Study On Refinement Of Grains And Low Temperature Sintering Properties Of BaTiO₃ Based Semiconductor Ceramic

With the rapid development of science and technology, the miniaturization, multifunctionalization and chip technology of electronic components have become as the mainstream. As an integral part of electronic components, the chip technology is also imperative. The main problem of preparing multilayer chip components PTCR is the preparation of fine grained ceramics and lower sintering temperature of PTCR ceramic in order to achieve co-firing between ceramic layers and electrodes. This thesis made the preparation of multilayer chip PTCR thermistor element as the ultimate goal, mainly studied on preparation of fine-grained ceramic powders and sintering PTCR ceramics with low temperature.Several kinds of nano BaTiO₃ powder were prepared by different methods. The effects of the reaction temperature, time and material match of the hydrothermal synthesis on the properties of nano BaTiO₃ were investigated. The particle size of BaTiO₃ increased with the reaction temperature and time increased. By optimizing the condition of reactive system, we could prepare pure BaTiO₃ powder with particle size of 32nm, and Ba / Ti of 0.9520 in perovskite structure. The sol - gel method could also synthesize BaTiO₃ powder with particle size of 100-200 nm.The effect of doping method (liquid deposition coating; conventional ball-milling mixing) on microstructure and electrical properties of nano-grained BaTiO₃ ceramics were investigated. The results showed that the liquid deposition coating method produced a homogeneous distribution of the additive in nano-grained BaTiO₃ ceramics, and obtained homogeneous microstructures. The samples with 0.3 mol% Y(NO₃)3 resulted in low room-temperature resistivity of 37.8Ω·cm, ratio of log (Rmax/Rmin) of 4.8 and temperature coefficient of resistance of 56%/℃. Two-step sintering method was used to control grain growth. The samples sintered at 1250℃for 5 mins resulted in the average grain size of 1-2μm, room-temperature resistivity of 46.8ΩΩcm, and ratio of log (Rmax/Rmin) of 3.5.In order to lowering the sintering temperature of BaTiO₃-based PTCR ceramics, the BaO-B2O₃-SiO₂-MnCl₂-LiF sintering aid was proposed to add in. The effects of BaO-B2O₃-SiO₂-MnCl₂-LiF sintering aid on microstructures and PTCR characteristics of BaTiO₃ ceramics were investigated. The experiment results indicated that PTCR ceramics with 0.5 mol% LiF could produce enough liquid at sintering process and result in low room-temperature resistivity of 151 cm and a resistivity jump of 5.6х10³.