静电场中多孔PZT95/5铁电陶瓷的通道电-机械击穿模型及分析

作为爆电电源的多孔PZT95/5铁电陶瓷具有极为重要的工程应用背景,但它在强电场作用下易发生电击穿失效,从而影响其放电效率,甚至造成电源失效。基于多孔PZT95/5铁电陶瓷材料在外电场作用下内部形成导电通道以致电失效的机制,通过通道内部局部放电及通道电-机械击穿机理,建立了导电通道诱导的多孔铁电陶瓷的电击穿模型并进行了相关的理论分析。基于本模型,给出了不同孔隙率下铁电陶瓷的电击穿临界电场强度,预测结果与实验测试结果吻合良好,且材料孔隙率越大,内部电击穿通道的特征尺寸越大,导致铁电陶瓷材料的电击穿临界场强显著降低。     

冲击波作用下Pb(Zr_(0.95)Ti_(0.05))O_3铁电陶瓷去极化后电阻率动态特性

在冲击波压力作用下,极化Pb(Zr_(0.95)Ti_(0.05))O_3(PZT95/5)铁电陶瓷会发生铁电-反铁电相变失去极化,由于冲击波压力高、作用时间短,伴随材料去极化相变出现的瞬态电导特性难以准确测试.本文建立了新的实验方法,采用脉冲电容器作为冲击波加载铁电陶瓷脉冲电源的输出负载,在冲击波压力约3.5 GPa的实验中直接测得铁电陶瓷的漏电流,计算得到PZT95/5铁电陶瓷去极化后的电阻率,变化范围为2.2×10~4—3.5×10~4?·cm;在实验数据的基础上,建立了动态电阻模型,对冲击波传播过程中PZT95/5铁电陶瓷去极化后的电阻率进行了分析,初步揭示了冲击波作用下PZT95/5铁电陶瓷去极化后电阻率的动态特性.     

极化状态与方向对单轴压缩下Pb(Zr_(0.95)Ti_(0.05))O_3铁电陶瓷畴变与相变行为的影响

利用数字图像相关性分析方法发展了全场应变光学测量技术,并原位实时测量了准静态单轴压缩下铁电PZT95/5陶瓷试件的轴向应变和横向应变.基于轴向应变、横向应变随着轴向应力的变化关系,讨论了极化状态和极化方向对PZT95/5铁电陶瓷的畴变与相变行为的影响.实验结果显示:单轴压缩下,未极化和Z轴极化PZT95/5铁电陶瓷都会发生畴变,而Y轴极化PZT95/5铁电陶瓷则不发生畴变;畴变促使Z轴极化PZT95/5铁电陶瓷的轴向应变和横向应变同时快速地增长,而对未极化PZT95/5铁电陶瓷的应变增长的影响非常微弱,这种差异性归因于电畴极轴不同的取向分布特征;通过应变分解分析,验证了畴变与相变过程是解耦的,并界定了畴变应变和相变应变的影响范围;与Z轴极化PZT95/5铁电陶瓷相比,未极化PZT95/5铁电陶瓷的相变开始临界应力和相变结束应力减小,而Y轴极化PZT95/5铁电陶瓷则明显增大,由此推论畴变对相变有一定促进作用.基于放电特性的实测结果,还讨论了极化方向对极化PZT95/5铁电陶瓷去极化机理的影响.实验结果显示:Z轴极化PZT95/5铁电陶瓷去极化机理是畴变和相变的共同作用,其中畴变占主导地位,而Y轴极化PZT95/5铁电陶瓷的去极化机理仅是相变.     

