电场下[001]cub切型弛豫铁电单品PMN-32PT电畴的极化反转

为研究弛豫铁电单晶PMN-32PT电畴在电场下的极化反转，利用偏光显微镜研究了电场下[001]cub切型PMN-32PT单晶电畴组态的变化，建立了极化反转模型．在[001]cub单晶切片中，当电场强度达到4kV／cm时，电畴开始极化反转，出现平行于电场方向的畴壁，畴壁沿垂直自身的方向运动，畴壁的运动实际是畴的横向扩张；当电场强度增至6kV／cm时，畴壁消失，又出现垂直于电场方向的新畴壁；而电场强度进一步增至10kV／cm时，新畴壁也消失，且电畴消光，这表明多畴已单畴化．     

电场对[100]cub切型PMN-PT单晶电畴组态的影响

采用偏光显微镜观察了电场作用下[100]cub切型PMN-PT弛豫铁电单晶电畴组态的变化.结果表明：在正向电场作用下,当电场强度超过2.45 kV/cm时,平行于电场方向小畴条带慢慢消失,当电场强度升高到7.15 kV/cm时,原畴壁逐渐消失,在接近电极附近试样上优先出现了垂直于电场方向的新电畴;在反向电场作用下,电场强度超过2.05 kV/cm时,电畴条带沿电场方向扩展,当电场强度升到7.15 kV/cm时,平行于电场方向电畴消失,而出现许多垂直于电场方向电畴;在交流电场驱动下,电畴以低于50 Hz的频率做周期性振动.     

退火对PMN-32PT弛豫铁电单晶电畴组态的影响

采用光学显微镜沿[001]方向观察了PMN-32PT弛豫铁电单晶的电畴形貌，考查了在不同温度下退火处理对电畴组态的影响．结果表明：在90℃以下退火后，PMN-32PT晶体的电畴基本保持室温组态，但局部出现微弯曲．在120～160℃退火后，PMN-32PT晶体电畴明显粗化，条带宽大，且局部由条带型转变为回字型．在210℃以上退火后，PMN-32PT晶体电畴条带规则，均匀细小．     

0．76PMN-0．24PT单晶极化前后的介电特性

研究电场对0．76PbMgl／3Nb2／303-0．24PbTi03（0．76PMN-0．24PT）单晶结构影响．采用介电特性测量的方法,分析了0．76PMN--0．24PT单晶在直流电场极化前后介电常数随温度和频率的关系．实验结果表明,0．76PMN-0．24PT单晶极化前后介电特性有明显的差异,电场作用使单晶的内部从微畴转变为铁电宏畴．     

元素分布和裂纹对PMN-32PT单晶电学性能的影响

为寻求PMN-32PT单晶电学性能不稳定的成因,利用准静态压电常数测试仪、数字电桥和EDS对[001]切型PMN-32PT 单晶的电学性能和成分分布进行了对比分析,并考察了裂纹对晶体电学性能的影响.结果表明,元素分布的不均匀是造成[001]切型PMN-32PT单晶电学性能不均匀的重要原因,其中Ti对晶体的压电性能有正的贡献而Nb与之相反,Mg对介电常数有正的贡献;裂纹对晶体的电学性能影响显著,在裂纹处,PMN-32PT单晶的电学性能急剧下降.     

PZN-9PT单晶生长及电学性能研究

弛豫铁电单晶是目前电子材料研究的热点,而制备技术是解决该材料应用的关键.为了考察PZN-9PT晶体的生长形态、结构和性能,本文采用高温溶液法生长了PZN-9PT单晶,采用XRD表征了其相结构,采用相关电学性能测试方法表征了其介电、压电、电滞回线和机电耦合系数等电学性能.研究结果表明,采用高温溶液法可以制备出纯钙钛矿结构的PZN-9PT单晶,晶体呈淡黄色多面体形态,其三方-四方相转变温度为89℃,居里温度为175℃,[110]切型PZN-9PT单晶的压电常数为339 pC/N,矫顽场为8.7 kV/cm.     

