Microstructure Development and Dielectric Properties of Potassium Strontium Niobate Ceramics

Sintering of a KSr₂Nb₅O₁₅ powder compact at 1350°C resulted in a duplex structure. Prefiring of the compact between 1200° and 1300°C inhibited the abnormal grain growth responsible for the duplex structure. The Curie temperature and dielectric constant were dependent on the microstructure.     

Depletion-layer Dielectric Properties of Positive Temperature Coefficient of Resistance Barium Titanate

For pure and impurity-added positive temperature coefficient of resistance (PTCR) barium titanate ceramic samples, a −11°C shift of the Curie point at the grain-boundary/depletion-layer region was observed. This result is obtained by fitting the PTCR grain-boundary resistance and capacitance data to a theory which combines a double-depletion-layer model with the Devonshire thermodynamic theory of barium titanate. The parameters used in the fitting are obtained from independent experiments. The shift of the Curie point is believed to result from the grain-boundary clamp ing effect near the cubic-tetragonal phase transition point.     

Microwave Dielectric Properties of Rutile Filled PEEK Composites

Ceramic-filled PEEK composites were prepared by sigma mixing followed by thermolamination. Rutile-grade titanium dioxide, particle size less than 5 μm, was used as the particulate filler in the PEEK matrix to tailor the dielectric properties of the composite matrix. The dispersion of the particular filler in the PEEK matrix was studied using scanning electron microscopy. The dielectric properties of the PEEK/TiO₂ composite materials were measured in the low frequency region up to 13 MHz using an impedance analyzer. Dielectric properties in the microwave region were measured using cavity perturbation technique to evaluate the use of the composites as packaging material. Experimental results were compared with theoretically predicted values using the Lichtenecker equation. The present study shows that temperature-stable packaging materials can be realized in the PEEK/TiO₂ systems by judiciously controlling the ceramic filler concentration.     

La1-xCaxMnO3团簇薄膜的介电和光学性质研究

利用溶胶-凝胶法制备La1-xCaxMnO3薄膜.利用X射线衍射(XRD)、反射偏光显微镜和电感-电容-电阻测定计(LCR)仪对其结构、形貌和性质进行表征.XRD结果表明薄膜为钙钛矿结构,经不同温度退火后发生微小偏离.偏光显微图像显示薄膜表面形貌为菊花状团簇;经不同温度退火后的薄膜反射色有很大差异,因此反射色不能作为鉴定La1-xCaxMnO3的依据.随着退火温度升高,薄膜的介电损耗降低,说明高的温度退火后,薄膜质量较高.     

球磨石用量对钛酸钡介电性能的影响

通过改变料球水的比例以及采用沉降测试、水煮损耗测试、温度特性、电导率和化学分析等测试手段，研究了在制备钛酸钡的球磨工艺中球磨石的用量对钛酸钡粉体均匀性及钛酸钡介电性能的影响。研究结果表明，采用不同的料球水比例制得的电容器性能差别很大，当球：料：水=0．5：1：1时制得的钛酸钡性能最好。     

Effects on Dielectric Properties of Modified Bismaleimide Resins

Abstract

Six modified bismaleimide (BMI) resin systems are developed. The modifier is diallyl bisphenol A, diallyl bisphenol A ether. TDE-85 epoxy/MNA anhydride, and styrene. respectively. In view of structure of those cured resins, relationships between structure and dielectric properties have been studied emphatically, while effects of postcure temperature and catalysts on dielectric properties were also shown. Results indicate that dielectric properties lie on structure of cured resin and postcure temperature; catalysts can strikingly improve the heat-resistance of materials, but has little effect on the dielectric properties. In addition, mechanical and thermal properties of neat resins were also shown.     

Dielectric Properties of Bagasse and its Constituents

Abstract

Dielectric properties of bagasse raw material and its constituents, cellulose and lignin was studied. The effect of γ-radiation of different doses (0–40 M rad) on the dielectric properties of these investigated samples was also studied. However, the study of the grafting process of these materials with acrylamide initiating with 7-radiation (dose 20 M rad) was also clarified. The dielectric properties of these grafted materials were also investigated.     

Enhanced Mechanical and Dielectric Properties of PU Networks with Hyperbranched Structures

We report a new polyurethane (PU) dielectric containing hyperbranched structures and metal nanoparticles. Silver nanoparticles were incorporated into the PU networks by using hyperbranched polyester (HBP) as a reductive template as well as the cross-linker. Simultaneously enhanced mechanical and dielectric properties were observed in the hyperbranched PU dielectrics. The branched macromolecular fractal provides a “covalent bridge” between the PU matrix and Ag nanoparticles, which contributed to the simultaneously enhanced mechanical and dielectric properties.     

