Debye-type Dielectric Relaxation Research Articles

Probing Dielectric Relaxation of Water at Electrochemical Interfaces with Low-Frequency SERS Spectroscopy

Dynamic and structural properties of hydrogen-bonded water molecules in liquid phase have a significant impact on many chemical and biological processes in aqueous systems. Therefore, the bulk behavior of water is quite actively studied from both experimental and theoretical point of view. In the frequency domain, collective motions of water molecules appear in the terahertz (THz) range. For example, the central frequency of Debye-type dielectric relaxation of water exists at around 1 cm-1, and that of the so-called fast Debye relaxation is found at around 10 cm-1. There are several spectroscopic means to obtain such low-frequency information in the bulk liquid of water. However, for interfacial water molecules interacting with a solid surface, their dynamic behavior of hydrogen-bond networks remains unexplored in the experimental research field, despite of the importance of such behavior to molecular-level understanding of heterogeneous electrochemical processes. The reason for lack of such information is due to lack of adequate surface-selective spectroscopic means. In this talk, in-situ observation of the relaxational and vibrational dynamics of water at electrochemical interfaces is demonstrated using low-frequency surface-enhanced Raman spectroscopy (SERS). In this spectroscopic method, not only intermolecular dynamics but also intramolecular vibrational behaviors of water can be simultaneously monitored due to the intrinsic nature of the inelastic scattering technique accessible in the wide frequency range covering both THz and mid-IR regions, which helps us to understand the relation between microscopic and macroscopic behaviors of water molecules.To obtain low-frequency SERS spectrum, volume Bragg grating filters were used for both monochromatization of He-Ne laser radiation of 632.8 nm and removal of Rayleigh scattered light [1]. SERS-active Au electrodes were prepared by electrochemical surface roughening of Au surface in 0.1M KCl solution. For SERS-active Pt electrodes, monoatomic Pt overlayers were formed on the roughened Au surfaces. SERS spectra for interfacial water were measured on these electrode surfaces under application of electrochemical potentials. The measured spectra were converted to density states of formats by reducing the Purcell factor, Bose-Einstein thermal factor, and frequency factor, which can unveil vibrational features in low-frequency range [2-5].The measured spectra clearly showed potential-dependent features in the THz region. According to the previously reported spectra for bulk water, these features were assigned to the fast Debye relaxation component and two intermolecular vibration modes of interfacial water layer. By analyzing the observed spectral features by the assistance of classical molecular dynamics (MD) simulations, we found that the potential-induced change of water orientation causes formation of local defects in hydrogen-bonded networks of interfacial water layer and the lateral mobility of such defects on negatively charged surface is larger than that on positively charged surface [6]. Figure shows the dynamical behavior of potential-induced defects in hydrogen-bonded networks of interfacial water molecules on negatively and positively charge surfaces. The details will be discussed in the presentation.[1] M. Inagaki, K. Motobayashi, K. Ikeda, J. Phys. Chem. Lett., 8, 4236-4240 (2017).[2] M. Inagaki, T. Isogai, K. Motobayashi, K. -Q. Lin, B. Ren, K. Ikeda, Chem. Sci., 11, 9807-9717 (2020).[3] M. Inagaki, K. Motobayashi, K. Ikeda, Nanoscale, 12, 22988-22994 (2020).[4] R. Kamimura, T. Kondo, K. Motobayashi, K. Ikeda, Phys. Status Solidi B, 259, 2100589 (2022).[5] T. Kondo, M. Inagaki, K. Motobayashi, K. Ikeda, Catal. Sci. Technol., 12, 2670-2676 (2022).[6] T. Isogai, M. Inagaki, M. Uranagase, K. Motobayashi, S. Ogata, K. Ikeda, submitted. Figure 1

Engineering DyCrO3 ceramics toward room-temperature high-κ dielectric applications