BiFeO3薄膜的溶胶-凝胶制备及其铁电和介电性质

采用Bi(NO3)3.5H2O和Fe(NO3)3.9H2O为原料,用溶胶-凝胶方法在Pt/Ti/SiO2/Si制备了BiFeO3薄膜。XRD研究表明在500℃以上退火薄膜能够获得良好的结晶。铁电性测试结果表明450℃和500℃退火的薄膜铁电性相对较弱。在430 kV/cm的测试电场下,剩余极化分别为0.255μC/cm2和0.36μC/cm2。而550℃和600℃退火的薄膜的铁电性相对较强,在相同的测试电场下剩余极化强度分别为2.27μC/cm2和2.97μC/cm2。介电性研究表明450—550℃退火的薄膜具有小的介电色散和介电损耗,而600℃退火的薄膜则具有大的介电色散和介电损耗。     

基于电场仿真的20 kV线路非接触式验电判据分析

20 kV配电线路相比10 kV配电线路因其能提高线路供电能力,在我国许多地方有应用,确定线路是否带电对检修工作人员的安全保障具有重要意义。对不同运行工况下的20 kV线路电场进行有限元仿真分析,在COMSOL软件中建立正常运行及故障工况下的仿真模型;探究导线水平排列以及三角排列对周围电场分布的影响,得出导线附近的电场分布规律,并分析某一相导线停电对线路电场分布的影响。基于相关分析初步提出了适用于20 kV线路的验电判据,若在导线正下方距离0.1 m范围内电场强度大于19.65 kV/m,即可判定此导线带电。所提出的验电判据可为后续验电装置的设计奠定一定的理论基础。     

高压输电铁塔上架设ADSS光缆位置的研究

全介质自承式(ADSs)通信光缆处于高电场强度区域时,会受到严重的电蚀.为了在高压输电线路铁塔上架设ADSS通信光缆,必须详细了解高压输电线路铁塔附近的电场分布.因此,采用了模拟电荷法对高压输电线路铁塔附近的电场进行了数值计算,得到了在不同相位下的220kV铁塔附近的电场分布图.经过数据处理获得了全工况下铁塔附近等于25kV/m,20kV/m,15kV/m的等场强线.将220 kV的ADSS通信光缆架设在低于25 kV/m的场强区,将大大降低电场对ADSS光缆的电蚀.     

利用电流变液阻尼器改变切削系统特性的研究

为了进一步对先前研制的一种基于电流变液阻尼器的切削颤振抑制结构进行系统的研究,对其静态和动态特性进行了实验和理论研究。结果证明,这种结构可以显著改变车刀刀杆的固有频率、阻尼性能等动态特性和静态特性,在零电场下刀杆的静柔度约0.5μm/N,电场强度为1.5kV/mm时减小到约0.3μm/N,2kV/mm时减小到约0.2μm/N;在零电场时刀杆的加载和卸载曲线是大致重合的,近似一纯弹性体;而在电场强度为1.5kV/mm和2kV/mm时加载与卸载曲线包绕的面积都明显增大;刀杆的阻尼比在3kV/mm时为0.05127,而1.5kV/mm和0kV/mm时分别为0.02882和0.02163。动柔度曲线显示:随着电场强度的增大,结构的阻尼比增大,共振峰值减小。利用这种结构具有可控动态性能这一优点,可以在线对机床车削振动进行有效控制。     

Phase field simulation of the 180°domain-switching process in PbTiO_3 single crystal under an antiparallel electric field

The process of 180°domain switching in PbTiO_3 single crystal under an antiparallel electric field was investigated by the three-dimensional phase field simulation,especially the effect of electric field on the type and duration of domain switching.It is found that the polarization reversal of domains takes place under an antiparallel electric field in PbTiO_3 single crystal.The results of the phase field simulation indicate that there is only 90°domain switching under a weak electric field.With the rise...     

An unconventional phase field modeling of domains formation and evolution in tetragonal ferroelectrics

Based on characteristic functions of variants, we developed an unconventional phase field modeling for investigating domains formation and evolution in tetragonal ferroelectrics. In order to develop this computational approach, we constructed the anisotropy energy of tetragonal variants, which is used instead of Landau-Devonshire potential in the conventional phase field method, resulting in that much fewer parameters are needed for simulations. This approach is advantageous in simulations of emerging ferroelectric materials. We employ it to study the formation and evolution of domains in tetragonal barium titanate single crystal, as well as the nonlinear behaviors under cyclical stress and electric field loading. A multi-rank laminated ferroelectric domain pattern, 90° domain switching accompanied by polarization rotation, and 180° domain switching accompanied by move of domain wall are predicted. It is found that the speed of 90° domain switching is slower than that of 180° domain switching, due to both polarization and transformation strain changed in 90° domain switching. It also suggests that large strain actuation can be generated in single crystal ferroelectrics via combined electromechanical loading inducing 90° domain switching. The good agreement between simulation results and experimental measurements is observed.     

