Dielectric Relaxation Research Articles

Dielectric relaxation and electrical conductivity property correlation in Gd-doped BBTO Aurivillius ceramics

Dielectric relaxation and electrical conductivity property correlation in Gd-doped BBTO Aurivillius ceramics

Electric field modulation of ERK dynamics shows dependency on waveform and timing

Different exogenous electric fields (EF) can guide cell migration, disrupt proliferation, and program cell development. Studies have shown that many of these processes were initiated at the cell membrane, but the mechanism has been unclear, especially for conventionally non-excitable cells. In this study, we focus on the electrostatic aspects of EF coupling with the cell membrane by eliminating Faradaic processes using dielectric-coated microelectrodes. Our data unveil a distinctive biphasic response of the ERK signaling pathway of epithelial cells (MCF10A) to alternate current (AC) EF. The ERK signal exhibits both inhibition and activation phases, with the former triggered by a lower threshold of AC EF, featuring a swifter peaking time and briefer refractory periods than the later-occurring activation phase, induced at a higher threshold. Interestingly, the biphasic ERK responses are sensitive to the waveform and timing of EF stimulation pulses, depicting the characteristics of electrostatic and dissipative interactions. Blocker tests and correlated changes of active Ras on the cell membrane with ERK signals indicated that both EGFR and Ras were involved in the rich ERK dynamics induced by EF. We propose that the frequency-dependent dielectric relaxation process could be an important mechanism to couple EF energy to the cell membrane region and modulate membrane protein-initiated signaling pathways, which can be further explored to precisely control cell behavior and fate with high temporal and spatial resolution.

Development of a complex strontium bismuth molybdate material: Microstructural, electrical, and leakage current characteristics for storage and electronic device application

In this article, synthesis (solid-state reaction) and characterizations of a complex strontium bismuth molybdate material have been reported. The scanning electron microscopic image suggests the existence of grains of various sizes and shapes that are evenly dispersed, accompanied by small pores. The Maxwell-Wagner dielectric dispersion, relaxation, and transport mechanism have been investigated utilizing dielectric, impedance, and conductivity spectrum within the studied experimental frequency (1 kHz–1 MHz) and temperature (25–500 °C) range. The energy storage efficiency is 56.13 %, calculated by the loop of electric polarization. The results of temperature-dependent resistance suggest that the prepared material can be used for PTC thermistors, sensors, and other related devices. The varistor constants β1 and β2 indicate the presence of non-Ohmic and SCLC conduction mechanisms, which are also suitable for electronic devices.

Study on the Properties of LiTaSiO5-based Lithium Ion Conductors Doped by Acceptors

Lithium-ion conductor plays an important role in the all-solid-state batteries. In this paper, the novel sphene structure LiTaSiO5 lithium-ion conductor material was taken as the research object. The lithium ion concentration can be changed by the acceptor doping of titanium ions. And further, the electrical properties of LiTaSiO5 lithium-ion conductor can be enhanced. Through the AC impedance spectroscopy measurement, the ion conductivity of Li1.1Ta0.9Ti0.1SiO5 sample can reach 1.93×10-5 S/cm at 333 K, which is higher than that of the parent LiTaSiO5 material at the same conditions. Combined with the results of dielectric relaxation spectroscopy, the higher ionic conductivity may be derived from the higher mobile lithium ion concentration in the Li1.1Ta0.9Ti0.1SiO5 compound. The research results have very important theoretical value for the research and design of new sphene-structure lithium-ion conductors.

Dielectric relaxation time of PVAc in terms of hole fraction calculated from the theory of Simha-Somcynsky

The relaxation behavior of chain molecular systems in terms of the free volume has been an ongoing significant approach to comprehend the structural defect connection. Using the recently proposed free volume model, we have investigated the relaxation time of the α-relaxation process of PVAc (polyvinyl acetate) as a function of the hole fraction−the so-called “thermo-occupancy” function−for a broad range of temperatures (320–460 K) and pressures (0–300 MPa). The model is based on merging the equilibrium theory of Simha-Somcynsky on the transport theory of the Eyring Significant Structure. We have discussed and compared this model with the current free volume model. The former is superior and more consistent than the latter. However, we have explored the derivative of the logarithm of relaxation with respect to the hole fraction, named relaxiholibility, which measures how the relaxation time changes with the hole fraction.

