Low Dielectric Loss Values Research Articles

A comprehensive study on the impact of RGO/MWCNT hybrid filler reinforced polychloroprene rubber multifunctional nanocomposites

Flexible dielectric chloroprene rubber (CR) nanocomposites reinforced by one-dimensional carbon nanotube (CNT)/two dimensional reduced graphene oxide hybrids have been prepared using two-roll mill mixing technique. Non-covalent π-π interaction between multiwalled carbon nanotubes (MWCNTs) and reduced graphene oxide (RGO) nanosheets and the secondary interaction between fillers and chloroprene rubber matrix are responsible for generating the effective load transfer between RGO/MWCNTs and CR. The prepared RGO-MWCNT hybrid nanocomposites with high dielectric constant (≈650), low dielectric loss (≈0.42) and high energy storage efficiency (78.6%) values are practically good enough to use as a low cost polymeric dielectric layer in transistors. Furthermore, the prepared nanocomposites showed excellent electromagnetic effectiveness; a maximum shielding efficiency of 11.87 dB @ 3.5 GHz was achieved at 4 phr of MWCNT loading. This excellent electromechanical performance can be ascribed to the synergistic effect of RGO-MWCNT hybrid suggesting that this novel hybrid nanocomposite serves as an attractive candidate in modern electronics and electric power systems.

Influence of spark plasma sintering temperature on the microstructures, dielectric and I–V properties of CaCu3Ti4O12 ceramics

CaCu3Ti4O12 (CCTO) ceramics were prepared by the sol–gel process and sintered by the spark plasma sintering (SPS) process at different temperatures. The SPS process temperature has an important effect on the microtopography of CCTO ceramics. The results of EDS and positron annihilation spectroscopy indicate that Cu2+ diffuses from the inside to the surface of grains during the sintering process at high temperature. The permittivity (εr) of CCTO ceramics at the corresponding frequencies increases with increasing SPS temperature. However, the frequency stability of εr over the frequency range 40–106 Hz wanes gradually. The CCTO ceramics sintered at 900°Cand 950 °C present very low dielectric loss values(about 0.02) near 10 kHz. The change in εr and tanδ for CCTO ceramics can be explained by the internal barrier layer capacitance (IBLC) model and AC (alternating current) impedance spectra. The results of I–V nonlinear characteristics for CCTO ceramics make clear that the potential barrier height has a positive effect on the value of nonlinear coefficient.

Black phosphorus nanoflakes/polyimide composite films with excellent dielectric and mechanical properties

Polyimides (PIs) and their composites hold promise as low-cost alternatives to conventional ceramic-based dielectrics. Nevertheless, they are far unsatisfactory for practice applications, mainly resulting from the low interfacial compatibility between PI matrices and inorganic fillers. Herein, black phosphorous (BP) nanoflakes/PI composite films with outstanding dielectric and mechanical properties were fabricated via an in situ polymerization pathway. Owing to the hydrophilic surface of BP nanoflakes resulting from slight oxidation during fabrication, the robust noncovalent interaction between BP and PI can be formed, leading to good interfacial compatibility between the two domains and thus well dispersion of BP in PI. Even with a low BP content of 2 wt%, the composite can reach a high-permittivity value of 8.6 at 102 Hz and a low dielectric loss value of 0.02. Moreover, the BP/PI composite films inherited the good mechanical performance of PI matrix due to homogeneous dispersion and low loading of BP.

Studies on conduction mechanism and dielectric properties of the nano-sized La0.7Ca0.3MnO3 (LCMO) grains in the paramagnetic state

The La0.7Ca0.3MnO3 nanograins are synthesized by sol-gel method. The phase crystalinity is confirmed by XRD profile analysis. TEM micrograph divulged polyhedral grains with an average size of 41 nm. Impedance, conductivity and dielectric properties are studied in the frequency scope of 102–106 Hz from room-temperature to 200 °C. The Cole-Cole plots of impedance exposed grain boundary dominance and it is further confirmed by Cole-Cole plots of modulus. In different frequency regime, the conductivity curves seem to obey different conduction mechanism up to 100 °C and after this temperature, only one type of conduction is observed. The dielectric constant and loss are enhanced slowly with the rise in temperature up to 100 °C and thereafter a gradual increase was noticed. The La0.7Ca0.3MnO3 nanoparticles having a low value of dielectric loss below 100 °C can be a possible candidate for nanocapacitor applications.

