Thermally Stimulated Discharge Current Research Articles

TSDC and EDX studies of pure and ferrocene doped Polysulfone

Thermally stimulated discharge current (TSDC) in Pure and Ferrocene doped Polysulfone (PSF) has been performed to identify the optimum conditions for the charge storage capacity of PSF. TSDC study in pure and ferrocene doped Polysulfone was carried out as a function of the voltage (250, 400, 550 and 700 V), the temperature of polarization (40, 50, 60 and 70 °C) and the amount of ferrocene doping (10, 50 and 100 mg) respectively. From the study, it is identified that an increase in the value of TSD current is obtained with an increase in the doping amount of ferrocene in PSF. The Maximum value of TSD current has been obtained for PSF doped with 100 mg of ferrocene as compared to pure PSF. Improvement in the value of TSD current has been pointed out with an increase in polarizing voltage from 250 to 700 V. A Shift in the relaxation peak has been reported toward the lower temperature with an increase in the doping amount. Reduction in the Activation Energy and relaxation time has been observed with an increase in the doping amount of ferrocene in PSF. Reduction in activation energy and relaxation time shows the improvement in the fast discharging current capacity of PSF due to ferrocene doping. The study demonstrates that best charge storage capacity of PSF is obtained, when it is doped with 100 mg of ferrocene at the polarizing temperature of 70 °C and at the Polarizing voltage of 700 Volt. The EDX study has confirmed the availability of Carbon, Oxygen and Sulphur elements in required proportion in PSF. The EDX study has also authenticated the improvement in the proportion of Iron element with an increase in the amount of ferrocene dopant in PSF. The EDX results of pure and doped PSF demonstrates the possibility to exploit the X-ray signal produced by the co-irradiation with secondary electrons to identify the elements in the sample.

Investigation of Electrical and Thermal Properties of Epoxy Resin/Silicon Carbide Whisker Composites for Electronic Packaging Materials

This article explores the potential of epoxy resin/silicon carbide whisker (EP/SiCw) composites (1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%) as the field-dependent conductivity (FDC) packaging materials for the high-voltage power modules by investigating their thermal and electrical properties at different temperatures. The cross-sectional morphology of the prepared materials is characterized by field emission-scanning electron microscopy (FE-SEM). The thermal analysis consists of differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The electrical properties, such as dc conductivity, dielectric spectroscopy, thermally stimulated discharge current (TSDC), space charge distribution, and dc breakdown strength, are measured. The molecular orbital energy levels of the EP and SiCw monomers are calculated by quantum chemical calculation (QCC) to analyze the effect of EP interfacial trap sites on the electrical properties. The effect of the EP/SiCw interfacial charges and electrical field distortion on the electrical properties of the EP/SiCw composites with different filler content is investigated by the finite-element method (FEM) simulation. It is found that the 2 wt% EP/SiCw composite has a better thermal performance. The 1 wt% has lower real permittivity, lower trap density, lower space charge accumulation, and higher breakdown strength. The EP/SiCw composites have a higher trap level than the pure EP. The nonlinearity percolation threshold of the EP/SiCw composites is 3 wt%. As the filler content increases, the nonlinear conductivity coefficient of the EP/SiCw composites becomes higher, whereas the breakdown strength decreases due to the electric field distortion near the electrodes caused by the apparent hetero charge accumulation at high filler content.

Effect of γ-irradiation on thermally stimulated depolarization current spectra of polyethylene-grafted-poly(Acrylic acid)

The graft copolymerization process of polyethylene (PE) with acrylic acid is performed using a 60Co-gamma irradiator, and the samples are irradiated at different doses, 30, 50, 70 and 100 kGy with a dose rate of 0.55 Gy/s. Global thermally stimulated discharge current (TSDC) spectrum of irradiated and non-irradiated PE-g-AAc has been investigated from RT to ∼ 440K. The TSDC spectrum of non-irradiated PE-g-AAc exhibited two relaxation processes. The first process is located at ∼ 329 K, and the second one is at ∼390 K. These processes are called dipolar and space charge relaxation, i.e. α- and ρ-relaxation, respectively. On the other hand, the position of these processes is shifted towards a higher temperature for irradiated samples. The activation energy for α-relaxation process of non-irradiated samples is ∼ 0.21 eV, while for irradiated samples, it is 0.34 eV. The thermal sampling technique (TS) has been applied to decompose the global TSDC spectrum of all samples into its elementary peaks. The molecular parameters, such as activation energy (Ea ), pre-exponential factor (τ 0), enthalpy (ΔH), entropy (ΔS) and Gibbs free energy (ΔG), are estimated for all samples. The compensation phenomenon has been verified for all samples in different ways, such as plotting ln τ 0 against Ea or entropy versus enthalpy.

