钙钛矿微波陶瓷显微组构和电学微结构与其高介电高损耗来源构效关系研究

Recently, the performance improvement and development of high-dielectric microwave ceramics are basically in the halting state, the key reason is that origination mechanism of high-dielectrics and large dielectric losses in microwave ceramics were not effectively elucidated. In order to resolve the probles, high-dielectric SrTiO3 ceramic system with perovskite structure is regarded as the objective studies in the project. The microcompositions and microstructures of the system were characterized by X-ray Photoelectron Spectroscopy, Raman Spectrum and Transmission Electron Microscope, et al. The electrical microstructures of the microwave ceramics were analyzed by AC Complex Impedance Spectroscopy, Conductive Atomic Force Microscope and Physical Property Measurement System, et al. Effect of size effect and sintering atmosphere on microcompositions, microstructures and electrical microstructures were also investigated in the microwave ceramics. Structure-properties raltion, origination mechanism of high-dielectrics and large dielectric losses of SrTiO3 ceramic system are systematically elucidated by the conjunction of microcompositions-microstructures and electrical microstructures obtained from the analysis. These will make a theoretical and experimental foundation on the studies and development of high-performance microwave ceramics with higher dielectric constants, low losses and high stability in the future.

近年来，高介电微波陶瓷的性能提高和发展基本处于停滞状态，一个关键的原因是其高介电高损耗的起源机理没有得到合理有效的解释。为解决这个问题，本项目以高介电钙钛矿SrTiO3体系微波陶瓷为研究主体，借助光电子能光谱仪、拉曼光谱和透射电镜等表征其显微组成结构；同时采用交流阻抗谱、导电型原子力显微镜和综合物理性能测试系统等分析陶瓷电学微结构；研究尺寸效应和烧结气氛对微波陶瓷显微组构和电学微结构的影响规律。把这些分析所得显微组构和电学微结构进行有机结合，综合阐述SrTiO3系微波陶瓷的构效关系和高介电高损耗起源机制。为将来研究与开发介电常数更高，兼具低损耗、高稳定的高性能微波陶瓷奠定理论与实验基础。

近10年来，微波陶瓷在保持谐振温度近零、Q×f值高于3000GHz的情况下，未见介电常数高于150的微波陶瓷，这主要是高介电微波陶瓷的高介、高损耗来源机制没有得到合理有效的阐明。为促进高介电微波陶瓷发展，本项目选择4类介电常数差异大的钙钛矿结构微波陶瓷进行了电学微结构分析。结果发现高介电性贡献主要来自于晶粒，晶界也有一定的贡献，其贡献程度与晶粒尺寸大小有关，而界面层则对高频介电性无响应；损耗相对较大的微波陶瓷晶粒和晶界损耗主要源于氧离子二次离子化，损耗较小陶瓷则来自于离子化的电子电导；晶粒与晶界电导均为欧姆型导电机制。晶粒微米级的微波陶瓷，其高频介电性贡献接近于单晶体（即完全本征贡献），晶体结构基本能反映陶瓷体的介电性影响；晶粒亚毫米级，晶界介电性贡献明显增大；亚微米级微波陶瓷，晶界介电性贡献进一步增加，意味着晶粒和晶界的异质行为减弱。研究过程中得到一些重要结果：（1）超高介电Li0.5RE0.5TiO3-Bi0.5Na0.5TiO3（RE=Nd, Sm）微波陶瓷，其εr =140~155，Q.f=1, 200~1,500 GHz，TCF <26 ppm/℃；（2）无钽超低损耗Mgn+1TinO3n+1微波介质陶瓷，其εr = 15~21，Q.f= 150, 000~350, 000 GHz，TCF= -45~-5.0 ppm/℃；（3）超低介电RE-Mg-Al-Si-Ti-O(RE为稀土)微波介质微晶玻璃，其εr = 3.8~6.0，Q.f= 15, 000~180, 000GHz，TCF=-5.0~+5.0 ppm/℃；（4）Sr0.2Ca0.488Nd0.208Ti1-xGa4x/3O3微波介质陶瓷，其εr = 43.7, Q.f = 60100 GHz，TCF= 8.3 ppm/℃。