Loss Factor Tangent Research Articles

Temperature-dependent dielectric response of free standing PVDF-MoS2 nanocomposite films

Poly(vinylidene fluoride) (PVDF) and its copolymers are known for possessing the highest electroactive response including dielectric constant, piezoelectric and ferroelectric effects which has a wide range of applications such as in energy transfer, energy generation and storage, monitoring and control, and include the development of capacitors, sensors, actuators and so on. We report an enhancement in dielectric properties in PVDF generated by the addition of MoS2 nanosheets. The addition of 1 wt% MoS2 nanosheets as a filler in PVDF, stabilize its beta phase over the alpha phase, resulting in a significant increase in dielectric constant (ε’) across a wide range of frequencies (100 Hz to 1 MHz) and temperatures (140 K- 340 K). The high dielectric constant was achieved by the PVDF-MoS2 nanocomposite while maintaining a relatively low tangent loss factor of 0.94. Such properties in soft polymer-based piezoelectric materials were previously challenging and unachievable. The nanocomposite exhibits excellent ferroelectric properties with 11 times enhancement in remnant polarization compared to pristine PVDF in ambient conditions. The stored energy density (Us) is 39.43 mJ/cm3 for the PVDF-MoS2 film. These lead-free and soft polymer-based nanocomposites can bring remarkable advances in various flexible sensors, data storage, and energy harvesting applications.

Structural, dielectric, and antimicrobial evaluation of PMMA/CeO2 for optoelectronic devices

In the current report, we have successfully synthesized nanocomposites of PMMA incorporating different doping of CeO2 through a chemical approach. XRD results reflects decent matching for CeO2 nanoparticles with 29 nm crystallite size. FTIR spectroscopy demonstrates the characteristic functional groups validating the successful formation of the composite. The optical study of PMMA and the nanocomposites has proven that the optical properties such as band gap, refractive index, optical permittivity, and loss tangent factor are affected by adding CeO2 to the PMMA matrix.The peak residing around 420 nm by UV measurements is allocated to occurring electrons photoexcitation from the valence to conduction band inherent in CeO2. The dielectric measurements were achieved using broadband dielectric spectroscopy upon a wide span of frequencies (10–1–107 Hz) and within temperatures from − 10 to 80 °C with a step of 10 °C. The permittivity decreases by adding CeO2 and the dielectric parameters are thermally enhanced, however, the temperature influence is based on CeO2 content, the higher the CeO2 amount, the higher the influence of temperature. The results of the nanocomposites revealed antibacterial activity counter to gram-positive bacteria strain (S. aureus, and B. subtilis), and gram-negative bacteria (E. coli, and K. pneumoniae), yeast (C. albicans, as well as fungi (A. niger). Inherently, the change in CeO2 concentration from 0.01 to 0.1 wt% delivers maximum influence against gram-negative bacteria. These PMMA CeO2-doped composites are beneficial for optoelectronic areas and devices.

Dielectric prοperties and cοmplex impedance οf the 0.69PbMg1/3Nb2/3Ο3– 0.31PbTiΟ3 relaxοr ceramic

ABSTRACT Impedance spectroscopy assessed dielectric properties of PMN at a single PT concentration. Real and imaginary impedance of (1−x) PMN–xPT materials were analyzed using this technique. Through electrical impedance spectroscopy, the loss tangent factor and electric modulus were determined, leveraging research on semiconductor conduction. The study also presented the synthesis and characterization of solid ceramic lead magnesium nibate-lead titanate (1−x) PbMg1/3Nb2/3-xPbTi3, representing a significant advancement in impedance spectroscopy research. The dielectric behavior was examined by studying the polarization evolution in response to the applied field, aiming to replicate the magnetic phase boundary configuration found in typical ferroelectric behavior. Temperature had a notable impact on the hysteresis loop, with increasing temperature and decreasing applied field resulting in decreased leftover polarization and increased coercive field. The impedance and complex modulus graphs exhibited distinct semicircle patterns attributed to higher grain boundary resistance and capacitance compared to (1−x) PMN-xPT. The Nyquist plot highlighted bulk effects.

