting. The average grain size of samples sintered at 1250℃was less than 1μm. The average room temperature resistivity of samples sintered at 1260℃was 327Ω·cm and the resistance rising rate could reach 1.059×10⁴. For the demand of environmental protection, aqueous tape casting process was systemically investigated. With the same raw material, green tape was prepared by aqueous tape casting. The average grain size of samples sintered at 1250℃was less than 2μm. The average room temperature resistivity of samples sintered at 1260℃was 385Ω·cm and the resistance rising rate could reach 4.304×10⁴.