High Values Of Dielectric Permittivity Research Articles

A design approach to obtaining highly polar liquid crystal dimers

ABSTRACT The synthesis and characterisation of 10 members of the [4[(E)-[4-[4-[ω-(4-cyanophenyl)phenoxy]alkyloxy]-3-nitrophenyl]methylideneamino]phenyl] 2,4-dimethoxybenzoates is reported in which the number of methylene units in the flexible spacer is increased from three to twelve. The mesogenic units are based on cyanobiphenyl and 3-nitrobenzylideneaniline benzoate and linked by the spacer such that their dipoles are parallel giving rise to a large longitudinal dipole moment. All 10 members of the series show a nematic phase, and the nematic-isotropic transition temperatures, TNI, and associated entropy changes show a strong dependence on the length and parity of the spacer. This behaviour is attributed to the average shapes of the molecules and their flexibility. The heptyl member was further characterised using dielectric spectroscopy revealing a high value of dielectric permittivity reflecting the large dipole moment of the molecules and possibly indicating local short-range ferroelectric order. The synthesis and characterisation of two members of the [4[(E)-[4-[4-[3-(ω-cyanophenyl)phenoxy]alkyloxy]-4-nitrophenyl]methylideneamino]phenyl] 2,4-dimethoxybenzoates are also described for which the difference in shape between odd and even members is reduced. Both dimers are exclusively nematogenic and the difference between TNI for the odd and even member is smaller reflecting the more similar molecular shapes. The potential for developing dimers that exhibit the ferroelectric nematic phase is discussed.

ELECTRON-BEAM SINTERING OF ZIRCONIUM DIOXIDE/TITANIUM CERAMICS FOR MICROELECTRONICS PRODUCTS

Zirconium dioxide (ZrO<sub>2</sub>) has excellent physical, chemical, and mechanical properties. These properties make it an excellent material for composite ceramics. High values of dielectric permittivity, mechanical resistance, and high radiation resistance allow it to be used to protect integrated circuits (ICs) from external influences. In this study, we fabricated ZrO<sub>2</sub>/titanium (Ti) ceramic composites by employing electron-beam sintering and a forevacuum-pressure plasma-cathode electron-beam source. We used a scanning electron microscopy method to study the properties of the ceramics after sintering. The results obtained showed that with an increase in the sintering temperature up to 1700°C, the Ti content in the near-surface layer of the composite decreased to almost 0. The depth of the region with low metal component content also increased with an increase in the sintering temperature and reached 2 mm in 3-mm-thick samples. This method can be used in the production of composite materials used in IC packaging.

Effect of sintering conditions on colossal dielectric properties of (Tb1/2Nb1/2)0.01Ti0.99O2 ceramics

In this study, we investigated various sintering temperatures (1200 °C−1450 °C) and durations (2–6 h) conditions for preparing (Tb1/2Nb1/2)0.01Ti0.99O2 (TNTO) ceramics. By employing high sintering temperatures (≥1350 °C) and extended sintering durations (≥4 h), we successfully achieved ultra–high dielectric permittivity values (ε′ ∼ 2.2 − 4.1 × 104) and remarkably low loss tangent values (∼0.025−0.079). Remarkably, the temperature coefficient of the TNTO ceramic, sintered at 1350 °C, exhibited exceptional stability, maintaining a value of approximately 15% even at 200 °C. Additionally, we examined the phase structure and microstructure of the TNTO ceramics to gain insights into their colossal permittivity (CP) behavior. The analysis revealed the presence of rutile TiO2 and TbNbTiO6 phases, and the ceramics exhibited a high–density microstructure under high–temperature sintering conditions. The impedance spectroscopy analysis revealed that the primary contributor to the observed CP behavior was the interfacial polarization mechanism. The observed increase in the ε′ value, correlated with the enlargement of the average grain size, can be attributed to the effect of the internal barrier layer capacitor. However, when the sintering time ≥4 h, the grain size did not significantly affect the ε′ value, possibly due to reaching the maximum capacity of electron production for the interfacial polarization process (i.e., the maximum intensity of polarizability). This study provides valuable insights into optimizing the sintering conditions for TNTO ceramics and related compounds, laying the groundwork for the development of a new CP oxide suitable for practical applications.