Structural, Frequency and Temperature Dependent Dielectric Properties of Zn2+ Substituted Ni-Co Based Spinel Ferrite (ZnxNi0.8−xCo0.2Fe2O4)

Zinc substituted nickel-cobalt ferrites, i.e., ZnxNi0.8−xCo0.2Fe2O4 (x = 0.0, 0.05, 0.10 and 0.20) with average crystallite size 100 nm were synthesized by citrate-gel auto-combustion method to investigate effects of Zn2+ substitution on the structural and dielectric properties. Both X-ray diffraction (XRD) and IR spectroscopy studies confirms the formation of pure cubic spinel structure. Variation of lattice parameter infers Vegard’s law linear dependence with the addition of Zn2+ concentration. The temperature-dependent behavior of dielectric and modulus spectra has been studied within the frequency range 100 Hz-100 kHz for different temperatures between 100 K and 400 K. It was concluded that the dielectric responses of ZnxNi0.8−xCo0.2Fe2O4 are found to be frequency dependent and thermally activated. Also, In the Zn doped ferrites variations of dielectric loss (tan δ) and the imaginary part of electric modulus (M") show the presence of the non-Debye type of dielectric relaxation. Rise in Zinc concentration leads to a decrease in dielectric constant (ε r) due to the declining of Fe3+–O–M2+ conducting network (M is Co or Ni). Here, we report a low loss tangent factor of the order of for the sample Ni0.6Zn0.2Co0.2Fe2O4 make this composition suitable for high frequency-applications at room temperature. The activation energy is calculated from electric modulus formalism and DC electrical conductivity and found to increase with further substitution of Zn2+ concentration.

Influence of excess bismuth oxide on the structural and dielectric characteristics of textured Bi4Ti3O12 ceramics

Bismuth titanate (Bi4Ti3O12), an Aurivillius family of ferroelectric oxide, has been widely investigated due to its large remnant polarization, high Curie temperature, high dielectric constant and relatively low tangent for the application in information memory storage devices. In this work, polycrystalline bismuth titanate ceramics samples with different amounts of excess Bi2O3 (3 and 5 wt%) were prepared using a low temperature, cost-effective molten salt synthesis method. The structural, microstructural and dielectric properties depend on the addition of excess Bi2O3 and the sintering duration of Bi4Ti3O12 ceramics. Moreover, the X-ray diffraction studies revealed the effect of excess bismuth oxide on the formation of preferential orientation along the c-axis. It is also observed that the orientation factor along the c-axis increases with an increase in the sintering duration for different content of bismuth oxide. The morphological studies revealed the oriented plate-like structure of bismuth titanate ceramics associated with the enhanced growth of grains. It is noticed from the EDAX analysis that the addition of excess bismuth oxide compensated the volatilization of bismuth ions in the crystal lattice of Bi4Ti3O12 ceramics. The dielectric property studies have exhibited a high value of dielectric constant (εr ~ 190), and low tangent loss factor (tanδ ~ 0.08) for the optimum bismuth oxide content of 5 wt% added Bi4Ti3O12 ceramics. Hence, we suggest that these materials could be utilized for the high energy storage capacity of non-volatile memory devices.

Effect of γ-radiations on the optoelectrical parameters of coumarin-poly vinyl alcohol composite thin films

This work aims to study the effect of γ-radiations on the optoelectrical parameters of coumarin-poly vinyl alcohol composite thin films at room temperature prepared by solution casting method. For these polymer composite films, the various parameters calculated from the refractive index and extinction coefficient were obtained from transmittance and reflectance spectra. The effect of radiations on the optical band gap, Urbach energy, tangent loss factor, volume and surface energy loss functions were studied. The effect of γ-radiations on the optoelectrical parameters like high-frequency dielectric constant, optical carrier concentration, relaxation time, optical mobility and optical resistivity derived from Drude theory were also discussed. Moreover, other parameters of interest under the investigation were optical conductivity, electronic polarizability, optical electronegativity, nonlinear optical susceptibility, optical, and chemical hardness. The impacts of γ-radiations on dispersion parameters like oscillator energy, dispersion energy, oscillator wavelength and oscillator strength were also studied by using Wemple-DiDomeenico single oscillator model.

