Investigations on the structural,mechanical, thermal,and electrical properties of Ce-doped TiO2/poly(n-butyl methacrylate) nanocomposites

This study focused on the fabrication of poly(n-butyl methacrylate) (PBMA) nanocomposites with various concentrations of cerium-doped titanium dioxide (Ce–TiO₂) nanoparticles via in situ polymerization technique. The structural characterization and the material properties of all the composites were analyzed by UV–visible, FTIR, XRD, SEM, DSC, TG, and tensile strength measurements. The UV–visible and FTIR studies confirmed the effective inclusion of Ce–TiO₂ nanoparticles into the PBMA matrix. The change in amorphous morphology of PBMA to a crystalline structure was observed from the XRD pattern. The SEM morphology revealed the attachment of nanoparticles in the polymer matrix. The inclusion of Ce–TiO₂ nanoparticles enhanced the glass transition temperature, and thermal stability of the PBMA matrix was revealed from DSC and TG, respectively. The tensile strength of PBMA was greatly enhanced by the addition of Ce–TiO₂ nanoparticles. The AC conductivity, dielectric constant, and dielectric loss studies were also performed in the frequency range 10²–10⁶ Hz, and it was observed that addition of Ce–TiO₂ nanoparticles greatly enhanced the electrical properties of PBMA. The change in dielectric constant with the addition of nanoparticles was correlated with a theoretical modeling study. This work also extended to study the role of Ce–TiO₂ nanoparticles in the reinforcing mechanism of the nanocomposite by comparing the actual tensile strength of the composite with different theoretical modeling. The high dielectric constant and tensile strength of composite are beneficial in designing lightweight and highly efficient nanoelectronic materials based on the family of polybutyl acrylates.

     

Spectroscopic, thermal, and dielectric studies of n-butyl 4-(3,4-dimethoxyphenyl)-6-methyl-2-thioxo-1,2,3,4 tetrahydropyrimidine-5-carboxylate crystals

Pyrimidines and its derivatives find different pharmaceutical applications. The n-butyl 4-(3,4 dimethoxyphenyl)-6-methyl-2-thioxo-1,2,3,4 tetrahydropyrimidine-5-carboxylate (abbreviated as n-butyl THPM) was synthesized. The n-butyl THPM crystals were grown by slow solvent evaporation technique using chloroform as a solvent. Yellowish, coagulated, and semi-transparent crystals having dimensions of 2 × 1.5 mm were grown. The crystals were characterized by powder XRD, FT–IR, SEM, TG–DTA–DSC, ¹H-NMR, and dielectric study. The crystals remained stable up to 150 °C and then started decomposing. The DSC suggested both endothermic and exothermic reactions. One broad exothermic peak was observed at 540.3 °C due to complete decomposition of the sample into the gaseous phase and reaction within the products. ¹H-NMR spectrum has been carried out to explain the molecular structure. The dielectric study was carried out in the frequency range from 50 Hz to 5 MHz at room temperature. The dielectric constant decreased as the frequency of the applied field increased. The variations of dielectric loss, a.c. conductivity, and a.c. resistivity were also studied with the frequency of the applied field.     

Dielectric properties of moist cellulose

The dielectric constant ?′ and the dielectric loss ?″ for cellulose fiber were measured over a frequency band 0.2 to 10 Mc/sec and a temperature range from ?20 to 80°C. Also, the variation of the dielectric behavior with relative humidity was measured at 25°C. From these data, both the specific resistivity R_s and the dissociation energy U₀ were calculated. The results showed that the dielectric constant increased with frequency and temperature. This may be due to the increase in the rotation and the polarization of the flexible part in the fiber. The variation of the dielectric loss with temperature showed a maximum absorption corresponding to the β-relaxation. For the moist fiber, it is found that as the relative humidity increases, the dielectric constant and the dielectric loss increase. This increase may be due to the presence of polar water molecules, to the freeing of the polar groups, and to the freeing of the ions in the fiber molecule as well as to the increase in the number of OH^? and H⁺ ions resulting from the ionization of water. A relation between the dielectric constant and resistivity at different humidities is represented graphically. From this relation, it is found that the dissociation energy is equal to 0.318 × 10^?12 and 5.46 × 10^?12 erg below and above 52% RH, respectively.     