Dielectric and microwave properties of ceramics of the Bi-Ti-O system

Dielectric and microwave properties of ceramics based on binary systems Bi2Ti2O7-TiO2 and Bi2Ti4O11-TiO2 were studied. In order to obtain dielectric materials with high stability of temperature coefficient of resonance frequency, high values of dielectric permittivity and quality factor modification of ceramics by chemical elements with different valence and ionic radii was performed. It is established, that on the basis of Bi2Ti4O11-TiO2 system, it is possible to receive microwave materials for manufacturing of resonators. It is shown that the introduction of different valence ions in the Bi2Ti2O7-TiO2 system allows to change its basic dielectric parameters in given limits and directed to choose the optimal composition of ceramics for the development of materials that can be used, for example, when creating storage capacitors.

Analysis of Raman, Mossbauer Spectra and Dielectric Behaviour of Sol-Gel Prepared Ni1-xCoxFe2O4 Spinel Ferrites

Single-phase spinel ferrites with formula of Ni1−xCoxFe2O4 where x values are varying from 0 to 1 with 0.25 steps were synthesized by sol-gel technique. Microstructure, cation distribution, valence state of iron and dielectric properties have been discussed. From the deconvoluted Raman spectra the positions of five Raman modes and intensity variation was calculated. Cationic arrangement in A and B sites was estimated from deconvoluted Raman peaks. The characteristic magnetic patterns of ferrites were given by room temperature Mossbauer spectra. Parameters like isomer shift, hyperfine magnetic field, quadrupole shift were estimated for all ferrites after fitting Mossbauer spectra. From XPS (X-ray Photoelectron Spectroscopy) analysis +3 ionic state for iron was found. Dielectric parameters were also studied for ferrites at room temperature. NiFe2O4 and Ni0.75Co0.25Fe2O4 had high values of dielectric permittivity, AC conductivity and loss tangent. The ferrite Ni0.5Co0.5Fe2O4 showed very less dielectric constant and conductivity values and dielectric loss resonance peak was around 1 kHz.

Effect of high pressure-high temperature treatment on the microstructure and dielectric properties of cobalt doped СaСu3Тi4О12

The results of studying the effect of high pressures and high temperatures (8 GPa, 1273 K) used in the process of thermobaric treatment of CaCu3-xCoxTi4O12 ceramics (x = 0; 0.4; 0.6), initially prepared by solid-phase synthesis, on the structure and electrical characteristics are presented. The dielectric parameters were evaluated in a temperature interval (293–1000) K in a frequency range 1 Hz–32 MHz. It was established that the value of dielectric permittivity ε of samples upon thermobaric treatment is an order of magnitude higher than ε of samples prepared by solid-phase synthesis. The main reasons for the high values of dielectric permittivity are both the intragrain effects related, among other things, to hopping mechanism of polaron motion, and the polarization effects provided by the presence microstructure inhomogeneities. The latter are nonconducting boundaries of conducting grains and, in some examined materials, microscopic-scale surfaces of inhomogeneities, which appeared due to deformation during thermobaric treatment. At high temperatures, oxygen vacancies make the main contribution to the observed values of dielectric permittivity.

Study of the spectroscopic, magnetic, and electrical behavior of PVDF/PEO blend incorporated with nickel ferrite (NiFe2O4) nanoparticles

Pure nickel ferrite nanoparticles (NiFe2O4 NPs) were prepared by the solvothermal method. Different concentrations of NiFe2O4 were added to PVDF/PEO blend to prepare the PVDF/PEO-NiFe2O4 nanocomposite films. The films were characterized using different techniques in detail. Pure NiFe2O4 NPs images have a semispherical shape and roundness of the edges, with average particle size ~ 4.3–8.8 nm, and polycrystalline structure. Pure NiFe2O4 NPs show that micrometrical agglomeration suggests the presence of pore-free crystallites on the surface. The spectroscopic techniques such as XRD, FTIR, and UV–visible have confirmed the interaction between PVDF/PEO and NiFe2O4 NPs. Still, the nanocomposites exhibit a smooth surface with typical spherulitic clusters revealing the semi-crystalline structure of the PVDF/PEO-NiFe2O4 nanocomposites. The values of ε′ and ε″ were increased as an increase of NiFe2O4 due to the high value of dielectric permittivity of NiFe2O4. The appearance of semi-circles in the plot of M″ with Log confirms the single phase of the samples. The dielectric measurements show that M′ is inversely proportional to ε′. At higher temperatures, M′ levels off at frequencies higher than those at lower temperatures because the relaxation processes were spread over a range of frequencies. The values of saturation magnetization of PVDF/PEO-NiFe2O4 films were linearly increased as an increase of NiFe2O4 indicates improvement in the magnetic vector arrangement. Due to the enhancement of the magnetic properties, they can further exploit the films for magnetic applications.