The search for a high-κ dielectric material that combines a high dielectric constant (ϵ′) and low dielectric loss is very crucial because of its widespread use in gate dielectrics to avoid the leakage current that arises due to continued miniaturization of present SiO2-based metal-oxide semiconductor field-effect transistor devices. RCrO3 (R is a rare-earth ion) materials have been at the center of interest because of their intriguing ferroelectric and magnetic properties, as well as their room-temperature colossal dielectric constant (CDC) values. Although CDC (ϵ′∼104) in RCrO3 materials is quite common, it is unsuitable for device applications since it is associated with a larger dielectric loss value (tan δ∼7 at 11 kHz). Here we have focused on polycrystalline DyCrO3, prepared using multiple synthesis techniques, and thoroughly investigated the origin and tuning of the various dielectric relaxations that give rise to CDC and large dielectric loss values. A clear understanding of the origin of dielectric relaxations enables us to design a specially synthesized DyCrO3 (SPS-DCO) in which the extrinsic dielectric relaxations driven large dielectric loss values can be completely suppressed and which is found to be associated with optimized high-κ dielectric properties [ϵ′∼130, tan δ∼0.06, and temperature coefficient of dielectric constant (TCϵ) ∼ 2280 ppm/K at 11 kHz, 300 K]. The only remaining intrinsic Debye-type dielectric relaxation in SPS-DCO arises due to electric-field-assisted charge hopping among various valences of Cr (investigated using x-ray photoelectron spectroscopy) that presently limits the lowest attainable loss value.

Impedance Spectroscopy and Study of Electrical Properties of Pb(Zr<sub>0.52</sub>Ti<sub>0.48</sub>)<sub>1-x</sub>Fe<sub>x</sub>O<sub>3-x</sub> (0≤x≤0.20) Ceramics

Iron substituted Lead zirconate titanate nanoparticles Pb (Zr0.52Ti0.48) 1-x FexO3-x (PZTFx) (for (x=0.00, 0.025, 0.05, 0.075, 0.10, 0.15 and 0.20) was prepared using the sol-gel route in the morphotropic phase boundary (MPB) region. The X-ray diffraction data revealed the formation of both rhombohedral and tetragonal structures. The microstructural properties of the compounds were examined through the scanning electron microscopy (SEM) technique. The impedance spectroscopy and conductivity spectroscopy were carried out over a wide range of temperatures (RT–400°C) and frequencies (100 Hz–2 MHz) to investigate the grain and grain boundary effect on the electrical properties of PZTFx. The complex impedance analysis data have been presented in the Nyquist plot which is used to identify the corresponding equivalent circuit and fundamental circuit parameters. Cole– Cole plots indicate Debye-type dielectric relaxation and the grain boundaries resistance is dominant at room temperature. The Nyquist plot showed the negative temperature coefficient of resistance (NTCR) character of PZTFx ceramics. The dielectric properties of (PZTFx) ceramics as a function of temperature are studied and displayed a resonance phenomenon for all samples. Temperature-dependent conductivity behavior indicated an Arrhenius type of thermally activated process in the low-temperature region. Activation energy has been calculated from the temperature-dependent DC electrical conductivity measurements for all the samples.

Fluorosumanenes as building blocks for organic crystalline dielectrics

Abstract Organic crystalline dielectric materials are attractive target in the field of materials chemistry. In their designing strategy, the molecular motion induced by the external dielectric field is required to maximize the polarization effect in the materials to realize a large dielectric constant. Especially, the molecular motion of curved-π aromatics such as C60 and their supramolecular complexes are the known to show characteristic smoothness in the solid state. In this context, we focused on the in-plane motion of the one of the representative buckybowl, sumanene (Sum) in its curve-to-curve-contacted columnar structure as the new platform of the motion for the emergence of dielectric response. The newly designed and synthesized fluorinated sumanene, 1,1-difluorosumanene (F2-Sum), which possesses two fluorine atoms on the same benzylic carbon of pristine sumanene showed a large dipole moment along the in-plane direction. Thermal analyses, variable temperature X-ray diffraction and IR measurements indicated the presence of in-plane motion of F2-Sum although no clear phase transition was involved. This thermal property of F2-Sum realized an anisotropic dielectric response with a Debye-type dielectric relaxation in the single crystalline state. Further trials to form the solid solution of Sum and F2-Sum in various mixing ratio realized the tuning of the dielectric property.

