Relaxor-like dielectric behavior in La2NiMnO6 double perovskite ceramics

The dielectric and conductive characteristics of La₂NiMnO₆ double perovskite ceramics were investigated together with the crystal structure. La₂NiMnO₆ ceramics crystallized in the monoclinic P2₁/n structure in which the Ni²⁺ and Mn⁴⁺ ions ordered periodically. Relaxor-like dielectric behavior combined with a giant dielectric constant step was observed in the present ceramics, and these unique dielectric characteristics should be attributed to the charge ordering of Ni²⁺ and Mn⁴⁺. The dielectric relaxation was well fitted by the modified Debye equation and Arrhenius law with the activation energy of 0.17 eV. The dc conductivity of La₂NiMnO₆ could be well fitted using a variable-range hopping mechanism instead of a band conduction mechanism.     

Homogenization principles and effect of mixing on dielectric behavior

This paper consists of two parts. First, a review of classical mixing principles lists the multitude of the various ways to characterize the effective permittivity of heterogeneous materials. Different connections between the various mixing formulas are underlined and the homogenization principles are classified into families of mixing rules. The second part emphasizes and analyzes the richness of the manner how the mixing process is able to create new types of dielectric behaviors, in particular with respect to enhancement of dielectric polarization, shifts of the dispersion parameters, and emergence of new effects in electrical response.     

Effect of zero-point energy on the dielectric behavior of strontium titanate

Barrett formula has been obtained in the framework of the effective field approach by including the zero-point energy. By fitting with experimental data of dielectric constant of SrTiO₃, we find that they agree in the whole temperature range fairly well if the zero-point energy is assumed to change from a small value at low temperature to a large value at high temperature.     

Resonant behavior of dielectric objects (electrostatic resonances)

Resonant behavior of dielectric objects occurs at certain frequencies for which the object permittivity is negative and the free-space wavelength is large in comparison with the object dimensions. Unique physical features of these resonances are studied and a novel technique for the calculation of resonance values of permittivity, and hence resonance frequencies, is proposed. Scale invariance of resonance frequencies, unusually strong orthogonality properties of resonance modes, and a two-dimensional phenomenon of "twin" spectra are reported. The paper concludes with brief discussions of optical controllability of these resonances in semiconductor nanoparticles and a plausible, electrostatic resonance based, mechanism for nucleation and formation of ball lightning.     

Broadband dielectric dispersion in ferroelectric P(VDF-TrFE) copolymer films

Ferroelectric polyvinylidenefluoride-trifluoroethylene copolymer films with different thicknesses are prepared by a solvent-cast technique, by spin coating, and by a horizontal Langmuir–Blodgett technique respectively. The frequency dependent dielectric permittivity of these films is investigated with varying sample thickness and varying temperature in the ferroelectric as well as in the paraelectric phase. A dielectric relaxation according to a Vogel–Tamman–Fulcher law of the relaxation times is found in all samples. However, the relaxation times extracted from the dielectric permittivity in the frequency range are not consistent with the relaxation times determined from the temperature range. An explanation for this behavior is given by a temperature dependent distribution of relaxation times. Additionally, in thin samples a second relaxation with a weak anomalous temperature dependence, i.e. an increasing relaxation time with increasing temperature, is observed at high frequencies. Detailed investigations show that this behavior can be attributed to an electrode effect.     

Relationships among group delay,energy storage,and loss in dispersive dielectric mirrors

We show that absorbed and stored electromagnetic energy are proportional to the reflection group delay in highly reflective dispersive dielectric mirrors over the high-reflectivity band.Our theoretical considerations are verified by numerical simulations performed on different dielectric mirror structures.The revealed proportionality between group delay and absorbed energy sets constraint on the application of ultrabroadband and/or dispersive dielectric mirrors in broadband or widely tunable,high-power laser systems.     

Enhanced dielectric properties and energy storage density of interface controlled ferroelectric BCZT-epoxy nanocomposites

Polymer nanocomposites with ferroelectric fillers are promising materials for modern power electronics that include energy storage devices. Ferroelectric filler, Ba_0.85Ca_0.15Zr_0.1Ti_0.9O₃ (BCZT) nanopowder, was synthesized by sol-gel method. X-ray diffraction (XRD) studies confirmed the phase purity and the particle size distribution was determined by transmission electron microscopy (TEM). Extended aromatic ligand in the form of naphthyl phosphate (NPh) was chosen for surface passivation of BCZT nanoparticles. Surface functionalization was validated by thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and impedance spectroscopy using slurry technique. The dielectric constant of surface-passivated BCZT nanopowder was ~155, whereas pristine BCZT nanopowder dielectric constant could not be assessed due to high innate surface conductivity. Furthermore, BCZT–epoxy nanocomposite films were prepared and analyzed by differential scanning calorimetry (DSC), dielectric spectroscopy, dielectric breakdown strength (DBS), and scanning electron microscopy (SEM). Owning to stronger polymer–particle interface, dielectric measurements of 5 vol.% NPh surface functionalized BCZT–epoxy nanocomposites indicated improved DBS and glass transition temperature (T_g), reduced dielectric loss, and enhanced energy storage density compared to untreated BCZT–epoxy composites and pure epoxy. The energy storage density of 30 vol.% NPh surface functionalized BCZT–epoxy nanocomposite of 20 μm film thickness was almost three times that of pure epoxy polymer of identical film thickness.     