Effect of PMN modification on the structural, microstructural, dielectric and ferroelectric properties of BT ceramics

(1-x)BT-xPMN (x = 0, 0.02, 0.04, 0.06, 0.08 and x = 1) ceramic samples were synthesized by solid state reaction route. XRD study confirmed the formation of single perovskite phase of the BT-PMN system. Increase in density with drastic decrease in average grain size was observed with the increase of PMN content. High value of room temperature dielectric constant (εr) with low value of dielectric loss (tanδ) at room temperature and at 10 kHz frequency was obtained in x = 0.06 ceramic samples, however low temperature coefficient of capacitance (from RT to 100 °C) was obtained in x = 0.08 ceramic samples.

The orange red luminescence and conductivity response of Eu3+ doped GdOF phosphor: synthesis, characterization and their Judd-Ofelt analysis

Present paper reports the synthesis of a series of Gd1-xEuxOF (0.01 ≥ x ≥ 0.09) phosphor by solid state route at low temperature. Characterizations such as powder x-ray diffraction (PXRD), Rietveld refinement, scanning electron microscopy, UV-Visible absorption, AC conductivity and photoluminescence (PL) spectroscopy were carried out. Rietveld refinement of powder XRD data confirms the crystallization of the compounds in rhombohedral structure. Investigation of PL under 395 and 465 nm excitation wavelengths is done. Upon substitution Gd3+ by Eu3+ ions in GdOF, the PL spectra exhibited emission at 5D0 → 7F0 (579 nm), 5D0 → 7F1 (593 nm), 5D0 → 7F2 (612, 620 nm), 5D0 → 7F3 (651 nm) and 5D0 → 7F4 (705 nm) transitions. JO theory parameterization variation from emission spectra is used to compute the intensity parameters (Ω2, Ω4) of phosphors. Using the intensity parameters the radiative lifetime (τrad), radiative transition probabilities (AT), branching ratio (β) are evaluated. Dielectric and AC conductivity of Gd1−xEuxOF (0.01 ≥ x ≥ 0.09) is studied in the frequency range from 100 Hz to 5 MHz at a temperature of 300 K. Studies reveal that the AC conductivity increases gradually beyond 30 kHz up to100 kHz and rapidly increases at 300 kHz. At lower frequencies, it is found that the compound exhibit high values of dielectric loss and dielectric constant, which decreased drastically with increasing frequency. The result so obtained reveals that present phosphors could be a possible source for orange red constituent in white LEDs and is best suited for microwave device applications because of its low values of dielectric loss.

Porous boron nitride/polyimide composite films with high thermal diffusivity and low dielectric properties via high internal phase Pickering emulsion method

This work offers a simple fabrication of porous boron-nitride-(BN)/polyimide-(PI) composite films with high thermal diffusivities and low dielectric constants by combining high-internal-phase Pickering emulsification (HIPPE) and subsequent hot-pressing. BN nanoparticles in composite foams were well dispersed and three-dimensionally connected following the surface of the PI skeleton used as the polymer matrix. The BN contents in the BN/PI composite foams were adjusted in the range of 20–80wt%. The porosities of the composite films were controlled according to the hot-pressing conditions such as the temperature. The porous BN/PI composite films exhibited high thermal diffusivities of 0.059–1.033mm2/s and low dielectric constants of 2.08–3.48 at 1GHz for BN contents of 20–80wt%. In particular, the BN/PI composite films had extremely low dielectric loss values, close to zero (<0.002) at high frequencies regardless of the BN content and pressing conditions.

