Type Relaxation Research Articles

Enhanced dielectric and magnetic properties of magnetodielectric La2−xPrxCoMnO6 for spintronic applications

La2−xPrxCoMnO6 (x = 0.5, 1.0, 1.5 and 2.0) double perovskites were prepared via sol gel method. X-ray diffraction peak profile inveterate the nonexistence of impurity phases in the prepared system. Rietveld refinement suggested that ordered monoclinic (P21/n) phase exist along with disordered orthorhombic (Pbnm) and rhombohedral (R3c) structural phases. A decrease in unit cell volume and lattice parameters is observed with increase in Pr content which is in agreement with the difference in ionic radii of La and Pr ions. Morphological and compositional study using FESEM with EDX suggested that grain size lies in micrometer range and signifies the purity of developed samples. Dielectric constant as well as tangent loss exhibit dispersive behavior at lower frequencies and higher temperatures. The strong effect of bond angle, anti-site disorder and grain size is observed on dielectric properties. Due to large bond angle and large antisite disorder, LPCMO2 exhibited largest value of dielectric constant among all developed compositions. Cole-Cole plots proposed a non-Debye type relaxation and indicated NTCR (negative temperature coefficient of resistance) behavior for the synthesized compositions. Ac conductivity showed increasing tendency with rise in both frequency as well as temperature. Increase in dc conductivity with temperature proposed semiconducting behavior of prepared samples that can be explained on the basis of Thermal activation (TA) and Variable range hopping (VRH) models. The saturation magnetization (Ms) showed a strong correlation with bond angle, tilting of CoO6/MnO6 octahedra and grain size i.e. LPCMO2 is having largest Ms whereas lowest Ms is exhibited by LPCMO3 which may be due to variation in exchange interaction which strictly depends on bond angle and tilting of MO6 octahedra. Enhanced magnetic properties make these materials useful for spintronic devices and magnetic storage. Dielectric and magnetic properties of the prepared samples depend strongly on ˂Co-O-Mn˃ bond angle and have same variation tendency with Pr substitution which indicates coupling between these properties.

Structural, raman, optical and electrical studies of pure and compound crystal of magnesium sulphateheptahydrate and threonine

Pure and compound crystal of magnesium sulphate heptahydrate(MSH) and threonine (THR) is grown from aqueous solution by slow evaporation method at room temperature. The reaction between MSH and THR is confirmed by TLC test. Good quality and transparent crystals are harvested. Pure MSH and THR crystallize in orthorhombic crystal system, while compound crystal shows the presence of both the phases of MSH and THR.The crystallite size is found using the various methods are employed to estimate the crystallite sizes and the lattice strain. The Raman spectra show the presence of characteristic normal modes of vibrations of pure MSH and THR in the compound crystal.The optical band gap is estimated by using K-M function. The various optical parameters such as extinction coefficient, refractive index, optical conductivity and skin depth have been calculated and analyzed with incident photon energy. The dielectric constant and loss of all the grown crystals have exhibited normal behavior over the frequency range considered. The total polarizability of the crystals is calculated by two theoretically methods and matches well with experimental results. The complex impedance and modulus spectroscopy studies suggested the presence of grain effect in all the samples and the same is successfully modelled using R-CPE parallel circuit. Non-debye type relaxation is confirmed from β-parameter. From the Jonscher’s plot, the ideal long range pathways and diffusion limited hopping mechanism is confirmed for all the samples. The results of pure crystal of MSH and THR are compared with the compound crystal and discussed accordingly in detail.

Automated model discovery for muscle using constitutive recurrent neural networks

