钛酸钡固溶体“芯-壳”纳米复合结构的制备及其高温介电性能的研究

With the increasing demands of passive components which are capable of working at high temperature, much attention has been paid to dielectrics satisfying EIA X8R/X9R specification(-55-150℃/200 ℃,（△C/C25）≤±15% or less), especially for multilayer ceramic capacitors( MLCCs) whose upper limit temperature reach 200℃.High temperature stable MLCCs find wide applications for automobile, oil drilling, aerospace application and military. In this project, The solid solutions BaTiO3-BiScO3、BiYbO3-BaTiO3、BaTiO3-Na0.5Bi0.5TiO3 are synthesized by solid state reactions and chemical method in order to find out good solid solution materials with high Curie temperature(Tc) and good dielectric property. The composition and grain size effect on microstructure and dielectric property will be studied in details. In order to improve the temperature coefficient of capacitance (TCC) for X9R specification, BaTiO3 based solid solution materials with high Tc will be modified with additives to form grain core-shell structure through uniform chemical coating technology. The influnces of the coating layer compositions, coating layer thickness, sintering temperature as well as sintering atmosphere on the ceramic microstructures and high temperature dielectric properties are investigated systematically. Two-step sintering technique is also used to further control the evolution of core-shell structure carefully and lower the sintering temperature. High temperature stable dielectric materials of good environment with excellent performance will be developed for X9R MLCC applications.The achivements of this project will provide scientific foundation and technology for manufacturing X9R MLCC components.

高温陶瓷电容器在汽车、石油钻探、航空航天、军工等领域都有着广泛的应用。但目前我国在150-200度高温下使用的X8R/X9R型多层陶瓷电容器(-55-150/200度, 电容变化率（△C/C25）≤±15%)完全依赖进口。因此本课题拟系统地研究BaTiO3-BiScO3、BaTiO3-Na0.5Bi0.5TiO3固溶体系的组成、晶体结构与介电性能关系，探索获得具有高居里温度的铁电固溶体；进一步通过掺杂剂的均匀化学包覆构建core-shell纳米复合结构以满足高温度稳定特性X9R的要求，研究纳米包覆组成、厚度、烧结气氛、烧结工艺（两段式、普通烧结）等对陶瓷微结构与介电温度特性的影响规律与形成机理，建立高温介电陶瓷温度稳定性与纳米尺度微结构控制的技术，研制出具有优异特性的高温陶瓷电容器材料。为制备环境友好的新一代高可靠性高温多层电容器提供科学依据和技术支撑。

高温陶瓷电容器在汽车、石油钻探、航空航天、军工等领域都有着广泛的应用。目前我国在200度高温下使用的X9R型多层陶瓷电容器(-55~200℃, 电容变化率（△C/C25）≤±15%)完全依赖进口。本课题研究了几种钛酸钡基固溶体系的组成与介电性能关系，获得了具有高居里温度的铁电固溶体；通过掺杂及均匀化学包覆构建core-shell纳米复合结构，制备了具有高温稳定性X9R的MLCC用介质材料，对材料的成分、粒径、结构与性能之间的关系做了大量系统性和创新性研究工作。.1）系统研究了BaTiO3-Bi0.5Na0.5TiO3 (BTBNT)、BaTiO3-Bi0.5K0.5TiO3(BTBKT)、BaTiO3-BiScO3、BaTiO3-BiYbO3固溶体组成、晶体结构与介电性能关系，结果表明BTBNT、BTBKT固溶体具有高的居里点（180-200℃）适合用于高温稳定型电介质材料。.2）研究了不同元素的掺杂对高居里温度BTBNT固溶体陶瓷晶粒core-shell微观结构形成与控制机制与高温介电性能变化规律。发现了Nb（Ta）是促使“芯—壳”结构形成的重要因素， Nb5+和Ta5+主要占据B位，形成壳部决定低温端性能，芯部为铁电性的BTBNT决定高温端性能，掺杂量决定芯壳比例，进而影响介电常数的温度稳定特性；而大离子半径的元素，如La3+、Nd3+、Sm3+等，主要占据A位，通过A-B位共掺，进一步合理调节“芯—壳”结构，实现高的温度稳定性。.3）通过化学包覆法和两段式烧结技术实现了精细控制晶粒的core-shell微观结构，进一步提升了材料的高温介电温度稳定性能。获得了兼顾高温稳定性和高介电常数性能优异的细晶X9R型无铅介质陶瓷材料。特别是两段式烧结可以将烧结温度降低到850℃，而室温介电常数高达2000，介电损耗小于2.0%，性能达到国际领先水平。.4）以BTBNT-Nb2O5为基体材料，通过MnO2,BCG等掺杂研制出可以在还原气氛下烧结与镍电极匹配的高温稳定型X9R介质陶瓷材料，室温介电常数1800 ~1900，介电损耗小于2.0%，填补了国内外空白。.项目研制出一系列性能优异的X9R型介电陶瓷材料, 为制备环境友好的高可靠性高温多层电容器提供了科学依据和技术支撑。