Electrical properties of alkali-activated materials against Portland cement

A first attempt was made to study the electrical properties of pastes and mortars prepared from the most common alkali-activated materials against those of Portland cement (PC). The properties included electrical conduction, dielectric constant, the real part of dielectric permittivity and loss tangent factor. The frequencies measured ranged from 100 MHz to 3 GHz. The most common starting materials such as slag, fly ash (FA) and metakaolin (MK) were used and activated with sodium silicate and sodium hydroxide solution to prepare geopolymer pastes and mortars. After curing, the specimens were tested under compression to determine the compressive strength. In addition, electrical properties were measured. The results showed that FA-based geopolymer and PC specimens exhibited similar electrical properties. MK- and slag-based geopolymer specimens also exhibited similar electrical properties but with lower conductivity compared with the other two types. The results also confirmed similar electrical properties of pastes compared to mortars.

Impact of Ho and Ce Ions Substitution on Structural, Electrical, and Dielectric Properties of Ni-Zn Ferrites

In the present study, influence of holmium (Ho) and cerium (Ce) ions on the electromagnetic properties of Ni0.67Zn0.33Fe1.9Ho0.1-xCexO4 ferrites (x = 0, 0.025, 0.05, 0.075, 0.1) synthesized by the self-ignited sol-gel method was studied. The XRD experiment was performed to determine the substitutional effects on structural parameters. FTIR spectroscopy and I-V measurements were carried out to analyze the spectral and electrical behavior of substituted samples. X-ray diffraction patterns revealed the FCC structure of the prepared samples The value of average crystallite size was noticed between 25.89-39.51 nm, while lattice constant was found in the range 8.37-8.41 Å. Both the low and the high frequency absorption bands were confirmed by FTIR technique. Tetrahedral band was noted in the range 463-495 cm-1 while octahedral band was observed in range 558-560 cm-1. The dc resistivity was observed to decrease with increase in temperature which indicates the semi-conductor like behavior of the prepared samples. Dielectric study showed that both the dielectric constant and the tangent loss factor were decreased with rise in the applied field frequency.

Synthesis and Characterization of CoFe2O4/MWCNTs Nanocomposites and High-Frequency Analysis of Their Dielectric Properties

Nanoparticles of CoFe2O4 were synthesized by chemical co-precipitation method. The CoFe2O4/MWCNT nanocomposites were synthesized with increasing contents of MWCNTs, i.e., 0.0, 2.0, 3.0, and 5.0% by weight via ultrasonication method in a dispersive medium using ortho-xylene. The synthesized cobalt ferrite nanoparticles and their nanocomposites were characterized by impedance analyzer, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), and x-ray diffraction (XRD) techniques. The XRD indexed patterns confirmed the face-centered cubic structure of CoFe2O4/MWCNT nanocomposites. The average crystallite size in all the samples was in the range of 15 to 35 nm. The decorations of CoFe2O4 on MWCNTs were confirmed by SEM images. The FTIR results showed two vibrational bands. With the increasing contents of multi-walled carbon nanotubes in the cobalt ferrite/MWCNT nanocomposites, the dielectric properties were also enhanced. At 1 MHz, dielectric constant, dielectric loss, and tangent loss factor were increased from 26, 15.1, and 0.580 for pure cobalt ferrite to 47, 28.9, and 0.614 for loading of 5% MWCNTs, respectively. At 1 GHz, dielectric constant, dielectric loss, and tangent loss factor were increased from 11.6, 0.33, and 0.028 for pure cobalt ferrite to 19.4, 0.61, and 0.031 for loading of 5% MWCNTs, respectively. Such a huge increase in the dielectric properties of cobalt ferrite and multi-walled carbon nanocomposites exploited their applications at high frequency.