The stiffness of soft biological tissues not only depends on the applied deformation, but also on the deformation rate. To model this type of behavior, traditional approaches select a specific time-dependent constitutive model and fit its parameters to experimental data. Instead, a new trend now suggests a machine-learning based approach that simultaneously discovers both the best model and best parameters to explain given data. Recent studies have shown that feed-forward constitutive neural networks can robustly discover constitutive models and parameters for hyperelastic materials. However, feed-forward architectures fail to capture the history dependence of viscoelastic soft tissues. Here we combine a feed-forward constitutive neural network for the hyperelastic response and a recurrent neural network for the viscous response inspired by the theory of quasi-linear viscoelasticity. Our novel rheologically-informed network architecture discovers the time-independent initial stress using the feed-forward network and the time-dependent relaxation using the recurrent network. We train and test our combined network using unconfined compression relaxation experiments of passive skeletal muscle and compare our discovered model to a neo Hookean standard linear solid, to an advanced mechanics-based model, and to a vanilla recurrent neural network with no mechanics knowledge. We demonstrate that, for limited experimental data, our new constitutive recurrent neural network discovers models and parameters that satisfy basic physical principles and generalize well to unseen data. We discover a Mooney–Rivlin type two-term initial stored energy function that is linear in the first invariant I1 and quadratic in the second invariant I2 with stiffness parameters of 0.60 kPa and 0.55 kPa. We also discover a Prony-series type relaxation function with time constants of 0.362s, 2.54s, and 52.0s with coefficients of 0.89, 0.05, and 0.03. Our newly discovered model outperforms both the neo Hookean standard linear solid and the vanilla recurrent neural network in terms of prediction accuracy on unseen data. Our results suggest that constitutive recurrent neural networks can autonomously discover both model and parameters that best explain experimental data of soft viscoelastic tissues. Our source code, data, and examples are available at https://github.com/LivingMatterLab.

Investigation on structural, thermal, electrical and optical properties of a new (OIH) material based Co(II)

At room temperature, a new compound with formula (C6H10(NH3)2)2[CoCl4]Cl2·H2O is successfully synthesized by slow evaporation technique. Then, it is characterized by X-ray diffraction to found that it crystallize in the monoclinic system, P21/c space group. The structure can be described by the alternation of organic and inorganic groups form a periodic 0-D network along the a axis. Hydrogen bonds have a crucial role in structure cohesion. In addition, this compound is characterized by infrared and Raman spectroscopy (FT-IR and FT-Raman), TG-DTG-DSC measurements in order to analyze the thermal behavior of the crystal and Hirshfeld surface (HS) analysis. The dielectric study was reported and reveals a good agreement with thermal measurements. Nyquist plots show a non-Debye type relaxation process and confirm that the complex impedance curves follow the Cole Cole law and the conductivity is assured by a hopping mechanism of H+ proton. The optical properties of the crystal were studied using optical absorption UV-visible and photoluminescence (PL) spectroscopy.

Enhanced electrostrains in PMN–xPZN solid solutions driven by a rather small electric field

AbstractPb(Mg1/3Nb2/3)O3 (PMN) relaxors have gained a lot of interest due to their unusual dielectric relaxation and high electrostrictive electrostrain. However, the Tm (temperature associated with maximum permittivity) of PMN is lower than room temperature, which limits their future development of electrostrain and practical applications. In this study, we increased the Tm by incorporating a relaxor ferroelectric (FE) end member Pb(Zn1/3Nb2/3)O3 (PZN) rather than a conventional high Curie temperature FE end member to create (1−x)PMN–xPZN solid solutions with x = 0.2–0.5. Their dielectric, FE, and electrostrain properties were systematically investigated. In x = 0.4 composition, we get a maximum electrostrain of 0.134% and an equivalent piezoelectric coefficient of 936 pm/V under a rather small driving field of 5 kV/cm. Furthermore, the electrostrain of the x = 0.5 is greater than 0.1% between 20 and 80°C, indicating its possible applicability in precision displacement actuators. Our findings not only clarify the electrostrain and electrostrictive properties of (1 − x)PMN–xPZN system but also show an innovative way to improve electrostrain properties by constructing relaxor–relaxor type solid solutions that can be applied to other FE systems.

