Search

The macromolecular dynamics of dendronized copolymer membranes (PECHs), obtained by chemical modification of poly(epichlorohydrin) with the dendron 3,4,5-tris[4-(n-dodecan-1-yloxy)benzyloxy] benzoate, was investigated. In response to a thermal treatment during membrane preparation, these copolymers show an ability to change their shape, achieve orientation, and slightly crystallize, which was also observed by CP-MAS NMR, XRD, and DSC. The phenomenon was deeply analyzed by dielectric thermal analysis. The dielectric spectra show the influence of several factors such as the number of dendritic side groups, the orientation, their self-assembling dendrons, and the molecular mobility. The dielectric spectra present a sub-Tg dielectric relaxation, labelled as γ, associated with the mobility of the benzyloxy substituent of the dendritic group. This mobility is not related to the percentage of these lateral chains but is somewhat hindered by the orientation of the dendritic groups. Unlike other less complex polymers, the crystallization was dismantled before the appearance of the glass transition (αTg). Only after that, clearing transition (αClear) can be observed. The PECHs were flexible and offered a high free volume, despite presenting a high degree of modifications. However, the molecular mobility is not independent in each phase and the self-assembling dendrons can be eventually fine-tuned according to the percentage of grafted groups.

Thermal conductive gap filler materials are used as thermal interface materials (TIMs) in electronic devices due their numerous advantages, such as higher thermal conductivity, ease of use, and conformity. Silicone is a class of synthetic materials based on a polymeric siloxane backbone which is widely used in thermal gap filler materials. In electronic packages, silicone-based thermal gap filler materials are widely used in industries, whereas silicone-free thermal gap filler materials are emerging as new alternatives for numerous electronics applications. Certainly, characterization of these TIMs is of immense importance since it plays a critical role in heat dissipation and long-term reliability of the electronic packages. Insubstantial studies on the effects of various chemical compounds on the properties of silicone-based and silicone-free TIMs has led to this study, which focuses on the effect of thermal aging on the mechanical, thermal, and dielectric properties of silicone-based and silicone-free TIMs and the chemical compounds that cause the changes in properties of these materials. Characterization techniques such as dynamic mechanical analysis (DMA), thermomechanical analysis (TMA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and broadband dielectric spectroscopy (BbDS) are used to study the mechanical, thermal, and dielectric characteristics of these TIMs, which will guide towards a better understanding of the applicability and reliability of these TIMs. The experiments demonstrate that upon thermal aging at 125 °C, the silicone-free TIM becomes hard, while silicone-based TIM remains viscoelastic, which indicates its wide applicability to higher temperature applications for a long time. Though silicone-based TIM displays better mechanical and thermal properties at elevated temperatures, dielectric properties indicate low conductivity for silicone-free TIM, which makes it a better candidate for silicone-sensitive applications where higher electric insulation is desired.

Aging of the relaxors and PbMg1/3Nb2/3O 3 in particular was extensively studied in last two decades. Most of the results were related to the low temperature glass-like region. No systematic data around the freezing temperatures were reported. To cover this still missing information we have studied the evolution of the dielectric spectra in the broad frequency region from 10 -1  Hz to 10 6  Hz both below and above the freezing temperatureTf≈240 K. Below freezing temperature the existence of the earlier reported waiting time-frequency scaling at frequencies below ≈50 Hz is confirmed. At higher frequencies this deviation from the scaling is observed that can be tentatively attributed to the complexity of the relaxing entities. Above T f aging is observed only in the restricted frequency interval below the maximum of the dielectric loss spectrum. The observed effect can be attributed to the hardening and narrowing of the dielectric loss spectra and decreasing of the dielectric strength with time. The explanation is proposed based on the concept of the creation of the degenerate polar nanoregions covering several chemically ordered regions (COR) (multi PNRs-MPNRs). These MPNRs are large compare to the PNRs located at the single CORs and some of them may become frozen resulting in the described spectra changes., (© 2023 IOP Publishing Ltd.)

Epoxy nanocomposites are promising materials for industrial applications (i.e., aerospace, marine and automotive industry) due to their extraordinary mechanical and thermal properties. Here, the effect of hollow halloysite nanotubes (HNT) on an epoxy matrix (Ep) was the focus of the study. The structure and molecular mobility of the nanocomposites were investigated using a combination of X-ray scattering, calorimetry (differential (DSC) and fast scanning calorimetry (FSC)) and dielectric spectroscopy. Additionally, the effect of surface modification of HNT (polydopamine (PDA) and Fe(OH)3 nanodots) was considered. For Ep/HNT, the glass transition temperature (Tg) was decreased due to a nanoparticle-related decrease of the crosslinking density. For the modified system, Ep/m-HNT, the surface modification resulted in enhanced filler–matrix interactions leading to higher Tg values than the pure epoxy in some cases. For Ep/m-HNT, the amount of interface formed between the nanoparticles and the matrix ranged from 5% to 15%. Through BDS measurements, localized fluctuations were detected as a β- and γ-relaxation, related to rotational fluctuations of phenyl rings and local reorientations of unreacted components. A combination of calorimetry and dielectric spectroscopy revealed a dynamic and structural heterogeneity of the matrix, as confirmed by two glassy dynamics in both systems, related to regions with different crosslinking densities.

