Dielectric Relaxation Research Articles

Model for the Shape of the Relaxation Spectrum in Glass Formers.

Traditionally the broadness of the spectrum of the relaxation times observed in glass-forming materials has been rationalized by local heterogeneity, where a variety of atomistic environments leads to spectrum of single-exponential relaxation responses. However, the assumption of heterogeneity can break down when tested against the shape of the relaxation spectrum. An alternative homogeneous scenario assumes that the relaxation is inherently multiexponential. A recently developed switchback model [Medvedev, G. A. Phys. Rev. E 2023, 107 (3), 034122] naturally results in a multiexponential wedge-like spectrum that is consistent with the dielectric relaxation, light scattering, and the NMR data. As a particular case the switchback model allows for the spectrum to become single-exponential; under the heterogeneous scenario this would require the heterogeneities to completely vanish, which is hard to justify. Using data from photobleaching experiments and molecular dynamic simulations, it is shown that the relaxation spectrum may become single-exponential under large anisotropic deformation. This is interpreted as an argument in favor of the homogeneous scenario and specifically the switchback model for the relaxation of the glass formers.

Thickness-dependent structural and growth evolution in relation to dielectric relaxation behavior and correlated barrier hopping conduction mechanism in Ni0.5Co0.5Fe2O4 ferrite thin films.

Ferrite thin films are explored due to their promising properties, which are essential in various advanced electronic devices. However, depositing a film with pure phase and uniform microstructure is challenging. The Ni0.5Co0.5Fe2O4 ferrite thin films are deposited using pulsed laser deposition (PLD) technique to explore the effect of thickness on structural properties, growth evolution, temperature-dependent dielectric behavior, and conduction mechanisms. Microstructural analysis revealed that the films are uniformly grown, exhibiting surface roughness ranging from  2 to 4 nm. The dielectric response, adhering to a modified Debye model, exhibited multiple relaxation processes, with notable changes in the dielectric constant and loss as film thickness increased. Impedance spectra exhibited both space charge and dipolar relaxation phenomena, corroborated by Cole-Cole and electrical modulus plots. The analysis of the imaginary electric modulus using the Kohlrausch-Williams-Watts (KWW) function revealed non-Debye-type relaxation in all deposited films, characterized by thermally activated broad peaks. Conductivity decreased up to a certain film thickness, and the frequency exponent derived from Jonscher's power law suggested a correlated barrier hopping model for AC conduction. Activation energies improved with film thickness up to 125 nm, consistent with a constant energy barrier for polarons during relaxation and conduction phases. The film with 125 nm thickness exhibited the optimal dielectric properties, with the maximum dielectric constant, minimum dielectric loss, and highest activation energy. These findings highlight the potential of dense, uniformly grown films with high dielectric constants and low dielectric losses for advanced electronic device applications.

Cooperative and Local Molecular Motion of High-Density Water in Glycerol Aqueous Solutions.

The glass-to-liquid transition of water, particularly in high-density water (HDW), has long been a controversial topic due to challenges posed by inevitable crystallization. In this study, we addressed this issue by creating homogeneous high-density glass from a dilute glycerol aqueous solution under high pressure. Using dielectric spectroscopy, we explored the glass transition of HDW in glycerol solutions across the full concentration range under high pressures. HDW was found to exhibit two distinct relaxation modes: one linked to cooperative motion and the other to noncooperative local motion. The fragility index classification of HDW, derived from the cooperative motion of water, suggests that HDW behaves as a "fragile" liquid, contradicting previous suggestions. Extrapolation to pure HDW indicates that the dielectric relaxation observed in pure HDW originates from noncooperative local water motion.

Molecular Motion in Supramolecular Ionic Crystal of Swiss Cheese Structure

Abstract In most molecular crystals, crystal structure collapses when solvent molecules are removed. We report the crystal of (isobutylammonium+)(dibenzo[18]crown-6)[Ni(dmit)2]−•0.4CH3CN with Swiss cheese-like structure, in which 60% of the CH3CN sites are voids. The motion of isobutylammonium+ adjacent to the void sites maintains the single crystallinity, which occupy an apparently larger volume than in the static state. This study opens up the possibility of developing novel relaxor dielectrics based on molecular motion in the crystal of partially occupied voids.