Facile Growth, Physical Characterization, and Dielectric Response of As-Grown NiO Nanostructures

Nickel Oxide (NiO) nanostructures were prepared via the hydrothermal technique to examine the structure, optical, and dielectric properties. Various structural, and optical parameters: such as crystal structure, lattice parameter, average crystallite size, average micro-strain, peaks of stretching vibrations, and optical band gap, have been evaluated. Furthermore, the as-prepared NiO nanostructures were used as a dielectric material in a capacitor. Comparatively, the obtained high values of dielectric constant, and low values of dielectric loss show the potential applications of NiO nanostructures as a dielectric material. A possible mechanism has also been illustrated to explain the dielectric behaviour of the as-grown nanostructures.

Preparation and characterization of magnesium aluminate (MgAl2O4) spinel ceramic foams via direct foam-gelcasting

Lightweight MgAl2O4 spinel ceramic foams with high mechanical strength and good dielectric properties were prepared with a direct foam-gelcasting method using MgAl2O4 and TiO2 (rutile phase, as sintering aid) powders. The effects of calcination temperature and foam volume on bulk density, apparent porosity, and on the mechanical and dielectric properties of the ceramic foams were investigated. Tailored porosity (75.14–82.46%), pore size (10–200 μm), dielectric constant (1.66–2.05), and compressive strength (4.0–14.3 MPa), were obtained based on the change of the foam volume in the foamed slurries, and the calcination temperature of porous ceramics. The compressive strength and dielectric constant of the as-manufactured spinel foam with a porosity of ~75.14% was as high as 14.3 MPa and 2.05, respectively. The spinel ceramic foam which had a porosity of 81.84% was prepared with a foam volume of 350 mL and a sintering temperature of 1500 °C, and exhibited heterogeneous pore structures, whereby large and open spherical cells involved in small circular windows on the internal walls with a mean pore size of ~66.26 μm and a grain size of ~8 μm. The experimental dielectric constant matches well with that calculated by the modified Bruggeman model. The dependence of the mechanical strength on the relative density can be represented by the Gibson and Ashby model. The fitted index values of the power relationship were 3.504 and 3.533, compared to the theoretical value of 1.5. The ceramic foam can potentially become a new type of electromagnetic wave-transmitting radome material due to its low dielectric constant (1.66–2.05) and dielectric loss (0.0026–0.006) values.

Effects of Zn2+ substitution on the sintering behaviour and dielectric properties of Li2Mg1−xZnxSiO4 ceramics

Silicates, the basis on which low-temperature-fired dielectric materials widely studied for applications in the fields of microwave integrated circuits, have been developing vigorously owing to their low dielectric constants and tangent loss values. In this work, Zn2+ was gradually substituted to Mg2+ to make the sintering temperature decreased and enhance the microwave dielectric properties of Li2MgSiO4. Li2Mg1−xZnxSiO4 (x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0) powders were prepared through solid-state reaction. Aiming to decrease the sintering temperature to approximately 900 °C, 3 wt% Li2O–B2O3–SiO2–CaO–Al2O3 glass was used as a sintering aid. The XRD patterns made it clear that the major crystalline phase of the materials was Li2(Mg,Zn)SiO4. A new unexpected crystalline phase of ZnxSiO4 appeared when the amount of Zn2+ substituted increased to more than 0.4. SEM micrographs demonstrated that when x = 0.4, the most homogeneous microstructure appeared. Meanwhile, the Q × f value and the relative density also reached to their peaks when x = 0.4, respectively. Moreover, 3 wt% LBSCA-doped Li2Mg0.6Zn0.4SiO4 ceramics exhibited excellent dielectric properties of er = 5.89, Q × f = 44,787 GHz and τf = − 71.65 ppm/°C when sintered at 900 °C. The material exhibited low relative permittivity and low dielectric loss and could thus be a potential candidate for LTCC device applications.