There is an urgent need for the development of elastic dielectric materials for flexible organic field effect transistors (OFETs). In this work, detailed analysis of the AC and DC electrical conductivity of a series of flexible poly(dimethylsiloxane) (PDMS) polymers crosslinked by metal-ligand coordination in comparison to neat PDMS was performed for the first time by means of broadband dielectric spectroscopy. The ligand was 2,2-bipyridine-4,4-dicarboxylic amide, and Ni2+, Mn2+, and Zn2+ were introduced for Cl−, Br−, and I− salts. Introduction of metal salt and creation of coordination bonds resulted in higher permittivity values increasing in an order: neat PDMS < Ni2+ < Mn2+ < Zn2+; accompanied by conductivity values of the materials increasing in an order: neat PDMS < Cl− < I− < Br−. Conductivity relaxation time plot as a function of temperature, showed Vogel-Fulcher–Tammann dependance for the Br− salts and Arrhenius type for the Cl− and I− salts. Performed study revealed that double-edged challenge can be obtained, i.e., dielectric materials with elevated value of dielectric permittivity without deterioration too much the non-conductive nature of the polymer. This opens up new perspectives for the production of flexible dielectrics suitable for gate insulators in OFETs. Among the synthesized organometallic materials, those with chlorides salts are the most promising for such applications.

Single-phase CuMoO 4 samples were prepared by a modified sol-gel method, and the functional relationship between dielectric properties of the samples and temperature (−130 °C–150 °C) or frequency (1 Hz–10 MHz) was investigated by measuring the dielectric spectrum. The temperature dependence of ε ́ and tan δ can determine the first-order phase transition (γ→α) in the CuMoO 4 material. Three thermally activated relaxations were observed in the frequency dependence of tan δ and M ́ ́. The results show that relaxation 1 is related to the hopping motion of partial charge carriers between Cu2+ and Cu+, so this relaxation of the low-temperature segments is attributed to polarization relaxation. Relaxation 2 and relaxation 3 are dominated by the oxygen vacancy motion, where relaxation 2 is due to a movement of singly ionized oxygen vacancies and relaxation 3 is the result of an ordered movement of doubly ionized oxygen vacancies. • The transition process from γ phase to α phase for CuMoO 4 is observed by dielectric means for the first time. • The dielectric relaxation mechanisms of CuMoO 4 related to oxygen vacancies and polarons are first proposed. • All research results open a new path for research methods and defect transmission mechanisms of related materials. [ABSTRACT FROM AUTHOR]

Electrodeposition technique is employed to prepare cuprous oxide (Cu2O) thin film on fluorine-doped tin oxide (FTO) conducting glass substrate through the reduction of copper lactate in alkaline solution at pH = 12.25. Structural, optical and dielectric properties of the prepared film is investigated by means of scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), UV–Visible absorbance, photoluminescence (PL) and broadband dielectric spectroscopy (BDS). The structural means (XRD, SEM and EDS) revealed the formation of self-assembled cubic microstructure of Cu2O with average grain size of around 1.5 μm. The UV–Vis absorbance spectrum gives optical band gap of 2.05 eV. The PL spectrums confirmed the presence of defect centers ascribed to various forms of oxygen (V O 1 + , V O 2 +) and copper ( V Cu 1 + ) vacancies which are responsible for the conduction in the Cu2O film. The conduction mechanism in the Cu2O film is successfully described by the correlated barrier hopping (CBH) model in which bipolaron hopping become prominent. The density of defect states N, the effective barrier height W and the hopping distance Rω are also calculated based on the CBH model. Two dielectric relaxation processes (β1 and β2) with Arrhenius temperature dependence and activation energies of 0.31 and 0.48 eV are observed. The fast β2-relaxation process with activation energy of 0.48 eV is attributed to the Maxwell–Wagner-Sillars (MWS) polarization while the slow β1-relaxation process with activation energy of 0.31 eV is due to the hopping of the oxygen and copper vacancies. [ABSTRACT FROM AUTHOR]