Polarizing Magnetic Field Effect on Some Electrical Properties of a Ferrofluid in Microwave Field

The complex dielectric permittivity, ε (f, H) = ε′ (f, H) − i ε″ (f, H), in the microwave frequency range f, of (0.1–3) GHz and polarizing field values H, in the range of (0–135) kA/m, was measured for a kerosene-based ferrofluid with magnetite particles. A relaxation process attributed to interfacial type relaxation was highlighted, determining for the first time in the microwave field, the activation energy of the dielectric relaxation process in the presence of the magnetic field, EA(H), in relation to the activation energy in zero field, EA(H = 0). Based on the complex permittivity measurements and the Claussius–Mossotti equation, the dependencies on frequency (f), and magnetic field (H), of the polarizability (α) and electrical conductivity (σ), were determined. From the dependence of α(f,H), the electric dipolar moment, p, of the particles in the ferrofluid, was determined. The conductivity spectrum, σ(f,H), was found to be in agreement with Jonscher’s universal law and the electrical conduction mechanism in the ferrofluid was explained using both Mott’s VRH (variable range hopping) model and CBH (correlated barrier hopping) model. Based on these models and conductivity measurements, the hopping distance, Rh, of the charge carriers and the maximum barrier height, Wm, for the investigated ferrofluid was determined for the first time in the microwave field. Knowledge of these electrical properties of the ferrofluid in the microwave field is useful for explaining the mechanisms of polarization and control of electrical conductivity with an external magnetic field, in order to use ferrofluids in various technological applications in microwave field.

A comprehensive molecular dynamics simulation of plastic and liquid succinonitrile: Structural, dynamic, and dielectric properties.

Molecular dynamics simulations at constant temperature and pressure were carried out to investigate the structural, dynamical, and dielectric properties of succinonitrile in its plastic and liquid phases at several thermodynamic states. A six-site united atom model was employed with a force field incorporating an intramolecular torsional term that accurately describes gauche and trans conformers. Analysis of the radial distribution function showed that succinonitrile adopts a body-centered cubic arrangement below its melting point, transitioning to a less ordered state in the liquid phase. In addition, examination of alignments between methylene bonds and the diagonals of the simulating cubic box revealed pronounced directional preferences in the plastic phase. The study of conformational states suggested that succinonitrile molecules predominantly adopt gauche conformations, which exhibit longer lifetimes than trans conformers. Spectral density analysis highlighted distinct peaks for different molecular sites, revealing significant differences between gauche and trans conformers. The correlation functions of bending and torsional angles, as well as vectors joining different atoms, illustrated a sensitivity to internal motions, which were notably faster for trans conformers. Differences in decay rates between trans and gauche conformers underscored the influence of gauche-trans transitions. The static dielectric constant, which has been derived from the total dipole moment, was primarily influenced by the contribution of the gauche conformers. In addition, the distance-dependent Kirkwood factor was computed, revealing antiparallel alignment at short distances. Finally, the dielectric relaxation time and the static dielectric constant values were compared with experimental data.

Configuration entropy and non-Arrhenius behavior in the α relaxation of glassy dielectrics

Applying Eyring equation to experimental data for the α relaxation of glassy dielectrics shows the fundamental role of the activation entropy in the relaxation dynamics. The combination of Eyring equation and compensation law gives access to other important parameters, such as the compensation temperature and the absolute value of the configurational activation entropy, ΔSC, in the Arrhenius regime. The non linear behavior observed at low temperatures is explained by the time and temperature variation of the configurational activation entropy. We propose that this change corresponds to the rarefaction of free equilibrium states as T is lowered. A simple method is proposed to calculate ΔSC from the change of free energy in the non linear regime. The lowest temperature limit of the a relaxation is not known but it seems unlikely that it would be the VTF or the Kauzmann temperatures. Brief comments on the physical significance of these two parameters are made. It is also shown that relaxation times are not invariant, as sometime suggested

The Study of Electrical Conductivity and Dielectric Relaxation in the Organic Ferroelectric Diisopropylammonium Iodide (dipaI)

