Dielectric Contribution Research Articles

An Atomic Insight into the Chemical Origin and Variation of the Dielectric Constant in Liquid Electrolytes

AbstractThe dielectric constant is a crucial physicochemical property of liquids in tuning solute–solvent interactions and solvation microstructures. Herein the dielectric constant variation of liquid electrolytes regarding to temperatures and electrolyte compositions is probed by molecular dynamics simulations. Dielectric constants of solvents reduce as temperatures increase due to accelerated mobility of molecules. For solvent mixtures with different mixing ratios, their dielectric constants either follow a linear superposition rule or satisfy a polynomial function, depending on weak or strong intermolecular interactions. Dielectric constants of electrolytes exhibit a volcano trend with increasing salt concentrations, which can be attributed to dielectric contributions from salts and formation of solvation structures. This work affords an atomic insight into the dielectric constant variation and its chemical origin, which can deepen the fundamental understanding of solution chemistry.

An Atomic Insight into the Chemical Origin and Variation of the Dielectric Constant in Liquid Electrolytes.

The dielectric constant is a crucial physicochemical property of liquids in tuning solute-solvent interactions and solvation microstructures. Herein the dielectric constant variation of liquid electrolytes regarding to temperatures and electrolyte compositions is probed by molecular dynamics simulations. Dielectric constants of solvents reduce as temperatures increase due to accelerated mobility of molecules. For solvent mixtures with different mixing ratios, their dielectric constants either follow a linear superposition rule or satisfy a polynomial function, depending on weak or strong intermolecular interactions. Dielectric constants of electrolytes exhibit a volcano trend with increasing salt concentrations, which can be attributed to dielectric contributions from salts and formation of solvation structures. This work affords an atomic insight into the dielectric constant variation and its chemical origin, which can deepen the fundamental understanding of solution chemistry.

Lattice contributions to the anisotropic dielectric response of rare-earth langasites

We investigate the phonon spectrum of pure and rare-earth substituted langasites. For electric fields oriented along the $c$ axis, a strong low-frequency phonon is observed, softening at lower temperature in all samples studied. The dielectric contribution and temperature dependence of this mode is the primary source of the large $[\ensuremath{\varepsilon}(0)\ensuremath{\sim}100]$ static dielectric permittivity observed in these systems. Softening of this mode with increasing mass of the rare-earth substitutes further suggests that langasites are close to a structural instability at low temperatures. The application of a magnetic field to a diluted Ho-langasite sample reveals a shift in the strong absorption band at THz frequencies associated with this soft lattice mode, suggesting spin-lattice effects may also be at play in these systems.

Terahertz Reading of Ferroelectric Domain Wall Dielectric Switching

Ferroelectric domain walls (DWs) are important nanoscale interfaces between two domains. It is widely accepted that ferroelectric domain walls work idly at terahertz (THz) frequencies, consequently discouraging efforts to engineer the domain walls to create new applications that utilize THz radiation. However, the present work clearly demonstrates the activity of domain walls at THz frequencies in a lead-free Aurivillius phase ferroelectric ceramic, Ca0.99Rb0.005Ce0.005Bi2Nb2O9, examined using THz-time-domain spectroscopy (THz-TDS). The dynamics of domain walls are different at kHz and THz frequencies. At low frequencies, domain walls work as a group to increase dielectric permittivity. At THz frequencies, the defective nature of domain walls serves to lower the overall dielectric permittivity. This is evidenced by higher dielectric permittivity in the THz band after poling, reflecting decreased domain wall density. An elastic vibrational model has also been used to verify that a single frustrated dipole in a domain wall represents a weaker contribution to the permittivity than its counterpart within a domain. The work represents a fundamental breakthrough in understanding the dielectric contributions of domain walls at THz frequencies. It also demonstrates that THz probing can be used to read domain wall dielectric switching.

