| Multilayer ceramic capacitors (MLCC) are important fundamental components of electronic information technology. To meet the requirements of the development of electronic system, MLCC are developing towards wide temperature, large capacitance and low cost. BaTiO3 based ferroelectric ceramics are one of the important materials of MLCC. The preparation of temperature-stable high dielectric constant ceramics sintered at medium temperature were researched in this dissertation, of which the principles and micromechanism was researched by modern methods such as XRD, SEM, TEM, EDS on the basis of crystal structure.1. The Pb(Ti0.55Sn0.45)O3 additives can shift the Curie temperature of BaTiO3 to 150oC. Pb2+ substitutes for A-site and Sn4+ substitutes for B-site in ABO3 structure, causing the constituent phase transition diffusion, so the Curie temperature was shifted to higher temperature. According to TEM, XRD, Pb(Ti0.55Sn0.45)O3 and BaTiO3 can form partial solid solution, and core-shell structure was observed. Due to the mutual effect between the core and shell, the temperature characteristics of the capacitance of the system were improved. Doped with Pb(Ti0.55Sn0.45)O3, the nonferroelectric phase Ti 0.1Sn(0.9O2,Ti9O17,TiO was decreased. It is calculated by XRD analysis that c/a ratio in the sample with addition of Pb(Ti0.55Sn0.45)O3 was increased, and the volume of crystal cell was decreased, which implied the enhancement of self-polarization in the system, so arising the augment of dielectric constant The bigger thickness of shell structure was formed due to the rapid diffusion of ion under high temperature,hence the dielectric constant was decreased. Meanwhile, the volume ratio of grain core to grain shell was decreased, which resulted in a significant improvement on the temperature characteristics of the capacitance.2. Bi3+substitutes for A-site in ABO3 structure, the Curie temperature was shifted to higher temperature and flattened, due to the structural phase transition diffusion. Doped with Bi2O3 additions, the new phases Bi4Ti3O12 was formed, and formed liquid phase during the sintering, so the sintering temperature was decreased from 1260℃to 1130℃. It is calculated by XRD analysis that doped with Bi2O3 additions, the c/a ratio was decreased, which implied the decrease of tetragonality in system, so the dielectric constant was decreased accordingly. Because of the interaction and superposition between core and shell and the interaction between the glass phase and grains, the temperature characteristics of the capacitance were improved.3. The nanometer BaTiO3 was doped into ceramics. The nanometer BaTiO3 can promote sintering ability and realize densification, so the dielectric constant was enhanced. The interaction between BaTiO3 and additives was enhanced, and the abundant core-shell structure was formed, so the smaller thickness of shell structure was obtained. The internal stress was enhanced, so the temperature characteristics of the capacitance were improved.4. The synthesis-BaTiO3 was doped into X8Rceramics, the ceramics satisfied X9R specification were producted. Doped with the synthesis-BaTiO3, the partial solid solution of Pb(Ti0.55Sn0.45)O3 was enhanced, and the PbO, PbTiO3 and Ti9O17 were suppressed. It is calculated by XRD analysis that the volume of crystal cell was decreased, and the c/a ratio was decreased resulted in the Curie temperature movement to lower temperature. The dielectric materials could be sintered at 1120℃by doping 3mol% synthesis-BaTiO3 into the ceramics, with a dielectric constant greater than 2200 at 25℃, dielectric loss lower than 1.7% and the temperature characteristics of the capacitance less than±15% from -55℃to 200℃.
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