Ferroelectric ceramics have been widely used in lots of fields,such as mechanical-electric transducer,ferroelectric memory,and energy storage devices.The dielectric breakdown process of ferroelectric ceramic has received much attention for years,due to the fact that this issue is critical in many electrical applications.Though great efforts have been made,the mechanism of dielectric breakdown is still under debate.The reason is that the electrical breakdown is a complex process related to electrical,thermal,and light effects.In the present work,we investigate the breakdown process of Pb0.99(Zr0.95Ti0.05)0.gsNb0.02O3 (PZT95/5) ceramic,which is a kind of typical ferroelectric ceramic working in the high voltage environments.The high voltage pulse generator is used in the breakdown experiments to apply a square pulsed voltage with an amplitude of 10 kV and a width of 7 μs.The resistivity change in the breakdown process is recorded by the high-frequency oscillograph in nano-second.The results show that there are two different breakdown types for our sample,i.e.body-breakdown and flashover.To better understand the breakdown mechanism of the PZT95/5 ceramic,the formation of the conductive channel in ceramic in the process is investigated by comparing the resistivity development in body-breakdown and flashover processes.The development of the conductive channel formation can be divided into three steps in body-breakdown.In the first step that lasts for the first 40 ns of breakdown,the conductive channel starts forming,with the equivalent resistance sharply decreasing to about 105 Ω in the mean time.Then,i.e.in the second step,conductive path grows into a stable one with the equivalent resistance decreasing to the magnitude of about 102 Ω.The resistance decreases slowly to about 130 Ω in the third step,which means that the conductive channel is completely formed.The channel formation of flashover can also be divided into three steps.The first step is similar to that of body-breakdown,with the equivalent resistance decreasing to about 105 Ω in about 40 ns.In the second step of flashover,the conductive path keeps growing into a stable one with the equivalent resistance decreasing to 102 Ω,but with a different resistance changing rate from that in body-breakdown,and the resistance decreases slowly to about 20 Ω in the end.Different behavior between the body-breakdown and the surface flashover can be explained by different carrier densities on the conductive paths in the two breakdown processes.In the body-breakdown,the carrier density in the conductive channel is higher than that in the surface flashover,which improves the electron transfer and reduces the resistance.This may explain the reason why the channel formation in body-breakdown is faster than in flashover.This study is helpful for further materials design and applications.%陶瓷作为应用非常广泛的一种材料,其电击穿问题一直是研究的重点和热点.由于击穿过程涉及热、光、电多场耦合效应,目前还没有一个普适的模型能够解释陶瓷击穿问题.针对此问题进行分析,实验中采用脉冲高压发生装置击穿陶瓷,通过对陶瓷击穿过程中等效电阻的研究,揭示了PZT95/5陶瓷样品体击穿和沿面闪络形成过程的异同.结果显示,在两种击穿模式下,陶瓷样品内部均会在40 ns左右形成导电通道,陶瓷等效电阻急剧下降至105 Q量级;然后体击穿与沿面闪络的导电通道以不同的速率继续扩展;电阻减小速率与导电通道上载流子的浓度有关,二者的等效电阻以不同速率减小,直至导电通道达到稳定.
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