铌镁酸铅-钛酸铅铁电阴极电子发射特性

研究了铌镁酸铅-钛酸铅铁电材料的铁电、介电性能对阴极发射阈值电压的影响, 以及铁电阴极发射电流与激励脉冲电压和抽取电压之间的关系, 并分析了其发射机理. 结果表明, 室温介电常数高、极化强度变化量大的弛豫铁电体0.9Pb(Mg_1/3Nb_2/3)O₃-0.1PbTiO₃具有较小的发射阈值电压; 铁电阴极电子发射与快极化反转和等离子体的形成有关; 由极化反转所致电子发射的自发射电流随激励脉冲电压的增大呈幂律增长关系, 其发射电流开始于激励脉冲电压的下降沿; 在抽取电压较大时, 发射电流随抽取电压的增大呈线性增长关系, 说明大电流主要取决于抽取电压; 其发射电流开始于激励脉冲电压的上升沿, 与“三介点”处的场增强效应和等离子体的形成有关; 当抽取电压为2500 V 时, 得到的发射电流幅值为210 A, 相应的电流密度为447 A/cm².     

伸缩-剪切模式自偏置铌酸锂基复合材料的磁电性能和高频谐振响应

选用多种切型铌酸锂(LiNbO_3)单晶,研究了铁基非晶合金(Metglas)/LiNbO_3叠层复合材料基于伸缩-剪切模式的磁电耦合性能,揭示了铌酸锂单晶压电系数与复合材料剪切磁电耦合系数的对应关系,在使用铌酸锂xzt/30~?切型时得到了最优化剪切磁电系数.通过SrFe12O19薄磁带提供偏置磁场,Metglas/LiNbO_3磁电复合材料可在没有外加直流磁场时实现剪切磁电响应,并在0.991 MHz和3.51 MHz频率时分别测出了谐振磁电系数,有望将铌酸锂基剪切磁电复合材料用于高频磁场探测.     

锆钛酸铅双层膜的铁电及光学特性研究

采用化学溶液沉积法在LaNiO₃涂布的硅晶片上制备了高度(100)择优取向,表面均匀、平整、致密无裂纹的PbZr_0.5Ti_0.5O₃/PbZr_0.4Ti_0.6O₃双层膜. 双层膜具有单一的钙钛矿相,同时拥有良好的铁电性能,剩余极化强度高达64μC/cm²,平均矫顽场仅为43.6kV/cm. 棱镜-薄膜耦合实验结果表明PbZr_{关键词： 铁电薄膜 平板光波导 锆钛酸铅 棱镜-薄膜耦合}     

掺铜铌酸钡钠中铜的形态形成特性

在铌酸钡钠（ＢＮＮ）的钨青铜结构形成范围内，适当的调整其成份组成，于氧化气氛中合成铌酸钡钠时，掺铜ＢＮＮ存在着自然形成Ｃｕ＾＋，Ｃｕ＾２＋的规律性，使用光电子能谱仪粒测定了掺铜ＢＮＮ铜的价态，讨论了Ｃｕ＾＋及Ｃｕ＾２＋在ＢＮＮ结构中占位以及掺铜ＢＮＮ晶体赋色的原因。     

铌酸锂马赫-曾德尔调制器偏置工作点的一种锁定方法

本文提出了一种锁定铌酸锂马赫-曾德尔调制器(MZM)偏置工作点的方法 ,通过引入一个特殊的测试电压和校准马赫-曾德尔调制器的最大输出光强,反馈信号受输入光功率的波动和探测器的暗噪声影响很小,偏置锁定精度可以达到±0.05°(标准偏差)。这种方法可以锁定铌酸锂马赫-曾德尔调制器传递函数上的任意工作点,且不需要加入额外的扰动信号,可以应用于连续变量量子密钥分发等领域。     