Influence of graphene oxide on the dielectric properties of biogenically synthesized ZnO nanoparticles

This study presents a novel and biogenic route to synthesize zinc oxide (ZnO) nanoparticles using Phoenix dactylifera fruit extract as a plant-mediated reducing agent. Graphene oxide (GO) was synthesized using the improved Hummer's method, and a series of GO-ZnO nanocomposites were produced by the ultrasonic-dispersion method. The structural and optical properties of the nanocomposites have been analyzed using XRD, TEM, FESEM-EDX, UV-vis. DRS, and FTIR spectroscopy. The results indicate that ZnO nanoparticles are deposited over GO sheets in the nanocomposites. The structural analysis and Rietveld refinement confirmed the successful synthesis of crystalline single-phase ZnO nanoparticles with a hexagonal-wurtzite structure. The influence of GO on the dielectric properties of green-synthesized ZnO nanoparticles was analyzed in the frequency range 20 Hz-2 MHz at ambient temperature. The results showed a significant increase in the dielectric constant and ac conductivity with growing GO content in the nanocomposites compared to that of pristine ZnO. Complex impedance analysis revealed the non-Debye type relaxation and a decreasing trend in the complex impedance value with increasing GO content. This novel biogenic synthesis approach is energy-efficient and environment-friendly, which can provide an effective route for low-cost and scaled-up production of nanocomposites for several applications.

Electrical and optical properties of a lead-free complex double perovskite BaNaFeMoO6: Photovoltaic and thermistor applications

In this communication, synthesis (solid-state reaction) and characterizations of a complex double perovskite BaNaFeMoO6 are reported. X-ray diffraction analysis (structure and lattice parameters) adopts a monoclinic structure while Raman spectroscopy provides information about the vibrational characteristics. Homogenous distribution of the grains is observed from the scanning electron microscope (SEM) whereas energy dispersive X-ray analysis (EDX) supports compositional consistency. Ultraviolet–visible (UV–vis) data provides a direct energy bandgap of 2.75 eV, which may be suitable for photovoltaic applications. The analysis of Maxwell-Wagner type of dielectric dispersion, resistance, relaxation, and transport mechanism are carried out using dielectric, impedance, modulus, and conductivity data recorded within an available range of frequency (1 kHz – 1 MHz) and temperature (25 °C – 500 °C). Both the theoretical fit of the Nyquist data using ZSIMPWIN software as well as temperature-dependent conductivity support a negative temperature coefficient of resistance (NTCR) nature. The scaling nature of modulus data supports the non-Debye type of relaxation. The obtained temperature-dependent thermistor constant (β), sensitivity factor (α), and activation energy make the prepared material suitable for thermistor-related device application. The study of polarization–electric field (P-E) loop suggests the possibility of ferroelectric nature in the reported material.

Impedance Study of Temperature-Stable Relaxor Dielectrics in the System of BCT-BMT Ceramics.

Preparation of a lead-free system (Ba0.8Ca0.2)TiO3-xBi(Mg0.5Ti0.5)O3 (BCT-BMT) with x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5 was carried out using a solid-state reaction technique. X-ray (XRD) diffraction analysis confirmed a tetragonal structure for x = 0, which shifted to cubic (pseudocubic) at x ≥ 0.1. From Rietveld refinement, a single phase with a tetragonal symmetry model (P4mm) was observed for x = 0, and however, for sample x = 0.1 and sample x = 0.5, the data are modeled to cubic (Pm3m). Composition x = 0 showed a prominent Curie peak, typical of ordinary ferroelectrics with a Curie temperature (Tc) ∼130 °C, modified to a typical relaxor dielectric at x ≥ 0.1. However, samples at x = 0.2-0.5 displayed a single semicircle attributed to the bulk response of the material, whereas a slightly depressed second arc appeared for x = 0.5 at 600 °C, indicating a slight contribution to the electrical properties, ascribed to the grain boundary of the material. Finally, the dc resistivity increased with the increase of the BMT content and the solid solution increased the activation energy from 0.58 eV at x = 0 to 0.99 eV for x = 0.5. Adding the BMT content eliminated the ferroelectric behavior at compositions x ≥ 0.1 and led to a linear dielectric response and electrostrictive behavior with a maximum strain of 0.12% for x = 0.2.

Investigations of Structural, Magnetic, and Electrochemical Properties of NiFe2O4 Nanoparticles as Electrode Materials for Supercapacitor Applications.