Impact of Co and Mn substitution on structural and dielectric properties of lithium soft ferrites

Co2+ and Mn2+ co-doped lithium spinel ferrites with the chemical composition Li0.5Fe2.5-0.5xCoxMnxO4 (x = 0.0–0.5) were fabricated by micro-emulsion method. The spinel structure with face centered the cubic phase was confirmed from the XRD study. The lattice constant was found to increase first from 8.369 to 8.374 Å and then decreased up to 8.367 Å, as the substitution level increased, attributed to the formation of the secondary phases. The crystallite size of nano ferrites was found in the range of 47 to 37 nm. Substitution of Co2+ and Mn2+ significantly enhanced the density of prepared ferrites. FTIR studies revealed the appearance of the characteristic vibration bands of Li0.5Fe2.5O4 between 550 and 650 cm−1 which were appreciably influenced by the concentration of Co2+ and Mn2+. The force constants showed an indirect variation with the bond lengths of A- and B -sites. The dielectric properties such as dielectric constant (εʹ), complex dielectric constant (εʹʹ) and tangent loss (tanδ) were analyzed between 1 MHz and 3 GHz. By increasing the frequency, εʹ, εʹʹ, and tanδ were decreased and have shown a dispersive behavior at higher frequencies due to the effect of space-charge polarization. The obtained low values of dielectric loss may refer these materials for applications in transformer cores and high-frequency devices.

Enhancement of switching/un-switching leakage current and ferroelectric properties appraised by PUND method of (Ba1-xCax)TiO3 lead free piezoelectric near MPB

Lead free perovskite (Ba1-xCax)TiO3 (BCT) (0 < x ≤ 0.4) ceramics were successfully prepared by Sol gel technique in lower thermal processing conditions than the solid solution method. The samples were calcined at 1000 °C/and they were sintered at 1200 °C. The structure, dielectric, leakage current and ferro-piezoelectric properties of perovskite (Ba1-xCax)TiO3 (0 < x < 0.4) were investigated. In Ca-doping range 0 < x < 0.3, pure single phase of BCT has been detected. Secondary phase of CaTiO3 has been detected for x = 0.4. The addition of Ca2+ has a negligible effect on the Curie temperature but it inhibits the grain dwindle. High permittivity and low dielectric loss values were achieved in the sample (Ba0.8Ca0.2)TiO3 due to Morphotropic Phase Boundary (MPB) coexistence. Anomalous switching leakage peak (∼2 kV/cm) was observed due to the domain switching. The (Ba0.8Ca0.2)TiO3 exhibits low leakage even in the absence of the electric field (Joff = 1.5368e−13 A/cm2), due to the enhancement of the microstructure properties. The Ferroelectric properties were estimated by P-E loop and Positive Up Negative Down (PUND) methods and the results are shown the remnant polarization estimated by P-E loop is almost back to leakage current contribution. Piezoelectric properties were enhanced in (Ba0.8Ca0.2)TiO3 (d∗33 = 498 pm/v) due to BT-CT phases coexistence.

Structural, thermal and dielectric behavior of Polyaryletherketone (PAEK)/CaCu3Ti4O12 (CCTO) nanocomposite films

Polyaryletherketone (PAEK)/CaCu3Ti4O12 (CCTO) nanocomposite films with various (0, 1, 5, 10 and 20) weight % CCTO were fabricated via melt-compounding followed by film extrusion process. CCTO nanoceramics (nCCTO) with a crystallite size of about 30–100 nm were prepared from oxalate precursor route. Thickness of the fabricated films was in the range of 50–80 μm, and these films were characterized for their structural, thermal, and dielectric behavior. X-ray diffraction analyses showed the presence of peaks corresponding to both PAEK and CCTO with varying intensities. Fourier transform infrared (FTIR) studies revealed that the chemical structure of PAEK was unaltered by the incorporation of nCCTO. Melting temperature of pure PAEK was about 372 °C, which did not change significantly with the addition of nCCTO. Thermo-gravimetric analysis was carried out to study the thermal stability of these nanocomposites. Frequency independent dielectric behavior was observed in case of all nanocomposite films. Room temperature dielectric permittivity of PAEK (3.3 at 10 kHz) was enhanced with the addition of nCCTO, and for 20 wt% loading a value of 4.5 was achieved. Low values of dielectric loss (0.005–0.009) were obtained for all nanocomposite films at 10 kHz. These nanocomposites can be explored as possible dielectric materials for capacitor applications.

