芯-壳结构超高温多层陶瓷电容器介质材料的制备与性能调控

Two disadvantages limit the ultra-high temperature multilayer ceramic capacitor (MLCC) applications: firstly, the temperature stability of dielectric properties are poor; secondly, the dielectric permittivity are still not high enough. In order to improve the dielectric temperature stability of the capacitor materials, new core/shell structure grain systems were designed and will be prepared using the hierarchical liquid phase method. Every dielectric layer in the grain has different Curie temperature. When the grain grow layer by layer, its performance will be the stack results of all the dielectric layers according to the Lichtenecher's law and multimodal effect. On this basis, Bi3+ shows a valence electron configuration of 6s26p0, which allows it to hybridize with the surrounding oxygen anions to improve the polarization of the ferroelectric material, and thus to improve its intrinsic dielectric capacitors. Therefore, Bi3+ will be introduced into A-sites of core/shell structure perovskite ceramic to improve the high temperature dielectric permittivity, as well as their interdependent relationships will be systematically and deep investigated. Consequently, this application not only enrich the ultra high-temperature ceramic capacitor dielectric material system but also provide an alternative direction for searching and developing the ultra-high temperature multilayer ceramic capacitor material. In additional, this study provide the experimental and theoretical supports for the design and performance of high performance high-temperature ceramic capacitor dielectric material to meet the ultra high-temperature MLCC applications.

困扰超高温多层陶瓷电容器介质材料应用的突出问题是介电温度稳定性较差和介电电容较低。针对介电温度稳定性差的问题，申请者提出通过分步式液相法制备芯-壳结构介电陶瓷，按照 Lichtenecher对数叠加原理及介电多峰叠加效应，具有不同居里温度的介质层进行包覆生长后，陶瓷材料介电常数呈现“多峰效应”，介温特性得到改善。在此基础上，本申请通过在芯-壳结构陶瓷钙钛矿的A位引入含6s电子对Bi，以提高铁电材料的极化强度，进而提高其本征介电电容，探索提高高温介电陶瓷介电电容的新途径，并揭示A位6s电子对对其宏观介电电容的影响规律，阐明其影响机制。本项目的完成不仅能够丰富超高温陶瓷电容器介质材料的材料体系，为超高温介电陶瓷的研究探索新的发展方向，而且能够为今后高性能高温铁电陶瓷的组分设计和性能调控研究提供实验和理论支持，为研发高温MLCC提供优秀的候选材料。

对超高温军用以及民用多层陶瓷电容器介质材料来说，同时兼具超高温度和较高介电电容具有重要意义。本研究采用分步式常压液相法制备芯-壳结构纳米粉体，期望在更宽的温度范围内产生“多峰效应”，最终得到满意的高温高介电高稳定性的陶瓷电容器材料。首先合成了平均粒径为100nm伪立方相的球形纳米晶[(Ba0.96Bi0.04)TiO3]和[(Bi0.5Na0.5)TiO3]。以不同含量低居里温度BaTi0.9Zr0.1O3作为壳部进行包覆，得到分散性较好的[(Ba0.96Bi0.04)TiO3]-BaTi0.9Zr0.1O3 [粉体1]和[(Bi0.5Na0.5)TiO3]-BaTi0.9Zr0.1O3 [粉体2]芯-壳复合粉体，并制成陶瓷。研究表明，随BaTi0.9Zr0.1O3包覆量增加，粉体1和粉体2对应陶瓷相结构没有发生明显变化，均为伪立方相结构，但陶瓷晶粒减小，原因可能是壳层在烧结过程中抑制陶瓷晶粒的生长；另一方面可能是因为壳层取代A、B位上的离子时产生的氧空位聚集在晶界处，通过阻碍晶粒间的接触而抑制晶粒的增长。在宽温度范围内，随着壳层含量的增加，粉体1陶瓷的介电温谱随着包覆量的增加展宽，但介电常数有明显下降；粉体2陶瓷的介电温谱随着壳层含量的增加，壳部和芯部对应的相转变温度均向低温方向移动。介电常数最大值随频率的增大向低频方向移动，出现弛豫现象，导致介温曲线在宽温度范围内出现“平台”，介电温度稳定性提高。壳层包覆为2.0mol%时，芯壳结构粉体-2对应陶瓷满足X9R标准；制备了(K0.5Na0.5)NbO3-0.1wt%Bi-BaTi0.9Zr0.1O3 [粉体3]芯-壳复合粉体和陶瓷。随壳部含量的增加，陶瓷相结构由正交相转变为伪立方相，陶瓷晶粒尺寸减小且均匀。同时陶瓷致密性减小，气孔数量增多。对应陶瓷的介电温谱随壳层包覆量的增加发生明显的变化。(1)芯部和壳层铁电体的居里温度向低温方向缓慢移动；(2)芯部对应的最大介电常数降低，壳部对应的介电常数增大，导致介温曲线在宽温度范围内出现“平台”，介电温度稳定性提高；(3)壳层包覆量为5.0mol%时，陶瓷在温度范围为200℃-400℃之间最大介电常数1500，容温变化率Δεr/εr150°C≤±15%，在宽温范围内产生“多峰效应”，最终得到满意的高温高介高稳定性的介电陶瓷材料，为扩展铁电陶瓷的使用温度范围提供新的思路。