Effects of different atomic passivation on conductive and dielectric properties of silicon carbide nanowires

Based on the transport and polarization relaxation theories, the effects of hydrogen, fluorine, and chlorine atom passivation on the conductivity and dielectric properties of silicon carbide nanowires (SiCNWs) were numerically simulated. The results show that passivation can decrease the dark conductivity of SiCNWs and increase its ultraviolet photoconductivity. Among them, the photoconductivity of univalent (H) passivated SiCNWs is better than that of seven-valent (Cl, F) passivated SiCNWs. In terms of dielectric properties, the passivated SiCNWs exhibit a strong dielectric response in both deep ultraviolet and microwave regions. Hydrogen passivation SiCNWs produce the strongest dielectric response in deep ultraviolet, while fluorine passivation SiCNWs produce the strongest dielectric relaxation in the microwave band, which indicates that atomic passivation SiCNWs have a wide range of applications in ultraviolet optoelectronic devices and microwave absorption and shielding.

Structure and dynamics heterogeneity in poly(vinyl acetal)s: The effect of side group length

Understanding on the structure and dynamics of poly(vinyl acetal)s is insufficient due to the complicated chemical structure and amorphous nature of this type of polymers. In this work, we investigate the effect of side group length on structure and dynamics heterogeneity at different length scales spanning from side group, segment, and polymer network by combing dynamic mechanical analysis (DMA), dielectric relaxation spectroscopy (DRS), solid-state NMR, and differential scanning calorimetry analysis (DSC). By increasing the length of acetal side group, its intrinsic dynamics slows down. Taking into account the scale of segment and networks, with the increase of acetal group length, the formation of cross-linking sites formed by the hydroxyl-rich domain is suppressed, the relaxation distribution of the segment widens, and the volume fraction of rigid component decreases. The effect of side group length on the structure and dynamics heterogeneity of poly(vinyl acetal)s at different scales results in significant changes in material properties such as the non-monotonic change in loss factor value (tan δ) and a monotonous reduction in glass transition temperature (Tg).

Detection of compatibilizer efficiency in conductive polymer blends by impedance spectroscopy: Microstructure evaluation approach

AbstractA novel approach of electrical impedance spectroscopy (EIS) is proposed to investigate the role of a compatibilizer on nanoparticle distribution in polymer blends with a co‐continuous morphology. Polypropylene/poly(ethylene‐co‐vinyl acetate) PP/EVA blends containing 3 vol% carbon nanotubes (CNT) with varying contents of polypropylene‐grafted‐ maleic anhydride (PP‐g‐MA) as compatibilizer were directly melt mixed. Microscopy, rheology, and thermodynamic analyses confirmed the distribution of CNTs in PP, EVA, and their interface. The EIS behavior of the blend nanocomposites was remarkably changed due to the formation of interphase by PP‐g‐MA/CNT. It was found that as the efficiency of compatibilizer increases the frequency dependency of the impedance diminishes showing a significant shift in the frequency cutoff from 104 Hz to 5 × 105 Hz. The EIS results also showed that compatibilizer can affect the loss factor. Incorporating 5 vol% or 10 vol% of the compatibilizer slightly reduced the loss factor, but a considerable reduction was observed at 20 vol% at which a conductive continuous interphase of compatibilizer formed at the interface. Moreover, the presence of compatibilizer led to a remarkable increase in dielectric constant by four orders of magnitude. EIS can effectively and comfortably trace the performance of a compatibilizer in a conductive polymer blend nanocomposite.Highlights EIS measurements describe microstructure of conductive polymer blend. EIS detects morphology development of a compatibilizer at varying contents. Migration of compatibilizer intensifies the Nyquist diameter decrement. Compatibilizer decreases dielectric relaxation time.

Dielectric Depiction of 1-Butyl-3-methylimidazolium Tetrafluoroborate/1-Butyl-3-methylimidazolium 1,4-Bis(2-ethylhexyl) Sulfosuccinate/Benzene Microemulsions: Percolation, Interface Polarization, and Electrical Parameters.