All-organic polymer blend dielectrics of poly (arylene ether urea) and polyimide: Toward high energy density and high temperature applications

The development of high-performance dielectric films with high energy density and temperature stability is extremely desired for modern electronics and power systems. Herein, a simple and low-cost approach is proposed to fabricate all-organic blend films prepared from poly (arylene ether urea) (PEEU) and polyimide (PI) via solution casting and thermal imidization process. The incorporation of PEEU in PI matrix significantly improved dielectric breakdown strength and dielectric constant of PI. More precisely, blend film with 15 wt% PEEU exhibited highest energy density 5.14 J/cm³ at 495.65 MV/m, with enhanced dielectric constant of 4.73 and very low dissipation factor of 0.299%. Furthermore, the dielectric properties of the PEEU/PI blend displayed wonderful temperature stability in the range of − 50–+ 250°C, and great frequency stability between 10 and 10⁶ Hz. The blend film also exhibited excellent heat resistance and presented valuable potential in thin film capacitors for high voltage direct current system.     

Dielectric properties of some semiconducting polyazophenylenes

The dielectric properties of a series of semiconducting polyazophenylenes were studied as a function of temperature and molecular weight in the temperature range 293–600°K and for molecular weights between 5,100 and 62,800 at a constant frequency of 1 kHz. The compounds studied included poly-2,4-diaminotoluene, poly-2,4-diaminoanisole, and poly-2,5-diaminotoluene. The dielectric properties are presented in the usual way in terms of a complex dielectric constant ε^* = ε′—jε″. Activation energies of relaxation processes were evaluated from the areas and widths of the dielectric loss factor, ε″, against reciprocal temperature at constant frequency. The dielectric activation energies were found to be roughly equal to the activation energies from the DC conductivity. This indicates that the conduction mechanism is based on rotational movements of molecules or parts of molecules.     

Optical and electrical properties of copper alumina nanoparticles reinforced chlorinated polyethylene composites for optoelectronic devices

The incorporation of transition metal oxide fillers into the polymer matrix through solution mixing polymerization imparts enhanced electrical and thermal properties. The present work focused on the optical properties, crystallinity, thermal stability, temperature-dependent conductivity, dielectric constant and modulus of chlorinated polyethylene/copper alumina (CPE/Cu–Al₂O₃) nanocomposites. Optical absorption measured using an ultraviolet–visible (UV–visible) spectrometer shows enhanced intensity and a blue shift for CPE/Cu–Al₂O₃ nanocomposites. The bandgap energy of CPE/Cu–Al₂O₃ nanocomposites was lower than pure CPE and minimum bandgap energy was recorded for a 7 wt% composites. The X-ray diffraction demonstrates that Cu–Al₂O₃ nanoparticles were uniformly introduced into the CPE matrix. Thermogravimetric analysis (TGA) manifests improved thermal stability of nanocomposites. Dielectric properties decrease with frequency, whereas AC conductivity increases with frequency, and both AC conductivity and dielectric properties increase with temperature. The maximum AC conductivity and dielectric constant were obtained for 7 wt % nanofiller loaded sample. For all systems, the activation energy for electrical conductivity decreases with rising temperatures. The experimental dielectric constant values of CPE nanocomposites were correlated with different theoretical models. The Bruggeman model was in good agreement with the experimental permittivity. The impedance experiments showed a decreasing trend with temperature, indicating the semiconducting nature of prepared nanocomposites.     

A novel fiber-grafting-sensing testing method for temperature deformation of piezoelectric composites

The deformation of piezoelectric composite has many deadly effects on the transducers and the sonar systems, but the relative testing method never been focused. Here we developed a novel fiber-grating-sensing method for the study of temperature deformation of the piezoelectric composites for the first time. With the increase of temperature, the deformations of the piezoelectric composite in three dimensions increased, and the increasing speeds (all speeds means slop of fitted line) were 1.4 × 10⁻³ (length), 1.8833 × 10⁻⁴ (width) and 3.1439 × 10⁻⁵ (thickness), respectively. After adding the deform information the data for the frequency constant and dielectric constant were revised. The decreasing speed of frequency constant lowered from −2.0373 to −2.0263. The increasing speed of dielectric constant lowered from 2.6779 to 2.6580 in the range of 25 °C–75 °C, and from 1.9647 to 1.9559 in the range of 75 °C–125 °C.     