Water and oxygen co-induced microstructure relaxation and evolution in CH3NH3PbI3.

Owing to perovskite possessing the outstanding optoelectronic properties, perovskite-based solar cells show prominent performance. The stability of perovskite-based solar cells hampers the progress of commercialization, so it is important to understand the microstructure mechanism of perovskite degradation under the humidity and oxygen environmental conditions. In this study, a meaningful Debye-type dielectric relaxation was observed under water vapor and oxygen co-treatment conditions. Interestingly, the relaxation was not observed under water vapor or oxygen treatment individually. This new dielectric relaxation is identified as a direct result of dipole jump, and its activation energy was measured to be 630 ± 6 meV. According to photoelectron spectroscopy and 13C nuclear magnetic resonance data, we suggest that the dipoles are formed by CH3NH3+ (MA+) and superoxide (O2-), which originate from the distorted crystal lattice and water vapor-weakened hydrogen bonds of Pb-I cages. In addition, the activation energy fitted by dielectric relaxation might be the energy of ion migration. This study contributes to understanding the mechanism of perovskite degradation from the view of microstructure relaxation and evolution, and also provides a method for the analysis of ion migration energy.

Effect of IL incorporation on ionic transport in PVdF-HFP-based polymer electrolyte nanocomposite doped with NiBTC-metal-organic framework

Ni-based metal-organic framework (MOF), nickel 1,3,5-benzene tricarboxylate (NiBTC) has been synthesized by solvothermal method and incorporated with ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4) at varying weight ratios to use as nanofiller in the polymer matrix of poly (vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP). The structural properties of MOF-NiBTC-based composite polymer electrolyte system upon IL incorporation have been investigated by XRD, FTIR, BET, scanning EXAFS and XANES techniques. Shifting of vibrational modes of –COOH groups is observed from FTIR spectra due to strong interaction of Ni metal cluster with BF4− anion of the IL. Local coordination structure and oscillation periodicity of Ni K-edge are investigated in R-space and k-space from the EXAFS as well as XANES spectra. Asymmetric oscillatory behavior with reduction in coordination number is observed upon IL incorporation due to strong interaction of guest IL with the host MOF-NiBTC. Dielectric relaxation and scaling of AC conductivity have been analyzed in the temperature range of 300–380 K and frequency range of 42 Hz–5 MHz. Non Debye type dielectric relaxation dynamics is observed due to short range hopping of ions. Ion concentration and temperature independent scaling behaviors are followed by the composite polymer electrolyte membranes. Optimum ionic conductivity of 6.5 × 10−3 S cm−1 and electrochemical stability up to 5.7 V have been obtained at 50 wt% of IL incorporation in the porous nanocomposite electrolyte system.

The novel dielectric relaxation behavior around the Curie point of (Ba0.7Sr0.3)0.96Y0.04TiO3 ceramics with giant effective permittivity

The temperature (80 K ∼ 423 K) and frequency (40 Hz ∼ 5 MHz) dependence of the permittivity were studied in (Ba0.7Sr0.3)0.96Y0.04TiO3 ceramics. A giant effective permittivity over 105 with a certain frequency and temperature stability and Debye-type dielectric relaxation behavior was observed. The complex impedance spectrum analysis reveals that the giant permittivity is due to the heterogeneous structure with a semiconducting bulk and high resistance electrode–ceramic interface. Deviating from low temperature (below 200 K) thermal activated behavior, the odd change of the characteristic relaxation frequency around the Curie point is observed and proven to be induced by the competition between the positive temperature coefficient of the resistance effect of the bulk ceramic and the dielectric anomaly of the surface layer capacitance, both of which originate from the ferroelectric–paraelectric phase transition.

Dynamics in Supercooled Secondary Amide Mixtures: Dielectric and Hydrogen Bond Specific Spectroscopies.

