一种研究粉末电致发光(EL)器件频率特性的新方法

提出了一种简单的研究粉末电致发光(EL)器件频率特性的新方法.用这种方法可以使用最少和最一般的设备条件很方便地测量粉末EL器件的有功电流、无功电流、损耗角和发光效率等重要参量及其随频率的变化特性.也可用来简单快速地测量介质和电容器的损耗特性. 试验并论证了方法的合理性,可行性及其物理依据.分析了方法的系统误差及随机误差.     

外延叠层多有源区激光器的结构优化设计

基于分离的非对称大光腔结构,对激射波长为905nm的外延叠层三有源区大功率脉冲半导体激光器的外延结构进行优化设计。通过优化近场光场模式、自由载流子吸收损耗、相邻发光区之间距离以及掺杂浓度分布等关键参数,提高了器件的脉冲峰值功率,降低了内损耗和远场垂直发散角。研制的1mm腔长、100μm条宽的三有源区大功率半导体激光器,经由150ns脉宽和6.67kHz重复频率的脉冲测试,在34.5A脉冲电流强度驱动下实现了122W的脉冲峰值功率输出。器件的斜率效率为3.54 W/A,单个发光区实现了折合91.75%的内量子效率和2.05cm-1的内损耗,水平方向和垂直方向上的半峰全宽远场发散角分别为7.8°和27.6°。     

磁场对基于Co铁磁薄膜的有机发光器件效率和电流的影响

制备结构为ITO/Co/NPB/Alq₃/LiF/Al的有机发光器件,测量了室温下磁场对器件发光效率和电流的影响.发现磁场强度小于80 mT时,器件发光效率随磁场强度的增加而增大,最大为18.8%,随磁场强度的继续增加发光效率的增强趋于饱和.效率的增加是Co的自旋极化的注入和磁场效应共同作用的结果,其中自旋极化注入起主要作用.在磁场强度小于60 mT时电流随磁场增强而增加,最大为6.9%,随磁场强度的进一步增加电流的增加有所减弱.产生这种现象的原因可归结为磁场相关的单线态极化子对的解 关键词： 有机电致发光 自旋极化 磁场效应     

薄板型介质材料复介电常数的无损测量

采用带法兰结构的TE01n圆柱谐振腔,用无损检测的方法测量薄板型微波介质材料的复介电常数。利用轴向模式匹配法对谐振腔内的电磁场进行了求解,给出了相对介电常数和损耗角正切的计算公式,并利用矢量网络分析仪对几种常用微波介质材料进行了测量,其结果表明:该测量方法对相对介电常数的测量误差不超过1%,而对损耗角正切的测量误差不超过10%。该方法还具备一腔多模的测试能力,测量频率可调,可用于介质材料频率特性的测量。     

钇掺杂钨酸铅晶体中的极化子和导纳谱

在室温至160 ℃范围内测量了掺钇钨酸铅(PWO∶Y)晶体的直流电导率,证明此时的载流子为极化子.观察到极化子由能带导电到跳跃导电转变引起的电导率极小.在此温区的交流导纳分析给出的交流电导率比直流电导率大三个数量级,说明此时的交流电导率主要是复介电常数的贡献.当样品的电导率和介电常数均随频率而变化时,从交流测量只能得到样品的总的导纳谱，而不能将其中的电导谱和介电谱分开. 关键词： 钨酸铅 电导谱 介电谱 导纳谱 极化子     

电磁波穿透墙体的衰减特性

 应用平面电磁波理论和菲涅耳公式分析了电磁波穿透不同介质的衰减特性,对不同的极化方式、入射角、介电常数、电导率、损耗角正切和频率下,电磁波在介质间的透射性能及介质中的传输衰减特性进行了分析,对常见的普通混凝土墙、37砖墙、24砖墙、石膏空心板、水泥泡沫板、木板和玻璃与频率的衰减特性进行了数值仿真,比较了新砌混凝土墙、实心粘土砖墙和多孔粘土砖墙的损耗特点,将仿真结果与实际测量及参考文献测量结果进行了比较,结果表明仿真的墙体频率衰减趋势与实际测量结果一致,衰减数值接近并略低于实测结果。     

(1-x)(K0.5Na0.5)NbO3-xSrTiO3陶瓷的弛豫铁电性能

通过对(1-x)(K0.5Na0.5)NbO3-xSrTiO3(0≤x≤0.15)陶瓷的相组成、晶体结构和介电性能的研究发现,该陶瓷为单一的钙钛矿结构相.当x含量较小(x＜0.1)时为正交相结构,x≥0.1时转变为四方相结构.随着SrTiO3掺杂量的增加,样品的致密度增加,样品由正常铁电相逐渐向弥散铁电相转变,且相变温度明显下降,其相变峰的半高宽D和临界指数γ,随 x 的增加而增加.样品损耗ε″r(复介电常数虚部)随温度T的变化表明低温时弛豫极化损耗起主要作用,高温时漏导损耗起主要作用.同时介电常数实部ε′r随频率的变化显示(1-x)(K0.5Na0.5)NbO3-xSrTiO3弛豫为德拜弛豫.     