Dielectric characteristics of a Ce3+-doped Sr0.61Ba0.39Nb2O6 single crystal with Cole–Cole plots technique

In this paper, we have investigated relaxation mechanisms and dielectric characteristics of an Sr_0.61−xBa_0.39Nb₂O₆Ce_x (abbreviated as SBN61 and x=0.0066) single crystal with dielectric spectroscopy measurements. The crystal undergoes a ferroelectric phase transition at 340 K. The temperature dependence of the real and imaginary part of the complex dielectric susceptibility in the vicinity of ferroelectric–paraelectric phase transition has been studied in the frequency region 100 Hz–10 mHz. The measurement of the dielectric constants of the real and imaginary parts shows strong frequency dependence. The investigations of the dielectric constant using Cole–Cole plots revealed a non-Debye-type dielectric relaxation for Ce⁺³-doped SBN61. It reveals the coexistence of the two dielectric relaxators in the vicinity of the phase transition.     

Preparation and characterization of nanoporous polyimide membrane by the template method as low‐k dielectric material

In order to decrease the resistance–capacitance delay and signal crosstalk in ultra large‐scale integrated circuits (ULSIC), dielectric materials with ultra low dielectric constants are developed to be the replacement of silicon dioxide. Introduction of air on the matrix material is an important method to reduce the dielectric constant, and polyimide (PI) is the most promising polymer to prepare porous matrix material for its distinct advantages. PI membrane with nanopores was prepared by the method of template method (i.e. thermolysis of polystyrene nanospheres in the matrix) following the synthesis of template. The nanoporous membrane was characterized by Fourier transformer infrared, scanning electron microscopy, thermogravimetric analysis, and the dielectric constant of which was measured. Results showed that uniform nanopores about 100–200 nm were formed in the PI membrane, and dielectric constant of which was decreased to 2.08 from 3.34. The nanoporous membrane can be applied as potential low‐k dielectric material in ULSIC. Copyright © 2015 John Wiley & Sons, Ltd.     

Structural,Magnetic, and Electrical Properties of Al3+ Substituted CuZn-ferrites

Nanocrystalline Cu_0.5Zn_0.5Fe_2-xAl_xO₂ (x=0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) ferrite materials were synthesized using standard solid state reaction technique. The effects of Al³⁺ contents on the structural, electrical, and magnetic properties were investigated. Single phase cubic spinel structure was revealed by X-ray diffraction analysis. The crystallite size was evaluated considering the most intense diffraction peak (311) using Scherrer formula. Lattice constant decreased, whereas porosity increased with the increase in Al³⁺ concentration. The value of saturation magnetization decreased with increasing aluminum contents. Temperature dependent value of direct current electrical resistivity has been determined. It is observed that the substitution of Al³⁺ has significant impact on the dielectric constant, tangent of dielectric loss angle and dielectric loss factor. The variation in dielectric properties was attributed to space charge polarization.     

Effect of Incorporating Aromatic and Chiral Groups on the Dielectric Properties of Poly(dimethyltin esters)

High‐dielectric constant materials are critical for numerous applications such as photovoltaics, photonics, transistors, and capacitors. There are numerous polymers used as dielectric layers in these applications but can suffer from having a low dielectric constant, small band gap, or ferroelectricity. Here, the structure–property relationship of various poly(dimethyltin esters) is described that look to enhance the dipolar and atomic polarization component of the dielectric constant. These polymers are also modeled using first principles calculations based on density functional theory (DFT) to predict such values as the total, electronic, and ionic dielectric constant as well as structure. A strong correlation is achieved between the theoretical and experimental values with the polymers exhibiting dielectric constants >4.5 with dissipation on the order of 10⁻³–10⁻².