宽带准连续光纤激光在周期极化铌酸锂中倍频特性的研究

双包层光纤激光器和非线性光学材料(如周期性极化的铌酸锂晶体,PPLN)相结合,开辟了实用性非线性光学器件的一个新领域。研究了准相位匹配周期性极化反转铌酸锂晶体对宽带准连续光纤激光倍频的温度特性和频谱特性。在理论上,从准相位匹配相位失配关系出发,推导了晶体温度与抽运源中心波长的关系以及温度响应带宽,并和已报道实验结果进行了比较,二者符合得很好。此外,还推导了倍频周期极化铌酸锂晶体对抽运基频光源的响应谱线带宽。在实验上,采用长度20mm,极化周期6．5μm,厚度0．5mm的周期极化铌酸锂晶体光纤激光器准连续宽带输出进行了倍频,获得了在不同控制温度下的倍频光光谱,并对此进行了详细分析。     

原子吸收光谱法测定岩石中铜、铅和锌的不确定度评定及方法改进

利用原子吸收光谱法进行地质样品中微量元素含量的测定简便、快速、准确、经济,目前在地质实验室中得到了广泛应用。然而复杂的前处理流程和测试过程都会不可避免地引入不确定度。根据《检验和校准实验室能力的通用要求》,实验室应适当进行测量结果不确定度的评定。本研究利用电热板消解,火焰原子吸收光谱法,测定国家标准岩石样品与采自胶东曲家金矿岩心样品中铜、铅和锌的含量。以空白样品测试结果标准偏差的三倍作为仪器检出限。标准样品及岩心样品测试结果均符合DZ/T 0130.3—2006中关于测试准确度与精密度的要求。在实验室内部,采用自下而上的方法进行测量结果不确定度的评定,确定了测量不确定度的来源,包括样品称量、样品定容、样品消解、标准系列的配制、标准曲线最小二乘拟合及重复性测量,准确计算了六个不确定分量的大小及扩展不确定度。其中,后四个分量是测量结果不确定度的主要来源。结果显示标准样品中铜、铅和锌含量测量结果不确定度均小于标准证书中给定的不确定度,岩心样品中铜、铅和锌的含量分别为（4.965±0.383）,（36.415±2.449）和（30.818±0.736）μg·g-1。对六个来源的不确定度进行比较,提出采用该方法测量岩石样品中铜、铅和锌含量时的几点改进：调整取样量或定容体积来提高待测溶液中元素浓度及吸光度、调整标准系列浓度使其与待测溶液中元素浓度相近、增加标准点和待测溶液测量次数、尽量使用相对标准不确定度小的移液管进行稀释操作等。将测量结果不确定度的评定作为有效工具,指导改进分析方法及测试流程,在岩石样品微量元素含量准确测定工作中具有重要的意义。     

ICP-AES测定铜-锌合金中锌及杂质元素砷、铅、锑和铋

采用ICP-AES同时测定铜-锌合金中锌、砷、铅、锑和铋含量,优化了样品溶样条件.方法检出限为0.0003%-0.0012%,回收率为86%-112%,RSD为0.30%-5.17%,测试结果表明,该方法是测定铜锌合金的简单准确快速的方法.     

微波消解-电感耦合等离子体-质谱法测定黑木耳中铅、镉、砷、铜、锌和铬

建立了微波消解法前处理,电感耦合等离子体-质谱法(ICP-MS)快速测定黑木耳中Zn、Cu、Pb、Cd、Cr、As等重金属元素的方法.该法采用内标法校正监测和校正信号的短期和长期漂移,提高仪器的稳定性,改善测定的精密度,校正一般样品的基体影响,建立了测定208pb、114Cd、75As的干扰方程以消除同质异位素重叠和多原子粒子的干扰.该方法能准确测定大米粉标准物质(GBW 10010)和茶叶标准物质(GBW 10016)中Pb、Cd、Cr、Zn、Cu、As的含量,黑木耳样品的加标回收率为94.0％-107.3％,RSD为2.5％-5.2％.     