Dielectric contribution of the IR absorption bands of porous organosilicate glass thin films on a platinum sublayer

Reduction of interconnect capacitance is one of the key ways to increase the speed of an ultra-large-scale integrated circuit (ULSI). A porous organosilicate glass (OSG) thin film on a platinum sublayer was used as a test vehicle for modelling the conductor–insulator electrodynamic properties in an ULSI. Investigation of the structure and residual effect on the dielectric contributions of the IR absorption bands is a direct approach to control the dielectric properties of the film. The absorption band dispersion was simulated by the Drude–Lorentz equations within a framework consisting of a two-layer medium model. The contributions to the dielectric permittivity of IR absorption bands in thin OSG films with different volume porosities were determined. It was shown that the total dielectric permittivity in the IR region was approximately 10% lower than that at low frequencies of the order of 100 kHz. An additional contribution can arise as a result of low-energy excitations and H2O electrodipole relaxation in the microwave—THz range.

Observation of the relaxation process in fluoroelastomers by dielectric relaxation spectroscopy

The complex dielectric permittivity of fluoroelastomers in response to both frequency and temperature variations was thoroughly investigated by dielectric relaxation spectroscopy. To characterize the various types of relaxation processes, the dispersion spectra of permittivity in the frequency domain were successively deconvoluted using a newly developed simulation program that uses the empirical Havriliak-Negami model based on the Debye dielectric model and conductivity contribution. At 233 K ≤ T ≤ 290 K, the α and β relaxation processes were independently observed; they merged at T ≥ 290 K. At T > 303 K, and both Maxwell-Wagner-Sillars (MWS) relaxation, known as interfacial polarization, and conductivity relaxation processes were observed. From the α relaxation process, which is related to the glass transition phenomenon, the glass transition temperature Tg was determined using the Vogel-Fulther-Tamman-Hesse (VFTH) temperature dependence law; the result was similar to the estimate of Tg obtained using differential scanning calorimetry. The temperature dependence of conductivity complies well with VFTH behaviors, whereas the β and MWS processes can be described using the Arrhenius temperature dependence law. The corresponding activation energies of the rotational side groups and DC conductivity were obtained.

Thermomechanical properties of honeycomb lattices from internal-coordinates potentials: the case of graphene and hexagonal boron nitride

Lattice dynamics in low-dimensional materials and, in particular, the quadratic behaviour of the flexural acoustic modes play a fundamental role in their thermomechanical properties. A first-principles evaluation of these can be very demanding, and can be affected by numerical noise that breaks translational or rotational invariance. In order to overcome these challenges, we study the Gartstein internal-coordinate potential and tune its 13 parameters on the first-principles interatomic force constants for graphene. We show that the resulting potential not only reproduces very well the phonon dispersions of graphene, but also those of carbon nanotubes of any diameter and chirality. The addition of a cubic term allows also to reproduce the dominant anharmonic terms, leading to a very good estimate of the lattice thermal conductivity. Finally, this potential form works very well also for boron nitride, provided it is fitted on the short-range (analytical) part of the interatomic force constants, and augmented thereafter with the long-range dielectric contribution. This consideration underscores how potentials based on short-ranged descriptors should be fit, in polar materials, to the short-range part of the first-principles interactions, and complemented by long-range analytical dielectric models parametrized on the same first-principles calculations.

Comparison of dielectric loss in titanium nitride and aluminum superconducting resonators

Lossy dielectrics are a significant source of decoherence in superconducting quantum circuits. In this report, we model and compare the dielectric loss in bulk and interfacial dielectrics in titanium nitride (TiN) and aluminum (Al) superconducting coplanar waveguide resonators. We fabricate isotropically trenched resonators to produce a series of device geometries that accentuate a specific dielectric region's contribution to the resonator quality factor. While each dielectric region contributes significantly to loss in TiN devices, the metal–air interface dominates the loss in the Al devices. Furthermore, we evaluate the quality factor of each TiN resonator geometry with and without a post-process hydrofluoric etch and find that it reduced losses from the substrate–air interface, thereby improving the quality factor.