基体电导率对0-3型铁电复合材料高压极化行为及损耗的影响

提出了一个0-3型聚合物基铁电复合材料的直流高压极化模型.模型中考虑了聚合物/铁电陶瓷界面处自由电荷的积聚及极化初始时刻的真实情况,利用拉普拉斯静电场方程,并结合边界条件,得到了直流高压极化过程中复合材料的极化强度、界面电流密度等随时间的演化方程,同时得到介电常数、介质损耗等物理特性的表达式.此外,实验制备了分别以环氧树脂E-44和铁电共聚物P(VDF-TrFE)为基体的两种0-3型铁电复合材料.从理论和实验两方面研究了基体电导率对极化行为以及介质损耗的影响.两方面结果均表明：随基体电导率增加,极化时间缩短,陶瓷相的极化强度及复合材料的整体电性能提高,但是漏电流及介质损耗增加.而且实验结果与直流高压极化模型的预测结果符合. 关键词： 铁电复合材料 电导率 极化 介质损耗     

Pb(Zr_(0.52)Ti_(0.48))O_3/YBa_2Cu_3O_(7-x)双层结构电学特性研究

该研究通过溶胶-凝胶结合PLD的方法,在LaAlO_3(LAO)基板上制备了具有良好的c轴取向的Pb(Zr_(0.52)Ti_(0.48))O_3/YBa_2Cu_3O_(7-x)(PZT/YBCO)双层薄膜。采用溅射法制备了Pt顶电极,在300K~50K温度范围内,对Pt/PZT/YBCO的电滞回线和J-V特性曲线进行研究,结果表明:300K时,Pt/PZT/YBCO的剩余极化强度约为22μC/cm~2,随着温度的降低,剩余极化强度基本保持不变同时矫顽场和临界导通电压(Vc)增大、漏电流减小,当YBCO进入超导态时,Vc随温度的变化规律发生改变。进一步研究了不同电压下Pt/PZT/YBCO的电流输运特性,当外加偏置电压较小时(临界导通电压以下),Pt/PZT/YBCO的电流输运特性主要符合欧姆导电机制,当外加偏置电压增大到临界导通电压以上时,电流输运特性主要符合肖特基发射机制。     

准全向平板超材料吸波体的设计

本文设计了一种具有准全向吸波特性的平板超材料吸波体,其准全向吸波特性是由超材料吸波单元的双面吸波、极化不敏感和宽入射角实现的.理论分析和仿真结果表明:该吸波体在6.18 GHz的确有一个双面吸波的吸收点,且吸收率对极化角和入射角均不敏感.提取的等效阻抗表明可以调节超材料的电磁响应使其在吸收频率处与自由空间阻抗匹配来抑制反射.仿真的能量损耗分布表明:该吸波体对电磁波的吸收主要源于基板的介质损耗;采用两种不同介质基板的设计可使前吸波体与后吸波体的耦合度明显降低、抑制耦合所导致的传输.该吸波体可能在许多领域具有 关键词： 准全向吸波 双面吸波 极化不敏感 宽入射角     

Photopyroelectric spectroscopy (P2ES) of electronic defect centers in crystalline n-CdS

The electrical and dielectric properties of mercuric iodide were studied at room temperature under various intensities and colours of light in the frequency range 1 Hz–10 kHz. In the high-frequency region (>40 Hz), the real part of the dielectric constant () is almost constant with frequency (f), colour and intensity of light. At lower frequencies, varies nearly as 1/f and monotonically increases with intensity (I) of the yellow (or green) light, whereas it is almost constant with red light intensity. This behaviour is discussed in the view of the different polarization contributions. The imaginary part of the dielectric constant () was found to vary as 1/f over the frequency range studied. This behaviour was observed whether the crystal was in dark or illuminated implying that the roomtemperature ac dark- or photo-conductivity () is independent of frequency. The observed variation of with intensity of yellow (or green) light was found to follow anI ^1/2 dependence and a weaker dependence for the red light. the red light. The conductivity behaviour is discussed in the view of the current theories.     

Glass transition (Tg) and dielectric loss in Na3PO4–Pb3(PO4)2–BiPO4 phosphate glasses

Thermal and dielectric loss properties of Na₃PO₄-Pb₃(PO₄BiPO₄ (Na₂O-PbO-Bi₂O₃-P₂O₅) phosphate glasses, have been studied by the differential scanning calorimetry (DSC) and electrical factor loss (tgδ) measurements. Experiments have been carried out from ambient temperature to 500°C and show a strong influence of sodium ions on T_g and tgδ.     

