Study On High Temperature (125℃,150℃,190℃) Stable BaTiO₃ Ceramic Dielectric System With High Dielectric Constant

The dissertation started with the analysis of the crystal structure of BaTiO₃, then studied the preparation of high-K X7R, high-K X8R and intermediate temperature sintering high-K X8R dielectric ceramic system by modern methods such as XRD, SEM, EDS etc.. The article also discussed the effect and microscopic mechanism of modified dielectric ceramic system and the effect of system component and procedure to the dielectric properties of the system.The effects of the agents such as Nb₂O₅, CoCO₃, MgO, CeO₂, Sm2O₃, MnCO₃, glass and procedure conditions to the dielectric properties of X7R BaTiO₃ were studied first. The mechanism of the modification of the system by the agents was also analyzed, and the core-shell structure was proved by the experiments. A perfect high-K X7R ceramic system with the following parameters was gained: sintering temperature 1240℃,ε≥5800 under 1 kHz,tanδ≤1.5%,-15%<Δε/ε<15% in the region of -55～125℃,ρv≥1×1012Ω·cm.Then a X8R ceramic system was gained by the studies of the effect and mechanism of adding Nb₂O₅ and MgO to BaTiO₃ system. The effect of changing the ratio of Ba/Ti was also studied. The further researches focused on the doping of PbTiO₃, PbO, Pb(Ti,Sn)O₃ and gained a perfect high-K X8R ceramic system with the following parameters by adding Pb(Ti0.6,Sn0.4)O₃ to the high-K X7R ceramic system: sintering temperature 1260℃,ε≥3200 under 1kHz,tanδ≤1.8%, -15%<Δε/ε<15% in the region of -55～170℃.With the doping of Bi2O₃, the system was able to be sintered under intermediate temperature. The ceramic system with the following parameters was found: sintering temperature 1180℃,ε≥2650 under 1kHz,tanδ≤1.1%, -15%<Δε/ε<15% in the region of -55～190℃.The lead-free materials was also studied in the paper. The substitution of (Na,Bi)TiO₃ for Pb(Ti_0.6,Sn_0.4)O₃ was researched and gained a ceramic system with the following parameters:ε≥2070 under 1kHz,tanδ≤2.7%.