直流老化及热处理对ZnO压敏陶瓷缺陷结构的影响

The Effect of DC degradation and heat-treatment on defects in ZnO varistor

在电场为3.2kV/cm,电流密度为50mA/cm2条件下对ZnO压敏陶瓷进行了115h的直流老化,研究了直流老化对ZnO压敏陶瓷电气性能及缺陷结构的影响.发现直流老化115h后ZnO压敏陶瓷的电位梯度、非线性系数分别从2845V/cm,38.3下降到51.6V/cm,1.1,介电损耗中的缺陷松弛峰被增大的直流电导掩盖,电模量中只观察到一个缺陷松弛峰,低频区交流电导率急剧增大并且相应的电导活化能从0.84eV下降到只有0.083eV.通过对直流老化后的ZnO压敏陶瓷在800℃进行12h的热处理,发现其电气性能和介电性能都得到了良好的恢复并有一定的增强,电位梯度、非线性系数恢复到3085V/cm,50.8,电导活化能上升到0.88eV.另外,其本征氧空位缺陷松弛峰也得到了一定的抑制.因此,认为热处理过程中氧在晶界处的扩散作用对ZnO压敏陶瓷的直流老化恢复起到了关键作用.

In this research, DC degradation for ZnO varistors at 3.2 kV/cm and 50 mA/cm2 for 115 hours was performed, and its effect on electrical properties and defects of ZnO varistors was investigated. It was found that the breakdown field and nonlinear coefficient drops sharply from 2845 V/cm to 51.6 V/cm and 38.3 to 1.1, respectively, when the DC degradaion time reaches 115 hours. For the degraded sample, the dielectric loss was dominated by the increase of conductivity so that some defect relaxation peaks cannot be observed is the DC degraded ZnO varistors. However, in electrical modulus plot, one relaxation peak can be observed. The conductivity in low frequency range increases greatly and the conductance activation energy drops from 0.84 to 0.083 eV. Additionally, the heat-treatment process of ZnO varistors at 800 ℃ for 24 hours was also performed. It is interesting to note that the electrical properties and the relaxation processes of ZnO varistor is restorable completely again after heat-treatment. The breakdown field and the nonlinear coefficient increase to 3085 V/cm and 50.8, respectively, and the activation energy of conductance increases to 0.88 eV. It is also found that the defect relaxation peak, which is shown in dielectric spectra corresponding to oxygen vacancy defect, is suppressed evidently by heat-retreating. Therefore, it is proposed that oxygen is likely to diffuse into the ZnO grain boundaries at the heat-treatment process, which can play an important role in restorability of the DC degraded ZnO varistor.