Dielectric behavior of TiC–PVDF nanocomposites

TiC/PVDF nanocomposite is prepared via simple blending and hot pressing route. Percolation theory was employed to explain the dielectric behavior of the TiC/PVDF composites. The dependence of the dielectric properties of the composite on both volume fraction of the filler and frequency is investigated. High dielectric constant (? = 540) and low loss (tan δ = 0.48) of the composites at 100 Hz have been observed near the percolation threshold (0.12). The composites show a weak frequency dependence towards the high frequency range (10–100 kHz), regardless of the TiC content. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Frequency- and voltage-dependent dielectric properties and electrical conductivity of Au/PVA (Bi-doped)/n-Si Schottky barrier diodes at room temperature

In this study, frequency and voltage dependence of dielectric constant (ε′), dielectric loss (ε″), loss tangent (tanδ), the real and imaginary parts of electric modulus (M′ and M″) and ac electrical conductivity (σ _ac) of an Au/PVA (Bi-doped)/n-Si Schottky barrier diode have been investigated in detail by using experimental C–V and G–V measurements in the wide frequency range of 5 kHz–10 MHz and the voltage range of ±2 V at room temperature. Experimental results indicate that the values of ε′,ε″, tanδ and σ _ac are strongly frequency and voltage dependent. It has found that the values of ε′,ε″ and tanδ decrease while the values of σ _ac, M′ and M″ increase. It is clear that the values of M″ show a distinctive peak with a U-shape and its position shifts towards the positive-bias region with increasing frequency. Such behavior of the peak can be attributed to the particular distribution of interface states located at the Si/PVA interface and interfacial polarization. It can be concluded that the interfacial polarization and the charge at the interface can easily follow the ac signal at low frequencies.     

Mn2+doping-induced-effects on commensuration and incommensuration of potassium zinc chloride crystal

Undoped and Mn²⁺-doped with different concentrations of potassium zinc chloride (KZC) crystals were grown from aqueous solutions by slow evaporation. The dielectric constant (ε), dielectric losses (tan?δ) and ac conductivity (σ_ac) of the crystals in the ferroelectric-commensurate, incommensurate and normal phases have been measured as a function of frequency, in the range 1–100?kHz, and temperature, in the range 300–580?K. Virgin samples were subjected to measurements of the frequency dependence at selected temperatures and measurements of the temperature dependence was then followed using the same samples. The increase of ε with T could be due to a combination of conductivity, structural variations and discommensuration (DC) formation and pinning as well. The increase of tan?δ with temperature was attributed to relaxation loss in addition to conduction loss, which increases more rapidly with temperature. The ac conductivity (σ_ac) and tan?δ along the polar axis of KZC increased significantly with increasing Mn²⁺ content while ε decreased. σ_ac changed with frequency according to a power law of the form σ_ac?=?f? ^s where 0.15<s<1.27. A linear decrease of ε and tan?δ with increasing the frequency was also found. The obtained results were treated by considering the effect of Mn²⁺-doping on stripples nucleation, DC evolution/annihilation, DC-lattice formation and DCs pinning by the crystal lattice and/or structural defects for virgin and thermally treated samples.     

(1-x)MgAl2O4-xTiO2 dielectrics for microwave and millimeter wave applications

The MgAl₂O₄ ceramics were prepared by the conventional solid-state ceramic route and the dielectric properties studied in the microwave frequency region (3–13 GHz). The phase purity and crystal structure were identified using the X-ray diffraction technique. The MgAl₂O₄ spinel ceramics show interesting microwave dielectric properties (ε_r=8.75, Q_uxf=68900 GHz (loss tangent = 0.00017 at 12.3 GHz), τ_f=-75 ppm/°C). The MgAl₂O₄ has high negative τ_f, which precludes its immediate use in practical applications. Hence the microwave dielectric properties of MgAl₂O₄ spinels were tailored by adding different mole fractions of TiO₂. The ε_r and Q factor of the mixed phases were increased with the molar addition of TiO₂ into the spinel to form mixtures based on (1-x)MgAl₂O₄-xTiO₂ (x=0.0-1.0). For x=0.25 in (1-x)MgAl₂O₄-xTiO₂, the microwave quality factor reaches a maximum value of Q_uxf=105400 GHz (loss tangent = 0.00007 at 7.5 GHz) where ε_r and τ_f are 11.035 and -12 ppm/°C, respectively. The microwave dielectric properties of the newly developed 0.75MgAl₂O₄-0.25TiO₂ dielectric is superior to several commercially available low loss dielectric substrates. PACS 77.22.-d; 84.40.-x; 81.05.Je     