Coherent superconducting qubits from a subtractive junction fabrication process

Josephson tunnel junctions are the centerpiece of almost any superconducting electronic circuit, including qubits. Typically, the junctions for qubits are fabricated using shadow evaporation techniques to reduce dielectric loss contributions from the superconducting film interfaces. In recent years, however, sub-micrometer scale overlap junctions have started to attract attention. Compared to shadow mask techniques, neither an angle dependent deposition nor free-standing bridges or overlaps are needed, which are significant limitations for wafer-scale processing. This comes at the cost of breaking the vacuum during fabrication, but simplifies integration in multi-layered circuits and implementation of vastly different junction sizes and enables fabrication on a larger scale in an industrially standardized process. In this work, we demonstrate the feasibility of a subtractive process for the fabrication of overlap junctions. In an array of test contacts, we find low aging of the average normal state resistance of only 1.6% over 6 months. We evaluate the coherence properties of the junctions by employing them in superconducting transmon qubits. In time domain experiments, we find that both, the qubit life- and coherence time of our best device, are, on average, greater than 20 μs. Finally, we discuss potential improvements to our technique. This work paves the way toward a more standardized process flow with advanced materials and growth processes, and constitutes an important step for the large scale fabrication of superconducting quantum circuits.

Pyroelectric performance, dielectric response and conductive mechanism of BCHT lead-free piezoelectric ceramics via powder injection molding

Lead zirconate titanate (PZT) ceramics exhibit excellent piezoelectric performance, which expands piezoelectric applications scope. However, the usage of toxic PbO causes serious harm to humans and ecological environment. Lead-free environment friendly (Ba0.85Ca0.15)(Hf0.10Ti0.90)O3 (BCHT) ceramics exhibit enhanced electrical properties when prepared via the powder injection molding process, relating to the polymorphic ferroelectric phases coexistence. Excellent pyroelectric properties are obtained in the BCHT ceramics, where pyroelectric anomaly and peak appear around 45 °C and 95 °C in temperature dependent pyroelectric coefficient and figures of merit, respectively, which can be attributed to the polymorphic phase transition and ferroelectric phase transition. Abnormal drastic change and large peak values of pyroelectric properties around the Curie temperature TC make the BCHT ceramics promising application for critical temperature detection. The dielectric response contribution was analyzed by Rayleigh formula fitting, where the reversible contribution takes major role at low temperatures and the irreversible contribution takes main effect at high temperatures. The conduction activation energy is 0.71 eV for the BCHT ceramics, which correlates with the increased oxygen vacancies induced by cations evaporation during sintering.

Temperature threshold for localized surface plasmon resonance in glancing angle deposited ultra-thin silver films

Low thickness silver (Ag) coatings (thickness ∼25 nm) were fabricated by electron beam evaporation technique equipped with glancing angle deposition (GLAD, 86°) arrangement at varrying substrate heating temperatures (viz 30 °C, 75 °C, 125 °C and 150 °C). Although all the GLAD-Ag films prepared up to 125 °C temperature were found to be plasmonic in nature, the localized surface plasmon resonance (LSPR) band was more prominent at 125 °C and disappeared at 150 °C temperature. The dielectric contribution in the overall dispersion of sample structure was maximum for 125 °C with dominating metallic contribution observed for 150 °C. Detailed investigation of 125 °C deposited GLAD-Ag sample revealed sharpening of the LSPR band with reduction in film thickness. The ultra-thin coating (∼5 nm) was found to be purely dielectric in nature with the most prominent LSPR band among the others. Overall, the substrate heating temperature of 125 °C was found to be the threshold for fabricating plasmonic GLAD-Ag films with the best result observed for the ultra-thin (∼5 nm) specimen.

Dielectric relaxation, magneto-dielectric coupling, and pyrocurrent anomaly in point defect controlled HoCrO3

HoCrO3, a member of the rare-earth chromate family, is known to exhibit an orthorhombic structure with Pbnm space group in bulk at room temperature. We have employed the pressure driven powder consolidation technique, spark plasma sintering, for synthesizing HoCrO3 powder-compact, which exhibits a superior quality with fewer defects over that synthesized by conventional solid-state sintering (resulting in a large reduction of charge carrier mediated extrinsic dielectric contribution). The powder compact shows magneto-dielectric coupling but does not exhibit a detectable ferroelectric phase in the range of 50 K to 300 K. Low temperature Raman spectra show structural distortions below 250 cm−1, indicating Ho ion displacements. Temperature evolution of the crystal structure using synchrotron x-ray diffraction reveals a probable structural phase transition below 240 K. Pyrocurrent measurement, together with synchrotron x-ray diffraction analysis, further points to a magneto-structural transition at 100 K.

