Dielectric Phenomena Research Articles

DIELECTRIC PHENOMENA AT PHASE TRANSITION TEMPERATURE OF NANOCOMPOSITES BASED ON FERROELECTRICS AND NANOCRYSTALLINE CELLULOSE ACETOBACTER XYLINUM

Dielectric phenomena at phase transition temperature for nanoparticles of triglycine sulfate (TGS) and Sodium Nitrite (NaNO2) embedded into the pores of bacterial nanocrystalline cellulose Acetobacter Xylinum have been investigated. It was shown that the phase transition temperature of these ferroelectrics at nanoscale level strongly changes as compared to those of the massif ferroelectrics: for hydrogen-containing triglycine sulfate nanoparticles the phase transition temperature was shifted to higher temperatures and for non-hydrogen-containing Sodium Nitrite nanoparticles – lower temperatures. The obtained results are explained by knowledge of size effects and the interaction between the matrix and ferroelectric inclusions through hydrogen-bond system as well as dipole-dipole interaction between TGS nanoparticles using a mathematical expansion based on Landau-Ginzburg-Devonshire theory.

IEEE Electrical Insulation Magazine, a Publication of DEIS

IEEE Electrical Insulation Magazine is involved, together with its sponsoring society, the Dielectrics and Electrical Insulation Society (DEIS), in providing leadership, coordination, and communication among those who are concerned with dielectric phenomena and measurements and with electrical insulating materials, including their behavior as it affects their use in electrical and electronic apparatus. The Magazine is specifically concerned with publishing articles on the development and characterization of the dielectric, chemical, mechanical, and environmental properties of all vacuum, gaseous, liquid, and solid electrical insulation and with utilization of these materials in circuits and systems under conditions of use. The Magazine is not an alternative to the IEEE Transactions on Dielectrics and Electrical Insulation for traditional academic research or review papers.

In Memory of Christian Mayoux 1936–2020

Christian Mayoux passed away on the 29th of October, 2020, at the age of 84, in Muret, a small town near Toulouse in the south of France, where he used to live since ten years. Christian was born in Pamiers, France, in 1936. He received the Doctorate degree (PhD) in 1961 from the University of Toulouse from which Paul Sabatier University was established in 1969. From 1963 to 1966, he was lecturer at the University before joining the French National Center for Scientific Research (CNRS) and the new born “Laboratoire de Genie Electrique de Toulouse” (LGET). The new lab was under the supervision of Professor R. Lacoste and focused its research on dielectrics and electrical insulation in the context of Electrical Engineering. The LGET researchers were fighting within the French research landscape to launch and organize the new domain of “engineering sciences”. Christian Mayoux investigated the effects of electrical discharges on dielectric surfaces, trying to understand the chemical and physical processes at play at different stages of the interaction. Transformation of the surface for short interaction time with the emergence of specific surface properties, but also surface degradation for longer interaction time, with deleterious effects for the material withstanding were put forward. Following this, a new approach where the surface of a polymer was exposed to different species -electrons, ions, metastables, UV, etc. was brought about with the objective to understand the individual and synergetic effects of each of the energy sources present in a partial discharge. Christian was quickly recognized by the international community for this pioneering work then developed internationally. Later on, starting in 1976, he began to focus on electrical treeing phenomena, and later on water treeing, following at the same time the ideas that emerged from his initial work on partial discharges. On top of that, Christian Mayoux was at the origin of several research areas that are still very active in LAPLACE (the successor of LGET), among them the dielectric barrier discharges at atmospheric pressure that become homogeneous under given circumstances, the luminescence phenomena occurring when an electric field is applied to a dielectric, or the mechanical deformation of a polymer under high electric field. Christian Mayoux received many invitations for giving invited lectures either at international conferences or during seminars. He was awarded the Whitehead Memorial Lecture at the Conference on Electrical Insulation and Dielectric Phenomena (CEIDP) in 2000.

Revisiting the phase sequence and properties of K0.5Na0.5NbO3 ceramics sintered by different processes

In this work, we revisit the phase transition sequence and the effect of the sintering process on the structural, dielectric and polar properties of K0.5Na0.5NbO3 ceramics prepared by conventional sintering, spark plasma sintering and spark plasma texturing. Herein, comparative experimental study of the lattice dynamics, polar and dielectric properties is presented. We observe that the phase transition sequence includes an unreported structural and polar phase at low temperatures, independently on the processing method. Contrarily, we observe apparent changes of the stability temperature interval of the different phases. The dielectric strength and the emergence of a dielectric relaxation phenomenon are also noticeably dependent on the processing method, which can be understood as an effect of the different grain size. The results here reported clearly show the possibility to change physical properties following different sintering routes in order to improve device performance.