The Study of Electrical Conductivity and Dielectric Relaxation in the Organic Ferroelectric Diisopropylammonium Iodide (dipaI)

Enhanced optical, dielectric and transport properties in PVDF based (La0.5Bi0.5FeO3)0.5-(BaTiO3)0.5 composites

In this comprehensive study, we investigated PVDF composites incorporating LaBiFeO3-BaTiO3 (LaBiFO-BaTO) perovskite fillers, focusing on their structural, optical, dielectric, impedance, modulus and DC-conductivity properties. The fabrication involved precise preparation of LaBiFO-BaTO perovskite via solid-state reaction, ensuring phase purity conducive to composite integration. Using a solution casting method, PVDF films with varying LaBiFO-BaTO concentrations (5 %, 10 %, and 15 % wt) were successfully synthesized. XRD confirmed the synthesis of single-phase LaBiFO-BaTO and revealed structural modifications in PVDF composites, highlighting improved filler-matrix interactions at higher concentrations. Scanning electron microscopy and atomic force microscopy depicted the morphological evolution and surface roughness changes with increasing filler content. Optical studies indicated a red shift in absorption spectra with higher LaBiFO-BaTO concentrations, correlating with a decrease in the direct band gap energy of the composites. Electrical characterization demonstrated enhanced dielectric properties and impedance behaviour in PVDF/LaBiFO-BaTO composites, suggesting their suitability for applications in capacitors and optoelectronic devices. This systematic investigation provides valuable insights into optimizing PVDF-based composites for advanced functional materials. The composites exhibit enhanced dielectric permittivity at room temperature, attributed to space charge polarization and the high dielectric constant of LaBiFO-BaTO. Dielectric loss (tanδ) remains minimal (<0.1), decreasing with frequency, indicative of low energy dissipation suitable for high-frequency applications. Further the dielectric relaxation have been examined using Havrilak-Negami model. Impedance and modulus analyses reveal temperature-dependent behaviours, with reduced impedance and enhanced charge transfer kinetics in higher concentration composites. DC conductivity measurements demonstrate increased charge transport properties with temperature, influenced by thermally activated charge hopping mechanisms. Overall, PVDF/LaBiFO-BaTO composites show promising characteristics for capacitors, sensors, and optoelectronic devices, suggesting avenues for further optimization and broader application in advanced technologies.

Emerging mixed electronic-ionic conductivity in double perovskite (La2/3Sr1/3)2(Sn1/3Fe1/3Cu1/3)2O6-δ: Phase transitions, structural, optical and dielectric study

We report on the eco-friendly synthesis of a double perovskite compound (La2/3Sr1/3)2(Sn1/3Cu1/3Fe1/3)2O6-δ, attractive for sustainable applications due to its unique structural and conductive properties. The incorporation of Cu2+ (3d9) ions into the B sites of the perovskite structure enhanced octahedral distortion via the Jahn-Teller effect. X-ray crystallography and Rietveld structural analysis revealed a significant deviation in the octahedra of (Cu/Fe)O6 and (Sn/Fe)O6 from the ideal perovskite structure, resulting in a decreased overlap between the atomic orbitals. The material displays a high dielectric constant, evidenced by impedance measurements across varying temperatures and frequencies. The analysis highlighted a considerable influence of the grain intrinsic properties and the grain boundary dynamics on both the conduction mechanism and dielectric relaxation. Notably, the introduction of dopants significantly reduces the bandgap energy to 2.7eV, compared to the 4.3eV of SrSnO3. The bandgap reduction factor measured here is lower than that of other reported double-doped SrSnO3 compounds. At 493K, a transition in DSC measurements suggests a structural change of the conductivity from a purely electronic to an electronic-ionic conductivity. The smaller bandgap and enhanced conductivity, coupled with phase transitions lead to a mixed conductivity making this material particularly effective for the use in energy storage technologies such as supercapacitors and batteries with the aim of improving their capacity and efficiency. Additionally, due to its temperature sensitivity, it also has the potential to be used as a valuable component in sensor applications.

