宏观电偶极子对聚丙烯铁电驻极体膜电荷储存及其动态特性的影响

Influence of macroscopic dipoles on the charge storage and charge dynamics of polypropylene ferroelectret films

利用栅控恒压电晕充电组合反极性电晕补偿充电法,研究了孔洞(单元电畴)内分布的空间电荷型宏观电偶极子的形成,及其增长对聚丙烯孔洞膜电极化期间的电流特性及电导率的影响.借助等温表面电位衰减测量、开路和短路热刺激放电电流谱分析等,讨论了宏观电偶极子及其密度变化时的聚丙烯孔洞驻极体膜电荷储存稳定性及电荷动态特性.实验结果说明:由电极化形成的宏观电偶极子的自身电场提高了聚丙烯孔洞驻极体膜的电导率,从而降低了驻极体膜电荷储存的稳定性.对呈现弱极化强度的孔洞驻极体膜,以孔洞为畴结构基本单元内的宏观电偶极子,其两性空间电荷的大部分仅仅分别沉积在透镜状孔洞上下两壁的两端.外激发脱阱电荷从脱阱位置的输运路径,主要是绕孔洞两边沿介质层迁移;而极化强度较高的样品,其两性电荷则分别分布在上下两壁的宽广区域内,脱阱电荷的大部分在驻极体电场驱动下从脱阱位置通过孔洞层间的介质层迁移并衰减.

In this work, influence of the formation of macroscopic dipoles with space charges enclosed in a void （electric domain） and their polarization enhancement on the charging current characteristic and the conductivity of cellular polypropylene （PP） film were studied by the corona charging with a grid in combination with the reverse-polarity corona charging compensation method. By measuring the＇isothermal surface potential decay and analyses of open-cireuit and short-circuit thermally stimulated discharging current spectra, the charge stability and charge dynamics of PP ferroelectrets in relation to the formation and density variety of macroscopy dipoles were also discussed. The experimental results indicate that the decrease of charge stability of cellular PP film with high polarization should be attributed to the increase of the conductivity induced by the self-field of macroscopic dipoles. For cellular electret film with weak polarization, macroscopic dipoles formed by space charges should only be trapped at two sharp ends of lens-like void and, therefore, detrapped charges will transport along the side surfaces at both ends of the void. When the sample has high polarization, the trapped charges are distributed in the whole surface layer of the void. Most of the detrapped charges excited by the electret field drift through the solid dielectric layer between adjacent voids, which leads to their decay.