Mode selection of Lamb waves for the evaluation of solid plates with liquid loading

This paper studies the mode selection of Lamb waves for evaluating solid plates with liquid loading. For this purpose, the Lamb wave selected should have the features such as zero normal displacement components at the plate surface in contact with liquid, small dispersion, and maximum group velocity. It is found that when the phase velocity of Lamb wave is equal to the longitudinal wave velocity of the plate material, its normal displacement at the plate surface is always zero. Through the numerical analyses, the specific S₂ Lamb wave that has zero normal displacement component at the plate surface, small dispersion and maximum group velocity compared with the other Lamb waves has been found. With respect to the specific S₂ Lamb wave, some experimental examinations have been carried out. It is found that the liquid loading on the plate surface has less influence on the specific S₂ Lamb wave signal but it can effectively eliminate the other signals. Moreover, the specific S₂ Lamb wave selected exhibits the capability of detecting multiple defects in the solid plate with the liquid loading. It can be concluded that the specific S₂ Lamb wave selected is suitable for the evaluation of solid plates with liquid loading.     

Changes in ferroelectric properties of lead indium niobate-lead titanate ceramics under compressive stress applied perpendicular to an electric field

The influences of perpendicular compressive stress on the ferroelectric properties of (1−x)Pb(In_1/2Nb_1/2)O₃-xPbTiO₃ (x=0.1-0.4) ceramics were investigated in this study. In general, with increasing compressive stress the coercive field and the dissipation energy of the ceramics were seen to increase. The stress-induced changes in the polarization, however, depended significantly on ceramic compositions. The observations were mainly interpreted in terms of competing influence of the domain switching through non-180° domain walls, clamping of domain walls, and the stress-induced decrease in the switchable part of spontaneous polarization.     

TE0导模干涉刻写周期可调亚波长光栅理论研究

通过棱镜耦合激发非对称金属包覆介质波导结构中的TE₀导波模式, 利用两束TE₀模的干涉从理论上实现了周期可调的亚波长光栅刻写. 分析了TE₀模式的色散关系, 刻写亚波长光栅的周期与激发光源、棱镜折射率、光刻胶薄膜厚度及折射率之间的关系. 用有限元方法数值模拟了金属薄膜、光刻胶薄膜和空气多层结构中TE₀导模的干涉场分布. 研究发现, 激发光源波长越短, TE₀ 模干涉刻写的亚波长光栅周期越小; 光刻胶越厚, 刻写的亚波长光栅周期越小; 高折射率光刻胶有利于更小周期亚波长光栅的刻写. 相较于表面等离子体干涉光刻, 基于TE₀ 模的干涉可在厚光刻胶条件下通过改变激发光源、棱镜折射率、光刻胶材料折射率、特别是光刻胶薄膜的厚度等多种方式实现对亚波长光栅周期的有效调控.     

各向同性板中盲孔缺陷的兰姆波拓扑成像

将拓扑成像用于各向同性板中盲孔缺陷的兰姆波检测。由于缺陷关于板中面是非对称的,兰姆波模式转换的影响不能忽略。成像方法是基于无缺陷参考媒质中两个超声场(直接声场和伴随声场)的计算。以传感器激励信号为声源,计算直接声场;以盲孔引起的兰姆波散射信号为声源,计算伴随声场。拓扑成像通过直接声场与伴随声场的相乘,可消除无缺陷处多模式混叠的干扰,提高成像分辨率。建立有限元模型,通过不同时刻的瞬态声场图可视化地显示多模式兰姆波在缺陷处的聚焦过程,揭示拓扑成像方法的物理机理。数值结果表明,相对于经典的延迟求和以及时间反转方法,拓扑成像对盲孔缺陷有更强的适应能力。即使对于复杂的包含模式转换的兰姆波信号,拓扑图像的质量依然没有受到影响。文中提出的成像方法对板类结构中非对称缺陷的兰姆波检测具有一定的应用潜力。     

Observation of relaxation modes in room temperature ferroelectric liquid crystal mixtures

The dielectric measurements in SmC* and SmA phases of a room temperature ferroelectric liquid crystal mixture FLC-6980 in the cells of different thickness in planer alignment have been carried out in the frequency range 100 Hz to 1 MHz. A relaxation mode (called NRM) whose dielectric increment is less than the Goldstone mode has been observed in the SmC* phase. This mode appears due to the surface effect. Goldstone mode and the soft mode was observable in the vicinity of SmC*-SmA transition temperature (T _C*A). The dielectric parameters of the Goldstone mode, new mode and the soft mode have been studied as a function of frequency and temperature. The calculated values for f_NRM, δε^NRM and distribution parameter α_NRM are found to be 325 kHz, 6 and 0.156 for 5μm thick planer cell at 37°C. It is seen that in the vicinity of theT _C*A, soft mode obeys the Curie-Weiss law given by mean field theory. The results have been compared with materials of large spontaneous polarization.     