NiO thin films with different annealing temperature and films thickness were fabricated by magnetron sputtering on the Pt/TiO x /SiO 2 /Si substrates. The XRD results show the crystallinity of films can be improved with the annealing temperature and films thickness increased. While the preferential orientation is affected by annealing temperature and films thickness. The SEM results show that the average size of the needle like grains shape increases gradually from 42.4 nm to 72.5 nm and the grains of films are seen to be more uniform, with a smoother and finer morphology with film thickness increasing. XPS measurements show that two valence states of Ni2+ and Ni3+ exist in NiO films with the Ni2+/ Ni3+ ratio 1.01. However, the Ni3+ refers to the structure that contains Ni2+ ions with holes and not to Ni 2 O 3 phase as observed from the XRD results and the O1s XPS spectra, making the grains conductive due to plenty of holes. It results the grains have a key contribution to dielectric behavior. The frequency domain spectroscopy shows the films thickness and annealing temperature have a significance influence on the dielectric constant and dielectric loss tangent. And the preferential orientation of NiO films play a non-negligible impact on the dielectric performance due to the polarized NiO (111) plane. • The NiO thin films with different annealing temperature and films thickness were fabricated by magnetron sputtering on the Pt/TiO x /SiO 2 /Si substrates. • The effect of films thickness on the surface morphology, preferential orientation and dielectric property were discussed. • The preferential orientation of NiO films play a non-negligible impact on the dielectric performance due to the polarized NiO (111) plane. • The NiO films undergo a texture transition from (220) to (111) crystallographic orientation with the annealing temperature rising. [ABSTRACT FROM AUTHOR]

The main purpose of this article is the in vitro study of elastin from the bovine neck ligament using dielectric spectroscopy in the alpha electric field dispersion region in the temperature range from 22 to 200 °C. The temperature dependence of the relative permittivity of wet elastin indicates a maximum of about 50 °C due to the thermal decomposition of loosely bound water, as well as a rapid decrease in this parameter above 185 °C. For a dry elastin, the change in relative permittivity with temperature represents only one peak of high temperature around 185 °C, corresponding to the glass transition temperature (Tg). Below Tg, the activation energy of conductivity for wet and dry elastin at 50 kHz, responsible for the breaking of hydrogen bonds between bound water molecules and hydrophilic polar groups of the main elastin chains, is 27 and 11 kJ mol−1, respectively, and above Tg, corresponding activation energy values associated with relaxation of the main chain increase to 72 and 34 kJ mol−1. In this article, dielectric processes related to the glass transition temperature, especially in the case of dry elastin, can play an important role in the use of solid-state elastin as a biomaterial for various tissue engineering applications. [ABSTRACT FROM AUTHOR]

Single phase Ca-substituted W-type hexaferrites Sr1-xCaxZn2Fe16O27(x = 0.00(0.25)1.00) have successfully been synthesized by using sol–gel self-combustion at 1300°C. These hexaferrites are investigated by x-ray difrractometry (XRD), scanning electron microscopy, energy dispersive x-ray spectroscopy, Fourier transform infrared spectroscopy, vibrating sample magnetometry, and vector network analysis. XRD analysis confirms the formation of a single W-type hexaferrites phase. The DC electrical resistivity increases with incrementing Ca contents. The morphology of all the hexaferrites shows hexagonal platelet-like structure. The prepared ferrites depict soft magnetic nature with high saturation magnetization, low coercivity and enhanced magnetic moments. The complex parameters such as complex permittivity and permeability decrease with the increasing Ca content. The prepared samples show good quality factor of 3 at 6 GHz, AC conductivity changes from 0.9 S/m to 0.5 S/m, and tangent loss decreases from 0.5 to 0.34 with Ca substitution. These improved characteristics make these hexaferrites valuable for devices such as microwave absorbers operated at higher frequencies. [ABSTRACT FROM AUTHOR]

The local and cooperative dynamics of atactic PS (a‐PS) were studied by broadband dielectric relaxation spectroscopy (BDRS) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR‐FTIR). The a‐PS has been subjected to thermal rejuvenation and subsequent quenching, short‐term aging (6 weeks), and long‐term aging (1 year) at ambient conditions. Where for the rejuvenated sample only an α‐ and a γ‐relaxation is observed, short‐term aging results in an additional β*‐relaxation that merges with the α‐relaxation at longer aging times. The γ‐relaxation is increasing in intensity and activation energy during aging. The α‐process shows no spectral changes and shift in the relaxation time upon aging. This may be attributed to a possible erasure of history of the material during the temperature‐sweep mode measurement. Fourier transform infrared spectroscopy (FTIR) results suggest that the energetically favorable trans‐trans (tt) conformers are increased in population with aging. © 2019 The Authors. Journal of Polymer Science Part B: Polymer Physics published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1394–1401 [ABSTRACT FROM AUTHOR]

The Sr 2 Bi 4 Ti 5 O 18 (SBT-5) ferroelectric thin films were prepared on Pt/Ti/SiO 2 /Si substrate using the sol-gel method and annealing in oxygen, air, and nitrogen. Their properties were measured. After annealing in oxygen, the films showed good crystallization and a larger average grain size of approximately 34.05 nm. XPS analysis clearly showed that annealing in oxygen inhibited the generation of oxygen vacancies in the films, which contributed to the melioration of the ferroelectric properties. The remanent polarization was 20.09 μC/cm2 and the coercive field was 75 kV/cm. When the electric field was 15 kV/cm, the leakage current density was approximately 3.88 × 10−7A/cm2, while the Ohmic conduction was the dominating leakage mechanism. Because the content of the oxygen vacancy in the samples annealed in oxygen atmosphere was lower, the fixing effect on the domain structure was weaker and the volume effect was not obvious, so the aging degree of the samples was low. The larger relative dielectric constant was 742, while the dielectric loss was 0.037 when the test frequency was 2.0 × 105 Hz. [ABSTRACT FROM AUTHOR]

