Landau theory of ferroelectric transition in long cylindrical nanoparticles

Using a phenomenological Landau theory, the size dependence on ferroelectric transition for free-standing long cylindrical nanoparticles is discussed. We derive the size dependence of the transition temperature, polarization profile as well as the static susceptibility. The transition temperature vanishes below a critical size where the static susceptibility shows divergence obeying Curie-Weiss law. In order to make this result compared with experiments, the average polarization and the susceptibility is computed with a Gaussian particle size distribution. The average polarization in such a case shows smearing with respect to the particle size whereas the divergence in the susceptibilty gets rounded. This might correspond to a size dependent soft mode which can be observed in Raman measurement.     

基于激光干涉测试技术的分离式Hopkinson压杆实验测试系统

分离式Hopkinson压杆（SHPB）实验的传统测试技术是基于应变片的电测技术,测试结果的可靠性强烈依赖于应变片与杆之间粘贴质量,受到人为因素的影响较大。本文中采用基于多普勒频移原理的双探头全光纤激光干涉测速技术,以粒子速度为监测目标,借助应力波传播理论,换算成试件的应变和应力,从而建立了SHPB实验的非接触光学测试系统。针对韧性和脆性两类材料,分别提出了激光正入射和激光斜入射两种测试技术。再以铝合金和PZT陶瓷为例,通过与传统的应变片测试结果以及DIC测量结果的对比分析,验证了两种测试技术的有效性。与传统的应变片测试技术相比,新的激光干涉测试技术具有免标定、抗干扰、可靠性高等许多优点,有助于实现SHPB实验测试系统标准化。

     

柔性作动器驱动的非线性系统随机振动的最优有界控制

柔性作动器具有低刚度、大变形等特征,这一方面使主结构具备了强的环境适应性,另一方面也使主结构易受外界微扰影响,从而降低其操作精度．本文以介电弹性体作动器驱动的单自由度非线性系统为研究对象,通过即时微调电压,抑制系统在平衡位置附近的随机振动．通过随机平均法降低系统维数,将原系统的控制问题转化为关于慢变过程的控制问题;结合随机动态规划原理及控制约束导出最优有界控制策略．该策略具干摩擦形式,具有能量耗散本质,在抑制系统振动的同时提高了系统的稳定性．数值研究表明：最优有界控制策略具有良好的控制效果、控制效率及较高的鲁棒性．     

Snap-through path in a bistable dielectric elastomer actuator

The dielectric elastomer (DE) has attracted significant attention due to its desired features, including large deformation, fast response, and high energy density. However, for a DE actuator (DEA) utilizing a snap-through deformation mode, most existing theoretical models fail to predict its deformation path. This paper develops a new finite element method (FEM) based on the three-parameter Gent-Gent model suitable for capturing strain-stiffening behaviors. The simulation results are verified by experiments, indicating that the FEM can accurately characterize the snap-through path of a DE. The method proposed in this paper provides theoretical guidance and inspiration for designing and applying DEs and bistable electroactive actuators.     

自适应结构多工况下强度控制的研究

对自适应超静定桁架结构的强度控制问题进行了研究，把模型从单一工况推广到了多工况，实现了理论的完整性，定义了结构工作状态系数， 分析了作动器的联入对结构强度的影响，利用超静定桁架的耦合特性和作动器的调节功能，把强度控制问题转化为数学规划问题，方法简单有效。     

(111)取向生长Pb(Zr0:95Ti0:05)O3纳米晶薄膜的铁电与热释电特性

" 在Pt/Ti/SiO2/Si基片上用溶胶-凝胶法与快速退火工艺制备了300 nm厚的锆钛酸铅Pb(Zr0:95Ti0:05)O3 (PZT95/5)反铁电薄膜．结果显示600~700 ℃晶化处理的钙钛矿PZT95/5薄膜具有高度(111)取向生长特性．薄膜的电性能测量采用金属-铁电-金属电容器结构．在20 V电压作用下,600~700 ℃晶化处理的PZT95/5薄膜显示出饱和电滞回线．在1 kHz下,600、650和700 ℃晶化的薄膜介电常数与损耗分别为519与0.028、677与0.029、987     

(Ni0.8Zn0.2Fe2O4)epoxy-PZT双层膜中的磁电效应

讨论了Ni_0.8Zn_0.2Fe₂O₄ (NZFO)与锆钛酸铅(PZT)的双层膜结构样品的磁电(ME)效应.NZFO粉料由溶胶-凝胶法制成，再经900℃热压，并高温烧结.在该双层膜中测量到了很强的磁电相互作用.发现横向的磁电效应比纵向效应大一个数量级，并且随NZFO烧结温度的提高而增加.当烧结温度从950℃上升到1380℃时，横向ME电压系数(α_E)的最大值变化范围为25.6 mV Am^-2≤α_E≤199.6 mV Am^-2.理论分析显示NZFO-PZT双层膜样品中ME效应源于NZFO与PZT之间相对良好的磁电耦合. 关键词： 镍铁氧体 PZT 热压法 ME效应     

(111)择优取向的Pb(Zr0.52Ti0.48)O3铁电薄膜的制备及研究

选用不同浓度的Pb(Zr_0.52Ti_0.48)O₃溶胶，用Sol-gel法在Pt/Ti/SiO₂/Si基片上沉积一层厚度不同的Pb(Zr_0.52Ti_0.48)O₃ (PZT52)过渡层，经400℃烘烤、550℃退火等程序后，再用Sol-gel法在PZT52过渡层上沉积Pb(Zr_0.52Ti_0.48)O _{关键词： PZT铁电薄膜 择优取向 过渡层 剩余极化强度}     

Ferroelectric PZT Thin Films by Sol-Gel Deposition

Sol-gel spin coating has a low thermal budget, is cheap compared to vacuum-based techniques and is now routinely used to produce dense, pore-free ferroelectric films. PbZrx Ti(1 – x)O3 (PZT) is utilized in most applications because it has a large remanent polarization, high piezo- and pyroelectric coefficients and optimized electromechanical coupling factors, depending on precise composition. This paper will review some of the principles and applications of PZT films and highlight using transmission electron microscopy some of the basic problems and solutions involved in producing device-quality material on Si-substrates.