Growth and characterisation of organic nonlinear optical single-crystal 4-nitrophenol grown by vertical Bridgman technique

An organic nonlinear optical single-crystal 4-nitrophenol was successfully grown by vertical Bridgman technique using single-wall ampule in size of 38 × 15 mm2. The lattice parameters and crystallinity of the title crystal were confirmed through the single crystal and powder X-ray diffraction studies, respectively. The UV–Vis–NIR spectral analysis addressed that the title crystal has a lower optical cut-off wavelength at 405 nm and exhibits transparency of 82% in entire visible and near-IR regions with a wide band gap of 2.84 eV. The hardness, Meyer’s index, stiffness constant, yield strength, fracture toughness, and brittle index of the grown specimen were systematically investigated using a Vickers microhardness tester. The low value of dielectric constant and dielectric loss for the present crystal enrolls that it is well suitable for microelectronic industry. The laser-induced damage threshold value of the grown specimen is found to be 17.66 GW/cm2. The Z-scan measurement was employed to calculate the third-order nonlinear optical parameters of the title crystal.

Effect of the CoFe2O4 initial particle size when sintered by microwave on the microstructural, dielectric, and magnetic properties

AbstractThe particle size of CoFe2O4 powders (average particle size of 350 nm) was reduced to 50 nm by high‐energy milling. In this paper, special attention was given for analyzing the densification and grain growth of both particle sizes (350 and 50 nm) subject to ultrafast sintering assays using microwave sintering and their effect on the magnetic and electric properties. The results indicated that the grain growth was 10 times higher for the nanoparticle system, reaching similar sizes of ~1 μm in both cases after sintering. The relative density values were higher (95%) in the nanoparticle system due to the wide distribution of particle sizes generated in the grinding process. Qualitatively inferred microscopy analysis showed high sinterability of fine particles with a narrow distribution of grain size when subjected to ultrafast firing processes. Magnetization measurements at room temperature clearly show the reduction of Hc with increasing grain size. Electric resistivity, dielectric constant (ε′), and dielectric loss tangent (tan δ) were measured as a function of frequency at room temperature. The low values of dielectric constant (ε′) and dielectric loss (tan δ) in the low frequency range, shown for all samples sintered by microwave, prove the excellent uniformity in the microstructure.

Effect of Sb doping on the electrical and dielectric properties of ZnO nanocrystals

The effect of antimony doping on electrical and dielectric behaviors of ZnO nanocrystals was investigated using impedance spectroscopy. The XRD diffractograms suggest that the ZnO lattice parameters are closely affected by Sb doping. The electrical conductivity of the ZnO nanocrystals depends obviously on the Sb amount. The variations of the resistivity and the dc conductivity with varied Sb content were correlated to lattice parameters variations and are consistent with the compensation phenomenon between electrons and holes which eventually induced by the appearance of p-type conductivity in the Sb-doped ZnO. The dielectric constants and the loss tangent were found to decrease with Sb amounts. Low values of dielectric loss with Sb doping suggest that Sb-doped ZnO is suitable way for low frequency devices applications. The study of the electrical modulus provided some evidence that the dielectric relaxation is thermally activated and reveals a spread in relaxation time for low Sb concentrations.

Structural, spectral, electrical, Z-scan and HOMO LUMO studies on new 2-amino-6-methylpyridinium 2-hydroxybenzoate crystal

Abstract New organic single crystals of 2-amino-6-methylpyridinium 2-hydroxybenzoate (2A6M2H) were grown by slow evaporation solution growth technique at room temperature. The grown crystal structure was studied using single crystal XRD. Crystalline nature and phases were confirmed by powder XRD analysis. FT-IR study was used to identify the functional groups present in the compound. UV-Vis study revealed that the lower cut off wavelength of the crystal is at 350 nm. The dielectric studies indicated the low value of dielectric loss at high frequency. Mechanical properties of the crystals were studied using Vickers microhardness test. The Z-Scan studies were conducted for the crystal using He–Ne laser.