The ac conductivity and dielectric response of bulk vanadyl 2,3-naphthalocyanine (VONPc) were investigated from 1 Hz to 106 Hz, at temperatures range from 288 K to 403 K. Thermal stability of the material was studied using thermogravimetric analysis (TGA). The structure phase was investigated using X-ray diffraction (XRD). The total conductivity was found to follow the universal power low σ(ω,T) = σ dc + Aωs. A temperature dependence and values greater than unity (super linear behavior) of the exponent factor s were found. Various types of activation energies were calculated and discussed. The calculated values of activation energies were found to be 0.27 eV, 0.23 eV and 0.21 eV for bulk conductivity (E b), dc conductivity (E dc) and relaxation process (E τ), respectively. The best conduction mechanism model that fit the observed exponent factors' values and behavior is the jump relaxation model as described by Funke. The real and the imaginary parts of the dielectric constant was observed to decrease as the frequency increases. The recorded value of the dielectric constant at high frequency is 3.3. • Ac conductivity and dielectric response of bulk vanadyl 2,3-naphthalocyanine (VONPc) were investigated using impedance spectroscopy technique. • Very good thermal stability up to 500 ᵒC was found. • Bulk conductivity, dc conductivity and the relaxation process activation energies were calculated. • Super linear frequency (s >1) and a temperature dependent of the frequency exponent factor. • The jump relaxation model as proposed by Funke was used to explain the conduction mechanism inside the material. [ABSTRACT FROM AUTHOR]

Dielectric relaxation studies of rat tail tendon collagen with anionic sodium dodecyl sulphate (SDS), cationic cetyltrimethyl ammonium bromide (CTAB) and nonionic Tween 80 in aqueous buffer solutions at four different temperatures have been carried out in the frequency range 1 GHz to 25 GHz using time domain dielectric spectroscopy. The frequency dependent normalized dielectric modulus function P of the collagen and surfactant solutions show up as peaks around 1–2 GHz which is due to the bound water around collagen macromolecule and surfactant micelles. For the collagen – surfactant complexes, the peak in normalized dielectric modulus function P is shifted towards high frequency side near 2–3 GHz upon addition of surfactants to collagen in buffer solution. The water structure around collagen is altered in the presence of micelle forming surfactant additives and this change may affect the degrees of freedom of their motion. Hence the significant changes are observed in the relaxation time of bound water around collagen macromolecule in the presence of surfactants. Further, it was observed that no considerable change in relaxation time of hydration water of the complexes with respect to change in temperature within the studied temperature range. The activation enthalpy and activation entropy for the dipolar orientation corresponding to the free water for the surfactants and their complexes with collagen have been calculated from the Arrhenius plot. Our thermodynamic results suggest that the two‑hydrogen-bonded model may be possible in SDS and Tween 80 environments, whereas the one‑hydrogen-bonded model is likely to be possible in buffer and CTAB environments. [ABSTRACT FROM AUTHOR]

We present the preparation of polystyrene-polyaniline composites by an emulsion polymerization technique. Polyethylene glycol and dodecylbenzenesulfonic acid were used as nonionic and anionic surfactants, respectively, for emulsion preparation. Fourier transform IR spectroscopy, UV–vis spectroscopy, and thermogravimetric analysis were used to characterize the composites obtained. Surface morphological investigations by scanning electron microscopy showed that the emulsion technique using polyethylene glycol produces the most homogeneously distributed composites. Thermal analysis in conjugation with broadband dielectric spectroscopy revealed that as the composite conductivity increased, the temperature at which the maximum degradation rate was achieved gradually decreased. The dielectric investigation showed the α-relaxation process in pure polystyrene has an activation energy of 10.8 kJ/mol and is accompanied by a dielectrically determined glass transition temperature of about 366 K. After addition of polyaniline, this α-relaxation process was masked by the conductivity contribution. Moreover, polyaniline prepared with the anionic surfactant had higher electrical conductivity than that prepared with the nonionic surfactant because of its ordering effect on the structure. Surprisingly, the dependence of the conductivity of the composites on temperature, regardless of the preparation method, has two different trends, and each can be attributed to a different mechanism of charge transport. • The conductivity mechanism in polyaniline composites is the same whatever the type of the other polymer in the composite. • The conductivity mechanism in polyaniline composites is the same whatever the preparation method. • DC conductivity of polyaniline composites have low activation energy below 50 C, which become higher between 50 and 100 C dependent on moisture. • Various techniques (FTIR, UV-vis and TGA) were used for qualitative investigation of polyaniline composites conductivity. [ABSTRACT FROM AUTHOR]