Magnetic nanoparticles of NiFe2O4 were successfully prepared by utilizing the sol-gel techniques. The prepared samples were investigated through various techniques such as X-ray diffraction (XRD), transmission electron microscopy (TEM), dielectric spectroscopy, DC magnetization and electrochemical measurements. XRD data analysed using Rietveld refinement procedure inferred that NiFe2O4 nanoparticles displayed a single-phase nature with face-centred cubic crystallinity with space group Fd-3m. Average crystallite size estimated using the XRD patterns was observed to be ~10 nm. The ring pattern observed in the selected area electron diffraction pattern (SAED) also confirmed the single-phase formation in NiFe2O4 nanoparticles. TEM micrographs confirmed the uniformly distributed nanoparticles with spherical shape and an average particle size of 9.7 nm. Raman spectroscopy showed characteristic bands corresponding to NiFe2O4 with a shift of the A1g mode, which may be due to possible development of oxygen vacancies. Dielectric constant, measured at different temperatures, increased with temperature and decreased with increase in frequency at all temperatures. The Havrilliak-Negami model used to study the dielectric spectroscopy indicated that a NiFe2O4 nanoparticles display non-Debye type relaxation. Jonscher's power law was utilized for the calculation of the exponent and DC conductivity. The exponent values clearly demonstrated the non-ohmic behaviour of NiFe2O4 nanoparticles. The dielectric constant of the nanoparticles was found to be >300, showing a normal dispersive behaviour. AC conductivity showed an increase with the rise in temperature with the highest value of 3.4 × 10-9 S/cm at 323 K. The M-H curves revealed the ferromagnetic behaviour of a NiFe2O4 nanoparticle. The ZFC and FC studies suggested a blocking temperature of ~64 K. The saturation of magnetization determined using the law of approach to saturation was ~61.4 emu/g at 10 K, corresponding to the magnetic anisotropy ~2.9 × 104 erg/cm3. Electrochemical studies showed that a specific capacitance of ~600 F g-1 was observed from the cyclic voltammetry and galvanostatic charge-discharge, which suggested its utilization as a potential electrode for supercapacitor applications.

Computing relaxations for the three-dimensional stable matching problem with cyclic preferences

Constraint programming has proven to be a successful framework for determining whether a given instance of the three-dimensional stable matching problem with cyclic preferences (3dsm-cyc) admits a solution. If such an instance is satisfiable, constraint models can even compute its optimal solution for several different objective functions. On the other hand, the only existing output for unsatisfiable 3dsm-cyc instances is a simple declaration of impossibility. In this paper, we explore four ways to adapt constraint models designed for 3dsm-cyc to the maximum relaxation version of the problem, that is, the computation of the smallest part of an instance whose modification leads to satisfiability. We also extend our models to support the presence of costs on elements in the instance, and to return the relaxation with lowest total cost for each of the four types of relaxation. Empirical results reveal that our relaxation models are efficient, as in most cases, they show little overhead compared to the satisfaction version.

Cerium-modified single perovskite CaMnO3: structural, dielectric, and transport properties

ABSTRACT In this communication, the synthesis (solid-state reaction) and characterization (structural, dielectric, and transport) of the CaMn0.9Ce0.1O3 ceramic (named, CMCO) are discussed. The CMCO has an orthorhombic crystal symmetry with an average crystallite size of 108.7 nm and lattice strain of 0.00375 respectively. The grains are distributed uniformly in a very compact manner so that highly dense material is formed and the ratio of average grain size to average crystallite size is about 21, which may be a possible reason for a better dielectric and conductivity mechanism. Raman's study confirms the presence of all constituent elements. The analysis of the dielectric properties suggests the presence of the Maxwell-Wagner type of dispersion. The study of impedance spectroscopy reveals how grains and grain boundaries play an important role to define conductivity mechanism and hence prove a non-Debye type of relaxation. The analysis of the resistance versus temperature plots supports NTC thermistor character.

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.

Deformation diagrams of amorphous polyimide (kapton H) in the state of moderate and deep cooling: Experiment and theory