氧含量对BiFeOδ多晶陶瓷介电特性的影响

采用固相反应法制备了不同含氧量的BiFeO_δ多晶陶瓷样品，利用HP4294A阻抗分析仪测量了样品的介电特性随频率和氧含量的变化，用正电子湮没寿命谱学的方法研究了样品中因氧含量的变化所引起的结构缺陷. 实验结果表明：引入氧空位和氧填隙离子缺陷都会使介电常数减小，而介电损耗则随氧含量的增加而增加，二者的变化范围均在10%—35%之间；对不同氧含量的BiFeO_δ样品，介电常数和介电损耗随测量频率的增加而减小. 氧空位的引入使得局域电子密度变小，正电子平均寿命τ_m增加. 在氧含量δ=2.99时电子密度最大(n_e=3.90×10²³/cm³)，继续增加氧含量对正电子寿命与局域电子密度的影响不大. BiFeO_δ样品的介电常数和介电损耗随氧含量的变化可以在空间电荷限制电导的框架下来理解.     

Equivalent circuit of silicon diodes subjected to high-fluence electron irradiation

Silicon diodes with a p ⁺-n junction made in a 48-μm-thick phosphorus-doped silicon epilayer (resistivity ρ = 30 Ω cm) grown on antimony-doped Si(111) wafers (ρ = 0.01 Ω cm) are studied. The diodes are irradiated by high-energy (3.5 MeV) electrons with fluences from 5 × 10¹⁵ to 2 × 10¹⁶ cm⁻². It is shown that the conventional equivalent circuit of the diode that consists of a parallel RC network and a series-connected resistor inadequately describes the dependence of the dielectric loss tanδ on variable current frequency f in the range 1 × 10²–3 × 10⁷ Hz. Another equivalent circuit is suggested that includes not only the capacitance and resistance of the n-base (the latter increases because radiation-induced defects are compensated for by shallow donors) but also the f dependence of the capacitance of the space-charge region, which is due to retarded charge exchange between deep-level radiation-induced defects.     

AC conductivity and dielectric relaxation in Ba(Sm1/2Nb1/2)O3 ceramic

The complex perovskite oxide a barium samarium niobate (BSN) synthesized by solid-state reaction technique has single phase with cubic structure. The scanning electron micrograph of the sample shows the average grain size of BSN∼1.22 μm. The field dependence of dielectric response and loss tangent were measured in the temperature range from 323 to 463 K and in the frequency range from 50 Hz to 1 MHz. The complex plane impedance plots show the grain boundary contribution for higher value of dielectric constant in the low frequency region. An analysis of the dielectric constant (ε′) and loss tangent (tan δ) with frequency was performed assuming a distribution of relaxation times as confirmed by the scaling behaviour of electric modulus spectra. The low frequency dielectric dispersion corresponds to DC conductivity. The logarithmic angular frequency dependence of the loss peak is found to obey the Arrhenius law with an activation energy of 0.71 eV. The frequency dependence of electrical data is also analyzed in the framework of conductivity and electric modulus formalisms. Both these formalisms show qualitative similarities in relaxation times. The scaling behaviour of imaginary part of electric modulus M″ and dielectric loss spectra suggest that the relaxation describes the same mechanism at various temperatures in BSN. All the observations indicate the polydispersive relaxation in BSN.     

The dielectric and piezoelectric behaviour of pyrolusite (polycrystalline ore of MnO2)

The variation of dielectric constant? of pyrolusite (sintered polycrystalline ore of MnO₂) with temperature, frequency and voltage has been studied within the frequency range 200 c/s to 10 kc/s. The samples studied show a very high value of dielectric constant ≈ 10⁵. The?-temperature curve indicates that? attains a maximum value at a certain temperature. The temperature at which? attains a maximum value appears to vary from sample to sample. At higher temperatures (i.e. higher than that at which? attains a maximum value),? decreases with temperature as?=c/(T?Θ). The dielectric constant is dependent on the frequency; it has a higher value at lower frequencies. The applied voltage across the specimen has a marked influence on the dielectric constant, which increases rapidly with voltage. A capacity with pyrolusite as dielectric shows a hysteresis loop (electrical). The dielectric loss factor tanδ is found to depend on temperature, frequency and voltage. Tanδ attains a maximum value at lower range of frequencies between 300 c/s to 700 c/s, for a given voltage, and temperature. This indicates the existence of dielectric relaxation for these specimens. Tanδ also varies exponentially with temperature. Samples of pyrolusite studied show a piezo electric effect as well. The electromechanical coupling coefficient is found to vary from 2·4×10^?5 to 8·8×10^?5 e.s.u/ dyne. Slabs cut from the samples of pyrolusite mineral were found to control the frequency of a Hartley oscillatory circuit. The resonant frequency range was found to increase as the thickness of the slab is reduced.