Yb离子抽运动力学及脉冲储能特性研究

从准三能级Yb离子的能级结构出发，建立了Yb离子的抽运和激光速率方程，结合解析和数值方法，研究了Yb激光介质的抽运动力学过程，包括抽运激发效率、最低抽运强度、激光能量提取效率等关键参数.比较了三类典型的Yb激光介质性能：Yb:S-FAP,Yb:YAG以及Yb:FP-glass.以放大自发辐射(ASE)为设计判据，重点研究了脉冲储能型Yb激光器的设计准则，包括增益介质的厚度与掺杂浓度.最后利用此模型给出了基于Yb:S-FAP以及Yb:YAG的100J级二极管抽运固体激光器(DPSSL)的总体设计参数.将对基于Yb激光介质的脉冲储能型DPSSL的设计提供有益的参考. 关键词： Yb离子 速率方程 抽运动力学 二极管抽运固体激光器     

Effect of dielectric layer on ferroelectric responses of P(VDF-TrFE) thin films

The dielectric layer in the sandwich structural device plays a very important role in determining the electrical properties of the ferroelectric film. In this paper, we investigate the effect of the dielectric layers with different thicknesses on switching performance of ferroelectric P(VDF-TrFE) thin films. The hysteresis loops become slanting with increasing thickness of the dielectric layer. A negative slope of the ‘real’ hysteresis loop is apparently observed which demonstrates negative capacitance effect caused by the dielectric layer. This behavior is simulated qualitatively by the Weiss mean field model considering an interfacial dielectric layer in series with a ferroelectric layer. The agreement between experiments and simulations supports that negative capacitance results from the positive feedback among electric dipoles. Furthermore, the switching time of the ferroelectric film increases with the increase of dielectric layer thickness. This study shows that the ferroelectric sandwich structure provides great potential towards low power negative capacitance devices.     

Heteronuclear energy pooling collisions: The Na(3P) + K(4P) reaction

An experiment has been performed in which two different atomic species - sodium and potassium - have been simultaneously excited in a cell by two resonant cw dye lasers and the fluorescence spectrum has been analysed by using an intermodulation technique to isolate the contributions due to the heteronuclear processes. The energy pooling collisions between Na(3P) and K(4P) have been observed for the first time and the relative collision cross sections have been measured.     

Spatial dispersion in metamaterials with negative dielectric permittivity and its effect on surface waves

The effect of spatial dispersion on the electromagnetic properties of a metamaterial consisting of a three-dimensional mesh of crossing metallic wires is reported. The effective dielectric permittivity tensor epsilon(ij)(omega, k) of the wire mesh is calculated in the limit of small wavenumbers. The procedure for extracting the spatial dispersion from the omega versus k dependence for electromagnetic waves propagating in the bulk of the metamaterial is developed. These propagating modes are identified as similar to the longitudinal (plasmon) and transverse (photon) waves in a plasma. Spatial dispersion is found to have the most dramatic effect on the surface waves that exist at the wire mesh-vacuum interface.     

等离子体介质阻挡放电氟化改性环氧树脂的时效性

等离子体对材料的改性效果随放置时间会有所减弱,即表现出一定的时效性,限制了等离子体改性技术的进一步发展。为了探究等离子体介质阻挡放电（DBD）氟化改性环氧树脂的时效性,利用等离子体介质阻挡放电实现了环氧树脂表面氟化改性,并利用扫描电镜（SEM）、表面轮廓仪、X射线光电子能谱分析（XPS）、接触角测试仪、高阻计和闪络电压、表面电位测试系统对改性前和改性后放置在25 ℃老化箱中0～30 d的环氧树脂表面进行了物理形貌和化学组分的表征以及电气性能的测试。测试结果表明,DBD氟化改性实现了氟元素在环氧树脂表面接枝,这使得环氧树脂表面能降低,表面电阻率减小,陷阱能级变浅,从而加快了表面电位衰减速度,进而提升了沿面闪络电压。同时,等离子体DBD氟化改性环氧树脂表现出一定的时效性,放置30 d后,氟元素含量减少,表面能增大,表面电位衰减速度略有减慢,闪络电压也有所下降,但仍高于未处理的试样。     

Lithium ion conductivity and dielectric properties of P(VdCl-co-AN-co-MMA)-LiCl-EC triblock co-polymer electrolytes