Dielectric and photo-catalytic studies of rapidly synthesized m-WO3 nano-particles

In this paper, monoclinic-WO3 nano-particles were successfully synthesized via co-precipitation method pursued by calcination at two thermal treatments 500 °C and 800 °C. Nyquist plots (Cole-Cole plot) and the tangent loss factor (tan δ) were discussed with frequency function in the range 1 Hz to 5 MHz for dielectric studies. Reduction in resistance and tangent loss factor has been observed in WO3 (800 °C) which is due to grain boundary contribution. Photocatalysis is attracting enormous attention towards addressing existing energy and environmental affairs via transforming visible light into chemical energy. For photocatalytic studies, MB dye was used as a toxic organic pollutant. Results shows that WO3 photo-catalyst calcined at 800 °C exhibits enhanced photocatalytic performance under visible light irradiation.

Temperature-dependent dielectric response of (1-x)PVDF/(x)BaTiO3 nanocomposite films

The PVDF/BaTiO3 nanocomposite films were prepared by solution casting method by using dimethylformamide as solvent. The dielectric constant and loss tangent of the PVDF and PVDF/BaTiO3 composites have been determined as functions of frequency (20 Hz–2 MHz) and temperature (80–425 K). A significant enhancement in dielectric constant ε′ is observed in composite samples. Tangent loss factor (tan δ) is maximum at lower frequencies due to interfacial polarization. In composite samples owing to the synthesis process, there is a phase transition in PVDF from α to β which results in the formation of dipolar relaxation. The dipolar nature of both the PVDF and PVDF/BaTiO3 nanocomposites is arrested below 200 K. The activation energy values (0.43–0.69 eV) associated with tan δ peak in the region 200–270 K are in agreement with the activation energy associated with a dipolar relaxation process. The relaxation time (τ) decreases with increasing BaTiO3 filler content while the number density of dipoles increases from 4.06 × 1021 cm−3 for pristine PVDF to 6.62 × 1023 cm−3 for (0.5)PVDF/(0.5)BaTiO3 composite and confirms a significant amount of dipolar relaxation in PVDF/BaTiO3 composites.

High porous carbon black based flexible nanocomposite as efficient absorber for X-band applications

The light weight and flexible nanocomposites comprising of high porous carbon black (CB) nanoparticles dispersed in the matrix of low density polyethylene (LDPE) are reported in this work as an efficient microwave absorbing materials for the X-band applications. The synthesized nanocomposites are characterized in terms of the x-ray diffraction and scanning electron microscopy analyses in order to understand the electromagnetic absorption process at micro level. The microwave scattering coefficients of the synthesized dielectric nanocomposites with various activated CB loadings are measured using the vector network analyzer, which are then used to extract the complex permittivity (ε) of these samples. The enhancement in the loss tangent factor with an increase in the activated CB loadings may be attributed to the elevated interfacial polarization at the activated CB - LDPE interface. The transmission line theory with metal backed condition is used to estimate the reflection losses in the synthesized nanocomposites. The minimum reflection loss of −17.54 dB at 10.05 GHz (maximum absorption of 98.24%) is achieved for 50 wt% activated CB/LDPE sample, while 10 wt% activated CB/LDPE sample offers the reflection loss of –9.24 dB at 10.22 GHz (maximum absorption of 88.08%) for common thicknesses of 2.4 mm. The synthesized nanocomposites (specific density ∼1.28 g/cc) with 50 wt% activated CB loading offers an outstanding absorption level in the X-band of microwave frequency and therefore can be used as light weight and flexible microwave absorber for X-band applications.

The mechanical properties of damping rubber reinforced by Wrap Knitted Spacer Fabric

Damping rubber, which is a blend of chlorinated isobutylene isoprene rubber (CIIR) and micromolecule resins (petroleum resins or rosin resins), was impregnated onto Wrap Knitted Spacer Fabric (WKSF) through solution method in order to produce damping rubber/WKSF composites. CIIR‐grafted–(maleic anhydride) (abbreviated as CIIR‐g‐MAH) was synthesized and used as a novel compatibilizer for damping rubber/WKSF composites. The loss tangent factor (tan δ) values decreased and the tan δ peak moved to a lower temperature after WKSF was added. The tensile strength of the damping rubber was improved significantly with the skeleton structure of WKSF. The addition of CIIR‐g‐MAH increased the tensile strength further. Interfacial shear strength showed strong interactive interface between the matrix and the polyethylene terephthalate (PET) fiber of WKSF after the addition of CIIR‐g‐MAH. Scanning electron microscopy showed the morphology of the fracture surface and the interfacial compatibilization mechanism was investigated. POLYM. COMPOS., 39:4434–4441, 2018. © 2017 Society of Plastics Engineers