斜入射冲击波加载下PZT95/5铁电陶瓷的放电特性研究

 研究了冲击波倾斜入射PZT95/5铁电陶瓷时的放电特性。结果表明，在小负载条件下，随着入射倾斜角的增加，PZT95/5铁电陶瓷放电电流波形前沿变缓，脉宽时间增加，波形从单脉冲方波演变成梯形波，甚至锐变成三角波。     

多孔未极化Pb(Zr0.95Ti0.05)O3铁电陶瓷单轴压缩力学响应与相变

通过添加造孔剂的方法制备了四种不同孔隙率未极化PZT95/5铁电陶瓷. 采用非接触式的数字散斑相关性分析(digital image correltation, DIC)全场应变光学测量技术, 对多孔未极化PZT95/5 铁电陶瓷开展了单轴压缩实验研究, 讨论了孔隙率对未极化PZT95/5铁电陶瓷的力学响应与畴变、相变行为的影响. 多孔未极化PZT95/5铁电陶瓷的单轴压缩应力-应变关系呈现出类似于泡沫或蜂窝材料的三阶段变形特征, 其变形机理主要归因于畴变和相变的共同作用, 与微孔洞塌缩过程无关. 多孔未极化PZT95/5铁电陶瓷的弹性模量、压缩强度都随着孔隙率的增加而明显降低, 而孔隙率对断裂应变的影响较小. 预制的微孔洞没有改善未极化PZT95/5铁电陶瓷材料的韧性, 这是因为单轴压缩下未极化PZT95/5铁电陶瓷的断裂机理是轴向劈裂破坏, 微孔洞对劈裂裂纹传播没有起到阻碍和分叉作用. 准静态单轴压缩下多孔未极化PZT95/5铁电陶瓷畴变和相变开始的临界应力都随着孔隙率的增大而呈线性衰减, 但相变开始的临界体积应变却不依赖孔隙率.     

冲击加载下PZT 95/5铁电陶瓷的脉冲大电流输出特性

极化了的PZT 95/5铁电陶瓷在冲击波作用下发生铁电相到反铁电相的结构相变，释放出被束缚的电荷，流经外电路，形成脉冲电流.基于这一原理，针对低感、低阻负载的要求，对PZT 95/5铁电陶瓷 LRC电路响应进行了理论分析，并开展了实验研究.实验采用多组PZT 95/5铁电陶瓷并联，获得了前沿小于500ns，峰值大于5kA的大电流. 关键词： PZT 95/5铁电陶瓷 冲击波 爆电电源     

爆电换能脉冲大电流输出研究

 基于爆电换能原理，使用掺铌的PZT 95/5陶瓷组装换能器件，在垂直工作模式下，对爆电电源LRC电路响应进行了理论分析，并开展了脉冲大电流输出实验研究。实验采用多组PZT 95/5铁电陶瓷并联，利用平面波发生器作为冲击加载手段，获得了峰值5 kA以上的脉冲大电流，初始电流上升速率可达10~20 GA/s。实验结果与理论设计符合较好。     

PZT-95／5陶瓷晶粒度对冲击波作用下击穿电压的影响

Zr：Ti比为95：5的PZT陶瓷(简称PZT-95／5陶瓷)在冲击波作用下由铁电相转变成反铁电相去极化产生脉冲电流，可以作为脉冲电源发生器。这种电源基于PZT陶瓷在冲击波作用下去极化释放出束缚电荷而工作的，只有在冲击波作用下其内部不发生电击穿的条件下，才能在外电路形成电能输出，因此，PZT-95／5陶瓷在冲击波作用下的电击穿问题在其中起着非常关键的作用。     

PZT 95/5铁电陶瓷的冲击压缩Hugoniot特性研究

 采用一级气体炮加载装置,利用加窗VISAR技术,对极化和未极化两种状态的PZT 95/5铁电陶瓷进行了逆向冲击实验,在0.52~3.8 GPa冲击压力范围内,得到了PZT 95/5铁电陶瓷两种状态的σ-u关系。对比文献已有实验数据显示,PZT 95/5铁电陶瓷的Hugoniot曲线与初始密度值密切相关,高密度的PZT 95/5铁电陶瓷在0~3.0 GPa压力范围内的σ-u关系接近线弹性,较低压力下不同极化状态的Hugoniot数据表明,PZT 95/5铁电陶瓷发生了冲击相变。     

