基于多元共掺杂CaCu3Ti4O12陶瓷缺陷结构的调控及电性能改性研究

With the extensive application of energy storage element in aerospace, military and power electronics system, requirements to small size, large capacity and high reliability of capacitor are increasing. Therefore, the perovskite-type material CaCu3Ti4O12 becomes the research focus due to its colossal dielectric constant, excellent frequency and temperature stability. The properties of CaCu3Ti4O12 ceramics are significantly dependent on its defects (such as intrinsic and extrinsic defects). How to improve the electrical properties of CaCu3Ti4O12 ceramics by controlling the defect structures remains a bottleneck in present study. This funding is proposed based on CaCu3Ti4O12 ceramics with multi-doping transition and non-transition metal elements. The defect structures will be controlled by a novel two step sintering method, liquid phase method and heat-treat in different atmospheres. The effect of doping elements on the density, bond and distribution of defects will be analyzed. And, the relationship of depletion layer barrier and polarization relaxation at domain boundary, grain boundary will be also clarified. It is expected that CaCu3Ti4O12 ceramics with high breakdown field, low loss and large nonlinear coefficient in a certain frequency and temperature range can be obtained. We believe our project will provide both experimental basis and experimental guidance for developing new colossal-dielectric-constant materials.

随着储能元件在航天、军事及电力电子系统的广泛应用，对电容器提出了体积小、容量大和可靠性高的要求。因此，具有巨介电常数，频率、温度稳定性高的类钙钛矿陶瓷材料CaCu3Ti4O12成为研究的热点。CaCu3Ti4O12陶瓷的各种性能强烈依赖于其本身的缺陷（本征和非本征）结构，如何对材料中的缺陷结构进行有效调控，从而改善电性能是CaCu3Ti4O12陶瓷研究的瓶颈问题。本项目基于多元共掺杂过渡/非过渡金属元素，拟通过新型的两步烧结法、液相法及热处理等方法对CaCu3Ti4O12陶瓷的缺陷结构进行调控，分析各元素对CaCu3Ti4O12陶瓷缺陷浓度、价态、分布等的影响，并明确畴界、晶界的耗尽层势垒、陷阱松弛极化状态等随制备过程、显微结构的关系。制备出高介电常数，在一定的频率和温度范围内击穿场强高、损耗较低、非线性系数大的CaCu3Ti4O12陶瓷，对开发新型的巨介电常数陶瓷提供实验支持和重要指导。

项目“基于多元共掺杂CaCu3Ti4O12陶瓷缺陷结构的调控及电性能改性研究”基本按照计划进行，并且顺利完成了项目计划的内容。该项目基于探索CaCu3Ti4O12陶瓷在高储能电容和压敏保护元件领域的应用，主要研究了Bi3+、Al3+，Ce4+、Zr4+，及Al3+、Zn2+等离子多元共掺杂对CCTO陶瓷性能的影响。其中Bi3+、Al3+共掺杂的CCTO试样，微观晶粒形状及尺寸分布更加均匀，维持高介电常数（~10000）的同时，介电损耗降低到0.03-0.04（10-1000 Hz），击穿场强和非线性系数达到了784 V/mm和5.0，并发现Bi3+、Al3+共掺将与CCTO电性能相关的晶界缺陷活化能级从0.67 eV提高到0.90eV。Zn2+离子掺杂可以取代Cu2+，介电常数在很宽频率范围内仍保持在1000-10000数量级，介电损耗可降至0.04。.通过空气、氧气和氮气对CCTO试样热处理，发现氧气气氛热处理可以有效降低低频损耗至0.03-0.04（1000Hz），并将试样的肖特基势垒高度从0.46eV提高到0.62eV，储能密度从7.7kJ/m3提高到26.5 kJ/m3，提升了约3.5倍。而还原气氛热处理将会导致CCTO陶瓷分解，失去其高介电特性和压敏特性。采用非线性最小二乘法对CCTO陶瓷cole-cole 图谱进行拟合分析，得到CCTO陶瓷巨介电常数主要有晶粒弛豫和晶界弛豫两部分贡献，其中晶粒弛豫占主导，约贡献60%。.通过直流老化研究，建立了CCTO电性能和其缺陷结构之间的关联，发现击穿场强和非线性系数随老化时间明显下降，低频电导损耗明显增大。老化后的势垒高度从0.57eV下降到0.31eV，对应的晶界电导活化能从1.16eV下降到0.69eV，表明CCTO电性能与其晶界电导活化能密切相关。另外，将研究CCTO陶瓷的分析方法拓展应用到ZnO陶瓷，制备出一种高击穿场强的ZnO压敏陶瓷，击穿场强和非线性系数分别达到3845V/mm和55。.本项目的研究成果将为CCTO陶瓷在多元共掺杂改性、不同气氛热处理及宏观电性能与微观结构之间的关联方面提供实验依据，为其它新型无机陶瓷的开发提供理论指导。