Single crystal study of competing rhombohedral and monoclinic order in lead zirconate titanate

Neutron diffraction data obtained on single crystals of PbZr(1-x)Ti(x)O3 with x=0.325 and x=0.460, which lie on the pseudorhombohedral side of the morphotropic phase boundary, suggest a coexistence of rhombohedral (R3m/R3c) and monoclinic (Cm) domains and that monoclinic order is enhanced by Ti substitution. A monoclinic phase with a doubled unit cell (Cc) is ruled out as the ground state.     

Optical whispering gallery modes in dodecagonal zinc oxide microcrystals

We have investigated optical modes in zinc oxide micropillars with dodecagonal cross section using polarization-resolved microphotoluminescence spectroscopy. Luminescence spectra of such pillars show series of resonance lines with characteristic line widths and spacings. The spectral positions of the observed lines can be explained assuming a circular two-dimensional dielectric resonator. Lowest radial mode numbers (n=1,2) indicate optical whispering gallery modes.     

Enhanced mechanical behaviour of lead zirconate titanate piezoelectric composites incorporating zinc oxide nanowhiskers

This paper reports that the lead zirconate titanate （PZT） piezoelectric composites incorporating zinc oxide nanowhiskers （ZnOw） were prepared by the conventional solid state processing. The whisker-dispersed PZT composites （PZT/ZnOw） presented a significant enhancement in the mechanical properties such as Young＇s modulus, tensile strength and compressive strength. Especially, the compressive strength increased from 153 MPa for the PZT to 228 MPa for the PZT/ZnOw composites. The reinforcement mechanism in strength of the composites was discussed. The me- chanical quality factors of the PZT/ZnOw composites increased considerably, while the piezoelectric constants and electromechanical coupling coefficient decreased slightly. The composites with good electrical and excellent mechanical properties are promising for further applications.     

Dynamic magnetoelectric effects in bulk and layered composites of cobalt zinc ferrite and lead zirconate titanate

Low-frequency magnetoelectric (ME) coupling is investigated in bulk samples and multilayers of cobalt zinc ferrite, Co_1-xZn_xFe₂O₄ (x=0–0.6), and lead zirconate titanate. In bulk samples, the transverse and longitudinal couplings are weak and of equal magnitude. A substantial strengthening of ME interactions is evident in layered structures, with the ME voltage coefficient a factor of 10–30 higher than in bulk samples. Important findings of our studies of layered composites are as follows. (i) The transverse coupling is stronger than the longitudinal coupling. (ii) The strength of ME interactions is dependent on Zn substitution, with a maximum for x=0.4. (iii) A weak coupling exists at the ferromagnetic-piezoelectric interface, as revealed by an analysis of the volume and static magnetic field dependence of ME voltage coefficients. (iv) The interface coupling k increases with Zn substitution and the k versus x profile shows a maximum centered at x=0.4. (v) The Zn-assisted enhancement can be attributed to efficient magneto-mechanical coupling in the ferrite. PACS 75.80.+q; 75.50.Gg;75.60.-d;77.65.-j;77.65.Ly;77.84.Dy     

一维多缺陷光子晶体的缺陷模

设计了一个多缺陷的一维光子晶体,并利用传输理论研究其透射谱.利用泰勒展式的一级近似,得到了缺陷模频率的解析表达式,进而得到紧束缚理论中的耦合因子.这些结论与实验结果或数值模拟相符合,可以很好地描述缺陷模的有关规律,对多通道滤波器的设计具有指导意义. 关键词： 光子晶体 缺陷模 紧束缚方法 耦合因子