Two dielectric relaxations located at approximately 10 and 300 MHz were analyzed in the microemulsion composed of the polar ionic liquid (PIL) 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]), the surface-active ionic liquid (SAIL) 1-butyl-3-methylimidazolium 1,4-bis(2-ethylhexyl) sulfosuccinate ([bmim][AOT]), and benzene. The curve of the dc conductivity vs PIL weight fraction shows two inflection points, namely, 16.69 and 27.90 wt %, which are used to divide the PIL/O, bicontinuous (B.C.), and O/PIL subregions. The critical exponents of percolation u = 0.75, 0.79, and 0.80 are suggested from the scaling dependence of dc conductivity on the PIL weight fraction, together with frequency dependences of both permittivity and loss angle, which all infer that static percolation occurs in the microemulsion. Only one dielectric relaxation at high frequency was observed in the PIL/O subregion, when the concentration increased to the boundary between the PIL/O and B.C. subregions; the second dielectric relaxation appeared at low frequency. The high-frequency relaxation is caused by interfacial polarization. The low-frequency relaxation is attributed to the dipole-oriented polarization of AOT-. When the oil content of the system was reduced, the interface became softer to allow more AOT- to rotate, and the cation shifted from moving around its long axis to rotating along its short axis. The static dielectric constant of [bmim][AOT] was given. The dielectric constants and conductivity of the dispersed and continuous phases in the PIL/O and O/PIL subregions were calculated from the dielectric parameters of high-frequency relaxation.

Hysteresis and Its Correlation to Ionic Defects in Perovskite Solar Cells.

Ion migration has been reported to be one of the main reasons for hysteresis in the current-voltage (J-V) characteristics of perovskite solar cells. We investigate the interplay between ionic conduction and hysteresis types by studying Cs0.05(FA0.83MA0.17)0.95Pb(I0.9Br0.1)3 triple-cation perovskite solar cells through a combination of impedance spectroscopy (IS) and sweep-rate-dependent J-V curves. By comparing polycrystalline devices to single-crystal MAPbI3 devices, we separate two defects, β and γ, both originating from long-range ionic conduction in the bulk. Defect β is associated with a dielectric relaxation, while the migration of γ is influenced by the perovskite/hole transport layer interface. These conduction types are the causes of different types of hysteresis in J-V curves. The accumulation of ionic defects at the transport layer is the dominant cause for observing tunnel-diode-like characteristics in the J-V curves. By comparing devices with interface modifications at the electron and hole transport layers, we discuss the species and polarity of involved defects.

Double Dielectric Relaxation of Oil Nanofluids with Graphite and Carbon Nanotubes

Double Dielectric Relaxation of Oil Nanofluids with Graphite and Carbon Nanotubes

Study of dielectric and electrical properties of novel lead-free double perovskite oxide

The current work focuses on the synthesis of lead free novel double perovskite oxide and detailed investigation of its dielectric and electrical characteristics. Single phase lead free double perovskite Pr2FeCrO6 (PFCO) is prepared by co-precipitation technique. Structural studies reveal orthorhombic structure with Pbnm space group. Scanning electron microscopic study shows mixed type of grains; spherical and rectangular grains forming layered structures with few pores. Bonding features and local structure are analyzed via FTIR and Raman spectroscopy. Optical absorption study show narrow energy band gap of 2.14 eV. Room temperature dielectric studies show colossal dielectric constant (∼104) with low loss. The dielectric relaxation dynamics are studied in the temperature range; 25° to 200 °C. The detailed investigation of electrical properties and conduction mechanism in PFCO is carried out via impedance spectroscopy.

Phase transitions and dynamics in ionic liquid crystals confined in nanopores.

We investigate the phase-transition behavior of ionic liquid crystals, namely 1-methyl-3-alkylimidazolium tetrafluoroborate, [Cnmim]BF4, confined in cylindrical nanopores using differential scanning calorimetry, x-ray scattering, and dielectric relaxation spectroscopy. Here, n is the number of carbon atoms in the alkyl part of this ionic liquid crystal. For n = 10 and 12, the isotropic liquid phase changes to the smectic phase and then to a metastable phase for the cooling process. During the subsequent heating process, the metastable phase changes to the isotropic phase via crystalline phases. The transition temperatures for this ionic liquid crystal confined in nanopores decrease linearly with the increase in the inverse pore diameter, except for the transitions between the smectic and isotropic phases. In the metastable phase, the relaxation rate of the α-process shows the Vogel-Fulcher-Tammann type of temperature dependence for some temperature ranges. The glass transition temperature evaluated from the dynamics of the α-process decreases with the decrease in the pore diameter and increases with the increase in the carbon number n. The effect of confinement on the chain dynamics can clearly be observed for this ionic liquid crystal. For n = 10, the melting temperature of the crystalline phase is slightly higher than that of the smectic phase for the bulk, while, in the nanopores, the melting temperature of the smectic phase is higher than that of the crystalline phase. This suggests that the smectic phase can be thermodynamically stable, thanks to the confinement effect.