DIELECTRIC RELAXATION PHENOMENA IN PARAELECTRIC PHASE OF NANOCRYSTALLINE-TRIGLYCINE SULFATE COMPOSITE

The aim of this work is to clarify dielectric relaxation phenomena in paraelectric phase of composites based on nanocrystalline cellulose and triglycine sulfate. Although the dielectric properties of this material were almost thoroughly investigated, but there has been no study devoted to relaxation anomalies in paraelectric phase. The results showed the presence of Debye-like relaxation at the entire studied frequency range 103 – 106 Hz under a weak electric field of 1 V.m-1 from phase transition temperature in the composite (54 ˚C) to 90 ˚C. In addition, the phenomena were observed at lower frequencies as compared to those of triglycine sulfate single crystals. The results were explained by the assumption based on critical slowing down occurred in the nanoparticles in the composite.

Frequency and thermal studies of dielectric permittivity and Raman analysis of Ba0.97La0.02Ti0.98Nb0.016O3

The dielectric properties of polycrystalline ceramic Ba0.97La0.02Ti0.98Nb0.016O3 (BLTi0.98Nb0.016), elaborated by a molten-salt reaction, were methodically characterized. Phase purity, structure and crystallinity were examined with X-ray diffraction at room temperature, demonstrating pure phase with tetragonal symmetries and a P4/mmm space group for our sample. The frequency and temperature dependence of the dielectric properties showed an excellent response. The real part of permittivity and dielectric tangent decreased with increasing frequency. This can be clarified by Maxwell-Wagner type of polarization as per with Koop’s theory. The temperature dependence of the dielectric properties was examined in the frequency range 1 kHz to 1 MHz. Mostly, these three regions of dielectric relaxations are begun from phase transitions beginning: a cubic-paraelectric to a tetragonal-ferroelectric “C” (at the Curie temperature Tc), after that to an orthorhombic-ferroelectric “T → O” (at TT → O), and lastly to a rhombohedral-ferroelectric “O → R” (at TO → R) resembling to those of pure Barium titanate (BaTiO3, BT). To clarify the dielectric phenomenon, the Curie-Weiss law is investigated. This method is used to describe the ferro–paraelectric transition. The degree of disorder of the Ba0.97La0.02Ti0.98Nb0.016O3 was assessing via the modified Curie-Weiss law. The Raman spectrum was measured at room-temperature, and their variation related to the chemical composition, which affirmed the tetragonal structure for Ba0.97La0.02Ti0.98Nb0.016O3.

Not So Far, Not So Close: A Configurational Study of a Carbon Nanotube Bundle for Better Dielectric Phenomena

Size of pores or spacing among nano‐protrusions such as nanotubes on an electrode surface greatly affects diffusive, viscous, and dielectric phenomena of electrolyte through openings. In this study, a configurational study was conducted to examine the effect of spacing among the single‐walled carbon nanotubes on dielectric and viscous phenomena. Behavior of a polar liquid, acetonitrile, was investigated by molecular simulations at two low densities. Results show that viscosity of the liquid is greatly enhanced by interaction with closely packed tubes' bundle. In conjunction with such increase in viscosity, relaxation of dipoles takes longer times inside such closed packed bundle. Most importantly, spacing among the tubes with diameter D should be at about D/2 in a direction for better dielectric phenomena.

Surface modification of polytetrafluoroethylene thin films by non-coherent UV light and water treatment for electrowetting applications

HypothesisThe electrowetting on dielectric or EWOD phenomenon is used in a wide range of applications, such as Liquid Lenses, Lab-on-Chip devices, or EWOD displays, among others. Its chemical resistance, electrical stability, ease of application, and low cost make polytetrafluoroethylene (PTFE) the preferred hydrophobic dielectric layer for such applications. However, the hydrophobic behaviour represents a challenge for spin coating other layers over its surface. As a consequence, several techniques are implemented to modify the surface of PTFE. These methods are complex, time-consuming, and produce morphology changes over the surface that are difficult and sometimes impossible to recover. In this work, we propose a new surface modification method that is based on a non-coherent UV light exposition method and a specific water treatment, that lead to a change from hydrophobic to hydrophilic, and a perfect recovery from hydrophilic to hydrophobic behaviour. ExperimentsIn this work, the fabrication of the hydrophobic layer treatment starts with the creation of a thin layer of alumina (Al2O3) over a glass substrate using an atomic layer deposition technique (ALD). A mixture of 10:1 FC40 solvent and Teflon Dupont AF1600 was coated over the alumina layer. The Teflon film was exposed to UV light produced by a low-pressure mercury (Hg) lamp for a period that ranges from 3−6 min. The results were analysed by scanning electron microscopy, x-ray spectroscopy, and static deionized water contact angle measurements. FindingsContact angles dependent on UV light exposure time were observed. From the scanning electron microscopy analysis, it was confirmed that the UV treatment does not produce morphology changes over the surface. Nevertheless, the x-ray spectroscopy revealed that the UV exposed samples react when they are brought into contact with deionized water, improving the adhesion of the surface. The original hydrophobic behaviour of the surface is recovered (up to 98 %) after 3 h of thermal treatment. Furthermore, the thermal recovery analysis reveals a correlation between the recovery percentage and the applied temperature.

