| BaTiO3-based ceramic is in the majority of material with high dielectric constant, and it is widely applied in filtering, by-pass, voltage stabilization, rectification, AC circuit-breakers and so on. However, the rapid development of electronic industry has led to a higher demand for the components, to realize the miniaturization and precision. The key to satisfy it is to prepare ceramic materials with higer dielectric constant. On the other hand, barium titanate ceramic only performs well in low frequencies(?1 kHz). Its dielectric properties are strongly depend on frequency, thus limiting its application. In view of the above problems, this paper took BaTiO3 as the base material for its obvious ferroelectricity. By solid-state method, BaTiO3 was modified by equivalent ions in A or B site and doped rare earth element. The effects of the modifying ions to the phase stucture, microstructure and dielectric properties were discussed, aiming at improving the dielectric constant at room temperature and frequency stability of BaTiO3 ceramic.Ba1-xCax Ti O3(x=0~0.20) solid solution took advantage of the quantum paraelectric state and excellent frequency stability of CaTiO3, and its structure and dielectric properties were investigated in this paper. The results showed that, the Ca2+ substitution caused a effective decrease in dielectric loss and frequency dependence, and it had little influence on the curie temperature and the shape of curie peak.With the increasing Ca2+ content, the breakdown strength increased. By comparison, Ba0.85Ca0.15TiO3 showed the best fit dielectric property to our purpose: frequency dependence ??r/?r=7.43 %, dielectric loss(at 1 kHz) tan?=0.011.Sn4+ can dissolve in the B-site of the BaTiO3 lattice, and gather the three phase transformation points of BaTi O3. Ba0.85Ca0.15 Ti O3 was chosen as the base composition, and 5~20 mol% Sn4+ were added. As a result, Sn4+ replacement caused a obvious broadening of the curie peak, indicating a diffuse phase transition. Owing to the superposition of each phase transition peak, dielectric constant at room temperature was improved. When Sn4+ content was 11 mol%, the sample possessed the maximum one(?r=11025). When Sn4+ content was 20 mol%, frequency dependence(??r/?r) was as low as 0.97 %, showing the optimal frequency character, while the dielectric loss(at 1 kHz) reached a fairly small value 0.0018.In order to further enhancing the dielectric constant at room temperature, rare earth element yttrium was chosen as the dopant. Ba0.85Ca0.15Ti0.89Sn0.11O3 ceramic was decided as the base material for its maximum dielectric constant in the BCTS series. In the result analysis, only when the Y3+ content was 0.5 mol%, was the dielectric constant enhanced(?r=13514). Y3+ acted as donor at a very low concentration, and cationic vacancies offered compensation. Once Y3+ content exceeded a certain amount, the compensating defects converted to oxygen vacancies, causing a drop in dielectric loss. When the Y3+ content reached 2.0mol%, the sample showed the lowest dielectric loss(tan?=0.0058). When the Y3+ content exceeded 0.5 mol%, the dielectric curves of temperature were flattened. But it showed no significant effect on optimizing the frequency stability of the base material. |
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