Polyitaconates: A New Family of "All-Polymer" Dielectrics.

This work presents the synthesis of new poly(itaconate)s containing sulfone or nitrile pendant groups through conventional radical polymerization together with their characterization and comparison with poly(methacrylate)s containing identical groups. Structural and thermal characterization has been carried out in terms of Fourier transform infrared spectroscopy, differential scanning calorimetry, nuclear magnetic resonance, and thermogravimetric analysis. Characterized by broad band dielectric spectroscopy (BDS), all polymers showed dielectric constant values between 7 and 10 (at 25 °C and 1 kHz) and relative low dielectric loss values (≈0.02). BDS measurements showed, for all the polymers analyzed, notorious subglass transitions even at temperatures below -100 °C, resulting in a broad temperature interval in which these polymers exhibit high dielectric constant and could work without high losses. Therefore, these materials seem to be good candidates for dielectric applications such as energy storage, among others.

Room-temperature multiferroic properties of Ba2+ doped 0.7Bi0.5Na0.5TiO3-0.3NiFe2O4 ceramics

The 0.7(Bi0.5Na0.5)1-xBaxTiO3-0.3NiFe2O4 samples (x = 0.02–0.12) have been synthesized through sol-gel method. Structure, micromorphology and the room-temperature multiferroic properties have been investigated, respectively. The characterization of structure and micromorphology reveals the coexistence of two different phases. In addition, lattice deformation and morphology variation can be clearly confirmed with doping Ba ions. Dielectric properties are improved evidently from x = 0.02–0.08 and then weakened from x = 0.08–0.12 with enough low values of dielectric loss for all the samples. The ferroelectric polarization demonstrates that room-temperature ferroelectric properties are monotonously enhanced with increasing content of Ba. The change tendency of magnetic properties is firstly decreasing and then increasing with the special content value of x = 0.08. Room-temperature magnetoelectric coupling effect is verified by the measurement of magnetoelectric coupling coefficient. The variation trend of magnetoelectric coupling coefficient with doping of Ba is similar to that of magnetic properties. The room-temperature multiferroic properties of 0.7(Bi0.5Na0.5)1-xBaxTiO3-0.3NiFe2O4 samples are related to the larger ionic radius of Ba. Furthermore, the special multiferroic behavior with x = 0.08 can be attributed to the morphotropic phase boundary effect with doping Ba.

Ultrasonically Synthesized Dielectric Microwave Absorbing Material from Coconut Coir Dust

Carbon rich natural agricultural wastes are outstanding potential candidates as microwave absorbing materials for new technological developments in electronics and telecommunication, radar and satellite systems. Fast developments in the field of electronics and telecommunication increases electromagnetic pollution due to electromagnetic interference resulting in new technological issues for stealth technology. To deal with these environmental issues, researchers have the challenges to produce low cost, eco-friendly microwave absorbing materials. This paper presents the synthesis and characterization of coconut coir dust based epoxy composites as microwave absorbers. An optimum blend of chemicals like acetone-ethanol (50–50%) is used for surface treatment of the raw coconut coir fibre. The Scanning electron microscopy study shows good dispersion of coconut coir dust in the epoxy matrix. Frequency dependence of both dielectric constant and dielectric loss are measured in the X-band frequency range (8.2–12.4 GHz). The average value of dielectric constant $$(\varepsilon ^{\prime})$$ 3.32, low value of dielectric loss i.e., 0.25 and the value of loss tangent i.e., 0.75 indicates significant attenuation of the microwave with high attenuation coefficient 1.35 and reduces the amplitude of the microwave. Absorption co-efficient and S11 and S21 parameters show good absorbing capacity of the materials in the same frequency range, with maximum reflection loss − 23.5 dB at 10 GHz frequency. The experimentally determined reflection loss quite well agrees with the calculated ones, which show the effectiveness of absorber for various practical EM wave absorption applications.