【作者】 黄集权；

【导师】 杜丕一；

【作者基本信息】 浙江大学 ， 材料学， 2006， 硕士

【摘要】 电介质材料主要应用于电容器和电绝缘体当中。随着电力电子设备发展的日新月异,电子元器件（如电容器等）向高储能、小型化的方向发展。这就要求人们不断研究和制备高介电常数复合材料。 渗流理论为高介电常数复合材料的研发提供了很好的指导意义。渗流理论是一种用来描述异相复合体系中某相的长程联结性的统计理论。对于导体—绝缘体复合材料,当导体的含量低于渗流阈值但又接近渗流阈值时,复合材料将具有异常大的介电常数。这种性质可以利用来制备高介电常数电介质材料。 在本文中,利用渗流理论研究了以不同形状和性质的无机导电体填充钛酸钡基体所形成的复合材料的介电性能。采用固相烧结的方法在氮气保护气氛中烧结制备了钛酸钡/乙炔黑复合材料、NiO-BaTiO₃复相材料、BaTiO₃-Ni复合材料、Fe-Ni-BaTiO₃三元复合材料以及BaTiO₃-Ni_0.5Zn_0.5Fe₂O₄复合材料,利用XRD和SEM等手段对材料的物相组成和微结构进行了分析,利用阻抗分析仪等仪器对材料的电性能、磁性能进行了研究。 研究结果表明: 对于导体/钛酸钡复合材料,一定量的导体的引入可以大幅提高材料的介电常数。而且渗流阈值的大小与导电相的形状、颗粒大小紧密相关。 （1）对于钛酸钡/乙炔黑复合材料,材料的致密度和钛酸钡颗粒度均随着烧结温度的升高而增大,从而导致渗流阈值随温度的升高而有所下降。当乙炔黑的含量在渗流阈值附近时,材料的介电常数得到了显著的提高,最高可达40000左右,比钛酸钡基体材料的介电常数有了12倍左右的提高,而且复合材料的介电常数随温度的变化并不明显。 （2）对于BaTiO₃-Ni复合材料和Fe-Ni-BaTiO₃三元复合材料,富有弹性的金属的引入在很大程度上稀释了材料的内应力从而降低了体系的介电损耗。与此同时,金属相的引入可以大幅提高材料的介电常数。值得注意的是,由于复合体系中钛酸钡晶体的晶粒尺寸较小,在渗流阈值附近材料的介电常数随温度变化不大,其电容量温度系数一般保持在10%左右,从而具有成为X7R电容器材料的更多还原

【Abstract】 Dielectric materials are mainly used for capacitors and electrical insulators. The incessant development of electronical industries and electric power industries calls for electronic components such as capacitors with high capacitance and small size. To satisfy these requirements, high dielectric constant composites attract more and more attentions.Percolation theory can be used to direct the research and development of composites with high dielectric constant. Percolation is a statistical concept that describes the formation of an infinite cluster of connected particles or pathways. The dielectric constant will increase singularly near the percolation threshold for composites made of an insulating matrix loaded with conductive or semiconducting particles. This gives interest for research of high permittivity composites.A series of novel composites, such as BaTiO₃-Acetylene black, BaTiO₃-NiO, BaTiO₃-Ni, BaTiO₃-Ni-Fe, BaTiO₃-Ni_0.5Zn_0.5Fe₂O₄, were created, and the microstructure and dielectric properties were investigated in this study.For the BaTiCVconductors composites, it is found that the introduction of conductors can enhance the dielectric constant obviously, and the percolation threshold depends on the shapes and sizes of fillers deeply.（1） For BaTiO₃-Acetylene black composites, the percolation threshold decreases with increasing temperature, as a result of the increase in density and the grain size of BaTi_O3. The introduction of acetylene black can enhance the dielectric constant obviously. A super high dielectric constant of about 40000 can be obtained in the composites, which is about 12 times more than that of BaTiO₃ without acetylene black doping. Moreover, the dielectric constant depends slightly on the temperature.（2） For BaTiO₃-Ni and BaTiO₃-Ni-Fe composites, it is found that the introduction of metal dilutes the internal stresses and leads to lower loss. Furthermore, the introduction of metal increases the dielectric constant observably. And it isnoticeable that the dielectric constant depends slightly on the temperature for composites near the percolation threshold due to the small grain size of BaTiO3.（3） The physical reason for the dielectric enhancement is the formation of a great deal of micro-capacitors as well as the induction of space charge polarization.For the BaTiO3-NiO composites, the results indicate that the Ni2+ ions might diffuse into BaTiO3 perovskite phase gradually during calcinations, and the perovskite phase of BaTiO3 consisted of different saturated solid solutions when sintering the composites at low temperature for a short time. The different composition of Ni2+ in the perovskite phase led to that the dielectric constant of the composite changed near the Curie point with temperature much more softly than that without doping Ni2+.For BaTi03-Nio.5Zno.5Fe204 composites, it is found that the percolation threshold is about 50 wt% NiojZno.sFeiO^ For composites near the percolation threshold, the permeability is about 10, and the dielectric constant reaches a maximal value of about 3000, while the dielectric loss remain as low as 0.10. This means that the BaTi03-Nio.5Zno.5Fe204 composites can have both high permittivity and excellent magnetism properties at the same time, which make for broadening the potential application of percolating composites with novel high dielectric constant.更多还原