Soft silicone elastomers exhibiting large actuation strains

AbstractPoly(dimethyl‐co‐methylvinyl)siloxane‐α,ω‐diols with 1.5, 5.5, and 8.5 mol% vinyl group contents, respectively, are obtained via an environmental friendly synthesis and used as platforms for further chemical modification via a green process. This chemical modification consists of UV‐activated thiol‐ene addition of 3‐chloro‐1‐propanethiol to the vinyl groups, as proven by NMR analysis. Cross‐linking with tetraethyl orthosilicate (in excess) of such modified polymers leads to dielectric elastomers with higher values of dielectric permittivity than those of non‐chemically modified vinyl copolymers cross‐linked under similar conditions. In addition, at high chloropropyl content, there is a significant decrease in Young's modulus, attributed to the plasticizing effect of the alkyl segment of the attached chloropropyl, and only a slight increase in breakdown strength is observed. All these changes induced by the chloropropyl group act synergistically in favor of the electromechanical performances of the resulting elastomers that exhibit large out‐of‐plane actuation strains of 53% and 61% for polar contents of 5.5 and 8.5 mol%, respectively, at an applied electric field of 40 V/μm. These are to the best of our knowledge the largest out‐of‐plane actuation strains from silicone elastomers reported in literature.

Fabrication of High Dielectric Materials Through Selective Insertion of Functionalized Reduced Graphene Oxide on Hard Segment of Thermoplastic Polyurethane.

The presence of microcapacitors near percolatrion threshold determines dielectric permittivity of a material. Motivated by this concept, we focused our work by preferentially allocating functionalized reduced graphene oxide (FRGO) in hard segment (disperse phase) of Thermoplastic polyurethane (TPU) by solution blending method and characterized. Morphological studies of TPU/FRGO nanocomposites established homogeneous dispersion of FRGO throughout the TPU matrix. It is noted that TPU/FRGO (1 phr) nanocomposites exhibit maximum increase in tensile strength (33%) and elongation at break (10%). Thermogravimetric analysis (TGA) showed maximum enhancement in onset of decomposition temperature (~6 °C) in 2 phr FRGO loaded TPU. Differential scanning calorimetry (DSC) analysis showed maximum reduction (~2 °C) in glass transition temperature (Tg) of soft segment of TPU followed by maximum improvements in melting temperature (~4 °C) as well as crystallization temperature (~22 °C) of hard segment compared to neat TPU. Further, a significantly high value of dielectric permittivity (401) is achieved in 1.5 phr loaded FRGO at 100 Hz due to the formation of significantly higher number of microcapacitors near the percolation threshold. It is anticipated that such thermally stable and mechanically strong high dielectric TPU/FRGO nanocomposites can find applications in the field of electronic devices.

Effect of Gd3+ Substitution on Thermoelectric Power Factor of Paramagnetic Co2+-Doped Calcium Molybdato-Tungstates.

A series of Co2+-doped and Gd3+-co-doped calcium molybdato-tungstates, i.e., Ca1−3x−yCoy xGd2x(MoO4)1−3x(WO4)3x (CCGMWO), where 0 < x ≤ 0.2, y = 0.02 and represents vacancy, were successfully synthesized by high-temperature solid-state reaction method. XRD studies and diffuse reflectance UV–vis spectral analysis confirmed the formation of single, tetragonal scheelite-type phases with space group I41/a and a direct optical band gap above 3.5 eV. Magnetic and electrical measurements showed insulating behavior with n-type residual electrical conductivity, an almost perfect paramagnetic state with weak short-range ferromagnetic interactions, as well as an increase of spin contribution to the magnetic moment and an increase in the power factor with increasing gadolinium ions in the sample. Broadband dielectric spectroscopy measurements and dielectric analysis in the frequency representation showed a relatively high value of dielectric permittivity at low frequencies, characteristic of a space charge polarization and small values of both permittivity and loss tangent at higher frequencies.