Effect of heating temperature on structural, magnetic, and dielectric properties of Magnesium ferrites prepared in the presence of Solanum Lycopersicum fruit extract

MgFe2O4 ferrite was synthesized in the presence of Solanum Lycopersicum fruit extract using sol–gel auto-combustion technique and heated from 650 °C to 1050 °C with the difference of 100 °C. The effect of heating temperature on phase purity, crystal structure, and magnetic as well as dielectric properties was systematically investigated. XRD analysis show that all samples consist of a single phase cubic spinel structure. The average crystallite size of heated samples varied from 10 to 26 nm, it was observed that crystallite size increases with the calcination temperature and average grain size was found in between 18 and 65 nm. SEM micrographs show that there is a drastic reduction in the grain size in the sample prepared in presence of tomato extract (65 nm) compared to the sample prepared without tomato extract (373 nm) and heated at 1050 °C for 4 h. All samples belong to soft ferrite (HC ~ 10 to 70 Oe) and possess a multi-domain structure. As heating temperature increases the values of both saturation magnetization (MS) and hyperfine magnetic field (Hhf) are found to increase. The frequency-dependent dielectric phenomenon was observed in all prepared samples and single one-fourth semi-circles observed in Nyquist plot because of the contribution of the grain boundaries over the grain conductions. M″ and Z″ vs frequency plots reveal the absence of Debye relaxation in prepared compositions.

Stability of fractional-order systems with Prabhakar derivatives

Fractional derivatives of Prabhakar type are capturing an increasing interest since their ability to describe anomalous relaxation phenomena (in dielectrics and other fields) showing a simultaneous nonlocal and nonlinear behaviour. In this paper we study the asymptotic stability of systems of differential equations with the Prabhakar derivative, providing an exact characterization of the corresponding stability region. Asymptotic expansions (for small and large arguments) of the solution of linear differential equations of Prabhakar type and a numerical method for nonlinear systems are derived. Numerical experiments are hence presented to validate theoretical findings.

Investigation of dielectric relaxation phenomena and AC electrical conductivity in graphite/carbon nanotubes/engine oil nanofluids

In this paper, we report an investigation on electrical conduction mechanisms of nanofluids based on commercial engine oil loaded with graphite (Gt) and multiwalled carbon nanotubes, at different concentrations. The impedance spectroscopy technique was used to measure the resistance and capacity characterizing each sample in a frequency range 100 Hz–1 MHz and a temperature range 300–400 K. Two formalisms were used to analyze the data: (a) the electrical conductivity which has found to follow the Jonscher’s law with single and double exponents for carbon nanotube concentrations below and above the percolation threshold, respectively, and (b) the complex impedance that has permitted to identify the relaxation peaks according to the Cole–Cole model. Both the two formalisms showed that when the carbon nanotube concentration is higher than the percolation threshold, a positive temperature coefficient and a remarkable change in conductivity were observed, suggesting that the presence of the carbon nanotube greatly affect the electrical properties of the engine oil as a result of additional polarization effect induced by these nanoparticles. Furthermore, the analysis of the temperature dependence of dc conductivity and relaxation time using the Arrhenius equation indicated the addition of carbon nanotubes into engine oil increase the activation energies.

Space Charges as Pre-breakdown Phenomena in Solid Dielectrics: A Concise Approach and Some Critical Comments

This short review deals with some aspects of space charges in solid dielectrics, and in particular in polymeric materials. The relationship between space charges and pre-breakdown events is discussed and the importance of space charges for the breakdown of solid dielectrics is emphasized.