Comprehensive properties analysis of epoxy composites synergistically toughened with liquid nitrile rubber and polyethersulfone

In this paper , epoxy resin (EP) composites with different phase structures were prepared by introducing hydroxyl-terminated liquid nitrile rubber (HTBN) and hydroxyl-terminated polyethersulfone (PES) individually or simultaneously into the resin matrix. The results revealed that the rational distribution of phase structure of rigid PES and flexible HTBN can effectively contributed to the enhancement in their mechanical and electrical insulation strengths. The synergistic effect of the two reinforcing fillers granted the optimized ternary composite a tougher structural network, leading to significant improvements of 73.13% and 18.98% in mechanical impact strength and electrical breakdown strength, respectively, compared to the pristine EP. Furthermore, compared to HTBN, PES exhibited inhibited HTBN dielectric interfacial polarization and EP molecular chain segment relaxation, resulting in decreased dielectric constant and loss in the composites. This study provide insights into the dielectric properties and design strategies for the development of resin-based dielectric materials, ensuring their broader applicability.

Origin of giant dielectric constant in Ta+Gd co-doped TiO2 single crystals by optical traveling floating zone method

The co-doped TiO2 polycrystalline ceramics have dramatic dielectric behavior (>104), but its source is still not completely clarified. Compared to ceramic materials, single crystals can maintain most of the original properties of the material and eliminate the grain boundary and pore interferences, thus facilitating the exploration of the source of the dielectric properties. Here, we chose Gd3+ with a moderate ionic radius as the acceptor ion and Ta5+ as the donor, preparing (Gd0.5Ta0.5)0.01Ti0.99O2 single crystals by the optical traveling floating zone method to investigate giant dielectric properties. It was found that a dielectric constant (ε′ ∼1.5 × 104), and a dielectric loss (tanδ ∼ 0.07) were achieved simultaneously in (Gd0.5Ta0.5)0.01Ti0.99O2 single crystals at 105Hz. Electrochemical impedance spectroscopy and XPS analyses indicate that the high dielectric properties are mainly attributed to electrons pinning defective dipoles clusters. In addition, dielectric relaxation behavior under DC bias suggests that electrode effects also affect the dielectric constant. This study provides insights for the origin of the large dielectric constant and the growth of single crystals in TiO2-based materials.

Influence of Bismuth Content on the Properties of Glass-Ceramics with Composition xBi2O3-(0.40-x)B2O3-0.15ZnO-0.45P2O5: Synthesis, Structural, Thermal Analysis, and Dielectric Relaxation Process

The glass-ceramics materials with the sample composition of xBi2O3-(0.40-x) B2O3-0.15ZnO-0.45P2O5 (BBZP) (where x = 0.10, 0.15, 0.20, and 0.25) have been prepared using the conventional melt-quenching technique. Different nanocrystalline phases embedded inside the glass-ceramic matrix have been characterised by analysing x-ray diffraction spectra. The obtained density values as well as molar volume increases with the rise of bismuth content. The network structure of the glass ceramic samples has been investigated employing Raman spectroscopy. The DSC analysis reveals the decrease in Glass transition temperature (Tg) (433K-416K), and crystallization temperature (Tc) (569K-556K) of the studied materials. The electrical properties of the samples have been investigated in the context of dielectric and modulus formalism. Different theoretical models have been employed to analyse the experimental data of dielectric and modulus spectra. The Nyquist plots of the materials have also been analysed employing relevant models. It has been shown that the higher bismuth containing samples are highly dense with high thermal stability. Such materials also have high dielectric strength. Analysis of these performance indicators suggests the possible applications of these materials in electrochemical devices.

Liquid-phase synthesis of a Li3PS4 solid electrolyte using ethyl isobutyrate as a synthetic medium

A β-Li3PS4 solid electrolyte was prepared via liquid-phase synthesis using ethyl isobutyrate as a synthetic medium. The precursor and solid electrolyte structures were characterized using thermogravimetry–differential thermal analysis and X-ray diffraction techniques. The dielectric relaxation analysis showed two relaxation regions, which revealed a bulk and grain boundary ionic migration process. At a temperature lower than 90°C, the frequency dependence of the dielectric constant of the prepared sample was different from that of glassy Li3PS4, indicating that the motion of the PS4 unit enhances the ionic conductivity of the Li3PS4 solid electrolyte. The ionic conductivities of the cold-pressed and warm-pressed pellets at 25°C were 6.8 × 10−5 Scm−1 and 3.6 × 10−4 Scm−1, respectively.

