铁电阴极制备与性能实验研究

 讨论了不同发射机理对铁电阴极材料性能的要求,对PZT（锆钛酸铅）系铁电陶瓷工艺过程中的关键步骤进行了研究。通过掺杂改性和改进预烧条件等手段,有效地改善了材料的性能参数,制备出相对介电常数大于3 000的弛豫相铁电陶瓷和压电常数大于500×10^-12C/N的铁电相铁电陶瓷。在初步的发射实验中,使用改进工艺后的PLZT8/65/35制备的铁电阴极,触发脉冲5.4 kV时,获得的发射电子电流密度达到800 A/cm^{2/sup>,远大于C-L定律计算的发射电流。}     

掺镧锆锡钛酸铅陶瓷极化强度变化量对电子发射电流强度的影响

铁电阴极因其优异的电子发射性能在高功率微波管的电子束源、平板显示技术以及宇航推进器等领域 有着广阔应用前景而日益受到人们的重视.大量研究表明,铁电阴极电子发射性能受阴极材料性能的影响. 在激励电场作用下,铁电阴极材料会产生表面非屏蔽电荷而引起极化强度的变化, 这表明铁电阴极电子发射性能可能与阴极材料的极化强度变化量存在着某种关系. 为研究阴极材料极化强度变化量对铁电阴极电子发射性能的影响,以掺镧锆锡钛酸铅铁电和反铁电陶瓷样品 作为阴极材料,通过正半周电滞回线测试得到阴极材料在不同电场强度下的极化强度变化量, 测量得到电子发射电流强度随激励电场的变化曲线,并分析了电子发射电流强度与极化强度变化量的关系. 结果表明,两种样品电子发射电流强度与极化强度变化量正相关.     

负脉冲激励下PLZST电子发射特征及发射机理研究

采用固态烧结工艺制备了位于反铁电/铁电相界附近的掺镧锆锡钛酸铅（PLZST）反铁电陶瓷样品.采用该样品作为阴极材料,研究了其在负脉冲激励电场下的电子发射行为.负脉冲激励下,0.5 mm厚PLZST反铁电陶瓷圆片发射阈值电压为500 V;当激励电压为500 V,抽取电压为3.5 kV时,得到690 A发射电流.结果表明,PLZST反铁电陶瓷发射阈值电压低,发射电流大,即使激励电场低于陶瓷的正向开关电场,仍能得到强发射电流.最后,讨论了PLZST反铁电陶瓷在负脉冲激励下电子发射内在机制. 关键词： 反铁电材料 铁电阴极 电子发射     

反铁电陶瓷的强电子发射特性研究

采用掺镧锆锡钛酸铅反铁电陶瓷作为阴极材料,研究了脉冲电压激励下陶瓷的电子发射特性.当激励电压为800V、抽取电压为0V时,得到1.27A/cm²的发射电流密度;当抽取电压增加到4kV时,获得1700A/cm²的发射电流密度.分析了发射电流随抽取电压的变化关系,讨论了反铁电陶瓷强电子发射的内在机理.结果表明：掺镧锆锡钛酸铅反铁电陶瓷能够在较低的激励电压(400V)下实现电子发射,发射电流远大于按照Child-Langmuir定律计算出的电流,三接点附近局域反铁电—铁电相变产生初始电子发射,初始电子电离中性粒子形成等离子体,增强了电子发射. 关键词： 铁电阴极 反铁电体 电子发射     

无铅铁电陶瓷电子发射性能

 铁电阴极材料，作为一种新型的功能材料，以其高的发射电流密度等优点而受到重视。鉴于目前研究的铁电阴极材料多局限于锆钛酸铅等含铅材料，作者采用无铅铁电陶瓷Na₁/2Bi_1/2TiO₃-BaTiO₃(BNBT)，进行了电子发射实验，获得发射电流密度达20A/cm²。初步实验结果表明，与锆钛酸铅相比，钛酸铋钠发射电流密度略低但性能稳定性较好。作为无铅铁电阴极，BNBT仍然具有良好的研究开发价值。     