In this paper, we employed Broadband Dielectric Spectroscopy (BDS) in order to determine the effect of the high pressure on the solubility limits of the amorphous flutamide within Kollidon VA64 matrix. In order to achieve this goal, drug-polymer systems have been examined: (i) at ambient pressure and both isothermal and nonisothermal conditions by means of BDS as well as Differential Scanning Calorimetry (DSC), to validate proposed method; (ii) at high pressure conditions (20 and 50 MPa) and elevated temperatures (343 K, 353 K and 363 K) by means of dielectric spectroscopy. Our studies revealed that regardless of applied pressure the solubility of the flutamide within the co-polymer matrix increases with increasing temperature at isobar conditions. Moreover, our results clearly indicate that with increasing pressure the solubility of the drug within the polymer matrix is decreasing at isothermal conditions. Therefore, during the solubility limit studies one should consider the situation in which by increasing the pressure (at constant temperature) would achieve an effect similar to the lowering of the temperature (at constant pressure). [ABSTRACT FROM AUTHOR]

Two thermoset systems based on maleimides and diglycidyl ether of bisphenol A (DGEBA) cured with p‐aminobenzoic acid were characterized in terms of thermal and electrical behavior. Thermal characterization has been undertaken by means of thermogravimetric analysis in nitrogen atmosphere up to 600°C using simultaneous thermogravimetric/Fourier transform infrared/mass spectrometry (TG/FT‐IR/MS) analysis. In the first stage of thermal degradation, the global kinetic parameters [activation energy (Ea) and preexponential factor (log A1 (s−1))] were calculated using the isoconversional method of Friedman. The energies variation as well as the shape of the differential thermal analysis curves suggests that the thermal decomposition process occurred in multiple stages. The evolved gases analysis was conducted by simultaneous TG/FT‐IR/MS coupled techniques. Dielectric relaxation spectroscopy characterization was also made. [ABSTRACT FROM AUTHOR]

Dielectric relaxation measurements on water–ethanolamine solvent mixtures have been carried out across the entire concentration range using Time Domain Reflectometry technique at 288 K, 298 K, 308 K, and 318 K over the frequency range from 10 MHz to 20 GHz. The mixtures exhibit a principle dispersion of the Davidson-Cole relaxation type at microwave frequencies. Bilinear calibration method is used to obtain complex permittivity ε*(ω) from complex reflection coefficient ρ*(ω) over the frequency range 10 MHz to 10 GHz. The excess permittivity (εE), excess inverse relaxation time (1/τ)E, Kirkwood correlation factor (geff) and thermodynamic parameters are also calculated to study the Solute-Solvent interaction. [ABSTRACT FROM AUTHOR]

This work allowed us to develop a new organic–inorganic hybrid chlorocadmate(II) of the formula (C 4 H 12 NO 3)CdCl 3 ·H 2 O. Single crystal X-ray diffraction shows that the complex crystallizes in the triclinic system with the P 1 ¯ space group. Hirshfeld surface analysis suggests that the stability of the material is ensured by hydrogen bonds. The IR and Raman spectra of the compound were studied. Dielectric studies confirm the thermal measurements. A new organic–inorganic hybrid centrosymmetric compound, (C 4 H 12 NO 3)CdCl 3 ·H 2 O, was synthesized by the slow evaporation method at room temperature and characterized by single X-ray diffraction (SCXRD). The results of the X-ray diffraction study demonstrated that this material crystallizes in the triclinic system with the space group P 1 ¯ and the following unit cell parameters a = 6.822(6) Å, b = 8.96(2) Å, c = 10.034(3) Å, α = 72.901(3)°, β = 71.927(3)°, γ = 89.099(3)° and Z = 2. In the crystal structure, the atomic arrangement is described as an alternation of organic and inorganic layers along the a-axis. The anionic layers are formed by [CdCl 5 O]− octahedrons, while the cationic layers are made up of [C 4 H 12 NO 3 ]+ cations. The crystal packing is governed by N H⋯Cl, N H⋯O, C H⋯Cl, O H⋯Cl and O H⋯O hydrogen bonds, forming a three dimensional supramolecular network. Hirshfeld surfaces and 2D fingerprint plots were determined for visualizing, exploring and quantifying the intermolecular interactions in the crystal lattice of the title compound. Infrared and Raman spectroscopy were reported at room temperature in the frequency domains 400–4000 cm−1 and 50–500 cm−1, respectively. Differential scanning calorimetry (DSC) revealed one exothermic peak located at around T 1 = 368 K. Electrical and dielectric properties were investigated as a function of temperature (300–430 K) in the frequency range 40 Hz–110 MHz. The electrical and dielectric studies were performed by means of impedance spectroscopy and dielectric permittivity ε ' , ε ' ' . Nyquist curves were well fitted to an equivalent circuit formed by parallel combination resistance and capacity fractal of the bulk. The frequency dependence of the alternative current (AC) conductivity was analyzed using the Jonscher law. Overlapping-large polaron tunneling (OLPT) and non-overlapping small polaron tunneling (NSPT) conduction mechanism models successfully explained the behavior of the exponent n. [ABSTRACT FROM AUTHOR]