Wide-bandgap fluorides/polyimide composites with enhanced energy storage properties at high temperatures

In advanced electronics and electrical power systems, polymer dielectric capacitors are favored for their high power density and great reliability. However, the low energy density at high temperatures constrains their use in emerging applications. To address this vital issue, herein, a novel calcium fluoride (CaF2) nanoparticle with a wide bandgap (∼12.1 eV) and moderate permittivity (∼10.0) is prepared by a simple direct precipitation method and then introduced into the polyimide (PI) matrix. The incorporation of the CaF2 nanoparticles increases the permittivity and reduces conduction loss simultaneously. Consequently, at 150 ℃, the PI film with 3 vol% CaF2 exhibits enhanced discharged energy density and breakdown field of 2.68 J cm−3 and 455.4 MV m−1, respectively. Besides, the composite shows a higher power density of 0.36 MW cm−3 and a faster discharge speed of 2.09 μs at 150 ℃ than that 2.93 μs of biaxially oriented polypropylene (BOPP) measured at 85 ℃. Notably, CaF2 nanofiller, as a deep trap, captures injected charges and alleviates the local electric distortion, as revealed by finite element simulation and thermally stimulated discharge current (TSDC) measurement. This work proposes a novel fluoride nanofiller to rationalize the energy storage improvement of high-temperature composites with potential wide application.

Tailoring Electric Field Distortion in High-Voltage Power Modules Utilizing Epoxy Resin/Silicon Carbide Whisker Composites with Field-Dependent Conductivity

This paper reports the performance of an epoxy resin/silicon carbide whisker (EP/SiCw) composite (1–5 wt %) as the field-dependent conductivity (FDC) layer for electric field reduction in the high-voltage power module. The experiments consist of a field emission scanning electron microscope (FESEM), thermal conductivity, Fourier transform infrared (FT-IR) spectroscopy, thermally stimulated discharge current (TSDC), space charge, DC conductivity, and dielectric spectroscopy. The DC conductivity and dielectric spectroscopy are used for DC and AC stationary electric field simulations, respectively. The electric field reduction of EP/SiCw composites in the power module is analyzed, and the void defect in the FDC layer is also identified. The observed percolation threshold of the EP/SiCw composites is 3 wt %, and the DC electric field near the triple point decreases significantly by 74.8% under 10 kV when a 5 wt % EP/SiCw composite is applied for the FDC layer. It was found that the efficient threshold operating frequency of the FDC layer is around 10 kHz. The FDC layer can significantly reduce the electric field under AC voltage below 10 kHz. Although the power loss with the FDC layer increases obviously without the FDC layer, it is still lower than 1 W at 1 MHz, which is negligible for industrial applications. Notably, the void in the FDC layer is identified by the slowly increased dielectric loss with the increase of frequency through dielectric spectroscopy simulation.

Improved Electret Properties of Poly(Vinylidene Fluoride)/Lithium Niobate Nanocomposites for Applications in Air Filters

AbstractIn this work, the electret properties of poly(vinylidene fluoride) (PVDF)/lithium niobate (LiNbO3, LN) nanocomposites are systematically studied. The LN nanoparticles are fabricated by hydrothermal synthesis followed by melt‐reaction. Their morphology and crystalline structures are characterized by scanning electron microscopy (SEM) and X‐ray diffraction (XRD). The PVDF/LN nanocomposite films are prepared by solution casting with N,N‐dimethylformamide (DMF) as the solvent or melt molding. The crystalline phases of PVDF in both pure samples and nanocomposites are checked by XRD and Fourier transform infrared spectroscopy (FTIR). The measurements of the dielectric and electret properties show that the LN nanoparticles significantly increase the dielectric permittivity (ε) and the thermally stimulated discharge current (TSDC) of the samples. Such materials have potential applications including for air filters and power generators. A demonstration shows that after the same charging process, the PVDF/LN nanocomposites can absorb larger amount of polystyrene (PS) foam microparticles or micrometer size test dusts than the pure PVDF.