Synthesis and characterization of a new hydrogen bonded side chain liquid crystal block copolymer and investigation of electrical properties

Abstract A new PEG-containing liquid crystalline side chain block copolymer HBC-PEG550 was prepared from poly(ethylene glycol)-b-poly(2-(diethylamino) ethyl methacrylate copolymer (BC-PEG550) and 8-(4-cyanobiphenyl-4′-oxy) octan-1-ol (LC8) by molecular self-assembly processes via hydrogen bond formation between amine group of HBC-PEG550 and hydroxyl group of the LC8. The formation of H bond was confirmed by using FTIR spectroscopy. The liquid crystalline behavior of the HBC-PEG550 was investigated by differential scanning calorimeter (DSC) and polarized optical microscopy. Dielectric properties of HBC-PEG550 and HBC-PEG550 has been studied by impedance spectroscopy. Real and imaginary parts of complex dielectric constant, impedance, and energy loss tangent factor for HBC-PEG550 and HBC-PEG550 have been characterized in the frequency range of 100 Hz–15 MHz.

Dielectric and gas transport properties of highly fluorinated polyimides blends

The physicochemical properties of highly fluorinated polyimide blends were studied in order to highlight the advantages of employing a high content of fluorine atoms to tailor the properties of polyimide materials. Thus, dynamo-mechanical analysis was used to evidence the physical phenomena taking place during heating. The trend of storage modulus, loss modulus and loss factor tangent with temperature during and after the α relaxation was explored. The dielectric spectroscopy was carried out to investigate the dielectric behaviour at different temperatures and frequencies and to evaluate the values of dielectric constant, dielectric loss and electrical resistance. The dielectric spectroscopy data were corroborated with the dynamo-mechanical analysis to highlight the sub-glass transitions encountered in these blend films. Dielectric loss diagrams showed sub-glass transitions in the form of γ and β relaxations mainly due to the segmental mobility of the polymer chain components. The gas separation performance of some of the investigated blends was assesed, and their ability to achieve simultaneously higher gas permeability and higher selectivity was demonstrated.

Mechanical, electrical and tribological properties of graphite filled polyamide-6 composite materials

Abstract In this study, the influence of adding graphite filler, on the mechanical, electrical and tribological properties of nylon-6 composites, is studied. Graphite fillers with different percentages, varying between 5 and 15 wt% were added to nylon-6 polymer material. Nylon-6 composite samples were prepared by the injection molding process. Tensile, impact, electrical and tribological tests were carried out and the dielectric permittivity tangent loss factor, tensile strength, modulus of elasticity, elongation at break, impact strength, specific wear rate and coefficient of friction properties were obtained. The results showed that the tensile strength, elongation at break, impact strength, and specific wear rate of nylon-6 composites, decrease with the increase in graphite filler weight ratio, while the modulus of elasticity, hardness, real part of dielectric permittivity, imaginary part of dielectric permittivity and dielectric loss, increase with increase in the filler weight ratio. Furthermore, it is observed that a rise in the relaxation time of ionic polarization is proportional to the increase in the amount of graphite in the medium and the dielectric conductivity and loss decrease proportionally after approximately 10 KHz. Finally, the maximum improvement in properties, in total, is recorded following the addition of 5 to 10 wt% graphite filler.