Dual-frequency liquid crystal materials are used in fast response electrooptic modulators in different devices for digital information displaying and processing. In an NLC mixture 2f-3333 (ROLIC, Switzerland) there are components with lateral dipole moment. Their molecular relaxation is investigated by a method of dielectric spectroscopy. Values of relaxation time and its activation energy, molecular friction coefficient, rotational diffusion are obtained. They are compared with data obtained by other methods like LC viscosimetry. [ABSTRACT FROM AUTHOR]

An electrically conducting two-component BeO-ceramic with the addition of micro- and nano-crystalline TiO2 powder is prepared that can be used as a material for scattered microwave radiation absorption in high-power electronic devices. The nature of the occurrence of electrical conductivity and absorption of the microwave field in (BeO + TiO2)-ceramics is not completely established. Impedance spectroscopy is used for the first time to investigate the electrical and dielectric characteristics of this ceramic in the frequency range from 100 Hz to 100 MHz in relation to presence of micro- and nano-sized TiO2 phase within the BeO ceramic composition. It is established that the static resistance of ceramics with addition of a TiO2 nanopowder is significantly reduced compared with the resistance of original ceramic with TiO2 micropowder. It is shown that real and imaginary components of the dielectric constant of the ceramic studied increase to abnormally large values with a reduction in frequency of the effective electric field, and in the high frequency range f ≥ 108 Hz the process of dielectric relaxation commences leading to an increase in dielectric loss angle. Dielectric properties of ceramic samples are determined under blocking conditions for through conduction. The effect of TiO2 micropowder additions on dielectric polarization processes with frequency increasing up to 12 × 109 Hz is considered. [ABSTRACT FROM AUTHOR]

The new iron-fluoride, based on bipyridine formulated as FeF 3 (2,2′-bpy) (2,2′-bpy = 2,2′-bipyridine), was obtained by hydrothermal synthesis. The crystalline structure was characterized by single crystal X-Ray diffraction data analysis. It crystallizes in monoclinic space group Cc , with a = 14.030(4) Å, b = 9.487(3) Å, c = 7.650(2) Å and β = 103.287(3)º. Moreover, it exhibits three-dimensional organic-inorganic network, resulting from the association of [FeF 4 N 2 ] ∞ chains pertaining to corner sharing FeF 4 N 2 octahedra extending along with the c-axis linked through weak C–H...F hydrogen bonds. The thermal analysis (TG, SDTA and DSC) of the title compound reveals the presence of the phase transitions at high temperature. In order to shed light on the electrical conductivity and dielectric properties of the title compound, we carried out, in the frequency range 200 to 2E5 Hz, impedance spectroscopy technique, in the temperature range 310–380K. The conductivity relaxation parameters of some H+ conducting in the FeF 3 (2,2′-bpy) material were determined from an analysis pertaining to electric conductivity data. Transport properties in this material appear due to proton hopping mechanism. Finally, the optical properties were evaluated by photoluminescence spectroscopy. Image 1 • A novel iron fluoride is determined by single crystal X-ray diffraction. • Thermal decomposition was studied by TG- SDTA and DSC. • The dielectric study reveals the phase transitions at high temperature. • Vibrational properties were studied by IR and Raman spectroscopy. [ABSTRACT FROM AUTHOR]

We propose a setup enabling electron energy loss spectroscopy to determine the density of the electrons accumulated by an electropositive dielectric in contact with a plasma. It is based on a two-layer structure inserted into a recess of the wall. Consisting of a plasma-facing film made out of the dielectric of interest and a substrate layer, the structure is designed to confine the plasma-induced surplus electrons to the region of the film. The charge fluctuations they give rise to can then be read out from the backside of the substrate by near specular electron reflection. To obtain in this scattering geometry a strong charge-sensitive reflection maximum due to the surplus electrons, the film has to be most probably pre-n-doped and sufficiently thin with the mechanical stability maintained by the substrate. Taking electronegative CaO as a substrate layer we demonstrate the feasibility of the proposal by calculating the loss spectra for Al2O3, SiO2, and ZnO films. In all three cases we find a reflection maximum strongly shifting with the density of the surplus electrons and suggest to use it for charge diagnostics. [ABSTRACT FROM AUTHOR]

Gelcasting is a method which allows for the production of high-quality ceramic-metal composites. In this work, the problem of local polymerisation in gelcasting of alumina-tungsten composite and metal influence on activation energy of glycerol monoacrylate was investigated. The broadband dielectric spectroscopy method was used for the first time to study the kinetics of gelation in ceramic processing. Polymerisation reaction rates constant of pure monomer, and monomer with ceramic and the metal filler, within the temperature range from 313 K to 333 K were determined. The obtained results were compared with rheological measurements. The calculated activation energy of polymerisation for monomer with 0.5 vol% of tungsten is 66 kJ/mol in comparison to a pure monomer which is 290 kJ/mol. This indicates the catalytic influence of metal on the polymerisation. Therefore, in the alumina suspension with tungsten polymerisation begins near the surface of the metal particles resulting in polymer structure inhomogeneity and lower mechanical properties of green bodies. [ABSTRACT FROM AUTHOR]