绝缘体二次电子发射系数测量装置的研制

 成功研制了测量绝缘体二次电子发射系数的测量装置，该装置主要由栅控电子枪系统、真空系统和电子采集系统组成，测量装置产生的原电子流的能量范围为0.8~60 keV。采用单脉冲电子枪法，测量了原电子能量范围为0.8~45 keV的多晶MgO的二次电子发射系数。测量中，收集极(偏置盒)离材料表面设置为约35 mm，偏置电压设置为 45 V。测量得到：用磁控溅射法制备的MgO的二次电子发射系数最大值约为2.83，处于 2~26范围内，其对应的原电子能量约为980 eV。这表明该装置测量的绝缘体二次电子发射系数是可信的，但用磁控溅射法制备的MgO的二次电子发射系数较低，这可能是制备MgO时引入了过多的杂质在MgO二次电子发射体里面所引起的。     

反铁电相变陶瓷低频发射换能器

在具有高阶形式的广义压电方程基础上,讨论掺镧改性锆锡钛酸铅PbLa(Zr,Sn,Ti)O3(PLZST)反铁电相变陶瓷的非线性机电耦合问题,得到类似传统线性压电方程的近似线性电致伸缩方程,给出了一种解决非线性反铁电相变陶瓷换能器电声转换问题的分析方法,即在直流偏置状态下对PLZST反铁电相变陶瓷的材料参数进行近似线性等效化处理进而分析换能器的电声转换问题.在此基础上,研制了水中谐振频率1.1 kHz新型反铁电相变陶瓷低频弯张换能器.湖上试验结果表明,与同结构同尺寸压电陶瓷弯张换能器相比,目前反铁电换能器样品的发射电压响应约高3dB,声源级高出9dB,并验证了本文所提出的分析非线性反铁电相变陶瓷换能器方法的正确性.     

基于相变换能机理的反铁电陶瓷水声换能器初探

阐述了改性锆锡钛酸铅Pb(Zr,Sn,Ti)O3(PZST)反铁电陶瓷作为一种基于相变换能机理的大应变电致伸缩材料的性能特征以及作为水声换能器新型有源材料的优势。采用掺镧改性锆锡钛酸铅PbLa(Zr,Sn,Ti)O3(PLZST)反铁电陶瓷材料首次设计制作了纵振式反铁电陶瓷水声换能器。试验结果表明,PLZST反铁电陶瓷用于水声换能器研制在技术上是可行的,与压电陶瓷换能器比较,目前反铁电换能器样品的等效发射电压灵敏度提高3~5dB以上。根据实验情况,认为在发射电压灵敏度和声源级方面具有进一步提升的潜力。     

利用X射线衍射技术对压电材料本征与非本征起源探究的研究进展

钙钛矿铁电压电材料具有高介电压电常数和高机电耦合系数等特点,在工业、消费电子和军事等领域具有广泛的应用,其压电性能起源的机理及与材料多尺度结构之间的关系一直是凝聚态物理和材料科学领域的研究热点.铁电材料的压电效应主要来源于本征的场致晶格畸变以及非本征的畴翻转和畴壁运动,理解并区分这两种压电效应的贡献机制对研究材料压电性能的起源具有重要意义.本文综述了近年来通过电场原位X射线衍射技术分析电场作用下材料晶格结构和畴结构变化的技术手段和研究方法,重点介绍了自第三代同步辐射光源和高速探测器获得长足发展以来,通过时间分辨衍射技术、单双峰拟合、全谱拟合、质心计算等方法开展压电材料本征和非本征贡献,以及电场诱导相变对其宏观性能影响的研究进展,期望通过对各类方法的介绍和回顾为多种压电材料的机理分析提供研究方法和技术支持.     

提高砷化镓二次电子发射系数的探讨

介绍了延长负电子亲和势二次电子发射材料砷化镓的逸出深度的设计,并给出了经过特殊设计的这种砷化镓的能级示意图,然后对通常的砷化镓和经过特殊设计的砷化镓的二次电子发射系数的理论值进行了比较,得出:当原电子入射能量较低（小于10 keV）时,两种砷化镓的二次电子发射系数差值较小;当原电子入射能量较高（大于20 keV）时,经过特殊设计的砷化镓的二次电子发射系数比普通砷化镓的二次电子发射系数大,而且随着原电子入射能量的升高,两种砷化镓的二次电子发射系数差值也在增大。     

太赫兹辐射场下的石墨烯光生载流子和光子发射

通过半经典的玻尔兹曼平衡方程理论研究了太赫兹辐射场下的石墨烯光生载流子和光子发射.研究得到了太赫兹辐射场下石墨烯的光生载流子浓度和光子发生率的解析公式.研究发现,掺杂电子浓度越小,或者温度越低,光生载流子浓度越大;掺杂电子浓度越大,或者温度越低,石墨烯的光子发射率越大.通过改变门电压或温度,可以有效地调控石墨烯光生载流子浓度和光子发射概率.理论研究结果和解析表达式对发展以石墨烯为基础的新型太赫兹光电器件具有重要的参考价值.     