Dynamical and passive characteristics of the Ag/TlGaSeS/Ag RF resonators

AbstractAg contacts on the surface of the TlGaSeS single crystals are observed to exhibit Schottky characteristics. The ideality factor of the Ag/ TlGaSeS/Ag device decreased from 5.2 to 1.3 by the reduction of series resistance effect on the I‐V characteristics. Cheung's model analysis revealed a series resistance and barrier height of 40.6 KΩ and 0.32 V, respectively. The device was run on the passive mode by injection with an alternating ac signal of variable frequency in the frequency range of 0‐120 MHz and recoding the device capacitance. Several resonance‐antiresonance positions in the range of 27‐350 KHz were observed. The tangent loss factor of the passive device was observed to decrease with increasing frequency. It exhibited a very low loss value of the order of 10−5 at 120 MHz. Such property is a characteristic of high performance tunable device being suitable as processor clock controller.

Transport properties of lead phosphate glass doped by cobalt, vanadium and chromium oxides

The electrical transport properties were investigated of a glass system of basic composition 50 mol. % Pb3O4–50 mol. % P2O5 containing CoO, Cr2O3 or V2O5 dopanys. The ac conductivity and the thermoelectric power were measured as a function of temperature. Properties such as dielectric constant, loss factor tangent and electrical conductivity are reported in the frequency range 200 Hz–100 kHz and temperature range 300–450 K. The variation in electrical conductivity with temperature was found to depend on the types of transition metal ions involved. The temperature dependence of the frequency exponent, s, was analyzed using different theoretical models. The variation of the thermoelectric power with temperature indicated the presence of more than one conduction mechanism for the investigated samples. This result was confirmed with the results of the dielectric properties at different frequencies. The introduction of cobalt ions in glass formers improves the electrical properties of non-crystalline ionic conductors.

Optical, magnetic and electrical investigation of cobalt ferrite nanoparticles synthesized by co-precipitation route

Aluminum substituted cobalt ferrite nanoparticles CoFe 2− x Al x O 4 (for x = 0.00, 0.25, 0.50) have been synthesized by the chemical co-precipitation route. The average crystallite size was calculated using the Scherrer formula and found within 17–27 nm range. The optical absorption spectra of all the samples showed two clear electronic transitions, first is around 0.75 eV while the second at about 0.84 eV. The later is identified by means of 4A 2 → 4T 1 ( 4F) transition while the former is attributed to the overlapping of the 4A 2 → 4T 1 ( 4F) transition of the tetrahedral Co 2+ ions and the Co 2+ + Fe 3+ → Co 3+ + Fe 2+ metal–metal charge transfer transition. The saturation magnetization at room temperatures was found to be 61.50 emu/g for pure CoFe 2O 4 nanoparticles, while it decreased with increasing Al 3+ concentration up to 52.00 emu/g (for x = 0.50). The Curie temperature was determined from AC magnetic susceptibility measurement. It was observed that Curie temperature decreased with Al 3+ concentration ( x) and DC electrical resistivity decreased with increase in temperature. Activation energy and drift mobility have been calculated from the temperature dependent DC electrical resistivity measurements for all the samples. The variation of dielectric constant, dielectric loss and tangent loss factor for all the samples have been studied as a function of frequency in the range 600 Hz to 1 MHz at room temperature.

Dielectric Relaxation of New Aniline Methyl Methacrylate Copolymer Synthesized by Gamma Irradiation Initiated Polymerization

A new copolymer based on gamma radiation initiated polymerization of methyl methacrylate in the presence of aniline was prepared for potential applications in electric fields. The electrical properties of the new material, such as permittivity, relaxation time and ac conductivity, were compared to the properties of poly(methyl methacrylate). The frequency and irradiation dose dependency of the loss tangent factor and dielectric constant showed a Debye dielectric relaxation process. The main objective of the dielectric investigation in this study was to provide a better understanding for the correlated hopping electron process involved in the conduction. On the other hand, for the ac conductivity, at room temperature, there was a deviation in the conduction mechanism of the correlated barrier hopping of electrons between paired and random defects. This deviation showed a maximum value for aniline methyl methacrylate copolymer irradiated at a dose of 30 kGy. The analysis of the data of the dielectric loss showed a well-defined peak at a frequency assigned to dipole relaxations in the system. The results indicated that the gamma irradiation results in the formation of some traps in the energy gap, which reduce the movement of the charge carriers. Also it can be stated that aniline acts as an effective protection agent against structural damage caused by gamma radiation in the copolymer matrix.