A comprehensive experimental and theoretical study of the regularities of active deformation at a constant rate of an amorphous polymer at room temperature and the influence of moderate and deep cooling on them was performed. The samples of amorphous aromatic polyimide (an analogue of kapton H) that are randomly cut fragments of the industrially produced thermoplastic film with a thickness of 25 μm were the object of the experimental study. The σ–ε diagrams of the tensile test, where σ and ε=ε˙t are the tensile stress and the relative strain, respectively, were recorded for 32 samples at three rates ε˙ = 7⋅10–5, 7⋅10–4, 6⋅10–3 s–1 under three temperatures T = 293, 77, and 4.2 K. In the state of deep cooling at T = 4.2 K, several samples were deformed as brittle glassy bodies – rupture after short elastic deformation. But the majority of the samples at all values of the experimental parameters (T,ε˙) had the rheological properties of rubber-like highly elastic materials (elastomers) with traditional tensile test diagrams: initial stage I of linear elastic deformation σI=Meε with Young’s modulus Me=Me(T); stage III of linear highly elastic deformation σIII=σfe+Mheε with modulus Mhe=Mhe(T) and conditional limit of elasticity σfe=σfe(T,ε˙); intermediate stage II of the relaxation type σII(ε;T,ε˙) with a nonlinear stress-strain dependence. The σ–ɛ diagrams of the individual samples with sufficiently high accuracy coincide with the graph of the function σ(ε;T,ε˙) which is the solution of the previously derived nonlinear rheological equation (V. D. Natsik and H. V. Rusakova, Fiz. Nizk. Temp.48, 281 (2022) [Low Temp. Phys.48, 253 (2022)]; Fiz. Nyzk. Temp.49, 246 (2023) [Low Temp. Phys.49, 228 (2023)]). In its derivation, a molecular-kinetic model was used: an amorphous polymer is considered as a set of statistically independent kinetic units, namely, molecular segments, and the elementary act of deformation is caused by thermomechanical activation of nonlinear excitations of these segments called elastons. The elaston mechanism of transformation of the deformation diagrams of amorphous polyimide samples under their moderate and deep cooling is discussed in detail: the transition between deformation states of warm and frozen elastomer, low-temperature effects of structural-deformation glass transition and deformation melting. Comparing the results of experiments and theory made it possible to obtain the empirical estimates for the macromechanical characteristics of the studied samples and the microparameters of elaston excitations. A significant and unsystematic (random) scatter of the macro- and micromechanical characteristics of the samples was revealed, which indicates a significant and random heterogeneity of the macro- and microstructure of the polyimide film from which they were made.

Structural, optical, electrical, and dielectric relaxation properties of rare earth containing sodium bismuth titanate [formula omitted] perovskite: Effect of ionic radius

The main focus of this work is to study the effect of the ionic radius of different rare earth dopant cations RE3+ (RE = La, Sm, Dy, and Ho) on structural and various physical properties of sodium bismuth titanate (Na0.5Bi0.5TiO3, NBT) based perovskite nanomaterials. The X-ray diffraction data indicate the successful formation of the rhombohedral phase (space group R3c) of NBT nano perovskite incorporated with various rare earth ions in Bi-site. The lattice parameters were found to increase linearly with the ionic radius of the dopant cation. The ionic radii and atomic mass of rare earth dopants appear to be essential factors in the grain growth of the prepared compositions. The grain growth results in better crystallinity of the sample by reducing the microstrain with the increase of dopant ionic radius. Field emission scanning electron microscopy and energy-dispersive X-ray spectra confirm the prepared compositions' phase purity and stoichiometry. The UV–Vis spectra reveal that La-doped NBT composition exhibits the lowest optical band gap, which unfolds the application of NBT-based perovskite as photoactive material. The ac conductivity and complex impedance spectra unveil that the composition with the largest ionic radius, i.e., La-doped NBT compound, exhibits the highest dc and bulk conductivity with the lowest activation energy. The frequency-dependent dielectric data follows Havriliak–Negami (HN) formalism and non-Debye type relaxation phenomena. Results also indicate that La-doped NBT composition exhibits the highest dielectric strength value. Thus, this study first elaborates that the increasing ionic radius of the rare earth dopant cation in the Bi-site of NBT perovskite improves its microstructural, optical, and electrical properties.