Lithium ion conducting polymer electrolytes based on triblock polymer P(VdCl-co-AN-co-MMA)–LiCl were prepared using a solution casting technique. XRD studies show that the amorphous nature of the polymer electrolyte has been increased due to the addition of LiCl. The maximum amorphous nature has been observed for 40 m% P(VdCl-co-AN-co-MMA)/60 m% LiCl samples. The FTIR study of the lithium ion conducting polymer membrane confirms the complex formation between the polymer P(VdCl-co-AN-co-MMA) and LiCl. The lithium ion conductivity is found to be 1.6 × 10^?5 Scm^?1 for the 40 m% P(VdCl-co-AN-co-MMA)/60 m% LiCl sample at room temperature. This value is found to be greater than that of pure polymer whose conductivity is found to be 1.5 × 10^?8 Scm^?1. To improve ionic conductivity, ethylene carbonate has been added as a plasticizer to the 40 m% P(VdCl-co-AN-co-MMA)/60 m% LiCl sample. When we add 0.6 m% of ethylene carbonate, it has been observed that the lithium ion conductivity has increased to 1.3 × 10^?3 Scm ^?1 . This value is two orders of magnitude greater than the 40 m% P(VdCl-co-AN-co-MMA)/60 m% LiCl sample. It is also observed from XRD patterns of 40 m% P(VdCl-co-AN-co-MMA)/60 m % LiCl/0.6 m % EC that the amorphous nature has been increased further. A dielectric study has been performed for the above membranes.     

Intriguing triboelectrification behavior of identical P(VDF-TrFE) polymers

We report an intriguing triboelectrification behavior of thermally treated P(VDF-TrFE) polymers. Cooled (C-) and annealed (A-) P(VDF-TrFE) films were prepared by the rapid cooling of the melt solution and the subsequent annealing, respectively. The C–P(VDF-TrFE) had sparse grains and small elastic modulus and surface charge density, while, the A-P(VDF-TrFE) had dense grains and large elastic modulus and surface charge density. When the polymers contacted ITO electrodes, the triboelectric outputs of C-(PVDF-TrFE) were larger than those of A-P(VDF-TrFE). When the polymers contacted each other, the triboelectric outputs of different P(VDF-TrFE) films were significantly larger than those of similar P(VDF-TrFE) films. Based on detailed X-ray photoemission spectroscopy results, we suggested that roughness-induced frictional heat and elastic modulus differences may play an important role in minute material and/or ion transfer during the triboelectrification of identical P(VDF-TrFE) polymers.     

3 dB桥误差对能量倍增器性能的影响

根据能量倍增器的工作原理,对3 dB桥误差引起的能量倍增器性能变化进行了理论分析,并对BEPC和BEPCⅡ直线加速器所使用能量倍增器的3 dB桥误差进行了讨论,为判断焊接后3 dB桥桥臂波导变形提供了理论参考。结果表明:无论是功率分配不平衡,还是相位关系偏离,都会使部分功率反射回速调管。功率分配不平衡和微波相位关系偏离值越大,则功率倍增因子下降得越多。     

3 dB桥误差对能量倍增器性能的影响

根据能量倍增器的工作原理,对3 dB桥误差引起的能量倍增器性能变化进行了理论分析,并对BEPC和BEPCⅡ直线加速器所使用能量倍增器的3 dB桥误差进行了讨论,为判断焊接后3 dB桥桥臂波导变形提供了理论参考。结果表明：无论是功率分配不平衡,还是相位关系偏离,都会使部分功率反射回速调管。功率分配不平衡和微波相位关系偏离值越大,则功率倍增因子下降得越多。     

Aging effect of SiO2 xerogel film on its microstructure and dielectric properties

The properties of porous SiO₂ xerogel film strongly depend on the aging process. The morphology of the surface modified SiO₂ xerogel film pre-aged for 1 hr at 70°C showed a two-dimensional structure. Aging for 12 h at 70°C and successive modification of the film induced some particle growth and a three-dimensional network structure. The microstructure of the modified SiO₂ xerogel films reflects the preformed structure during aging. The surface modification induced the changes of surface coverage from –OC₂H₅ and –OH bonds to –CH₃. However the content of surface chemical species was almost same regardless of aging time. The porosity of the modified sample pre-aged for 12 h at 70°C was 89%. The calculated/measured dielectric constants were 1.31/1.42, respectively     

Influence of polymer dielectric surface energy on thin‐film transistor performance of solution‐processed triethylsilylethynyl anthradithiophene (TES‐ADT)

This study investigates the correlation between surface energy of polymer dielectrics and the film morphology, microstructure, and thin‐film transistor performance of solution‐processed 5,11‐bis(triethylsilylethynyl) anthradithiophene (TES‐ADT) films. The low surface energy polyimide (PI) dielectric induced large grains with strong X‐ray reflections for spin‐cast TES‐ADT films in comparison to high surface en‐ ergy poly(4‐vinyl phenol) (PVP) dielectric. Furthermore, thin‐film transistors based on spin‐cast TES‐ADT films on PI dielectric exhibited enhanced electrical performance, small hysteresis, and high stability under bias stress with carrier mobility as high as 0.43 cm²/Vs and a current on/off ratio of 10⁷. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)