多层铁电陶瓷击穿分析及优化

建立了多层串联PZT95/5爆电换能组件3维数值模型,对固化封装条件下陶瓷介质击穿问题进行了计算分析,计算结果表明:在不改动器件外部结构尺寸条件下,采用等厚度PZT95/5叠片结构布局对进一步提高输出电压方面存在瓶颈。为克服上述影响以及降低爆电换能组件击穿概率,提出了PZT95/5铁电陶瓷非等厚度布局解决方案。为实现上述设想,通过引入不等式约束条件计算得到一组非等厚度优化布局,将爆电换能组件所用PZT95/5铁电陶瓷数量减至19片,同时有效实现该布局下,各片PZT95/5陶瓷电压均低于对应厚度击穿电压的优化目标。     

Enhanced energy storage behaviors in free-standing antiferroelectric Pb(Zr_(0.95)Ti_(0.05))O_3 thin membranes

Free-standing antiferroelectric Pb(Zr_(0.95)Ti_(0.05)O_3(PZT(95/5)) thin film is fabricated on 200-nm-thick Pt foil by using pulsed laser deposition.X-ray diffraction patterns indicate that free-standing PZT(95/5) film possesses an α-axis preferred orientation.The critical electric field for the 300-nm-thick free-standing PZT(95/5) film transiting from antiferroelectric to ferroelectric phases is increased to 770 kV/cm,but its saturation polarization remains almost unchanged as compared with that of the substrate-clamped PZT(95/5) film.The energy storage density and energy efficiency of the substrate-clamped PZT(95/5) film are 6.49 J/cm~3 and 54.5%,respectively.In contrast,after removing the substrate,the energy storage density and energy efficiency of the free-standing PZT(95/5) film are enhanced up to 17.45 J/cm~3 and 67.9%,respectively.     

Ferroelectric sources and their application to pulsed power: areview

We present in this review an account of recent research into the use of ferroelectrics as electron beam sources for pulsed power applications. The work is reviewed according to the ferroelectric material used and the switching process employed. Most of the current research uses PLZT or PZT, which can be ferroelectric, antiferroelectric, or paraelectric depending on the stoichiometry. Switching is accomplished by the application of a fast-rising electric field to the ferroelectric material. The most commonly used materials are PLZT 2/95/5 and PLZT 8/65/35 or PZT (with no lanthanum): in the former case, the applied field switches the material from the antiferroelectric state to the ferroelectric state, and in the latter cases, around a hysteresis loop. Results have been reported with ferroelectric cathodes where current densities of up to a few hundred amperes per square centimeter have been achieved, with pulse durations of several microseconds. With shorter duration pulses and PLZT cathodes, repetition rates of up to 2 MHz have been achieved. In this paper, we focus on the results reported in the literature, and include a brief account of the physical interpretation of the data. The possible use of ferroelectric sources for pulsed power applications is indicated     

铁电体电源中介质电阻特性及对输出电荷的影响

爆炸驱动铁电体脉冲电源利用铁电陶瓷在冲击压力作用下去极化释放电荷而产生电流,可以作为脉冲功率源的初始电源,也可直接驱动高阻抗负载产生脉冲高电压。通常情况下,铁电陶瓷可以看作理想的绝缘体,但在数GPa冲击波压力作用下,铁电陶瓷电阻率可能会明显下降并形成漏电导,使部分去极化释放电荷在铁电陶瓷内部流失,导致铁电陶瓷剩余极化电荷输出效率下降。以PZT95/5铁电陶瓷作为初始储能介质,以爆炸冲击波加载PZT95/5铁电陶瓷释放电荷对脉冲电容器充电,充电结束后电容器电压维持期间检测到明显的反向电流,根据铁电陶瓷输出电流和工作电压,得到冲击波作用过程中铁电陶瓷的瞬态电阻率曲线,并分析了电阻率下降对输出电荷的影响。进一步研究表明,冲击压力在铁电陶瓷边侧产生的稀疏波是引起电荷输出效率降低的主要因素,而铁电陶瓷电阻率下降对电荷输出效率的影响很小。     

On the feasibility of the coulomb explosion of a metal

The mechanism of the Coulomb explosion of a metal in an external pulsed electric field is discussed. In the case of a low-frequency field, when its frequency is lower than the frequency of electron collisions, it is impossible to reach the conditions of the Coulomb explosion of a metal if the field pulse duration is shorter than the time of electron energy relaxation upon elastic collisions, and the electron temperature is well above the Fermi energy and the work function. In the case of a high-frequency field, e.g., in a powerful pulse of ultraviolet laser radiation, the Coulomb explosion can occur if the field strength is well above the intraatomic field strength (i.e., when the laser power density is ≥10¹⁹ W/cm²).     