Boosting Enzyme Activity in an Anhydrous Gas Flux with Amphiphilic Polymers

AbstractGas‐phase enzymatic catalysis offers great potential for both green synthesis and the efficient degradation of volatile chemicals. However, solid enzymes often exhibit extremely low activity compared to their counterparts in native aqueous phase. Although a few immobilization methods have succeeded in increasing activity by preserving enzyme structure, approaches for boosting enzyme activity remain underdeveloped. In this study, we propose a general and facile method to boost enzyme activity in the gas phase, which utilizes amphiphilic polymers to energize enzyme conformational dynamics and thus enhance enzyme catalysis kinetics. The triblock copolymer Pluronics with low melting points were co‐lyophilized with Candida antarctica lipase B (CalB), yielding Pluronic/CalB powders that appeared a 70‐fold increase in activity compared to free CalB powder. Low‐field nuclear magnetic resonance (LF‐NMR), solid‐state nuclear magnetic resonance (ssNMR) and dielectric relaxation spectroscopy identified the enhancement of enzyme dynamics on the µs–ms timescale, whereas Fourier transform infrared spectroscopy (FTIR) detected structural perturbations of the native enzyme in Pluronic/CalB. The apparent activity of the enzyme/polymer powders correlated positively with both enzyme dynamics and polymer flexibility. These findings provide new molecular physical insights into gas‐phase enzyme catalysis, which are essential for advancing enzyme applications in nonnatural scenario.

Contribution of Protonation to the Dielectric Relaxation Arising from Bacteriopheophytin Reductions in the Photosynthetic Reaction Centers of Rhodobacter sphaeroides

The pH dependence of the free energy level of the flash-induced primary charge pair P+IA− was determined by a combination of the results from the indirect charge recombination of P+QA− and from the delayed fluorescence of the excited dimer (P*) in the reaction center of the photosynthetic bacterium Rhodobacter sphaeroides, where the native ubiquinone at the primary quinone binding site QA was replaced by low-potential anthraquinone (AQ) derivatives. The following observations were made: (1) The free energy state of P+IA− was pH independent below pH 10 (–370 ± 10 meV relative to that of the excited dimer P*) and showed a remarkable decrease (about 20 meV/pH unit) above pH 10. A part of the dielectric relaxation of the P+IA− charge pair that is not insignificant (about 120 meV) should come from protonation-related changes. (2) The single exponential decay character of the kinetics proves that the protonated/unprotonated P+IA− and P+QA− states are in equilibria and the rate constants of protonation konH +koffH are much larger than those of the charge back reaction kback ~103 s−1. (3) Highly similar pH profiles were measured to determine the free energy states of P+QA− and P+IA−, indicating that the same acidic cluster at around QB should respond to both anionic species. This was supported by model calculations based on anticooperative proton distribution in the cluster with key residues of GluL212, AspL213, AspM17, and GluH173, and the effect of the polarization of the aqueous phase on electrostatic interactions. The larger distance of IA− from the cluster (25.2 Å) compared to that of QA− (14.5 Å) is compensated by a smaller effective dielectric constant (6.5 ± 0.5 and 10.0 ± 0.5, respectively). (4) The P* → P+QA− and IA−QA → IAQA− electron transfers are enthalpy-driven reactions with the exemption of very large (&gt;60%) or negligible entropic contributions in cases of substitution by 2,3-dimethyl-AQ or 1-chloro-AQ, respectively. The possible structural consequences are discussed.

