Fabrication And Research On Lead-free Capacitor Ceramics With Perovskite Type Structure

The effects of composition and crystal lattice of lead-free ceramics with perovskite type structure, which is employed in dielectric capacitor applications, have been widely investigated. And then, aiming at exploring materials with high dielectric performance and relaxer character, a theoretical model of normal random distribution of Curie point has been put forward, which can tell the influence of the fluctuation in content and structure of micro-domains on the Curie point of the ceramics.Firstly, we study the Ce and Cu doping effects on dielectric properties, crystal lattice and the microstructure of BaTiO3 ceramics. Ce4+ replace Ti4+ ions in B-site of perovskite type structure, which restrain the spontaneous polarization. Owning to the shifting of Curie point towards low temperature, the permittivity becomes higher at room temperature; Cu doping can enhance the mass transfer in liquid phase during the sintering process, as a result, the microstructure is changed and the sintering temperature is lowered.And then, the crystal lattice and dielectric performance of (Bi0.5Na0.5)TiO3- BaTiO3 have been analyzed. The permittivity is lifted in whole temperature range, because of the ion vacancy generating during the substitution of Ba2+ on Na+. Due to the stuffing of BaO in Bi3+ and O2- vacancies, the dielectric loss is depressed. Meanwhile, the high lattice energy of morphotropic phase boundary (MPB) and the appearance of tetragonal contribute a lot in the enhancement of dielectric property. Y3+ doping presses the dielectric peak of ceramics; Ce doping restrains the loss tangent of BNBT6 samples, which shows similar function in BaTiO3 ceramics. Then, we analyze the phase transition process of BNT-based ceramic by studying the thermogram of permittivity.Further, we synthesize Ba(ZrTi)O3 ceramics and find MPB in 20-30at% of Zr content, in which trigonal and tetragonal coexist. Owning to the high lattice energy, the permittivity and relaxation property are improved notably. Then, we investigate the Y3+ doping in Ba(Zr0.25Ti0.75)O3 sample and conclude that there are two step in the substitution of Y3+ on original ions, combining the X ray diffraction analysis and thermogram of permittivity; Ce doping doesn't enhance the dielectric properties much, but we detect a phenomenon of semi-conduction in the sample with 0.4 and 0.6at% Ce4+ content.Finally, combining the theory of random process and experimental results of Ba(ZrTi)O3-based ceramics, we put forward the theoretical model of normal random distribution of Curie point, basing on the theory of composition fluctuation. Then we verify the model with the experiment data, and the results match up well. The model offers a guide for exploring new lead-free ceramics with high relaxation and dielectric property for capacitor applications.