The domain structure and polarization retention properties of PT/PZT/PT ferroelectric thin film

The highly oriented perovskite-phase PT/PZT/PT ferroelectric thin film was pre- pared by sol-gel method. The domain structures and polarization retention proper- ties were investigated by scanning force microscopy. The amplitude and phase images of piezoresponse show complex various contrasts of dark, bright and gray. The complex variation of contrast in piezoresponse images results from the per- plexing orientation of grains and arrangement of domains in the ferroelectric films. The bright and dark areas in phase images correspond to top-to-bottom and bot- tom-to-top polarization oriented c-domain, respectively. The gray areas are c-domains with the polarization vector deviating from the direction normal to the film plane. The surface potential images of EFM are bright contrast, which is due to positive charges trapped on the film surface after being polarized by positive volt- age. And the brighter contrast is obtained from the higher electric field. The time-dependent surface potential images and line potential profiles show that the potential decays with time. And the decay in the region polarized by higher electric field is faster, especially at 15 min. This indicates that the polarization retention is related to the polarized electric field. Better retention properties may be obtained from a proper polarized electric field.     

Ferroelectric properties of Bi3.4Ho0.6Ti3O12 thin films prepared by sol-gel method

We have prepared the Ho-substituted bismuth titanate (Bi_3.4Ho_0.6Ti₃O₁₂, BHT) thin films on Pt/Ti/SiO₂/Si substrates using sol-gel method. The crystal structure and morphology of the films were characterized using X-ray diffraction and atomic force microscopy. The BHT film shows a single phase of Bi-layered Aurivillius structure and dense microstructure. The 2Pr and 2Ec of the 600-nm-thick BHT film were 38.4 μC/cm² and 376.1 kV/cm, respectively at applied electric field 500 kV/cm. The dielectric constant and dielectric loss are about 310 and 0.015 at a frequency of 1 MHz, respectively. The Pr value decreased to 93% of its pre-fatigue values after 4.46×10⁹ switching cycles at 1 MHz frenquency, and the BHT film shows good insulating behavior according to the test of leakage current. Supported by the Hubei Province Natural Science Foundation (Grant No. 2007ABA309)     

凝并区放电类型对电凝并装置去除亚微米粉尘效果的影响

通过改变电凝并装置凝并区的放电类型,提出了粉尘在正负脉冲电场中的异极性荷电新方法.并将其与交变电场放电条件下粉尘的除尘效率进行了对比研究,结果表明,当集尘区板间平均场强为5kV/cm、凝并区为脉冲电场且脉冲电压峰值10kV时,除尘效率达到了97％,比凝并区为交变电场且交变电压为10kV时提高了1％.     

反射式小型光学电场传感器

为了同时实现对直流电场、交变电场和瞬态电场的测量,通过琼斯矩阵计算,建立基于泡克尔效应的反射式光学电场传感探头的理论传感模型,分析铌酸锂晶体长度、晶体切型、温度以及封装应力对探头传感性能的影响. 制备尺寸Φ5 mm×80 mm,理论电场测量范围为±439.2 kV/m的反射式小型光学电场传感探头,搭建相关的电场传感系统并表征传感探头在10~5000 Hz交变电场、直流场、8.2~12.4 GHz高频微波场下的传感性能. 实验结果表明,该光学电场传感器在直流?12.4 GHz电场频率范围内具有较好的电场响应,在无外加电场时长时间内信号漂移量小于0.08‰,分辨力至少为3 V/m,实际可测量范围为10^?3~10² kV/m,有望应用于高功率微波探测和电力系统领域的直流、ms级及ns级暂态电场监测.     

储能电容与光导开关的工作模式

介绍了以光导开关为核心的高压纳秒电脉冲系统组成.半绝缘GaAs光导开关在初始偏置电场26.7 kV/cm条件下受到1 ns、光能20 μJ、波长1 064 nm激光照射.根据SRH模型和有限元法计算载流子浓度和光导开关时域电阻,考虑Blumlein 传输线等效电容电压的时域变化,进行了输出脉冲的模拟计算.模拟和实验表明...