Discharge Energy Efficiency Improvement of P(VDF-HFP) Copolymers Thin Films by Stretching and Electron Beam Irradiation

Toward improving the applications for energy-based technology, dielectric polymers is getting attention due to its relatively high dielectric constant, dielectric breakdown and flexibility, with easily preparation, lightweight and low cost. Dielectric contribution and polarization responses lead to different shape and size of hysteresis loop. This work presents the techniques on reducing domain size for slimmer loop, indicating lower energy loss. As-casted P(VDF-HFP), stretched P(VDF-HFP) and electron irradiated-stretched P(VDF-HFP) thin films were prepared by solution casting method. The irradiation was prepared by emitting electron beam. The dielectric and AC conductivity properties were investigated by LCR meter, while polarization-electric field loops were observed by P-E loop instrument. The results show that stretching and electron beam irradiation significantly increase the dielectric constant of P(VDF-HFP). Their ability on modifying the domain size leads to reduce P-E loop of P(VDF-HFP), followed by reducing energy loss but improving storage energy density and discharge energy efficiency.

A Semi-Analytical Model of High-Permittivity Dielectric Ring Resonators for Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) is an imaging technique exploiting the magnetic resonance (MR) of specific nuclear spins, like protons. In this article, MR probes based on dielectric ring resonators are investigated from a theoretical approach. We take advantage of the high-permittivity and low-loss properties of the ceramic material used for manufacturing these probes for microscopy applications. Magnetic resonance microscopy (MRM) aims at imaging tiny samples with a sufficient resolution to distinguish small details. In this framework, compact resonators, called volume probes, contain the investigated sample and are used for both signal transmission and reception. The newly developed semi-analytical model enables the estimation of the frequency of the first transverse electric mode of a cylindrical resonator. It also provides a method to compute the corresponding magnetic field distribution, the dielectric losses contributions from the probe and the sample, and the signal-to-noise ratio (SNR). The proposed approach aims at providing design guidelines for dielectric probes.

Defect engineering of codoped visible light photosensitized TiO2:WN thin-films for efficient electro-photocatalysis

Abstract Anionic doping, such as nitrogen doping is widely used to visible-light photosensitize TiO2. Unfortunately, this promotes the formation of oxygen vacancies (VO), reducing the per-photon efficiency of TiO2:N. Herein we propose a solution based on defect engineered acceptor-donor passivation of the electronic defects. This is achieved through the in-situ codoping of TiO2 by both W and N dopants, using an RF-magnetron sputtering deposition process. Compositional and structural analyses revealed that we were successful in incorporating both dopants in substitutional locations in the TiO2 lattice. Where nitrogen doping was confirmed to narrow the Eg of the material from 3.2 eV down to ∼2.3eV regardless of doping scheme. Most importantly, high frequency dielectric spectroscopy revealed that codoping greatly reduced VO concentrations, as tracked by their GHz dielectric contribution. Confirming the passivating interplay between both codopants. Finally, these optoelectronic improvements were shown to directly translate into threefold improved visible-light driven net-photocurrents.

Intrinsic and extrinsic dielectric contributions to the electrical properties in CaZrO3-doped KNN-based electrical/optical multifunctional ceramics

In this work, (0.9985 − x)(K0.49Na0.49Li0.02)(Nb0.8Ta0.2)O3–0.0015Ho2O3–xmol%CaZrO3 (KNLNT–Ho–xCZ) lead-free piezoelectric ceramics were prepared by traditional solid-state reaction method. Dielectric, ferroelectric, photoluminescence properties and Rayleigh behavior were studied. The addition of CaZrO3 caused the orthorhombic to tetragonal phase transition temperature TO–T to decrease, and when x ≥ 0.02, the phase structure was converted from orthorhombic–tetragonal coexistence phases to pseudo-cubic one. With the addition of CaZrO3, grain size showed a decreasing trend. Under a wavelength of 453 nm excitation, a strong green emission (~ 551 nm) was observed, corresponding to the transitions of 5S2 → 5I8. Furthermore, Rayleigh analysis showed that doping CaZrO3 reduced the grain size and clamped the domains, making the domain wall movement and domain switching difficult, thus weakening the extrinsic contribution of ceramics.

Influence of dielectric layers on estimates of diffusion coefficients and concentrations of ions from impedance spectroscopy.

