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1、任何电介质都不可能是理想的绝缘体，它们内部总是或多或少地具有一些带电粒子（载流子），例如可以迁移的正、负离子以及电子、空穴和带电的分子团。,2.2 固体电介质的电导,2.2 Conductance of solid dielectrics,No dielectrics could be the ideal insulator. There is charge particles (charge carrier) in the dielectrics more or less such as moveable positive and negative ions, electrons, hole
2、s, and charged molecule cluster.,在外电场的作用下，某些联系较弱的载流子会产生定向漂移而形成传导电流（电导电流或泄漏电流）。表征电介质导电性能的主要物理量即为电导率 或其倒数电阻率 。,Some weak correlation charge carrier will conduct oriented drift under the external electric field which creates conduction current (conduction current or divulge current). Conductivity or it
3、s reciprocalresistivity are used to characterize dielectric conductive property,固体电介质的电导按导电载流子种类可分为离子电导和电子电导两种，前者以离子为载流子，而后者以自由电子为载流子。在弱电场中，主要是离子电导。,Solid dielectrics conductance could be divided into ion conduction and electron conduction according to the types of conductive carriers. The former on
4、e takes ions as charge carrier. The latter one takes free electrons as charge carrier. Ion conduction is dominant in the weak electric field.,2.2.1 固体电介质的离子电导 2.2.1 Ion conduction of solid dielectrics 2.2.2 固体电介质的电子电导 2.2.2 Electron conduction of solid dielectrics 2.2.3 固体电介质的表面电导 2.2.3 Surface cond
5、uction of solid dielectrics,本节内容 Contents in this section,固体电介质按其结构可分为晶体和非晶体两大类。对于晶体，特别是离子晶体的离子电导机理研究得比较多，现已比较清楚。然而在绝缘技术中使用极其广泛的高分子非晶体材料，其电导机理尚未完全搞清楚。,Solid dielectrics could be divided into crystal and non-crystal according to its structure. For crystal, research work has focused on the ion conduct
6、ion mechanism of ion crystal and now it is quite clear. However, conduction mechanism of polymer non-crystal material which has been widely used in insulation technology is not clear yet.,1. 晶体无机电介质的离子电导,本征离子电导 Intrinsic ion conduction 弱束缚离子电导 Weakly bound ion conduction,晶体介质的离子来源有两种：,Ion conduction
7、 of crystal inorganic dielectrics,Two sources of ions of crystal dielectrics,2. 非晶体无机电介质的离子电导,无机玻璃是一种典型的非晶体无机电介质，它的微观结构是由共价键相结合的 或 组成主结构网，其中含有离子键结合的金属离子。,Ion conduction of non-crystal inorganic dielectrics,Inorganic glass is a typical kind of non-crystal inorganic dielectrics whose microstructure is
8、 a main structure net composed of and combined by covalent bond. The net contains metal ions combined by ionic bond.,玻璃结构中的金属离子一般是一价碱金属离子（如 ）和二价碱土金属离子（如 等）。这些金属离子是玻璃导电载流子的主要来源，因此玻璃的电导率与其组成成分及含量密切相关。,Generally, metal ions in the glass structure is one valence alkali metal ions such as and divalent al
9、kali earth metal ions such as . These metal ions are the main source of glass conductive carriers. So the glass conductivity is closely related to its composition and content.,3. 有机电介质中的离子电导,非极性有机介质中不存在本征离子，导电载流子来源于杂质。通常纯净的非极性有机介质的电导率极低，如聚苯乙烯在室温下 。,Ion conduction in the organic dielectrics,Non-polar
10、 organic dielectrics whose conductive carriers come from impurities do not exist intrinsic ions. Generally, the conductivity of pure non-polar organic dielectrics is extremely low. For instance, the conductivity of polystyrene at room temperature is,在工程上，为了改善这类介质的力学、物理和老化性能，往往要引入极性的增塑剂、填料、抗氧化剂、抗电场老化
11、稳定剂等添加物，这类添加物的引入将造成有机材料电导率的增加。,In engineering, in order to improve mechanical, physical and aging properties of this kind of dielectrics, additives such as polar plasticizer, filler, antioxidant, anti-electric field aging stabilizer need to be added. Adding this kind of additives will result in incr
12、easing conductivity of organic material.,2.2.2 固体电介质的电子电导,固体电介质在强电场下，主要是电子电导，这在禁带宽度较小的介质和薄层介质中更为明显。,2.2.2 Electron conduction of solid dielectrics,Solid dielectric is mainly electron conduction under high field strength, further it shows more obviously in the dielectric with narrow forbidden band an
13、d sheet dielectric.,电介质中导电电子的来源包括来自电极和介质体内的热电子发射，场致冷发射及碰撞电离，而其导电机制则有自由电子气模型、能带模型和电子跳跃模型等。,The sources of electron conduction in the dielectric include thermal electron emission from the inside of electrode and dielectric, field induced cold-emission and collision ionization. Accordingly the conducti
14、on mechanisms contain the free electron gas model, band model and electric-hopping model.,晶体电介质的电子电导 The electronic conductivity of dielectric crystals,根据晶体结构的能带模型，离子晶体和分子晶体中的电子多处于价带之中，只有极少量的电子由于热激发作用跃迁到导带，成为参与导电的载流子，并在价带中出现空穴载流子。导带上的电子数和价带上的空穴数主要取决于温度和晶体的禁带宽度 及费米能级 。,According the band model in cry
15、stal structure, electron in ionic crystal and molecular crystal is mainly on the valence band, only a few transit to conduction band and become current carriers concerned with conduction owing to the thermal agitation action, and hole carrier is occurring on the valence band. The electron number on
16、conduction band and hole number on valence band mainly lie on the temperature and the width of forbidden band in crystals and Fermi energy-level .,一般取下式来估计具有不同禁带宽度 的晶体材料在不同温度下的电子和空穴本征浓度。,(2-21),The intrinsic concentration of electron and hole in the crystal materials with different width of forbidden band under different temperatures is estimated by the following formula commonly.,晶体电子电导电流密度： Electron conducti