     

Analysis of the lattice thermal resistivity due to the presence of electrons at low temperatures: Application to phosphorus-doped Ge

The temperature-dependence of the extra lattice thermal resistivity of a doped sample due to the presence of electrons has been studied at low temperatures for the first time by analysing the extra lattice thermal resistivity due to electrons of five samples of phosphorus-doped Ge having different carrier concentrations in the range 1.2×10²³–1.1×10²⁴ m^?3 in the temperature range 1–5 K. The variation of the extra lattice thermal resistivity of a doped sample due to electrons with the parameters η^* (the reduced Fermi energy),m ^* (the density of states effective mass),E _D (the deformation potential constant) andn (the carrier concentration) which are responsible for the electron-phonon scattering relaxation rate has also been analysed for the first time in the present study. A distinction has been made between non-peripheral and peripheral phonons in the present analysis. An analytical expression is reported for calculation of an approximate value of the extra lattice thermal resistivity of a doped sample due to the presence of electrons at low temperatures.     

Effect of solvent on the methanol JHCOH value

³J_HCOH, which depends on solvent dielectric constant (ε), has been calculated by the INDO MO finite perturbation method incorporated with “Solvaton Theory”. The calculation results agree with the experimental finding that ³J_HCOH decreases with increase of ε.The respective contributions of conformational change and dielectric constant variation to the effect of solvent on experimental values of ³J_HCOH are discussed separately because ³J_HCOH, the vicinal coupling constant, is known to be sensitive to conformational change. It is concluded that ε contributes more to the change of the experimental value of ³J_HCOH by solvents.     

On the percolative behavior of carbon black cross-linked polyethylene systems

The dielectric properties of peroxide cross-linked polyethylene–carbon black composite systems are described in the frequency range between 10 and 10⁷ Hz as a function of frequency and carbon black loading. Very high values for the dielectric constant were obtained when measuring conductive samples. A percolative model gives a suitable explanation, within experimental limits of the properties of the systems studied.     

Enhanced dielectric performance and energy storage of PVDF‐HFP‐based composites induced by surface charged Al2O3

In order to enhance dielectric properties and energy storage density of poly(vinylidene fluoride‐hexafluoro propylene) (PVDF‐HFP), surface charged gas‐phase Al₂O₃ nanoparticles (GP‐Al₂O₃, with positive surface charges, ε’ ≈ 10) are selected as fillers to fabricate PVDF‐HFP‐based composites via simple physical blending and hot‐molding techniques. The results show that GP‐Al₂O₃ are dispersed homogeneously in the PVDF‐HFP matrix and the existence of nanoscale interface layer (matrix‐filler) is investigated by SAXS. The dielectric constant of the composites filled with 10 wt % GP‐Al₂O₃ is 100.5 at 1 Hz, which is 5.6 times higher than that of pure PVDF‐HFP. The maximum energy storage density of the composite is 4.06 J cm^?3 at an electrical field of 900 kV mm^?1 with GP‐Al₂O₃ content of 1 wt %. Experimental results show that GP‐Al₂O₃ could induce uniform fillers’ distribution and increase the concentration of electroactive β‐phase as well as enhance interfacial polarization in the matrix, which resulted in enhancements of dielectric constant and energy storage density of the PVDF‐HFP composites. This work demonstrates that surface charged inorganic‐oxide nanoparticles exhibit promising potential in fabricating ferroelectric polymer composites with relatively high dielectric constant and energy storage. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 574–583     

Two‐Photon Voltmeter for Measuring a Molecular Electric Field

We present a new approach for determining the strength of the dipolar solute‐induced reaction field, along with the ground‐ and excited‐state electrostatic dipole moments and polarizability of a solvated chromophore, using exclusively one‐photon and two‐photon absorption measurements. We verify the approach on two benchmark chromophores N,N‐dimethyl‐6‐propionyl‐2‐naphthylamine (prodan) and coumarin 153 (C153) in a series of toluene/dimethyl sulfoxide (DMSO) mixtures and find that the experimental values show good quantitative agreement with literature and our quantum‐chemical calculations. Our results indicate that the reaction field varies in a surprisingly broad range, 0–10⁷ V cm^?1, and that at close proximity, on the order of the chromophore radius, the effective dielectric constant of the solute–solvent system displays a unique functional dependence on the bulk dielectric constant, offering new insight into the close‐range molecular interaction.     

