Synthesis of BaTiO_3-based PTCR Powders via a Liquid Phase Process

Ultrafine BaTiO3-based powders used for making positive temperature coefficient of resistance (PTCR) were synthesized by two chemical steps: polyacrylamide gel process and liquid phase coating process. Firstly, doped BaTiO3-based powders were synthesized by polyacrylamide gel process at rather low temperature, and the physical and chemical characteristics of the gels and the precursor powders were investigated by DSC, TG, XRD, TEM. The results showed that single phase of (Ba, Sr)TiO3 was obtained when the gel was calcined at 700℃ for 2h, and the mean diameter of grains d50 was 1.155μm. Secondly, acceptor and sintering aid were coated by an aqueous solution containing acceptor and additive. The microstructure characterization and sintering behavior of the PTCR powders and PTC effect of the ceramic samples derived from the PTCR powders were investigated. Ceramic samples with low room temperature resistance 17.5Ω, ratio of the maximum resistivity to the minimum (Rmax/Rmin) 104 and temperature coefficient of resistivity (α) 12% were obtained.