Space Charges as Pre-breakdown Phenomena in Solid Dielectrics: A Concise Approach and Some Critical Comments

Space Charges as Pre-breakdown Phenomena in Solid Dielectrics: A Concise Approach and Some Critical Comments

Super-fast fabrication of self-ordered nanoporous anodic alumina membranes by ultra-hard anodization

Although the fast fabrication of long-range ordered porous anodic alumina (PAA) membranes has already been realized by hard anodization, achieving super-fast oxide growth rates has been still very challenging. Herein, we report a new generation of the anodization process, called ultra-hard anodization (UHA), in which the mean growth rate of self-ordered PAA reached 2900 µm/h in the first 80 s of the process, resulting in a membrane thickness of 58 µm. By comparison, the same thickness can be obtained using the conventional hard anodization and mild anodization processes in 2400 s and 10 h, respectively. While the current density (J) reaches a high value of 2400 mA/cm2, burning and dielectric breakdown phenomena are avoided by controlling the barrier layer temperature and the diffusion length. In addition, the mechanism of oxide growth is explained on the basis of the high field theory and the diffusion-limited path of ionic species through the nanopores, taking into account the effect of temperature and sprinkling rate of electrolyte on J. By blending 0.3 M oxalic acid with phosphoric or sulfuric acid separately, the UHA process is also performed at target voltages ranging from 85 to 150 V, thereby allowing for a wide range of interpore distances. From a practical point of view, we synthesize high aspect ratio polymer nanowires (up to 320 µm) in the resulting membranes. Our findings open a new approach for the super-fast fabrication of the self-ordered PAA, facilitating the development of nanodevices and their commercial applications.

Gd doping effect on structural, electrical and dielectric properties in HoCrO3 orthochromites for electric applications

Abstract In this work, we investigate the structural, electrical and dielectric properties of HoCrO3, Ho0.9Gd0.1CrO3 and HoCr0.9Gd0.1O3 orthochromites successfully synthesized by the sol-gel process. Our samples were characterized by scanning electron microscopy, energy dispersive and X-ray diffraction (XRD) at room temperature. The XRD analysis shows that the samples crystallize in the orthorhombic system with the Pbnm space group. Depending on frequency in the range [40–107Hz] and temperature in the range [160–440K], the electrical properties were explored by impedance spectroscopy measurements. The obtained results demonstrate that the DC electrical conductivity decreases by doping HoCrO3 with Gd in A-site and increases if Gd occupies the B-site of the perovskite. The parent sample shows a semiconductor behavior until 400K where a transition to a metallic one appears. For doped samples, the transition temperature is estimated at 420K. The AC conductivity measurements can be described by the Jonscher power law and the conduction mechanism can be related to the cationic disorder. Electrical results reveal that the contribution of grains and grain boundaries in the conduction process differs according to the site of the doping by gadolinium. Furthermore, the impedance plots were well described by an adequate equivalent circuit taking into account the contributions of grains and grain boundaries. Colossal dielectric permittivities of the order of 105 F/m are obtained and were attributed to the Maxwell-Wagner interfacial effect. The dielectric losses can be described by Giuntini law and the dielectric relaxation phenomenon is shown to be obscured by the DC-conductivity process. The capacitance values are in the order of 10−2 μF for all studied compounds. These results can conduct the use of our compounds towards the electronic devices industry.

Phase-selective conductivity enhancement and cooperativity length in PLLA/TPU nanocomposite blends with carboxylated carbon nanotubes

Transmission electron microscopy, temperature-modulated differential scanning calorimetry, and broadband dielectric spectroscopy were employed to characterize ternary nanocomposites consisting of carboxylated carbon nanotubes (CNT) dispersed in a blend of two immiscible polymers, poly(L,lactide) (PLLA) and thermoplastic polyurethane (TPU). The nanocomposite blends were obtained by melt-compounding of PLLA and TPU in the presence of 0.2 wt-% CNT, either in the presence or absence of a Joncryl® ADR chain extender for PLLA, leading to reactive and non-reactive melt mixed samples. In both cases, the binary PLLA/TPU blend is characterized by phase separation into submicron TPU droplets dispersed in the PLLA matrix, and displays two separate glass transition temperatures. The carbon nanotubes are present either inside the TPU phase (samples obtained without chain extender), or at their boundaries (reactive-melt mixed samples). The effect of the sub-micron confinement of the TPU component is to decrease the cooperativity length of the primary segmental relaxation of this polymer, which is accentuated by the presence of the CNT fillers. Depending on the type of sample, five or six distinct relaxations are observed by means of dielectric spectroscopy, which we are able to assign to different dielectric phenomena. Our dielectric data show that the CNT fillers do not contribute directly to the long-range charge transport in the nanocomposite blends, consistent with the nanocomposites morphology, but rather result in a shift of the Maxwell-Wagner-Sillars space-charge frequency associated with charge accumulation at the PLLA/TPU boundary. Such shift testifies to a selective conductivity enhancement of the TPU phase due to the filler.

