Preparation And Dielectric Properties Of B-site Doped Barium Titanate Ceramics

Barium titanate with a perovskite structure is noteworthy for their exceptional dielectric, piezoelectric properties with corresponding electronics applications, and is mostly used to make multilayer ceramic capacitor (MLCC) materials. Routes for synthesis barium titanate and doped barium titanate have been a focal point in the field of inorganic solid chemistry. Sol-gel auto-combustion synthesis and Sol-gel process offer exciting possibilities for the synthesis of high purity, homogeneous, ultrafine powders which meet the need of electronic components in factual application. Therefore, the preparation and dielectric properties of barium titanate ceramics with B-site doped were chose as the research task. Barium titanate powders and ceramics with B-site doped were prepared by sol-gel process using oleic acid (OA) as surfactant and sol-gel auto-combustion. The effect of doped concentration and technical parameter on the phase and dielectric properties of barium titanate powders and ceramics were investigated in this paper to get the optimal doped concentration and technical parameter to meet the Y5V standard of EIA.The main research contents are as follows:1. The Nb-doped BaTiO₃ nano-sized powders with particles about 70 run were prepared by Sol-gel auto-combustion process.The Nb-doped BaTiO₃-based powders were mainly in cubic BaTiO₃ phase and the phase of Ba₆Ti₁₇O₄₀ appears when the Nb concentration was 5.0mol%. Cubic BaTiO₃ phase was transformed into tetrahedral BaTiO₃ phase in the sintering procedure. When the Nb concentration was 1.0mol% and sintering temperature were 1250℃(for 2 hours) respectively, the maximum dielectric constant of as-sintered ceramics was 5539, the lowest dielectric loss was 0.008.2. The Ag-doped BaTiO₃ powders were prepared by sol-gel process using OA as surfactant, and the nanometer scale powders (53 nm) were mainly in cubic BaTiO₃ phase. After sintering, the ceramics were completely consisted of the tetrahedron BaTiO₃ phase. The dispersibility of the powders calcined at 900℃for 2h was improved.And the relative density of the ceramic sintered at 1280℃for 2h was 98.5%,room temperature dielectric constant reached 7669, and the dielectric loss was 0.027 when the ratio of [Ti(OBu)₄]/[OA] was 1:1.3. The nano-sized and homogeneous of Sn-doped BaTiO₃ powders and ceramics were prepared by Sol-gel process. The optimum calcining and sintering temperature were 1000℃and 1350℃for 2 hours respectively. And the Sn-doped BaTiO₃ powders were cubic phase solid solution, the Curie temperature was shift to low temperature, the dielectric constant increased firstly and then decreased with the increase of Sn⁴⁺ content. When the Sn⁴⁺ content was 0.05mol%, the dielectric constant (19235) was the highest and the dielectric loss was 0.042. In the system of BaSn_xTi_1-xO₃, the multiphase ceramics of multiphase coexistence can be got by mix sintering and selecting the appropriate high and low temperature compose ratio.4. The multiple compose coexistence BaTiO₃ based powders and ceramics doped with Sn⁴⁺, Zr⁴⁺ and rare earth were prepared by Sol-Gel method. When the content of Y³⁺ was 0.07 mol%, the temperature-stable were enhanced; The Curie temperature was shift to low temperature and the dielectric constant of ceramics increases firstly and then decreases with the content of Zr⁴⁺ increased; When the content of Zr⁴⁺ was 0.11 mol% the dielectric constant was 5869 and the dielectric loss was 0.041; at the high temperature segment, the dielectric constant was good when the content of Sn⁴⁺ was lower than 0.085mol%; When the content of Sn⁴⁺ was higher than 0.085mol%, the dielectric constant of BaTiO₃ based ceramics was decreased andε-T curve was widen. The ceramics with the content of 0.07,0.085, 0.10mol% Sn⁴⁺ can met the standard of Y5V.