Dielectric Properties of Binary Solvent Mixtures of Dimethyl Sulfoxide with Water

In this paper, the dielectric properties of water-dimethylsulfoxide (DMSO) mixtures with different mole ratios have been investigated in the range of 1 GHz to 40 GHz at 298 K by using a molecular dynamics (MD) simulation. Only one dielectric loss peak was observed in the frequency range and the relaxation in these mixtures can be described by a single relaxation time of the Davidson-Cole. It was observed that within experimental error the dielectric relaxation can be described by the Debye-like model (β ≈ 1, S.M. Puranik, et al. J. Chem. Soc. Faraday Trans. 1992, 88, 433 – 435). In general, the results are very consistent with the experimental measurements.     

Synthesis and Dielectric Properties of Polyimide-Titania Hybrid Composites

A new class of polyimide-titania (TiO₂) composites with chemical bonds between the polyimide and titania system has been synthesized by the sol–gel reaction and characterized. The hybrid composite films were obtained by the reaction of lysine-organotitane monomer, which is formulated as [(EtO)₃Ti (lysinate)]_2, followed by polycondensation with dianhyride in N-methyl-2-pyrrolidone (NMP) solution, followed by heating at 100, 200, and 300 °C. The presence of chemical bonds between polyimide (PI) and titania has great effect on the properties of polyimide films, especially on their thermal and dielectric properties. The dielectric constants of the resultant nanocomposites are lower than the usual polyimide films due to the increased free volume and less polar Ti–O–Ti groups, and can be tuned by varying the molar ratio of tetraethoxysilane (TEOT) in the feed. The polyimide units offer additional advantages of imparting thermal and mechanical strength.     

聚苯胺改性PVDF薄膜的结构与介电性能研究

本文通过溶液共混方法制备了聚苯胺改性PVDF薄膜,运用XRD、SEM和DSC技术分析了复合材料结构,并探讨了聚苯胺含量和频率对复合薄膜介电性能的影响。结果表明:适量PANI的加入能够诱导PVDF结晶,提高其结晶程度。随着聚苯胺含量的增大,复合材料薄膜的介电常数、介电损耗迅速升高。     

PPE/EP体系的介电性能和耐溶剂性研究

利用扫描电镜、差示扫描量热仪以及高频介电仪研究了聚苯醚(PPE)/环氧树脂(EP)体系的相分离、耐热性和介电性能,并利用质量损失法研究了PPE/EP体系的耐溶剂性,结果表明:PPE/EP混合物的耐热性和介电性能均随着PPE含量的增加而提高,而耐溶剂性则随着PPE含量的增加而降低,在PPE/EP体系中加入三烯丙基异氰酸酯(TAIC)可有效地提高PPE/EP体系的耐溶剂性;当PPE含量大于30%时,PPE/EP混合物的介电性能显著提高,耐溶剂性显著下降。     

Mn含量对Al掺杂PMN-PMS-PZT陶瓷介电性能的影响

采用传统的固相烧结法制备了Pb1.07[(Mn1/3Nb2/3)1/2(Mn1/3Sb2/3)1/2]0.08(Zr0.828Ti0.092)O3+x wt%Al2O3+y wt%MnO2(x=0.1,0.3,0.5,0.7;y=0.00,0.02,0.04,0.06,0.08,0.10,0.12)热释电陶瓷,在对不同组分Al掺杂PMNPMS-PZT陶瓷材料介电性能对比寻优的基础上,逐步增加Mn的含量,研究不同Mn增量下,对最优Al掺杂PMNPMS-PZT热释电陶瓷相结构、晶粒生长以及介电性能的影响。通过X射线衍射仪(XRD)分析显示Al掺杂PMNPMS-PZT陶瓷和在最优Al掺杂基础上增加Mn的含量都不会引入新的杂相,扫描电子显微镜(SEM)分析表明当x=0.30,适当增加Mn的含量,有助于陶瓷晶体的均匀致密,但一旦添加过量则又会产生不好的影响。实验结果表明:采用530℃排塑,烧结1190℃,保温2 h,当x=0.30,y=0.08时,PMN-PMS-PZT热释电陶瓷具有较好的相结构和介电性能,其中介电常数εr约为210,介电损耗tanδ约为0.16%,压电系数d33约为66.00 pC/N。     

Microwave Freeze Drying of Apple Slices Based on the Dielectric Properties

Freeze drying (FD) yields the best quality of dried apple slices but requires a long drying time and is not cost-effective. To mitigate these problems, a microwave freeze drying (MFD) technique was developed to dry apple slices. The relationship between corona discharge and microwave power at various pressures and initial moisture content conditions was studied to avoid the possibility of corona discharge during MFD. It was found that with change of moisture content and temperature of samples during MFD, the dielectric property also changed, which resulted in dynamic microwave dissipation. Based on the dielectric property of samples, a changed microwave loading scheme can lead to perfect product quality and greatly reduce the drying time; thus, MFD can be used to replace the traditional FD technique.     