We present the analysis of the impedance spectra for a binary electrolyte confined between blocking electrodes with dielectric layers. An expression for the impedance is derived from Poisson-Nernst-Planck equations in the linear approximation taking into account the voltage drop on the dielectric layer. The analysis shows that characteristic features of the frequency dependence of the impedance are determined by the ratio of the Debye length and the effective thickness of the dielectric layer. The impact of the dielectric layer is especially strong in the case of high concentrated electrolytes, where the Debye length is small and thus comparable to the effective thickness of the dielectric layer. To verify the model, measurements of the impedance spectra and transient currents in a liquid crystal 4-n-pentyl-4^{'}-cyanobiphenyl (5CB) confined between polymer-coated electrodes in cells of different thicknesses are performed. The estimates for the diffusion coefficient and ion concentration in 5CB obtained from the analysis of the impedance spectra and the transient currents are consistent and agree with previously reported data. We demonstrate that calculations of the ion parameters from the impedance spectra without taking into account the dielectric layer contribution lead in most cases to incorrect results. Application of the model to analyze violations of the low-frequency impedance scaling and contradictions in the estimates of the ion parameters recently found in some ionic electrolytes are discussed.

Investigations of dielectric properties of wolframite A0.5Zr0.5NbO4 ceramics by bond theory and far-infrared spectroscopy

In this study, intrinsic dielectric properties of monoclinic A0.5Zr0.5NbO4 ceramics (A = Mn, Zn, Mg, Co, Ni) with wolframite structure were investigated by chemical bond theory, infrared and terahertz spectroscopy. According to bond theory, Zr–O bonds and A-O bonds with larger bond susceptibility values provide majority contributions to relative permittivity; while Nb–O bonds dominate the structural stability and oxygen polyhedron distortion. Intrinsic dielectric properties calculated via far-infrared reflectivity spectroscopy are close to experimental properties, which indicates that most of dielectric contributions come from absorptions of structural phonon oscillation and infrared modes of dielectric response in A0.5Zr0.5NbO4 ceramics vary with A-site ions. Furthermore, intrinsic properties estimated by terahertz time domain spectra also testify the effectiveness of theoretical dielectric properties.

Li5Ti2O6F: a new low-loss oxyfluoride microwave dielectric ceramic for LTCC applications

Use of microwave dielectric ceramics can significantly promote the development of communication devices. The primary criteria for determining their applications are excellent microwave dielectric properties and suitability for co-firing with cheap metals (e.g., Ag, Al). This study first reports the low-temperature synthesis of Li5Ti2O6F with a cubic rock salt structure. Li5Ti2O6F was prepared at 880 °C and had er of 19.6, Q × f of 79500 GHz, and τf of − 29.6 ppm/ °C. The infrared reflectivity spectrum revealed that the dielectric contribution of Li5Ti2O6F in the microwave range was mainly affected by phonon absorption. Experimental study indicated that Li5Ti2O6F had good chemical compatibility versus Ag electrode at 880 °C for 2 h. Given these characteristics, Li5Ti2O6F ceramics exhibited potential for low-temperature co-fired ceramic technology.

Collective infrared excitation in rare-earth GdxLa1−xB6 hexaborides

Using Fourier-transform infrared spectroscopy and optical ellipsometry, room temperature spectra of complex conductivity of single crystals of hexaborides Gd$_x$La$_{1-x}$B$_6$, $x$(Gd)$=0$, 0.01, 0.1, 0.78, 1 are determined in the frequency range 30$-$35000$~cm^{-1}$. In all compounds, in addition to the Drude free-carrier spectral component, a broad excitation is discovered with the unusually large dielectric contribution $\Delta$$\varepsilon$=5000 -- 15000 and non-Lorentzian lineshape. It is suggested that the origin of the excitation is connected with the dynamic cooperative Jahn-Teller effect of B$_6$ clusters. Analysis of the spectra together with the results of DC and Hall resistivity measurements shows that only 30$-$50$\%$ of the conduction band electrons are contributing to the free carrier conductivity with the rest being involved in the formation of an overdamped excitation, thus providing possible explanation of remarkably low work function of thermoemission of Gd$_x$La$_{1-x}$B$_6$ and non-Fermi-liquid behavior in GdB$_6$ crystals.