Development and Characterization of 3D Printed Multifunctional Bioscaffolds Based on PLA/PCL/HAp/BaTiO3 Composites

Bone substitute materials are placed in bone defects and play an important role in bone regeneration and fracture healing. The main objective of the present research is fabrication through the technique of 3D printing and the characterization of innovative composite bone scaffolds composed of polylactic acid (PLA), poly (ε-caprolactone) (PCL) while hydroxyapatite (HAp), and/or barium titanate (BaTiO3—BT) used as fillers. Composite filaments were prepared using a single screw melt extruder, and finally, 3D composite scaffolds were fabricated using the fused deposition modeling (FDM) technique. Scanning electron microscopy (SEM) images showed a satisfactory distribution of the fillers into the filaments and the printed objects. Furthermore, differential scanning calorimetry (DSC) measurements revealed that PLA/PCL filaments exhibit lower glass transition and melting point temperatures than the pure PLA filaments. Finally, piezoelectric and dielectric measurements of the 3D objects showed that composite PLA/PCL scaffolds containing HAp and BT exhibited piezoelectric coefficient (d33) values close to the human bone and high dielectric permittivity values.

Giant dielectric constant, dielectric relaxations, and tunable properties of Sm2/3Cu3Ti4O12 ceramics

AbstractThe polycrystalline Sm2/3Cu3Ti4O12 (SCTO) ceramics have been prepared by solid‐state reaction. The crystallinity of the compound has been investigated by Rietveld refinement which has revealed a cubic structure with space group Im3. It is observed that at low frequencies, SCTO ceramic exhibits tremendously high values of dielectric permittivity ε′, larger than 32,000, at room temperature. Two distinct, thermally triggered, dielectric relaxations have been noted. This mechanism has been confirmed through impedance analysis of the ceramics. The complex impedance plane shows three semicircles, which confirm the existence of two dielectric relaxations in SCTO ceramics. In general, the electrical as well as dielectric behavior of SCTO ceramics are seen to be reasonably analogous to those of CaCu3Ti4O12 (CCTO) ceramics. The emergence of the enormous dielectric constant in SCTO ceramic is accredited to the combined effect of polarization both at the sample‐electrode interface as well as at the insulating grain boundary interface. The SCTO ceramics are identical to the CCTO ceramics in their structure and composition and hence, as the above results indicate, the IBLC effect mechanism, originally put forward for CCTO ceramics, is furthermore plausible to account for the mammoth values of dielectric constant in SCTO ceramics.

Кристаллическая структура и диэлектрические свойства керамических материалов на основе AgNbO3

Using the data of qualitative X-ray phase analysis, it was shown that in a wide concentration range at 1223 K compounds based on silver niobate are formed in the condition of the heterovalent substitution of tungsten(VI) ions for niobium(V) ions. These compounds are isomorphic to a perovskite-type structure. Microprobe analysis data allows to determine the homogeneity of the analyzed samples and the correspondence of their experimental compositions to the theoretical ones for the formula Ag1-xNb1-xWxO3. Using the data of X-ray diffraction analysis (Rietveld method) in the Crystallography Data Analysis Software – GSAS, the crystal structure of the obtained compounds was refined. The surface morphology of samples having been obtained at 1373 K was investigated by scanning electron microscopy (SEM). It was shown that with an increase of Nb5+ to W6+ substitution degree for Ag1-xNb1-xWxO3 ceramic samples in the range of the (0.2≤x≤0.8) molar ratio, the average particle size for the studied compositions grows from 1.3 to 5.2 μm, respectively. For the obtained ceramic compounds based on silver niobate with a perovskite-like structure (tetragonal distortion), the temperature-frequency dependences of dielectric parameters in the range 300-900 K were studied. It was found that samples slowly cooled from 1373 K are characterized by low values of (ε ~ 10) and loss (tgδ ~ 0.004 at f = 1 kHz) at room temperature. The ceramics obtained are characterized by relatively high values of dielectric permittivity ε at low frequencies and/or high temperatures. The dielectric parameters of the obtained ceramics are similar to the characteristics of so-called "colossal" dielectric constant materials. The revealed features of the dielectric characteristics of quenched ceramics apparently result from Maxwell-Wagner relaxation at intercrystalline contacts.