Effects of the substitution by copper on structural, optical and dielectric properties of the spinel LiFe2O4

Spinel lithium ferrites are of great importance in fields of technological applications. Their characteristics are subject to several studies to investigate the involved mechanisms. We prepared the spinel Li0.2Cu0.8Fe2O4-d ferrite by the solid-state method and we studied the effect of copper incorporation. X-ray diffraction confirms the Li0.2Cu0.8Fe2O4-d compound crystallizes with a cubic spinel structure with space group Fd3‾m. The morphology micrograph shows that the grains are agglomerated in asymmetrical formations. Nyquist plots exhibits significant contribution of grains and grain boundaries. Both modulus and impedance results confirm that Li0.2Cu0.8Fe2O4-d sample exhibits a Cole-Cole relaxation type. The AC conductivity variation shows a dispersive behavior governed by the jump relaxation model. Hopping conduction is explained by two theoretical models. The first is attributed to the correlated barrier-hopping model at low temperature, and the second corresponds to the non-overlapping small polaron tunneling mechanism at high temperature. The dielectric behavior shows a polarization effect. Optical properties show that the band gap value is equal to 1.47 eV. Finally, the magnetization curve indicates that our sample present a phase transition and evidences the presence of ferromagnetic behavior.

Chemical engineering at morphotropic phase boundary: Interplay with thermally stabilized ultra-high energy storage and electrocaloric response

We have performed systematic investigations on (Ba0·85Ca0.15)-(Ti0·90Zr0.10)O3 [BCTZ] morphotropic phase boundary [MPB] composition co-doped with Mg and Nb [MN]. X-ray diffraction patterns revealed that the synthesized samples crystallized with perovskite phase. Surface morphology, assessed through scanning electron microscopy, emphasizes that the grain size decreases with MN content. Modified Curie-Weiss analysis suggests the relaxor type characteristics of BCTZ-xMN (x = 0.0, 0.025, and 0.05) samples. Recoverable energy density (Wrec) attains maximum value near the ordering temperature. Maximum value of Wrec is found to be ∼54, 77 and 50 mJ/cm3 for x = 0.0, 0.025 and 0.05, respectively, which is an indication of the additional promising features of MPB composition BCTZ-0.025 MN towards energy storage operations. Further, we have calculated maximum entropy change involved in tetragonal to cubic phase transition, at electric field of 16 kV/cm, to be (ΔSmax) ∼ 0.70, 0.75 and 0.22 Jkg−1K−1, corresponding to x = 0.0, 0.025 and 0.05 composition, respectively.

Analysis of negative magnetization and dielectric studies in holmium substituted samarium iron garnet

We have used solid-state reaction approach for the preparation of polycrystalline samples of (Sm1-xHox)3Fe5O12(x=0.0 to 1.0) and the phase formation is verified by the refinement of X-ray diffraction patterns using Ia3‾d space group. The lattice constant is found to be decreased while the average grain size increases with Ho doping. The transition temperature (TC) for ferrimagnetic to paramagnetic state decreases from 561 K to 541 K for x=0.0 to x=1.0. Also, M−T plots demonstrate that every sample exhibit spin reorientation transition and with Ho doping the spin reorientation transition temperature (TSR) is reducing from 65K(x=0.0) to 20K(x=1.0). Interestingly, negative magnetization is observed for x=0.4 sample and is confirmed by applying different magnetic fields. Moreover, magnetic compensation is also observed in samples with x≥0.4. The Nyquist plots extracted from complex impedance spectra show the deviation from the ideal Debye type relaxation. It is observed that the dielectric constant has increased from 104 to 106 in the lower frequency zone with x varying from 0.0 to 1.0 making them a promising material for microwave applications.

Magnetic and electrical investigations of low dimensional Co0.5Zn0.5−xCuxFe2O4 nano ferrites

In this present work, low dimensional Co0.5Zn0.5−xCuxFe2O4 (x = 0.01, 0.02, 0.03, 0.04 and 0.05) (CZCFO) ferrite nanoparticles are engineered by modified sol-gel method, with citric acid (C6H8O7) as a fuel. Here we investigate the room temperature structure, magnetic, X-ray photoelectron spectroscopy, and electrical properties of CZCFO nanoparticles. The X-ray diffraction patterns of CZCFO samples, confirm the formation of pure a cubic structure, Fd-3m space group, and Rietveld refinement technique used to extract the atomic level structural information for all the compositions. Debye Scherer’s equation is used to estimate the crystallite size and micro strain, the obtained values are around 8–13 nm and 0.6246 × 10−3 respectively. The particle surface morphology was examined by Field emission scanning electron microscopy (FE-SEM), showing aggregated grains with a sponge-like structure. The Fourier transform infrared spectroscopy (FTIR) technique confirms the presence of functional groups and the formation of the spinel structure for all the samples. Room temperature M-H loops indicate the ferrimagnetic nature for all the samples and it is noticed that increasing saturation magnetization (Ms) and coercivity (Hc) for increasing dopant. X-ray photoelectron spectroscopy (XPS) technique is used to estimate the elements with an electron state of atoms within the material and determine the valance states at respected octahedral and tetrahedral sites. The frequency-dependent dielectric constant and loss tangent imply that, significantly decreases as increasing frequency and later, becomes almost linear. This typical nature reflects the Maxwell–Wagner type of polarization by Koop's theory. Additionally, room temperature complex impedance spectroscopy reveals the non-Debye type of relaxation and the Cole-Cole plot shows the semi-arc nature. Relative permeability studies at room temperature remark the decay in all samples.

