Comment on “The Impact of Composite Effect on Dielectric Constant and Tunability in Ferroelectric‐Dielectric System”

A comparison between 2D and 3D Finite Element Method based simulations on the tunability properties of ferroelectric – linear dielectric composites is presented. Dependences of the effective permittivity and tunability on the concentration of the linear phases are presented and it is shown that there are important differences between the two approaches. The appropriateness of such simulations in describing realistic composite systems is discussed, too.     

Reply to Comment on “The Impact of Composite Effect on Dielectric Constant and Tunability in Ferroelectric‐Dielectric System”

In the comment on “The Impact of Composite Effect on Dielectric Constant and Tunability in Ferroelectric–Dielectric System”, Padurariu et al. proposed that a 2D system and a 3D system are not exactly similar: with the increase in dielectric content, the tunability of 2D system increases first and the tunability of 3D system decreases gradually. However, in my recent work, an abnormal increase in tunability was observed in the simulation result of 3D ferroelectric–dielectric model: with the increase in dielectric content from 0 to 60 vol%, the tunability increased from 22.8% to 31.4%.     

Anomalous Correlation between Dielectric Constant and Tunability in (Ba,Sr)TiO3–MgO–Mg2SiO4 Composite Ceramics

(Ba, Sr)TiO₃–MgO–Mg₂SiO₄ composite ceramics were prepared by a solid‐state reaction method. The microstructures, microwave dielectric characteristics, and tunability of composite ceramics were investigated. An anomalous correlation between tunability and dielectric constant was observed: with the increase in Mg₂SiO₄ content and the decrease in MgO content, the dielectric constant of (Ba, Sr)TiO₃–MgO–Mg₂SiO₄ composite ceramics decreases, but the tunability increases. The anomalous increased tunability is beneficial for tunable microwave applications and can be attributed to the redistribution of the electric field. For 50Ba_0.5Sr_0.5TiO₃–(50?x)MgO–xMg₂SiO₄, the dielectric constant was decreased from 164.2 to 126.5 by increasing Mg₂SiO₄ content from 5 to 45 wt% and the tunability at 3.9 kV/mm increased from 11.5% to 15.2%.     

Dielectric Constant Characteristics of a New Composite Dielectric Material

Dielectric characteristics of a new composite dielectric material composed of a ceramic and a plastic resin were investigated. The composite material has two requirements: it must display stable characteristics and be adaptable to mass production. The first requirement can be met by using a ceramic material, such as the TiO₂-rich part of the BaO-PbO-Nd₂O₃TiO₂ system. The second requirement can be fulfilled by using a polyoxymethylene resin. The new composite dielectric, composed of a ceramic (40 vol%) and a polyoxymethylene resin (60 vol%) and produced by injection molding, exhibits a dielectric constant of 12.1. It also displays extremely low temperature dependence in a range of −20° to 140°C as well as low frequency dependence over a range from 1 kHz to 10 MHz.     

高介电聚氨酯基复合材料的制备与性能研究

以聚氨酯弹性体(Polyurethane Elastomers,PUE)为基体,以具有高介电常数的铜酞菁齐聚物(Copper phthalocyanine oligomer,CuPc)为填料,并且为改善两者的相容性,通过化学方法将部分CuPc接枝到聚合物链上,制备了具有高介电常数的聚合物基纳米复合材料。在100Hz时,CuPc含量为15wt%的纳米复合材料的介电常数高达440左右,是PUE与CuPc简单共混物的8倍多。介电常数的迅速提高归功于CuPc粒子在纳米复合材料中分散性的改善与粒径的大大减小导致的复合体系中界面交换耦合效应的显著增加。     

Electric Field Effect on Dielectric Constant of Glycine Phosphite

Study of the effect of an external electric field on the dielectric constant in the paraelectric phase of ferroelectric glycine phosphite crystals has been performed. The dielectric constant behavior under the bias external field has been analyzed in the framework of Landau theory. It is shown that the ferroelectric phase transition is of the first order very close to a tricritical point and the calculated value of the thermal hysteresis is ΔT ≅0.1 K.     

碳化钛/聚酰亚胺高介电复合薄膜的制备及性能研究

采用机械共混法将经硅烷偶联剂改性的碳化钛粉体掺杂入聚酰亚胺中,制备了碳化钛/聚酰亚胺复合薄膜。分析了不同碳化钛粒子含量对复合薄膜的显微结构、力学性能及介电性能的影响。实验结果表明,随着纳米TiC含量的不断升高,复合薄膜的拉伸强度呈现先上升后下降的趋势,复合薄膜的耐电击穿场强迅速下降。与此同时,复合材料的介电常数则显著提高。     

分子结构对聚酯及其粉末涂料介电常数的影响

合成了不同分子结构的聚酯树脂,并将其配制成粉末涂料,考察了酯键密度、非对称性链段含量、玻璃化温度(T_g)、软化点、相对分子质量及其分布等因素对聚酯树脂及其粉末涂料表观介电常数的影响规律。结果表明:聚酯相对分子质量及其分布对聚酯及其粉末涂料的介电常数影响单调性明显,酯键密度对粉末涂料介电常数的影响次之,T_g、软化点和聚酯链段的非对称性对粉末涂料的介电常数影响不明显。     