CaCu2.8Ni0.2Ti4O12 ceramics were elaborated using the solid-state reaction technic. The pellets were annealed at 1000 °C for 24 h. The X-ray diffraction (XRD) analysis proves the main phase formation of our sample crystallize in the cubic structure with Im 3 ¯ space group. The diffuse reflectance analysis allow us to calculate the optical band gap energy which is equal to 3.172 eV. The dielectric properties of our compound were studied using complex impedance spectroscopy showing a lowering in dielectric loss (tan δ = 0.07) at 1 kHz and at room temperature. The impedance studies reveal the presence of temperature dependent dielectric relaxation. Thus, the electrical modulus studies show that the relaxation is associated with grain boundaries effects. The activation energy calculated from the electric modulus spectra, related to the electrical relaxation, is found to be 0.60 eV. This result suggests the hopping mechanism of oxygen vacancies produced at grain boundaries in relaxation processes. [ABSTRACT FROM AUTHOR]

In this work, the dielectric properties of nanocomposites based on poly(2,2,2‐trifluoroethyl methacrylate) copolymer (PMATRIF) and vinylbenzyl‐functionalized montmorillonite (MMT) nanoparticles prepared via in situ free radical polymerization were studied. The effect of different loadings of (MMT) filler (in weight ratios of 1, 3, and 5%) on the molecular dynamics and polarization of PMATRIF was investigated using broadband dielectric spectroscopy from 10−1 to 106 Hz and at temperatures between 20 and 170°C. For PMATRIF matrix, the real part ε′ and the imaginary part ε″ of the dielectric permittivity curves revealed four dielectric processes β, α, αβ, and ionic conduction phenomenon. Furthermore, it was found that incorporating MMT led to an increase in the dielectric losses and generated additional relaxation processes known as Maxwell–Wagner Sillars polarization. Calculation of the activation energy for the different processes revealed that α relaxation followed the Vogel–Fulcher–Tammann–Hesse dependency while the other processes were suitably fitted with the Arrhenius law. In order to probe matrix/MMT interface properties, dielectric strength of the interfacial polarization Δε is calculated by fitting the dielectric permittivity through the known Havriliak–Negami model. POLYM. COMPOS., 40:3333–3341, 2019. © 2018 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

As a donor and acceptor separately, Nb5+ and Al3+ are used to substitute Ti4+ in the ixiolite ZnTiNb2O8 system for the first time. The dielectric responses in the terahertz range of this system are initially studied based on the data from terahertz time‐domain transmitted spectroscopy. Combined with ligand field theory, the formation of a secondary phase of ZnAl2O4 is reasonably explicated. Then, the origins of the lower dielectric loss and the terahertz wave absorption coefficient are determined to be the high chemical bond covalency and effective phase control. For the composition of ZnTi0.85(Al0.5Nb0.5)0.15Nb2O8 sintered at 1180°C, a low dielectric loss (<5 × 10−3 @ 0.5 THz) and absorption coefficient (<10/cm @ 0.5 THz) are obtained, which make this kind of material propitious for developing terahertz dielectric devices. [ABSTRACT FROM AUTHOR]

Composite systems of epoxy resin and SrTiO3 nanoparticles have been prepared and studied in different filler concentrations. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) revealed that there was a successful filler integration and fine dispersion in the polymer matrix. Moreover, Broadband dielectric spectroscopy (BDS) was employed for the determination of the dielectric response of all manufactured systems. Dielectric results divulge three relaxation processes which are referred to: (a) glass to rubber transition of the polymer matrix (α-mode), (b) re-arrangement of polar side groups of the polymer matrix (β-mode) and (c) interfacial polarization between systems' components. It was found that all nanodielectric systems exhibit enhanced dielectric properties which are mainly attributed to the semiconductive nanoinclusions and to the extended interface between the polymer matrix and the nanofiller. Finally, dynamic analysis of the relaxation processes was also performed. Vogel–Fulcher–Tammann equation describes the α-mode's loss peak dependence on temperature, whereas the β-mode follows the Arrhenius expression. In case of β-mode it was found that the presence of the nanoinclusions hinders the orientation of the matrix's polar side groups. [ABSTRACT FROM AUTHOR]