Alkylacetamide-based model peptides display an intense Debye-type dielectric relaxation. In order to explore the extent to which this feature has to be regarded analogous to that in other supramolecular liquids, notably the monohydroxy alcohols, we applied broadband dielectric, time-dependent solvation, and near-infrared spectroscopies as well as shear rheology and various nuclear magnetic resonance techniques to mixtures of N-methylacetamide (NMA) or N-ethylacetamide (NEA) with N-methylformamide. Compared in the modulus format, dielectric relaxation, solvation dynamics, and mechanical response indicate a common global and local dynamics. The present spin-relaxation measurements reflect motional processes which are significantly faster than the dominant Debye dielectric response, and a similar conclusion is drawn from measurements of the shear viscosity. The NH overtone stretching vibrations reveal a temperature-dependent hydrogen-bond equilibrium that changes its characteristics near temperatures of 325 K. Finally, dielectric low-temperature data recorded for (NEA)0.4(NMF)0.6 mixed with 2-picoline indicate the existence of a critical concentration akin to the situation in various monohydroxy alcohol mixtures.

Structural, ac conductivity scaling and magnetodielectric behaviour of a partially disordered insulating ferromagnetic double perovskite Eu2NiMnO6

Double perovskites are interesting materials with immense prospects for technological implications. A ferromagnetic double perovskite Eu2NiMnO6 with a rare-earth ion was synthesised by a solid state ceramic route. Room temperature x-ray powder diffraction study of the compound revealed a monoclinic P21/n structure associated with anti-phase tilting of the distorted MnO6 and NiO6 octahedra, which influenced its magnetic, electrical, transport and magnetodielectric properties. Analysis of the structural and magnetic data indicated about ~10% disordered arrangements of the Ni/Mn cations and an onset of ferromagnetic-type ordering around temperature Tc ~ 150 K. True long-range ferromagnetic ordering was not obvious because of the observed large difference of field-cooled and zero-field cooled magnetisation below the ferromagnetic ordering around Tc. Eu2NiMnO6 showed quite a high room temperature dielectric permittivity (~103) with moderately low loss (loss tangent ~1.09 at a typical frequency of 10 kHz), and also a considerably low field magnetodielectric response (~10% at 11.6 kHz and at low external field of ~1 T) was observed. Typical Debye-type dielectric relaxation behaviour was revealed from the analysis of the dielectric constant data and interesting scaling behaviour was exhibited by both ac conductivity and electric modulus. Such a high dielectric low loss ferromagnetic double perovskite might be considered as a potential candidate for applications in devices.

Synthesis and characterization of coprecipitation-prepared La-doped BiFeO3 nanopowders and their bulk dielectric properties

Nanocrystalline Bi1−xLaxFeO3 (x = 0, 0.05, 0.1, 0.2, and 0.3) powders with particle sizes of about 50–90 nm were prepared by a simple co-precipitation method. The prepared powders were characterized by X-ray diffraction (XRD), Fourier trans form infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray absorption spectroscopy (XAS), and vibrating sample magnetometer (VSM) techniques. The morphologies of all the Bi1−xLaxFeO3 powders were spherical in shape. The main phase of BiFeO3 with rhombohedral structure was observed in all Bi1−xLaxFeO3 powders. A pure BiFeO3 phase was observed in the powder with x = 0.3 only whereas impurity phases of Bi2O3, Bi24Fe2O29, and Bi25FeO40 were observed in other powders. Grain size of Bi1−xLaxFeO3 ceramics decreased with increasing La doping concentration. The undoped BiFeO3 sample exhibited a high dielectric constant of 1.1 × 104 at room temperature in a low frequency range. The dielectric constant of BiFeO3 ceramics increased after substitution by La3+. A Debye-type dielectric relaxation at low temperatures was observed, which was attributed to the carrier hopping between Fe2+ and Fe3+ ions.