The effect of pulsed electric fields on biological cells:experiments and applications

The effect of pulsed electric fields with amplitudes in the range of 100 V/cm-100 kV/cm on bacteria and aquatic nuisance species has been explored. The pulse duration was so short that heating of the biological matter could be neglected. The electrical energy required for lysing of bacteria, or stunning of aquatic species, decreases when the pulse duration is reduced. For lysing of Eschericia coli, this tendency has been proven to hold for pulsewidths as short as 60 ns. For macroorganisms, however, it was found that for pulsewidths of less than 5 μs, the tendency is reversed: the energy required to affect the macroorganisms increases again. This minimum in energy, or maximum in efficiency, respectively, can be understood by taking the time required for electrical charging of the cell membrane into account. Applications of the pulsed electric field technique (PEFT) are in biofouling prevention, debacterialization of liquids, and in the field of medicine. A series of field tests on biofouling prevention in a cooling system with untreated water as coolant has demonstrated the economic feasibility of the electro-technology     

脉冲电场防治水生生物附着

为探究脉冲电场对防治水生生物附着效果的影响因素,确定有效防治附着生物所需的最低电场条件,搭建了脉冲电场试验平台,通过人工脉冲形成线产生近似方波的脉冲,统计不同条件下大型溞死亡率和形态结构发生的变化,通过函数拟合得到了脉冲电场诱导死亡率与电场强度、总等效处理时间、脉冲注入能量密度之间的函数关系,并以某干渠工程为例介绍了脉冲电场防治大型溞的参数选取原则和平台搭建方法。结果表明,脉冲电场对大型溞的处理效果与电场强度、总等效处理时间和脉冲注入能量密度都呈正相关关系。电场强度介于0.5～1.5 kV/cm之间时,电场强度每增加0.5 kV/cm,诱导死亡率增加35%左右。电场强度高于2.0 kV/cm、总等效处理时间大于900μs或脉冲注入能量密度高于80 J/L时,脉冲电场都可以产生80%以上的诱导死亡率。     

Measurement of flow fluctuations in single longitudinal mode pulsed dye laser

A simple technique had been demonstrated for measuring flow-induced fluctuations in the single longitudinal mode (SLM) pulsed dye laser. Two prominent frequency components of 10.74 Hz and 48.83 Hz were present in the output of the Nd:YAG-pumped SLM dye laser. The flow-induced frequency component of 48.83 Hz was present due to the revolution per minute of the motor attached to the magnetically coupled gear pump. The time average bandwidth of 180 MHz has been obtained for this SLM dye laser. The effect of pump pulse energy on the bandwidth of the SLM dye laser was studied. The bandwidth of the SLM dye laser was increased to 285 MHz from 180 MHz, when the pump pulse energy was increased to 0.75 mJ from 0.15 mJ for a constant dye flow velocity of 0.5 m/s.     

短脉冲激光刻蚀加工铜材料的机制

 利用数值模拟方法，研究波长1 064 nm、脉冲宽度介于1~20 ps的激光在刻蚀铜靶时，单次脉冲作用下非平衡场刻蚀和热平衡刻蚀两种机制的竞争过程。结果表明：随着脉冲宽度的增加，刻蚀过程由非平衡电荷分离场刻蚀占主导地位转变为热平衡刻蚀起主要作用，且脉冲宽度和激光峰值功率密度增大到一定程度后，各种电子加速机制在不同时刻开始突显，电子能量分布出现多峰结构。在能量密度为15 J/cm2的激光作用下，1和5 ps脉宽对应的非平衡场刻蚀深度分别为110和101 nm，10和20 ps脉宽分别为25和18 nm。