Improved electro-optical and dielectric properties of polymer dispersed liquid crystal doped with disperse dye red 1 and carbon nanoparticles

ABSTRACT Disperse dye red 1 (DR1) and carbon nanoparticles (CNPs) were doped separately to form polymer dispersed liquid crystal films, namely, DPDLC & CPDLC. Nematic liquid crystal (LC) and photopolymer NOA-65 were used to prepare these composite films using polymerisation-induced phase separation (PIPS) technique. In this research work, it is demonstrated that the minute concentration (0.05% wt./wt.) of DR1 and CNPs controls the LC droplet alignment and LC droplet size in polymer dispersed liquid crystal (PDLC) film. The effect of DR1 and CNPs on PDLC film has been investigated in terms of LC droplet size, transition temperature, voltage-transmittance characteristic, contrast ratio, response time, haze, and dielectric measurements. The obtained results reveal that the threshold voltage values of the composite film get reduced from 34.87 V (undoped) to 10.19 and 9.26 V, for 0.05% of DR1 and CNPs doping, respectively. The DR1 (0.05%) doped film shows improved contrast of the undoped film as compared to CNPs (0.05%) film, whereas CNPs (0.05%) doped film shows a faster response time of 2.81 ms as compared to DR1 (0.05%) doped film (3.14 ms). Dielectric analysis of undoped, DPDLC, and CPDLC films represents Debye type relaxation mode.

Insights into the Structural and Dielectric Behavior of Composites Produced from EPDM Waste Processed through a Devulcanization Method and SBR.

Ethylene propylene diene monomer (EPDM) is one of the most used polymers in the world. It is an elastomer, which means that the existing cross-linking between the main chains of the polymer created during the vulcanization process makes its recycling difficult. In this paper, a possible solution to this issue is studied. The devulcanization of EPDM is achieved by a thermomechanical process followed by microwave irradiation. These combined treatments suppress the cross-linking, yielding a material (EPDMd) that can be successfully blended to form composites. A common elastomer, styrene butadiene rubber (SBR), has been selected as the matrix. The new SBR/EPDMd composites can be useful as elastomeric dielectric materials and can contribute to the recycling of the discarded EPDM. To provide a better understanding of their microstructure and its relationship with their micro- and macroscopic behavior, samples containing 20 and 40% of EPDMd have been tested by thermogravimetric and dielectric analysis, focusing on variables such as the thermal properties of the blends, permittivity, electric modulus, conductivity, and activation energies. The results show interesting changes linked to the presence of EPDMd in the SBR matrix, such as the displacement of the β dielectric relaxation toward higher frequencies. The correct integration between the two phases is confirmed by the absence of any Maxwell-Wagner-Sillars type relaxation in their dielectric behavior. The presence of additives in the EPDMd samples has an effect on the conductivity, mainly due to the conductive aluminum silicate present in the EPDMd, which acts toward increasing some key dielectric features like conductivity and permittivity and decreasing the insulation of the final SBR/EPDMd materials. The inclusion of EPDMd also affects the α relaxations (low frequencies) and suppresses the β relaxations (high frequencies). The samples showed a non-Debye dielectric behavior. In short, a compact and well-integrated material with a dielectric behavior is created, which exhibits interesting differences from the reference SBR matrix. Finally, it is concluded that the compounds tested are suitable for applications as electrical insulators.