摘 要

钛酸钡（BaTiO₃）基陶瓷因其低的介电损耗、高的介电常数和优良的电绝缘性能，在电介质储能方面有较大的应用潜力。本论文采用柠檬酸盐法制备Ba_0.95Ca_0.05Zr_0.3Ti_0.7O₃（简称BCZT）超细粉体，采用固相烧结法来制备BCZT陶瓷样品。考察BCZT陶瓷样品的结构、烧结性能和介电性能。研究氧空位的运动对BCZT陶瓷样品介电性能的影响，着重考察强电场下与氧空位运动相关的极化行为，分析氧空位运动与电击穿行为和储能性能的关联。

采用柠檬酸盐法，在650 °C合成了具有单一钙钛矿结构的BCZT超细陶瓷初级粉体，其平均颗粒粒度为80 nm。采用固相烧结法制备了BCZT陶瓷样品，当烧结温度为1280 °C和1320 °C时，制备出的BCZT陶瓷样品达到95%的相对密度，平均粒径分别为1.20 μm和1.32 μm。

研究了弱交流测试信号下BCZT陶瓷样品的介电性能。通过交流阻抗谱的测试确定了BCZT陶瓷样品中存在氧空位，并且氧空位的含量随烧结温度的提高而增加。介电频谱的研究结果表明，氧空位的运动引起了Maxwell-Wager界面极化效应和高频下介电损耗的上升，同时对交流电导率也有贡献。

研究了强电场下BCZT陶瓷样品的储能特性。研究结果表明，氧空位的运动在强电场作用下表现为长程迁移。氧空位在电极附近的聚集是引发样品表面的电击穿行为的重要原因，减少氧空位的含量有利于提高陶瓷样品的击穿强度。在140 kV/cm的场强下，1280 °C烧结的BCZT陶瓷样品的储能密度达到0.56 J/cm³，储能效率为72.4%。

关键词：BaTiO₃；氧空位运动；强电场；击穿行为

Abstract

Barium titanate (BaTiO₃)-based dielectrics have been recognized as prospective candidate materials for energy storage capacitor utilizations due to their low dielectric loss, high dielectric constant and good insulation properties. In this work, superfine powder of Ba_0.95Ca_0.05Zr_0.3Ti_0.7O₃ (BCZT) was synthesized by a citrate method. The ceramic specimens were fabricated from the superfine powders by a solid-state sintering process. The structure, sintering behavior and dielectric properties of the ceramic specimens were inspected. The influences of oxygen vacancies to the dielectric properties were studied. The contribution of oxygen vacancies to the electric breakdown behavior of the specimens under strong electric field was investigated.

The powders of BCZT derived from the citrate method at calcination temperature of 650 °C showed superfine morphology with average particle size of around 80 nm. The ceramic specimens sintered at 1280 °C and 1320 °C, respectively, attained a relative density above 95%. The two ceramic specimens showed dense microstructures with average grain sizes of 1.20 μm and 1.32 μm, respectively.

The dielectric responses relative to weak AC testing signals were surveyed. The existence of oxygen vacancies as charge carriers in BCZT ceramic specimens was confirmed by means of complex impedance analysis, which indicated that the amount of oxygen vacancies was increased with elevating sintering temperature. Moreover, it was demonstrated that the motion of oxygen vacancies in the specimens led to dielectric anomalies, such as interfacial polarization (or Maxwell-Wager) behavior at low frequencies and increased dielectric loss at high frequencies. In addition, the information regarding the motion of oxygen vacancies in the specimens was achieved by diagnosing the AC conductivity spectra.

The energy storage properties of the ceramic specimens under high electric field were investigated. The results indicated that movements of oxygen vacancies under high electric field were long-range migrations. The aggregation of oxygen vacancies toward electrodes is believed to be contributive to the occurrence of electric breakdown behaviors. Therefore, reducing the amount of oxygen vacancies in the specimens is suggested to be favorable for improving their breakdown strength. At the electric field of 140 kV/cm, the ceramic specimen sintered at 1280 °C showed an energy storage density of 0.56 J/cm³ and an energy storage efficiency of 72.4%.

Key words: BaTiO₃; Oxygen vacancies movements; High electric field; Electric breakdown behavior

目 录

第一章 绪论 1

1.1 储能电容器 1

1.2 储能电介质材料 1

1.2.1 陶瓷介电材料 1

1.2.2 聚合物介电材料 2

1.2.3 陶瓷聚合物复合介电材料 3

1.3 BaTiO₃基储能电介质材料的研究 3

1.4 本论文的研究设想 6

1.4.1 研究思路 6

1.4.2 研究内容 7

第二章 样品的制备、测试与表征 8

2.1 样品的制备 8

2.1.1 粉体的合成 8

2.1.2 陶瓷样品的制备 9

2.2 结构分析和介电性能测试 9

2.3 样品的表征 12

2.3.1 粉体的表征 12

2.3.2 陶瓷样品的表征 14

第三章 BCZT陶瓷样品的介电性能研究 17

3.1 陶瓷样品的介电频谱研究 17

3.2 陶瓷样品的交流电导率研究 18

3.3 陶瓷样品的交流阻抗谱研究 19

3.4 陶瓷样品的储能特性研究 23

3.5 陶瓷样品的电击穿行为研究 24

第四章 结论 28

参考文献 29

致 谢 32

第一章 绪论

1.1 储能电容器

存储和释放电荷是电容器的基本功能。电容器作为储能元件在电子电路中存在广泛的应用，其基本工作原理如下图1-1中平行板电容器所示。在两平行板之间充满了均匀的电介质，电介质内部在外电场的作用下将感应出偶极矩。在电介质材料与电极接触的界面上会产生束缚电荷，增加电荷总量。

图1-1 平行板电容器示意图

相比于其他类型的储能器件，储能电容器有着明显的优势，即它的电学性能稳定、充放电速度快、循环使用次数高等。民用方面，储能电容器已在新型发电装置和电力推动载具中得到应用^[1,2]。而目前，传统的储能电容器很难满足现代社会和科技发展的需要，其主要缺点在于储能密度较低。研发出具有高储能密度的电介质材料是储能电容器发展的重要方向。

储能电容器中电介质的储能密度可用以下公式计算^[3]：

（1-1）

其中，为电介质材料的储能密度，为真空介电常数，为耐压强度，为工作场强，为电介质材料在工作电场下的相对介电常数。由此可见，要得到高的储能密度，则电介质材料需具有高的耐压强度，且能在高工作电场下具有高的介电常数。

1.2 储能电介质材料

1.2.1 陶瓷介电材料

铁电陶瓷材料和反铁电陶瓷材料是陶瓷介电材料的主要组成部分。其中介电常数高且热稳定性好的铁电陶瓷材料在中、低频电容器中得到了广泛应用。钛酸钡（BaTiO₃）铁电陶瓷材料本身具有高的介电常数，而且可通过A位施主掺杂来进一步提高其介电常数，这有利于获得高的储能密度。相比于介电常数的增大，陶瓷材料储能密度的提高更依赖于介电击穿强度的增加。理论计算结果表明，钛酸盐类铁电陶瓷材料的介电击穿场强可以达到10³ kV/cm的水平^[4]。但因受到了第二相、气孔、晶界、表面和内部缺陷等因素的影响，铁电陶瓷材料在较低的电场（几百个kV/cm的水平）下即被击穿。所以，提升铁电陶瓷的介电击穿强度是提高其材料储能性能的关键及难点。