PZN—PFN—PFW三元系高介电常数材料的研究

本文研究了Pb(Zn_(1/3)Nb(2/3))O_3-Pb(Fe_(1/2)Nb_(1/2))O_3-Pb(Fe_(2/3)W_(1/3))O_3三元系电容器材料。居里温度在室温附近的配方组成,能在870°～890℃烧结而具有较高的介电常数。讨论了少量添加剂对三元系材料介电性能的影响。钙钛矿型结构的配方组成具有高的介电常数和较低的电容温度系数。     

Enhanced Dielectric Constant for Efficient Electromagnetic Shielding Based on Carbon-Nanotube-Added Styrene Acrylic Emulsion Based Composite

An efficient electromagnetic shielding composite based on multiwalled carbon nanotubes (MWCNTs)-filled styrene acrylic emulsion-based polymer has been prepared in a water-based system. The MWCNTs were demonstrated to have an effect on the dielectric constants, which effectively enhance electromagnetic shielding efficiency (SE) of the composites. A low conductivity threshold of 0.23 wt% can be obtained. An EMI SE of ~28 dB was achieved for 20 wt% MWCNTs. The AC conductivity (σ _ac) of the composites, deduced from imaginary permittivity, was used to estimate the SE of the composites in X band (8.2–12.4 GHz), showing a good agreement with the measured results.     

掺杂PST薄膜的制备与介电调谐性能研究

采用Sol-Gel法在Pt／TiO2／SiO2／Si衬底上制备了多种不同组分的（Pb0.3Sr0.7）1-xKxTiO3（PST）（x=0,1mol％,2．5mol％,5mol％）多层均匀薄膜,并研究了它们的介电调谐性能。发现掺杂后薄膜的晶粒尺寸明显减小,介电常数降低及介电损耗减小。1MHz时,随K含量的从0增加至5mol％,薄膜的介电常数从841降低至539,而介电损耗由0．134减小到0．058,其微波介电综合性能改善。     

高介电常数微波介质陶瓷的发展及研究现状

对高介电常数微波介电陶瓷中的BaO-Ln2O3-TiO2、复合钙钛矿CaO2-Li2O2-Ln2O3-TiO2及铅基钙钛矿体系的发展及研究现状进行了概述,归纳了研究中存在的问题,同时对未来的发展趋势做了预测.对新型填满型钨青铜结构陶瓷也进行了简要的介绍,指出其具有良好的发展前景,但其介电弛豫性需要进一步的研究.     

Experimental Investigation of Scaling Laws for Electrospraying: Dielectric Constant Effect

ABSTRACT

Experiments were performed to investigate the effect of liquid dielectric constant on existing scaling laws for the electrospraying process. The variations of the droplet size and the emitted current were measured as a function of the dielectric constant for the electrospray operating in the cone-jet mode. Eight different solvents with dielectric constants, κ, ranging from 12.5 to 182 were tested. The residue particle size distributions were measured using a TSI scanning mobility particle sizer, (SMPS). The produced liquid droplet sizes were then calculated from the known solution concentrations. The results show that: (1) For the produced droplet size, D_d , experimental data are in agreement with the scaling law (G(κ) = 1.66κ ^?1/6) proposed by Gañán-Calvo et al. (1994) for solvents with high dielectric constants. The derivation in low dielectric constant cases may be that the assumption of Gañán-Calvo (1994) on the characteristic length may not hold for the present system; (2) for the emitted current, I, experimental data deviate from those given by Fernández de la Mora and Loscertales (1994) except for the case of benzyl alcohol. The difference may be partially explained by the use of different electrolytes. A larger deviation is found in comparing with the equation, f(κ) = 6.46κ^1/4, provided by Gañán-Calvo et al. (1994). The reasons may be due to the inapplicable characteristic length assumption and the role of ion drifting current in the total emitted current. Based on the experimental data collected, some problems are pointed out regarding the criteria proposed in the previous studies for predicting the minimum liquid feed rate. A formula is given based on these data to estimate the maximum feed rate and to explain the observations reported in Chen et al. (1995).     

Pseudo Phase Diagram and Microwave Dielectric Properties of Li2O–MgO–TiO2 Ternary System

Li₂O–MgO–TiO₂ ternary system is an important microwave dielectric ceramic material with excellent properties and prospect in both scientific research and application. A phase diagram of the Li₂O–MgO–TiO₂ ternary system was established in this article, based on earlier research results and our present work. Microwave dielectric properties with compositions in different regions of the phase diagram have been analyzed. We found that the 0.33 Li₂MgTi₃O₈–0.67 Li₂TiO₃ ceramics sintered at 1200°C exhibited excellent dielectric properties: Q × f value = 80 476 GHz (at 7.681 GHz), ε_r = 24.7, τ_f = +3.2 ppm/°C. We also designed two ceramic systems in the Li‐rich region of the Li₂O–MgO–TiO₂ ternary system, which received little attention in the past decades, because many excellent single‐phase ceramics, such as Li₂MgTiO₄, Li₂MgTi₃O₈ and MgTiO₃, have been found in the Ti‐rich region. The ceramic systems have low sintering temperatures but also relatively poor dielectric properties.     