Effect of the nature of the dopant element on the physical properties of X-PrCaMnO system (X = Cd, Sr, and Pb)

The solid-state reaction method was used to fabricate Pr0.65Ca0.25X0.1MnO3 manganite compounds with X = Cd, Sr, and Pb. X-ray diffraction (XRD), magnetometry, and impedance spectroscopy technique are used to study the structural, magnetic, electrical, and dielectric properties. The X-ray diffraction reveals that all samples crystallize in the orthorhombic system. The magnetic measurements on all samples show the presence of charge ordering transition at high temperature followed by an antiferromagnetic transition. From dc-conductivity analysis, all samples display the presence of semiconductor behavior. It is observed that the lowest obtained value of the activation energy (Ea) corresponds to the Pb-doped sample. The activation energy deduced from the dc-conductivity (Ea)σ matches very well with that estimated from relaxation time (Ea)relax, indicating that the relaxation process and the electrical conduction are related to the same origin. For each X dopant, the ac-conductivity is obeyed to the Jonsher law. The analysis of the impedance spectra highlights the presence of non-Debye relaxation phenomenon. Dielectric results show that the Pb doped sample has better dielectric properties than Cd and Sr doped ones. The dielectric properties are strongly dependent on both temperature and frequency. Dielectric constants decrease with frequency, and their behaviors have been interpreted based on space charge polarization according to Maxwell-Wagner’s two-layer model. The observed high conductivity and high dielectric permittivity values suggest that our compounds may be suitable for applications in electronic devices.

Broad-band measurements of dielectric permittivity in coaxial line using partially filled circular waveguide.

The full-wave analysis was applied for a coaxial line (i.e., transmission line) that has a "short-circuited" discontinuity. The discontinuity has a radius less than or equal to the inner radius of the coaxial line. The "sample region" can be considered as a partially filled circular waveguide. Such a structure is very practical and is of particular interest for the dielectric spectroscopy applications. It takes into account the inhomogeneous field distribution, which is the limiting factor for the determination of high dielectric permittivity values at microwave frequencies. The direct problem was solved by using the mode-matching technique, and the relationship between the complex reflection coefficient and the dielectric permittivity of the cylindrical sample was obtained. By solving the inverse problem, it is possible to obtain the complex dielectric permittivity from the experimental values of the scattering matrix. The results were verified by the finite element modeling of the system and applied for particular materials. The correspondence between these approaches is excellent. This method is very suitable for the determination of permittivity, which exceeds several thousands (it is applicable for any type of material). It extends the frequency range where the permittivity can be determined reliably. There is no necessity to prepare samples with different geometries (i.e., surface area and thickness).

High tunability in lead-free Ba0.85Sr0.15TiO3thick films for microwave tunable applications

Lead free ferroelectric Ba0.85Sr0.15TiO3(BST) thick films were successfully deposited by screen printing process on Ag–Pd/Al2O3 substrates. The microstructure of the samples was analyzed by scanning electron microscope (SEM) and X-ray diffraction (XRD). The thick films showed a good adhesion to the Ag–Pd/Al2O3 substrate, a porous microstructure and uniform thicknessesof about 10 μm. The dielectric properties of BST thick films were studied over a wide frequency range (10-1 Hz to 106 Hz) and in a large temperature range from 25 °C to 350 °C. The AC conductivity in BST thick films was systematically investigated. Ferroelectric characterizations and tunability were also studied at room temperature by polarization cycles P(E) and capacitance C(E) measurements. The high values of dielectric permittivity and tunability (67%) combined with low dielectric loss (tgδ) make Ba0.85Sr0.15TiO3 thick films one of the encouraging candidates for microwave tunable applications.