Preparation and characterization of CaCu3Ti4O12 powders by non-hydrolytic sol–gel method

CaCu₃Ti₄O₁₂ (CCTO) powders were prepared via a non-hydrolytic sol–gel (NHSG) method by using acetylacetone as chelating agent and ethylene glycol as solvent. The samples were characterized by TG–DSC, Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscope. The dielectric properties of ceramics were also measured. The pure perovskite-like CCTO powders were obtained by heat treatment at 800 °C for 2 h. The average particle sizes of CCTO powders calcined at 800 °C were approximately 350–450 nm. The samples sintered at 1,000 °C showed the mean grain size of 2.5–4 μm. Specially, the ceramics exhibited high dielectric constant (1.19 × 10⁵–1.40 × 10⁵) and low dielectric loss (0.051–0.1) in the temperature range of 30–110 °C. Moreover, with the NHSG method the period of synthesis process was greatly shortened.     

Ba0.6Sr0.4TiO3/聚偏氟乙烯-聚甲基丙烯酸甲酯复合材料的制备及其介电性能

采用流延热压工艺制备Ba_0.6Sr_0.4TiO₃(BST)/聚偏氟乙烯(PVDF)?聚甲基丙烯酸甲酯(PMMA)复合薄膜,研究了PMMA含量对复合材料微观组织结构和介电性能的影响规律。结果表明,BST相能够均匀分散在聚合物基体中,归因于PMMA与PVDF良好的相容性,2种聚合物之间的界面不分明;随着PMMA含量的增加,复合材料的介电常数先降低后升高,耐击穿强度和介电可调性先增加后减少。PMMA含量(体积分数)为15%的BST/PVDF?PMMA₁₅复合材料的综合性能最佳:介电常数为23.2,介电损耗为0.07,耐击穿强度为1412 kV·cm^-1,在550 kV·cm^-1偏压场下,介电可调性为26.2%。     

Study of structural,electromagnetic and dielectric properties of cadmium substituted Ni–Zn nanosized ferrites

Sol-gel auto-combustion method was adopted to prepare Cd²⁺ ions substituted Ni–Zn nanosized ferrites having a chemical formula Ni_0.5Zn_0.5-xCd_xFe₂O₄ (0.0 $\le x\le 0.4)$. Their structural, electromagnetic, and dielectric properties were investigated by using XRD, FE-SEM, EDS, FTIR, VSM, and IS. The XRD analysis revealed a single-phase cubic structure of all samples. The addition of cadmium increased the lattice constant and cell volume of Ni–Zn ferrite due to the difference in the ionic radii between Cadmium (0.97 ?Å) and Zinc (0.74 ?Å). FESEM images showed irregularly shaped grain sizes in the range of 40 to 73 ?nm with random orientations and some agglomeration. The FTIR analysis also confirmed the presence of spinal ferrite phase functional groups in all samples. The saturation magnetization decreased (from 89.51 to 71.32 emu/g) with increasing cadmium content. However, the remanent magnetization and coercivity parameters increased with an increase in cadmium content. The dc resistivity as a function of the temperature of all samples was investigated, and the activation energies were found to be in the range of 0.48 to 0.51 ?eV. The dielectric loss decreased with increasing cadmium content. However, the dielectric constant and dielectric loss tangent (tan) varied non-monotonically with increased cadmium content.     

Dielectric properties and surface morphology of swift heavy ion beam irradiated polycarbonate films

Swift heavy ion beam irradiation induces modification in the dielectric properties and surface morphologies of polycarbonate (PC) films. The PC films were irradiated by 55 MeV energy of C⁵⁺ beam at various ions fluences ranging from 1 × 10¹¹ to 1 × 10¹³ ions cm^?2. The dielectric properties (i.e., dielectric constant, dielectric loss, and AC conductivity) and surface morphologies of pristine and SHI beam irradiated PC films were investigated by dielectric measurements, atomic force microscopy (AFM), and optical microscopy. The dielectric measurements show that the dielectric constant, dielectric loss, and AC conductivity increase with ion fluences and temperature, however, the dielectric constant and AC conductivity decrease while dielectric loss increases with frequency. AFM shows the increase in average roughness values with ion fluences. The change of color in PC films has been observed from colorless to yellowish and then dark brown with increases of ion fluence by using optical microscopy.