Control of Dielectric Constant and Loss in Alumina Ceramics

The dissipation factors and dielectric constants of alumina ceramics containing less than 100 ppm of impurities and of specimens doped with Si, Ti, Ca, Mg, Fe, and Cr ions were measured in the region 10² to 8.5 × 10⁹ cps and 25° to 875° C. Multiple regression analysis of the data at 500° C and 10⁶ cps showed a linear relation between impurity concentration and tan δ, with a correlation coefficient of 0.93. Si ions caused the greatest rise of tan δ, Mg and Ti were second, Ca third, and Cr and Fe had no significant influence. These effects diminished with rising frequency and became negligible in the microwave region. Activation energies of conduction for pure and doped alumina were estimated from measurements of δ at 10⁵ cps and 500°C. Values between 1.2 and 1.6 ev were calculated for all compositions except the one containing Mg²⁺, for which 2.0 ev was obtained. At low frequencies, the dielectric constant (k') rose exponentially with temperature, reflecting a similar rise in the number of free charge carriers contributing to interfacial polarization. At higher frequencies the temperature variation of k' fell to a shallow positive slope of about 120 ppm per °C. This coefficient was not influenced by low concentrations of impurities but could be effectively compensated without excessive loss by additions of 10 to 20% SrTi0₃.     

Dielectric Properties of Ultra‐Low Sintering Temperature Al2O3–BBSZ Glass Composite

Ceramic composites of B₂O₃–Bi₂O₃–SiO₂–ZnO (BBSZ) glass mixed with Al₂O₃ (10–50 vol%) were sintered at 450°C, and their microstructural and dielectric properties investigated. Dense structures were obtained when the Al₂O₃ content was lower than 30 vol%. Raman, XRD, and FESEM showed the existence of a secondary phase, Bi₂₄Si₂O₄₀, in all samples. The dielectric properties of the composite with 30 vol% addition of Al₂O₃ showed good dielectric properties with ε_r of 14.8 and 20.8 and 32.5 at 100 kHz and 100 MHz and 1 GHz, respectively. The tanδ values at the same frequencies were 0.004 and 0.006 and 0.016. The results show that BBSZ glass with different amounts of Al₂O₃ exhibit widely applicable relative permittivity values and affordable loss and are thus promising candidates for ultra‐low sintering temperature applications.     

煤粉及伴生矿物颗粒的介电性质研究

对煤粉的介电常数进行了研究.煤的分子结构、化学组成直接影响煤的介电常数,低变质程度煤的介电常数较高;随着煤化程度增加,介电常数减少,到中变质程度的烟煤阶段,介电常数最低;但是,随着煤化程度的进一步加深,介电常数又开始增加,在无烟煤阶段介电常数迅速增加.文章从理论上证明了煤及矿物混合颗粒群的介电常数满足立方根相加规律,为静电分选和摩擦电选技术提供理论依据.     

Ferroelectric–Dielectric Composites Model of Ba0.5Sr0.5TiO3/Mg2AO4(A = Ti,Si) for Tunable Application

The correspondence between the theoretical model and the experimental results of the dielectric response in two‐phase composites of Ba_0.5Sr_0.5TiO₃ and Mg₂AO₄ (A = Ti, Si)was studied. The Ba_0.5Sr_0.5TiO₃ (BST50)/Mg₂AO₄ composites in 2‐2 model structure consisting of BST50 layers and Mg₂AO₄ layers were fabricated by tape casting and multilayer technique. The 3‐0 model of the two‐phase composites is fabricated by conventional ball mill mixing and solid‐state reaction process. The ceramics samples with dense structure were obtained because the coefficient of thermal expansion (CTE) of Mg₂SiO₄ (12.84 ppm/°C) and Mg₂TiO₄ (12.11 ppm/°C) ceramic specimens are close to the pure BST50(13.15 ppm/°C) ceramic. The microstructure, dielectric, and tunable properties of 2‐2 and 3‐0 model composites were investigated. The experimental results agree well with the theoretical prediction in 2‐2 model. An important feature of 2‐2 model composites is that the DC field is efficiently applied to the high‐permittivity ferroelectric phase. With the increase in Mg₂AO₄ volume fraction q, the tunability of the composite remains almost unchanged whereas the permittivity greatly reduced in the 2‐2‐//model. These results show that the 2‐2‐//model sample is good candidates for the tunable devices.     

偶联剂对制备环氧-低熔点金属复合材料的影响

通过相反转法制备环氧-低熔点金属复合材料。采用偶联剂改善了低熔点金属在基体中的分散性,利用扫描电子显微镜和数字电桥研究了金属粒子分散性对复合材料结构和性能的影响。结果表明,采用相反转法和合适的偶联剂能使低熔点金属均匀地分散在环氧树脂基体中,有效地增加复合材料的介电性能。