Correlation between flash sintering and dielectric breakdown behavior in donor-doped barium titanate ceramics

The present work investigates the influence of donor doping and its concentration on the flash sintering behavior of barium titanate. The characteristic of non-ohimic conductivity during flash event shows that flash sintering is associated with dielectric breakdown due to the similar physical phenomena. The polarization of dielectric particle contributes to the enhancement of local electric field strength. The magnified electric field caused by local charges accumulation gives rise to dielectric breakdown phenomenon during flash sintering. The SEM measurement indicates an obvious breakdown channel through the inside of sample, which provides a convincible evidence for dielectric breakdown. In addition, the impacts of temperature and field on carrier activation and migration are emphasized. Eventually, the non-ohmic conductivity can be explained by the physical phenomenon of dielectric breakdown described by Poole-Frenkel Emission.

Spectroscopic, Optical and Dielectric Investigation of (Mg, Cu, Ni, or Cd) Acetates’ Influence on Carboxymethyl Cellulose Sodium Salt/Polyvinylpyrrolidone Polymer Electrolyte Films

Solid polymer electrolytes, which have a low bandgap and a high dielectric constant, are an interesting technology for optoelectronic applications and supercapacitors. This work studies the influence of Mg, Cu, Ni or Cd acetates on the structural and optical properties and the dielectric relaxation phenomena in carboxymethyl cellulose sodium salt (CMC)/polyvinylpyrrolidone (PVP) blends. The dielectric behavior, ac conductivity and electrical modulus formalism were investigated in a frequency range of up to 1 MHz at room temperature. X-ray diffraction energy dispersive x-ray, Fourier transform infrared spectroscopy and scanning electron microscopy, revealed modifications of the films’ structural and chemical compositions and their morphology. UV–Vis and dielectric properties measurements revealed that the Cu and Mg salts had more distinctive influences on the optical properties, ac conductivity ($$ \sigma_{\rm{ac}} ) $$ and relaxation behavior. Cu and Mg reduced the optical bandgap Eg of the CMC/PVP blends from 5.1 eV to 4.7 eV and 3.6 eV, respectively, but increased $$ \sigma_{\rm{ac}} $$ from 8.61 × 10−5 S/cm to 1.34 × 10−4 S/cm and 1.81 ×10−4 S/cm, respectively. The dielectric measurements revealed an increase in the dielectric constant and dielectric losses for the composite films, which reflect the enhancement of the dielectric polarization of the films. The electric modulus spectra, calculated relaxation time and Argand plots confirmed an improvement in the ionic conductivity of the composite films. These results indicate that the incorporation of the acetate salts is a simple approach to widening the technological importance of CMC/PVP blend films for some optoelectronic devices and Cu and Mg battery applications.

Annealing-temperature dependence of the electrical properties of Ba0.8Pb0.2TiO3 as a PTC material

In this research, we investigate how the annealing temperature affects the electrical properties of Ba0.8Pb0.2TiO3 as a positive temperature coefficient material. The material was synthesized via solid-state sintering. The grain size was varied by varying the annealing temperature between 850 °C and 1000 °C for 4 h. Characterization via X-ray diffraction showed that a single-phase compound was formed exhibiting a tetragonal phase. The microstructure was observed using scanning electron microscopy. Average grain size was observed to be between 5 and 10μm. The electrical properties as characterized using impedance spectroscopy showed the presence of grain and grain-boundary contributions in the annealed samples. Dielectric constant and dielectric relaxation phenomenon as a function of annealing temperature have been studied.

On dielectric relaxation equation for anisotropic polarizable reacting fluid mixtures

In this paper a linear theory for dielectric relaxation phenomena in polarizable reacting fluid mixtures is developed, in the frame of thermodynamics of irreversible processes with internal variables. The microscopic irreversible phenomena giving rise to dielectric relaxation are described splitting the total specific polarization in two irreversible parts and introducing one of these partial specific polarizations as internal variable in the thermodynamic state vector. The phenomenological equations for these fluid mixtures are derived and, in the linear case, a generalized Debye equation for dielectric relaxation phenomena is derived. Special cases are also treated. Linear theories for polarizable continuous media with dielectric relaxation phenomena were derived in the same frame of non-equilibrium thermodynamics with internal variables in previous papers by one of the authors (LR). A phenomenological theory for these phenomena was developed by Maugin for complex materials, using microscopic considerations and introducing articular partial polarizations per unit mass. The obtained results in this paper have applications in several fields of applied sciences, as, for instance, in medicine and biology, where complex fluids presenting dielectric relaxation, are constitued by different types of molecules, with own dielectric susceptibility and relaxation time.