The Universal Scaling of Dielectric Response as a Tool in the Description of a Complex Dynamic of 4′-Butyl-4-(2-methylbutoxy)azoxybenzene (4ABO5*)

The results of dielectric relaxation spectroscopy of the chiral liquid crystal 4′-butyl-4-(2-methylbutoxy)azoxybenzene in the crystal phase are presented. The scaling procedure showed complex molecular dynamics and allows one to decompose the observed relaxation process into two closely located relaxation processes around the short molecular axis. Temperature dependences of relaxation times characterizing flip-flop motions (rotation around the short molecular axis) and rotation around the long molecular axis are of the Arrhenius type.

Anatomy of the dielectric behavior of methyl-m-toluate glasses during and after vapor deposition.

Glassy films of methyl-m-toluate have been vapor deposited onto a substrate equipped with interdigitated electrodes, facilitating in situ dielectric relaxation measurements during and after deposition. Samples of 200nm thickness have been deposited at rates of 0.1 nm/s at a variety of deposition temperatures between 40K and Tg = 170K. With increasing depth below the surface, the dielectric loss changes gradually from a value reflecting a mobile surface layer to that of the kinetically stable glass. The thickness of this more mobile layer varies from below 1 to beyond 10nm as the deposition temperature is increased, and its average fictive temperature is near Tg for all deposition temperatures. Judged by the dielectric loss, the liquid-like portion of the surface layer exceeds a thickness of 1nm only for deposition temperatures above 0.8Tg, where near-equilibrium glassy states are obtained. After deposition, the dielectric loss of the material positioned about 5-30nm below the surface decreases for thousands of seconds of annealing time, whereas the bulk of the film remains unchanged.

Understanding the dielectric relaxation of liquid water using neural network potential and classical pairwise potential

Understanding the role of hydrogen bond networks in determining the relaxation dynamics is essential for understanding natural phenomena in liquid water. Classical pairwise additive models have been widely utilized for elaborating the underlying mechanism behind the relaxation phenomena. However, they have shown their limits due to either the absence or inaccurate descriptions of many-body and medium-to-long-range interactions. This work demonstrates that the Deep Potential Molecular Dynamics (DPMD) model trained with SCAN functional help calculate the dielectric constant at the accuracy of the first-principles simulations. The DPMD model outperforms the classical force fields (SPC/Fw and TIP4P/ε) in predicting dielectric spectra especially in replicating high-frequency excesses, attributed to its adeptness in simulating intricate hydrogen bond networks. Through a comprehensive analysis of the simulation results, it becomes evident that only the DPMD model effectively accommodates a wide range of hydrogen bond coordination scenarios thereby characterizing the intricate nature of the hydrogen bond network. This adaptability stems from the intricate interplay of many-body interactions and intramolecular dynamics. In addition, orientation defects within the DPMD model play a significant role in shaping the potential energy barrier due to the adaptability.

Structural, morphological, optical, magnetic and impedance spectroscopic properties of Ni0·5Fe2·5O4 nanoparticles synthesized by the self-combustion method

The synthesis of Ni0·5Fe2·5O4 nanoparticles was successfully carried out by the self-combustion method using glycine as fuel. Analysis of the XRD measurements indicates the formation of a cubic spinel monophase with the space group (Fd-3m) and a nanometric crystallite size. According to the optical study, this sample shows strong absorption in the visible range with a gap energy of 3.7 eV, making it a good candidate for optoelectronic and photovoltaic applications. Complex impedance spectroscopy was carried out in the temperature range 300–480 K with the frequency varying between 40 Hz and 5 MHz. The frequency dependence of the dielectric constant was explained in terms of charge carrier transport between Fe2+ and Fe3+, while its temperature dependence indicates dielectric relaxor behavior. The scaling law shows a perfect superposition of impedance and modulus spectrum in the temperature range studied which confirms that the increase of temperature does not bring any change on the mechanism of relaxation. For the electrical properties, the conductivity study shows a semiconducting behavior with a predominance of the Non-Overlapping Small Polaron Tunneling (NSPT) model over the conduction process. The dc conductivity and jump frequency are positively correlated by the extracted activation energies. Summerfield scaling leads to the superposition of the conductance spectra into a single main curve, confirming the validity of this approach. The low value of the dielectric loss and the high value of the permittivity at room temperature and at low frequencies make this sample a potential candidate for energy storage and microwave devices. In addition, the dependence of the magnetisation on the applied magnetic field has been studied in depth by adjusting the hysteresis cycle by different laws of the saturation approach.