Dielectric Relaxation in Ferroelectric Polymer Films

The dielectric dispersion of poly(vinylidene fluoride-trifluoroethylene) copolymer films prepared using the Langmuir-Blodgett technique is studied. All films of different composition and thickness undergo a Debye type dielectric relaxation. It is found that the relaxation time τ depends on the thickness of the film.

The Effects of Substituent Grafting on the Interaction of pH-Responsive Polymers with Phospholipid Monolayers

pH-responsive amphiphilic polymers with suitable graftings have demonstrated highly efficient cell membrane activity and hence are promising applicants for drug-delivery. Grafting the hydrophobic amino acid l-phenylalanine and the hydrophilic methoxy poly(ethylene glycol) amine onto the pendant carboxylic acid moieties of a linear polyamide, poly(l-lysine isophthalamide), can effectively modify the amphiphilicity and conformation of the amphiphilic polymers. Here, the interactions of these polymers with phospholipid monolayers adsorbed on mercury (Hg) electrodes have been studied. AC voltammetry (ACV), rapid cyclic voltammetry (RCV), and electrochemical impedance spectroscopy (EIS) have been applied to monitor phospholipid monolayer associations with different polymer concentrations under different pH values. The polymers interact reversibly with the monolayer shown by altering the monolayer capacitance and inhibiting the phospholipid reorientation in electric field. Polymer grafting enhances the pH-mediated conformational change of the polymers which in turn increases their phospholipid monolayer activity. The most significant monolayer interactions have been observed with the polymer grafted with hydrophobic l-phenylalanine. A low level of PEGylation of the backbone also increases the monolayer activity. The polymer/DOPC interactions have been represented with an impedance model, which takes account of the interaction giving rise to an increase in monolayer capacitance and inhomogeneity and a Debye type dielectric relaxation. The extent of penetration of the polymers into the monolayer is inversely related to the electrical resistance they give rise to during the Debye relaxation. The cell membrane activities of these amphiphilic polymers have been successfully mirrored in this supported DOPC monolayer system, isolating the key parameters for biomembrane activities and giving insight into the mechanism of the interactions. The conclusions from this study provide strategic directions in material design catering to different requirements in biomedical applications.

Communications: High-pressure dielectric scaling study of a monohydroxy alcohol

Glass forming monohydroxy alcohols show an exponential Debye-type dielectric relaxation, which proceeds slower than the structural relaxation. Dielectric high-pressure measurements of 2-ethyl-1-hexanol reveal that isochronal scaling is violated. Temperature-volume scaling was found to be valid separately for the Debye-type and for the structural relaxation, yielding a scaling exponent of γ≈1.8.

Dielectric relaxation and polaronic conduction in double perovskite La2MgMnO6

The dielectric and conductive characteristics of double perovskite La2MgMnO6 were investigated together with the mixed-valence structure. The magnetic characterization and x-ray photoemission spectroscopy analysis showed the co-presence of Mn3+ and Mn4+. A Debye type dielectric relaxation with an activation energy of 0.33 eV was observed in La2MgMnO6 ceramics. The relaxorlike dielectric characteristic was attributed to the dipolar effects coming from charge carrier hopping between Mn3+ and Mn4+. The dc conductivity of La2MgMnO6 was well fitted using adiabatic small polaron theory, and also correlated with the mixed-valence structure of Mn3+/Mn4+.

