ZnO压敏陶瓷的介电谱

在-160℃-200℃温度范围内、0.1 Hz-0.1 MHz频率范围内测量了 ZnO压敏陶瓷的介电频谱, 发现可以采用电导率谱低频端的类直流特性来表征晶界Schottky势垒的电子输运过程, 获得的Schottky势垒高度为0.77 eV. 基于背靠背双Schottky势垒模型, 提出当存在直流偏压时, 势垒高度将随直流偏压线性增大. 基于此势垒模型计算了ZnO压敏陶瓷单晶界的直流偏压大小, 进而计算出晶粒平均尺寸为6.8 μm, 该理论值与通过扫描电子显微镜断面照片获得的测量值的偏差在5%以内. 可见采用介电谱不但可以获得势垒高度实现电气性能的表征, 还能获得晶粒尺寸实现显微结构的表征.

Dielectric spectra of ZnO varistor ceramics

In this paper,the dielectric spectra of ZnO varistor ceramics are measured by Novocontrol wide band dielectric spectrometer in a temperature range of—160℃-200℃and frequency range of 0.1 Hz-0.1 MHz.It is found that electron transportation can be characterized by the flat region on a low frequency side of cr’-f curve.The Schottky barrier height is 0.77 eV obtained fromσ’-f curve,which is consistent very well with the data from I-V curves given in other literature.On the basis of back-to-back double Schottky barrier model,Schottky barrier height corresponding to electron transportation across grainboundary is explained to be the energy difference between interface state and barrier top.According to this explanation,Schottky barrier height will increase linearly with the increase of DC voltage applied.The linear variation of barrier height with the increase of DC voltage applied is confirmed experimentally.Finally,the theoretical value of averaged grain size is obtained to be 6.8μm,which is almost identical to 6.5μm measured from SEM images.Therefore,the macroscopic electrical properties and the microstructure can be expressed at the same time by dielectric spectra.