Tracing the slow Arrhenius process deep in the glassy state-quantitative evaluation of the dielectric relaxation of bulk samples and thin polymer films in the temperature domain.

The slow Arrhenius process (SAP) is a dielectric mode connected to thermally activated equilibration mechanisms, allowing for a fast reduction in free energy in liquids and glasses. The SAP, however, is still poorly understood, and so far, this process has mainly been investigated at temperatures above the glass transition. By employing a combination of methods to analyze dielectric measurements under both isochronal and isothermal conditions, we were able to quantitatively reproduce the dielectric response of the SAP of different polymers and to expand the experimental regime over which this process can be observed down to lower temperatures, up to 70K below the glass transition. Employing thin films of thicknesses varying between 10 and 800nm, we further verified that the peak shape and activation energy of the SAP of poly(4-bromostyrene) are not sensitive to temperature, nor do they vary upon confinement at the nanoscale level. These observations confirm the preliminary trends reported for other polymers. We find that one single set of parameters-meaning the activation barrier and the pre-exponential factor, respectively, linked to the enthalpic and entropic components of the process-can describe the dynamics of the SAP in both the supercooled liquid and glassy states, in bulk and thin films. These results are discussed in terms of possible molecular origins of the slow Arrhenius process in polymers.

Engineered nanocomposites through embedding of smaller “organic inorganic” nanoparticles in thermoplastic Poly(2-Vinylpyridine) polymer matrix

Polymer nanocomposites (PNCs) are significant for modern and future applications owing to their multifunctionality promoted by morphology and tailored interfaces between the constituents. However, ‘forward’ engineered polymer (host) composites with smaller size nanoparticles (guest) providing desired properties remains challenging as they depend upon nanoparticles aggregation, size, shape, and loading (volume or weight) fraction. This study strategically designs and develops PNCs comprising thermoplastic poly (2-vinylpyridine) (P2VP) polymer matrix impregnated with spherical polyhedral oligomeric silsesquioxane (N-POSS) nanoparticles (diameter ∼2–5 nm) and anisotropic planar nitrogenated graphene nanoribbons (GNR, strip width ∼5–10 nm) commensurate with polymer chain radius of gyration, Rg, (or segment length ∼1.5 nm) and comparable energy scales of electrostatic interaction and attractive hydrogen bonding. We investigated static and dynamic structure and thermophysical properties to correlate with interfacial regions and the results are compared with larger graphene oxide (GO, lateral dimension ∼100–200 nm) nanosheets and silica (SiO2, ∼25–50 nm) particles. While electron microscopy revealed nanoparticle distribution, the lattice bonding, conjugation length, and mechanical properties are determined from micro-Raman spectroscopy and atomic force microscopy, respectively. The differential scanning calorimetry provided a measure of glass transition temperature, Tg, with positive shift of ∼10–18 °C with nanoparticles loading indicating strength of structural relaxation/chain rigidity behavior and thermogravimetric analysis displayed increased thermal stability and conductivity (decreased interfacial resistance). We also measured temperature dependent dc electrical conductivity and dielectric relaxation spectroscopy gaining insights into percolation and dynamic interfacial layer. This study signified understanding of interactions and interfacial regions, key element to demystify the microscopic structure-property relationships.

High Energy Density Achieved in Novel Lead-Free BiFeO3-CaTiO3 Ferroelectric Ceramics for High-Temperature Energy Storage Applications.

The development of high-performance electrostatic energy storage dielectrics is essential for various applications such as pulsed-power technologies, electric vehicles (EVs), electronic devices, and the high-temperature aviation sector. However, the usage of lead as a crucial component in conventional high-performance dielectric materials has raised severe environmental concerns. As a result of this, there is an urgent need to explore lead-free alternatives. Ferroelectric ceramics offer high energy density but lack stability at high temperatures. Here we present a lead-free (1 - x)BiFeO3-xCaTiO3 (x = 0.6, 0.7, and 0.8; BFO-CTO) ceramic capacitor with low dielectric loss, high thermal stability, and high energy density up to ∼200 °C. The introduction of CTO (x = 0.7) to the BFO matrix triggers a transition from the normal ferroelectrics to the relaxor ferroelectrics state, resulting in a high recoverable energy density of 1.18 J cm-3 at 190 °C with an ultrafast dielectric relaxation time of 44 μs. These results offer a promising, environmentally friendly, high-capacity ceramic capacitor material for high-frequency and high-temperature applications.