Microwave and infrared dielectric response of tunable Ba 1−xSr xTiO 3 ceramics

The dielectric properties, infrared (IR) dielectric response and Raman spectra of tunable microwave (MW) Ba 1− x Sr x TiO 3 ( x = 0.4, 0.5, 0.6 and 0.7) ceramics were studied systematically as functions of composition and temperature. It was found that, with increasing the content of Sr from 40% to 70%, the permittivity of the Ba 1− x Sr x TiO 3 ceramics decreased from 7200 to 640 while the dielectric tunability decreased from 50.1% to 5.4% measured at 10 kHz. It is particularly interesting that the MW dielectric loss tangent was significantly decreased from 1.5 × 10 −2 to 7.4 × 10 −4. Complex permittivity spectra obtained by fitting the infrared data were also extrapolated to MW frequency and compared with the dielectric data near 1 GHz. For the samples with x = 0.4 and x = 0.5, the dielectric loss measured at ∼1 GHz was much higher than that calculated at 10 GHz, which is presumably due to the Debye-type dielectric relaxation in GHz region. However, the dielectric loss of the samples with x = 0.6 and x = 0.7, extrapolated from IR range, was in agreement with that measured at MW frequency. Low-temperature Raman scattering showed that the band at 760 cm −1 assigned to the Ti−O 3 torsional mode markedly sharpens and shifts upward with increasing content of Sr. This is an indication that the bonding between cations and anions was tightened due to the substitution of Ba with Sr, which explains well the decrease in dielectric permittivity, loss and tunability with increasing concentration of Sr.

Dielectric spectroscopy of ultrathin ferroelectric polymer films

The dielectric dispersion of poly(vinylidene fluoride-trifluoroethylene) copolymer films prepared using the Langmuir-Blodgett technique is studied. All films of different compositions and thicknesses undergo a Debye-type dielectric relaxation. The phenomenon of critical slowing down is investigated. It is found that the relaxation time τ and the kinetic coefficient ξ depend on the thickness of the film.

Dielectric Dispersion in Ultrathin Ferroelectric Polymer Films

Dynamic dielectric measurements were carried out for Langmuir-Blodgett films based on vinylidene fluoride with trifluoroethylene copolymers P(VDF/TrFE). Debye-type dielectric relaxation has been revealed for all films of different composition and thickness. The values of the relaxation time and the damping coefficient depend on the film thickness. Frequency and temperature dependences of conductivity have been investigated.

Dielectric relaxations and dielectric response in multiferroic BiFeO3 ceramics

Single-phase multiferroic BiFeO3 ceramics were fabricated using pure precipitation-prepared BiFeO3 powder. Dielectric response of BiFeO3 ceramics was investigated over a wide range of temperature and frequency. Our results reveal that the BiFeO3 ceramic sintered at 700 °C exhibited high dielectric permittivity, and three dielectric relaxations were observed. A Debye-type dielectric relaxation at low temperatures (−50 to 20 °C) is attributed to the carrier hopping process between Fe2+ and Fe3+. The other two dielectric relaxations at the temperature ranges 30–130 °C and 140–200 °C could be due to the grain boundary effect and the defect ordering and/or the conductivity, respectively.

Dielectric relaxations of yttrium iron garnet ceramics over a broad temperature range

Dielectric response of Y3Fe5O12 ceramics was investigated over broad temperature and frequency ranges. Three dielectric relaxations were identified in the temperature range from 125to620K. A Debye-type dielectric relaxation at low temperatures (125–320K) with an activation energy of 0.29eV is shown to originate from the carrier hopping process between Fe2+ and Fe3+. In a higher temperature range (320–620K), a low frequency (f≦10kHz) dielectric relaxation with an activation energy of 0.84eV most likely arises from the inhomogeneous structure, such as grain boundaries. Another dielectric relaxation in a wider frequency range has a similar activation energy with conduction (Ea=1.00eV) suggests that it can be attributed to the conduction.

SWITCHING AND DIELECTRIC RELAXATION IN NANOSTRUCTURE FERROELECTRICS FROM LANGMUIR-BLODGETT COPOLYMER FILMS

ABSTRACT The switching kinetics and dynamic dielectric measurements were carried out for multilayered ferroelectric Langmuir-Blodgett (LB) films based on vinylidene fluoride-trifluoroethylene copolymers P(VDF-TrFE). The switching kinetics of ultrathin films with thickness of 5–15 nm is well described by Landau-Khalatnikov equation and shows the critical behavior. Debye type dielectric relaxation has been revealed and investigated in the ferroelectric phase of LB films. The temperature dependence of relaxation time τ has a critical slowing-down phenomenon near the phase transition. The values of τ and damping coefficient ξ obtained from dielectric relaxation are by many orders of value smaller then the values of switching time and ξ characterizing the ferroelectric switching of ultrathin films.