强电流铁电阴极电性能参数与发射结果的关系研究

 在实验结果的基础上,从理论上阐述了材料的电滞回线、介电常数、压电常数等性能对电流发射性能的明显影响,并通过材料的掺杂改性提高材料的性能参数,从而达到了提高发射电流密度的目的。     

Characteristics of backing impacts on the performance of the thickness mode piezoelectric transducer

The impacts of the thickness, the specific acoustic impedance and the mechanical loss factor of the backing on the performance of the thickness mode piezoelectric transducer are systemically studied, which are focused on the effective electromechanical coupling coefficient and the mechanical quality factor near the center frequency. The results show that with contin?uous increasing of the backing thickness, the effective electromechanical coupling coefficient and the mechanical quality factor are found rapidly declined by oscillation way. With the increase of the difference value of the acoustic impedance between the backing material and the piezoelec?tric material, the effective electromechanical coupling coefficient deceases and the mechanical quality factor increases. Under condition that the thickness of the piezoelectric material is fixed, the effective electromechanical coupling coefficient is found declined with the increase of the mechanical loss factor by monotonous way. The mechanical quality factor has minimum value and the electric characteristic curve tends to be smooth in a given frequency range. The equivalent circuit theory result is in good agreement with the ones by finite element method and the experimental results. The work mentioned above provides a theoretical guidance for the design and experimental fabrication of the thickness mode piezoelectric transducer.     

Dynamics of the mechanoluminescence induced by elastic deformation of persistent luminescent crystals

When a composite of suitable dimension formed by mixing the microcrystalline or nanocrystalline persistent luminescent materials in epoxy resin is deformed at a fixed pressing rate, then the elastico mechanoluminescence (EML) emission takes place after a threshold pressure, in which the EML intensity increases linearly with the applied pressure. When the applied pressure is kept constant or decreased linearly, then the EML intensity decreases with time, in which depending on the prevailing condition, the EML intensity initially decreases at a fast rate and then at a slow rate or sometimes it decreases exponentially having only one decay time. When a small ball is dropped from a low height onto the film of a persistent luminescent material, then initially the EML intensity increases with time, attains a peak value and then it decreases initially at a fast rate and later on at a slow rate. In this case, both the peak EML intensity and the total EML intensity increase linearly with the height through which the ball is dropped onto the film. Considering the piezoelectrically induced detrapping model based on successive detrapping of exponentially distributed traps a theoretical approach is made to the dynamics of light emission induced by elastic deformation of persistent luminescent crystals and thin films. It is shown that the EML intensity depends on several parameters such as pressure, pressing rate or strain rate, temperature, density of filled electron traps, piezoelectric constant near defect centers, etc. Both, in the case of slow deformation and impact stress, the fast decay time is related to the time-constant for the decrease of pressing rate of the samples and the slow decay time of EML is related to the lifetime of electrons in the shallow traps lying in the normal piezoelectric region of the crystals. Both, the EML produced during the release of pressure and the EML produced during the successive applications of pressure take place due to the detrapping of retrapped electrons in the vacant electron traps near activator ions, in which retrapping is caused by the thermally released electrons from the filled shallow traps lying in the normal piezoelectric region of the crystals, which get filled during the detrapping of stable traps at the time of increase of pressure. On the basis of the proposed model, the dependence of EML intensity on different parameters, dynamics of EML and physical concepts of the threshold pressure, characteristic piezoelectric field for detrapping, coefficient of deformation detrapping, nonlinear increase of the EML intensity of some crystals at high pressure and higher EML intensity in the crystals having higher coefficient of deformation detrapping can be satisfactorily understood. A good agreement is found between the theoretical and experimental results. It is shown that the present study may be helpful in tailoring the intense persistent elastico mechanoluminescent materials having long lasting time.     