Relaxor ferroelectric behavior of La substituted BPZT ceramics

Barium titanate (BT) based compounds have been of great importance in the fabrication of multilayer ceramic capacitors. Several substitutions are used to tailor its structural, electrical and ferroelectric properties. Substituent like zirconium (Zr) for titanium results in decrease in non-centrosymmetric tetragonal to centrosymmetric cubic phase transition temperature (Curie temperature). Whereas substituent like lead (Pb) for barium results in the increase in the Curie temperature. Here we are reporting effect of lanthanum (La) substitution on the properties of Zr and Pb co-substituted BT. The system Ba_0.80−xLa_xPb_0.20Ti_0.90Zr_0.10O₃ with x = 0 and 0.01 was selected for study of structural and dielectric properties. Samples were prepared using solid state ceramic route. X-ray diffraction studies (XRD) were used to confirm single phase structure. Dielectric properties were studied as a function of frequency and temperature. Composition with x = 0.01 was found to show relaxor behavior.     

Dielectric Properties and Optimization of Parameters for Microwave Drying of Petroleum Coke Using Response Surface Methodology

The dielectric properties of petroleum coke at five temperatures between 20 to 100 ^° C, covering different moisture content levels at 2.45 GHz, were measured using an open-ended coaxial probe dielectric measurement system. The effects of drying temperature, duration of drying, and sample mass on the moisture content and dehydration rate of petroleum coke was assessed utilizing the response surface methodology. The dielectric constant, loss factor, and loss tangent were all found to increase nearly linearly with increase in moisture content. Three predictive empirical models were developed to relate the dielectric constant, loss factor, and loss tangent of petroleum coke as a linear function of moisture content from 3–10%. An increase in temperature between 20 to 100 ^° C was found to increase the dielectric properties. The penetration depth was observed to increase linearly with decrease in moisture content in the range of 3 to 10%. A predictive empirical model was developed to calculate penetration depth for petroleum coke. Two mathematical models were established and analyzed using RSM to describe the relationship between the microwave drying conditions and the responses, moisture content, and dehydration rate. Statistical analysis with response surface regression showed that microwave drying temperature, duration of drying, and sample mass were significantly related to moisture content and dehydration rate. Based on the RSM analysis, the optimum process conditions were estimated to be a microwave drying temperature of 75 ^° C, drying duration of 10 sec, and sample mass of 60 g, with the resultant moisture content being 0.34 at a dehydration rate of 2.94 g/min.     

Dielectric and photoelectric properties of Sm2O3 regulated by ZnO

With the trend of electronic information technology towards miniaturization, integration and intelligence, higher requirements are put forward for the performance of dielectric ceramic materials. In this paper, a series of doped samples Sm₂O₃-xZnO (x = 0, 0.1, 0.2, 0.4, 0.6, 0.8) were successfully prepared by the traditional solid state reaction method, and the complex dielectric properties of the ceramic samples were investigated as a function of temperature (100 K–400 K) and frequency (10²–10⁶ Hz) separately. A new phase Zn_6.76Sm_2.58O_10.6 was found in all samples, and all samples were complex. At a higher temperature, 350 K, with the increase of ZnO doping content, the maximum dielectric constant is 434.7, the dielectric loss is as low as 0.0098, and the dielectric performance is significantly increased compared with room temperature. UV–Vis DRS test showed that the absorbance of the sample increased with the increase of ZnO content, and the side reaction showed that the dielectric constant and dielectric loss of the sample were improved under the action of UV light. These provide an experimental basis for the application of samarium based dielectric ceramics.     

Dielectric characteristics of polyimide CP2

High-performance aerospace-grade polyimides such as CP2 fulfill many important roles in a wide range of applications. A thorough understanding of the polymer matrix’s physiochemical properties is an important consideration when developing polymer nanocomposite materials. In this work, we report the dielectric properties of polyimide CP2 including the primary and two secondary dipole relaxations, and their thermal characteristics by way of temperature variable impedance spectroscopy (10⁻² to 10⁶ Hz, −40 to 225 °C). Special emphasis has been placed on detailing the characteristic phenomena near CP2′s glass transition (199 °C). The consequences of residual DMAc solvent on CP2′s overall loss and relaxation characteristics are also discussed.     

Dielectric and Piezoelectric Properties of PZT Substituted with Samarium

The paper reports influence of samarium substitution on the properties of a PZT composition near MPB. Samarium (Sm) was varied from 0 to 0.02/FU. The samples were prepared by standard double sintering ceramic method. XRD analysis showed all samples to be of single phase. Dielectric properties were studied as a function of temperature and frequency. All the samples show well defined ferroelectric behaviour. Remanence ratio ( P r / P s ) was found to increase with increasing Sm concentration. Piezoelectric change coefficient d 33 decreases with increase in Sm.     

Complex Dielectric Properties of the Sapwood of Aspen,White Birch,Yellow Birch,and Sugar Maple

The dielectric properties of four Canadian eastern wood species were measured as a function of moisture content and temperature, at frequencies between 0.4 and 2.47 GHz using the cavity perturbation technique. The temperature was varied from ? 20 to 58°C and moisture content from 40 to 136%. Dielectric properties varied with moisture content, wood temperature, and microwave frequency. However, the influence of moisture content and microwave frequency overshadowed the influence of wood species and wood temperature. The dependencies were established for the selected species and discrepancies are discussed, namely concerning their implication when used in wood industry (nondestructive testing, heating, and drying).