聚合物材料空间电荷陷阱模型及参数

A space charge trapping model and its parameters in polymeric material

采用电声脉冲测量技术研究了直流电场下低密度聚乙烯材料的电荷入陷和脱陷特征.发现在不同电场周期下样品的电荷衰减呈现不同的特征,为此提出了一个简单的基十两陷阱水平的入陷和脱陷模型,并计算了相应的参数.如陷阱能级和密度.确定了不含任何添加剂的低密度聚乙烯样品中存在的两种水平的陷阱能级分别为:较浅陷阱能级0.77-O.81 eV对应的浅陷阱电荷密度为(1.168-1.553)×10^(19)m^(-3);较深陷阱能级0.96-1.01 ev对应的深陷阱电荷密度为(1.194-4.615)×10^(18) m(-3)。.最后初步验证了材料的深陷阱能级和对应的深陷阱电荷密度随老化而增加,可考虑将模型中的两能级陷阱参数作为老化诊断特征参量.

In this paper,characteristics of charge trapping and detrapping in low density polyethylene under dc electric field are investigated using the pulsed electroacoustic technique.It is found that the charge decay shows very different features for the samples with different periods of applied electric field.A simple trapping and detrapping model based on two trapping levels is proposed to qualitatively explain the observation.At the same time,numerical simulation based on the above model is carried out to extract parameters（trap depths and concentration） related to the material.It is found that the space charge decaying in the first few hundred seconds,corresponding to the fast changing part of the slope,is trapped in a shallow trap with a depth in a range between 0.77 and 0.81 eV,and the trapped charge density reaches（1.168-1.553）×10^（19） m^（-3） in the sample volume measured.At the same time,the space charge that decays at longer time,corresponding to the slower part of the slope,is trapped in a deep trap with a depth in a range of 0.96 and 1.01 eV,and the trapped charge density is（1.194-4.615）×10^（18） m^（-3）.The trap depths and charge densities of both shallow and deep traps may increase with ageing,and the parameters of two energy wells can be used as an indication of the material aging.