背衬参数对厚度模压电换能器特性的影响

系统研究了厚度模压电换能器的背衬厚度、声阻抗率及机械损耗因子对换能器振动性能影响,重点分析了在所关心频率附近的有效机电耦合系数和机械品质因数。计算结果表明,随着背衬厚度增大,换能器的有效机电耦合系数和机械品质因数均震荡减小;背衬声阻抗率与压电片声阻抗率差值增大,换能器有效机电耦合系数减小,机械品质因数增大;保持压电片厚度不变,增大背衬的机械损耗因子,换能器有效机电耦合系数单调减小,机械品质因数有极小值,在给定频率范围内电特性曲线趋于光滑。用有限元方法验证了等效电路计算方法的正确性,并对比了换能器的测试结果和计算结果。计算所得规律为厚度模压电换能器的设计和实验制作提供了理论依据。      

对称磁电层合板磁电转换效应理论研究

磁致伸缩和压电层合材料通过磁致伸缩和压电效应的乘积可以获得大的磁电效应.通过材料的力学本构方程，建立了对称磁电层合板磁电耦合的静态力学模型；采用ANSYS 80多物理场有限元分析软件，对层合结构的磁电转化效应进行了数值计算，并与理论计算值进行了对比.研究结果表明：磁致伸缩/压电的厚度比增加使磁电电压系数增大；所推导的磁电电压系数公式的计算值与等效电路模型推导的公式计算值符合很好；有限元数值计算结果介于两种模型的计算结果之间. 关键词： 磁电效应 层合板 本构方程 有限元分析     

Piezoelectric non-linearity in PbSc0.5Ta0.5O3 thin films

Epitaxial (001)-oriented PbSc_0.5Ta_0.5O₃ (PST) thin films were deposited by pulsed laser deposition. Local piezoelectric investigations performed by piezoelectric force microscopy show a dual slope for the piezoelectric coefficient. A piezoelectric coefficient of 3 pm/V was observed at voltages up to 0.8 V. However, at voltages above 0.8 V, there is a steep increase in piezoelectric coefficient mounting to 23.2 pm/V. This nonlinear piezoelectric response was observed to be irreversible in nature. In order to better understand this nonlinear behavior, voltage dependent dielectric constant measurements were performed. These confirmed that the piezoelectric non-linearity is indeed a manifestation of a dielectric non-linearity. In contrast to classical ferroelectric systems, the observed dielectric non-linearity in this relaxor material cannot be explained by the Rayleigh model. Thus the dielectric non-linearity in the PST films is tentatively explained as a manifestation of a percolation of the polar nano regions.     

Theory of magnetoelectric effect in double-layer ferromagnetic-piezoelectric structures

A theory of magnetoelectric effect in double-layer ferromagnetic-piezoelectric plate-shape structures is presented. Using the material and motion of continuum equations, an expression for the magnetic coefficient is derived in terms of the parameters characterizing the magnetic and piezoelectric phases. It is shown that in the region of electromagnetic resonance there is a considerable increase in the magnetoelectric coefficient value. A relationship is obtained between the ferromagnetic and piezoelectric thicknesses for which the magnetoelectric coefficient is maximal. The coefficients calculated for the structures based on permendure — plumbum zirconate-titanate are given, and the results of calculations are compared to the experimental data.__________Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 3–6, December 2004.     

Structural, dielectric and piezoelectric properties of nonlinear optical γ-glycine single crystals

Gamma glycine was synthesized and the single crystals were grown by the slow evaporation method in the presence of lithium nitrate. Structure and crystalline nature of the grown γ-glycine crystal was confirmed by X-ray diffraction technique. It was found to crystallize in the trigonal system with space group P3₁. The chemical composition was determined by NMR. Fourier transform infrared studies revealed the functional groups present in the grown crystal and UV-vis-NIR spectra revealed the transmission properties of the crystal specimen. Surface morphology of the grown crystal was studied by scanning electron microscopy (SEM) and elemental composition was confirmed by energy-dispersive spectrometry (EDS). The second-order nonlinear optical property of the material was investigated by Kurtz powder technique and the relative second harmonic efficiency of γ-glycine was estimated to be higher than that of KDP. The dielectric measurement was carried out as a function of frequencies at room temperature and the results were discussed. The samples have shown piezoelectric behavior with a fairly good piezoelectric charge coefficient (d₃₃) of 7.37 pC/N. Photoluminescence studies showed emission peak around 350 nm. Thermo gravimetric and differential thermal analyses were employed to understand the thermal and physio-chemical stability of the synthesized compound.     

Quantum effect on parametric amplification characteristics in piezoelectric semiconductors

Using QHD model the parametric interaction of a laser radiation in an unmagnetised piezoelectric semiconductor has been studied. It is found that the Bohm potential in the electron dynamics enhances the gain coefficient of parametrically generated modes whereas reduces the threshold pump intensity.