Fe-intercalated few layers reduced graphene oxide: A unique material for supercapacitor applications

Although intensive research has been carried out on composite materials containing transition metal (TM) oxides and graphene for supercapacitor application, the field remains totally unexplored to intercalate TM atoms in few layer reduced graphene oxide (rGO) to design high performance supercapacitors. The major advantages are the enhancement in porosity and formation of trap states at the Fe sites for better charge storage capacity. Therefore, in the present work, Fe-intercalated few layer rGO samples are synthesized to enhance the interlayer separation from 0.34 to ∼1 nm. The enhancement of interlayer separation is characterized by x-ray diffraction, which shows a single peak at a 2θ value of 8.7°, indicating the layered type material with an interlayer separation of 1 nm. Large enhancement in specific capacitance to about 896 F/g and a high energy density of 31 W h/kg is observed in this highly porous material. All these results of enhancement in specific capacitance and energy density are explained on the basis of trap states created at the Fe sites and large enhancement in porosity due to Fe intercalation. Cyclic stability to about 85% after 8000 cycles is also verified. Quantitative evaluation of trap states and modification of charge transport are observed. Due to trap centers, a high value of dielectric permittivity is achieved.

Metasurface Resonator for 1.5 T MRI Based on BaTiO3 Host Material.

Magnetic resonance imaging (MRI) is a widely used clinical tool for medical diagnosis and therapy. Several research studies focus on passively improving MRI sensitivity using high dielectric constant (HDC) materials and metamaterials. In this work, we investigate a new metasurface resonator which can enhance local transmit and receive efficiency in 1.5T MRI. The metasurface has been realized with an array of non-magnetic rods embedded in two blocks of a BaTiO3 aqueous mixture. BaTiO3 when mixed with water exhibits high dielectric permittivity values in the 40-200 MHz range, allowing the design of a compact and safe device for practical use in an MRI scanner. Simulation results show 50% enhancement of the magnetic field in the region-of-interest. The resonance frequency of the metasurface is also validated experimentally with a small loop antenna and a vector network analyzer (VNA) in a laboratory-controlled environment.

Microstructure and Dielectric Properties of Naturally Formed Microcline and Kyanite: A Size-Dependent Study

The present article reports the crystal defect-mediated changes in electrical characteristics, especially, dielectric properties, of naturally formed microcline and kyanite in two different size fractions. A facile top-down synthesis approach has been adopted to achieve the nanosized samples. Structural and morphological studies have been carried out using X-ray diffraction, field emission scanning electron microscopy, and Fourier transform infrared spectroscopy. Phase purity and microstructural characteristics of the samples were investigated by performing the Rietveld refinement method. Microstructural analysis reveals that the sample size has been greatly reduced to the nano regime after the mechanical ball-milling process, and the milling process eventually introduced some defects in the nanosized samples. UV–vis spectroscopy reveals the optical absorption characteristics and the band gap values of the samples. A major outcome of the present study is the enhancement of the defect states naturally formed samples using the mechanical milling method and the defect-mediated electrical response with varying temperature and frequency. Remarkably high dielectric permittivity values (77.3 × 103 for AF2 and 8.036 × 103 for KY2) in the nanosamples along with low tangent losses and good industrial feasibility of synthesis make the nanosized samples a potential material for fabricating low-cost energy storage devices.

Salt concentration and temperature dependent dielectric properties of blend solid polymer electrolyte complexed with NaPF6

Solid polymer electrolytes consisted of poly (ethylene oxide) (PEO) and poly (vinyl) pyrrolidone (PVP) with sodium hexafluorophosphate (NaPF6) salt has been prepared by solution cast technique. The influence of salt concentration and temperature on the complex permittivity, complex conductivity, loss tangent, and complex modulus have been analyzed systematically. The complex permittivity decreases with the increase of frequency and high value of dielectric permittivity in the low-frequency window is attributed to the electrode polarization effect. The peak in the loss tangent plot shift toward high frequency with the addition of salt and increase of temperature clearly indicates the decrease of the relaxation time. The temperature dependent analysis suggests that dielectric properties, dc conductivity, and the molecular chain segmental dynamics increase with the increase of temperature owing to the thermal activation of dielectric properties. The ion migration and dc conductivity are effectively improved by the addition of salt. Aforementioned estimated results strongly convincing its use for the device applications