Synergistic insights to ion-doped hydroxyapatite: bridging XRD, electrical impedance, dielectric characteristics, and antibacterial properties

ABSTRACT In this work, ion-doped hydroxyapatite materials were synthesized using the sol-gel technique. XRD analysis confirmed the purity of the products, with no secondary peaks observed. Doping with manganese, lithium, potassium, and zinc ions resulted in a crystalline size of 47–48 nm. Fourier transform infrared spectroscopy validated the structural bands, while scanning electron microscopy and energy-dispersive X-ray spectroscopy revealed nano-rod-like particles with sizes ranging from 30 to 80 nm in length and 13 to 40 nm in width. Impedance spectroscopy and dielectric relaxation studies showed electrical behaviour following the Maxwell-Wagner mechanism and non-Debye type relaxation. The materials exhibited strong antibacterial properties, making them promising for medical implant applications.

Effect of milling time on structural and electrical properties of thermomechanically synthesized of Ba0.1 (Bi0.45Na0.45)TiO3 nanoceramics for ferroelectric random-access memory device

Lead-free Ba0.1(Bi0.45Na0.45)TiO3 (BBNTO) nanoceramics were synthesized using high-energy ball milling, followed by a solid-state reaction method. XRD analysis of the microstructure indicated the formation of tetragonal symmetry. The crystallite size of the nanoceramic powder decreased from ∼ 28 nm to 10 nm after milling for 0, 30, 60, and 90 hours. The dielectric properties of the nanoceramics showed significant improvement, with a diffuse phase transition occurring around 80 °C). The dielectric constant increased with temperature across various frequencies, reached a maximum value at approximately at temperature ∼ 380 °C. At lower temperatures and higher frequencies, the relative permittivity and tangent loss depend on the crystallite size and milling duration. Impedance spectroscopy data analysis revealed size-dependent impedance characteristics and dielectric relaxation. The ac conductivity plot adhered to the Arrhenius relation, and the calculated activation energy confirmed the negative temperature coefficient of resistance (NTCR) behavior. P-E loops confirmed ferroelectric properties, indicating potential for use in future ferroelectric-based storage devices.

Calculation of Dielectric Spectra by Molecular Dynamics: 4-Cyano-4'-hexylbiphenyl in its Nematic Phase.

We employ classical molecular dynamics simulations to predict the experimentally validated dielectric spectra of a bulk 4-cyano-4'-hexylbiphenyl (6CB) system in the nematic phase at temperatures of 300 K and 290 K. We separately analyze the dielectric spectra parallel to the nematic director and perpendicular to it. They show different intensities and different relaxation times, with the parallel relaxation being slower (hundreds of nanoseconds) than the perpendicular (about 1 ns). We investigate various molecular motions as possible mechanisms for the observed macroscopic dielectric behavior by determining their characteristic time scales. We find that the parallel dielectric relaxation is realized by "head-over-heel" flips of 6CB molecules that invert their dipole moment. The perpendicular dielectric relaxation is traced to a combination of the precession of the long molecular axis (dipole axis) around the director and reorientations of the phenylene rings around the long-axis. Dihedral-angle transitions in the n-hexyl tails do not contribute to the dielectric signal.

Nonlinear dielectric response and conductivity characteristics of epoxy resin in high voltage AC electric field

Abstract High-voltage dielectric and AC conduction behaviors of epoxy resin (EP) insulation are beneficial for the design and application of solid-state power electronic devices. This study investigates the nonlinear dielectric response and AC conduction characteristics of EP. The dielectric relaxation characteristics, including permittivity and AC conductivity of the EP samples, were investigated using high-voltage dielectric spectroscopy and the ionic polarization model. The results demonstrate a nonlinear increase in the relative permittivity and AC conductivity concerning the AC electric field. The increase in AC conduction under a high-frequency electric field is attributed to the reduction in the threshold field for charge injection caused by elevated temperatures. Considering the dielectric response and carrier hopping, it is evident that the nonlinear dielectric response of EP primarily originates from the ionic process under high electric fields. Ionic polarization, in conjunction with ion-hopping conduction, enhances the dielectric loss at high frequencies and electric fields, thereby facilitating the nonlinear conversion of AC conduction. The equivalent free volume is likely to increase in high-frequency fields. This phenomenon leads to an increase in AC conduction and even dielectric breakdown. This study offers a pivotal theoretical framework for the design and application of high-frequency insulation.