A survey of relaxation processes in glasses exhibiting ionic and electronic–ionic conductivity mechanisms is presented. Electrical conductivity and dielectric properties are investigated using complex impedance spectroscopy in a frequency range from 0.1 to 106 Hz and a temperature range from 253 to 423 K. The results reveal that ionic conduction depends on the alkali concentration and ion mobility while electrical conduction is only slightly influenced by alkali ions and a mixed electronic–ionic conduction can occur. The Jonscher's expression of ac electric conductivity is modified by adding a new term taking into account the displacement current density associated with the dielectric relaxation. The change in the activation energy depends upon the chemical composition indicating a changeover of the predominant conduction mechanism from ionic to polaronic. Quantum mechanical tunneling (QMT) model was suggested to describe the conduction mechanism of alkali-silicate glass G1 where frequency exponent s < 1. However, small polaron tunneling (SPT) model was applied to describe conductivity of semiconductor glass G2 (alkali-silicate glass with iron ions) with s > 1, whose conduction mechanism may be considered in terms of the optical phonon assisted hopping of small polarons between overlapping states. The electrical modulus exhibited relaxation character. [ABSTRACT FROM AUTHOR]

We report the magnetic and dielectric behavior of multiferroic bismuth ferrites synthesized using milling-annealing processes and tailored through the crystallite size reduction and the microstrain generated by mechanical milling. For synthesis, stoichiometric mixtures of Bi 2 O 3 and Fe 2 O 3 were mixed and milled for 5 h using a ball to powder weight ratio of 10:1 by high-energy ball milling and annealed at 650 °C. Subsequently, was carried out the Crystallite Size Reduction by Milling-Process at different milling times, in a range of 0–60 min, using a ball to powder weight ratio of 50:1 adding 5% wt. of methanol. X-ray diffraction and Rietveld analysis were used to evaluate the crystallite size and microstrain of the crystal structure. Morphology was studied by scanning electron microscopy, and magnetic behavior was evaluated using vibrating sample magnetometry. The powders obtained from Crystal Size Reduction by Milling-Process were sintered using spark plasma sintering in a 10 mm diameter graphite die at 750 °C. The effect of spark plasma sintering was evaluated by X-ray diffraction, Rietveld analysis, vibrating sample magnetometry and broadband dielectric spectroscopy. The results show a transformation from BiFeO 3 phase to Bi 2 Fe 4 O 9 phase for longest Crystallite Size Reduction by Milling Process time. Relationships between microstructural transformation and oxidation-reduction reactions, as well as antiferromagnetic-ferromagnetic changes, are discussed. Dielectric properties were found to decrease with high Crystallite Size Reduction by Milling-Process. Also, an unusual ratio was observed in magnetodielectric coupling which increases with Crystallite Size Reduction by Milling-Process time. • BiFeO 3 particles were obtained by high energy ball milling and annealing at 650 °C. • Crystallite Size Reduction (CSR) process produces nanocrystalline particles. • CSR promotes a change in the magnetic order from antiferromagnetic to ferromagnetic. • SPS promotes a partial phase transition from BiFeO 3 to Bi 2 Fe4O 9. • BiFeO 3 sintered by SPS shows multiferroic behavior and magnetodielectric coupling. [ABSTRACT FROM AUTHOR]

This paper describes a method for estimating model parameters $\varepsilon _{s}$ and $\Delta \varepsilon = \varepsilon _{s} - \varepsilon _{\infty }$ from the peaks in the imaginary permittivity and loss-tangent spectra. The analysis describes how measured parameters obtained from an impedance spectrometer, the magnitude of the impedance, and phase angle, are directly converted into complex permittivity and loss tangent. As an application, the method is used to detect and quantify the crystallization of skim-milk powder, which shows a dramatic change in the Debye parameters as it converts from the amorphous to crystalline state. [ABSTRACT FROM AUTHOR]

In this work regenerated cellulose was prepared by phosphoric acid as a primarily step in preparation of biodegradable foam. Copper nanoparticles (Cu-NPs) were embedded onto the cellulosic suspensions followed by freeze drying process. The scanning electron microscopy (SEM) revealed the presence of individual chunky regenerated cellulose fibers in the dimensions of micro that enhanced tendency to aggregate during drying. X-ray diffraction (XRD) demonstrated that, the treatment of cellulose with concentrated phosphoric acid led to defibrated cellulose with lower crystallinity index than original cellulose fibers. The study provided insights about the influence of the Cu-NPs on the structure, thermal stability and the electrical contributions of the considered cellulose-based foam. The electrical and dielectric properties were studied by means of the broadband dielectric spectroscopy. The dielectric spectra were dominated by an anomalous behavior of the permittivity as illustrated versus frequency of the investigated samples. The real part of conductivity follows the universal power law at higher frequencies. The foam loaded Cu-NPs exhibit biodegradability and highly efficient antimicrobial activity against Staphylococcus aureus , Pseudomonas aeruginosa , and Candida albicans. • Ecofriendly biodegradable, antimicrobial, semiconductor foam was prepared. • Micro-fibrillated cellulose was prepared by phosphoric acid treatment. • Cu-NPs were synthesized using CuSO 4 as precursor and starch as capping agent. [ABSTRACT FROM AUTHOR]