Enhanced breakdown strength of aligned-sodium-titanate- nanowire/epoxy nanocomposites and their anisotropic dielectric properties

In this work, sodium titanate (Na2Ti6O13) nanowire/epoxy nanocomposites with different nanowire alignments and thicknesses were fabricated by employing the DC electric field during curing process. Nanocomposites showed obvious anisotropic dielectric properties. When nanowires were aligned perpendicularly to the electric field directions (X-Y-aligned), the breakdown strength (EB) of nanocomposites with thickness of 1 mm and 0.5 wt% nanowires increased by 9.6% or 11%, compared to that of pure epoxy or no-alignment nanocomposites. When the thickness decreases to 10 μm, the EB enhancement further increased to 87%, compared to that of no-alignment samples. Thermally stimulated discharge current (TSDC) results indicated that more electronic deep traps were introduced perpendicular to alignment direction of nanowires and more shallow traps existed in the direction parallel to the oriented nanowires. The origin of the anisotropy in EB of nanocomposites was studied by analyzing the orientations of interfaces and the nanowires’ anisotropic crystal structure. This work gives invaluable guidelines for designing of thermoset functional materials.

Measurement of AC and DC relaxation properties in polyvinyl chloride (PVC) nanocomposites

In present investigation, thin film of polyvinylchloride (PVC)/silicon dioxide (SiO2)/montomorillonite (MMT) nanocomposites were prepared by solution casting method. AFM analyzed the grain size, particle size, roughness and dispersion of nanofillers in PVC nanocomposites. However, FTIR describes the molecular interaction of nanofillers in PVC structure. The AC and DC relaxation properties of these nanocomposites were measured by means of dielectric spectroscopy and thermally stimulated discharge current (TSDC) respectively. The dielectric spectroscopy has been applied to measure dielectric constant and tangential loss at different frequencies and temperatures; then, it has been specified the effectiveness of nanoparticles on dielectric performance as compared with pure PVC. The permittivity of these nanocomposites is enhanced remarkably, which can be understood by the interfacial polarization effect. The high dielectric constant of value 37 is obtained in the nanocomposite with 4 wt.% MMT at 50 Hz. The temperature dependent dielectric constant could be explained on the basis of free volume available for free charge carriers and MWS relaxation process. The dielectric characteristics are highly influenced by nature of fillers and can be understand by the frequency and temperature dependence of the interfacial relaxation. TSDC peaks are originated due to α-relaxation process and MWS relaxation process.

Study of human blood under influence of magnetic field by AC dielectric and thermally stimulated discharge current methods

The aim of the present work is to study the effect of magnetic field on thermally stimulated discharge current (TSDC) characteristics and dielectric properties of human blood and to derive the useful parameters for the evaluation of DC and AC relaxation process. The TSDC and dielectric parameters of blood samples have been recorded under the influence of magnetic field. In low-frequency region, $$\varepsilon^{\prime}$$ decays rapidly and attains almost constant value in higher-frequency region; however, variation of imaginary part of permittivity is not similar to $$\varepsilon^{\prime}$$ . The variation of complex permittivity e* is characterized by a broad peak. The area of curves decreases with the increase in applied magnetic field. The dielectric loss (tan δ) varies from 0.4 to 1.8. The tan δ is characterized by a peak in lower-frequency region. The origin for variation of dielectric properties is the reduction in impedance and change in conductivity under the influence of electric and magnetic field. The TSDC maxima are observed at 54 ± 3 °C and 75 ± 5 °C with heating rate of 3 °C min−1 assigned as β and α peak, respectively. The height of peak is observed to be increased with forming magnetic field; however, positions of peaks are almost same.

Effect of interface in dielectric relaxation properties of PEMA–BaZrO3 nanocomposites

XRD peaks demonstrate the interaction of nanoparticles with polymer matrix. It is evident from the dielectric data that observed change in dielectric parameters would result from appropriate changes in chain mobility due to nanoparticles–polymer interactions. FT-IR spectra represent the significant changes in intensity, shape and position of the different vibrational bands corresponding to –OH stretching, C–O–C stretching, C–H stretching and C–O–C in C–H stretching modes occur as a result of the incorporation of BaZrO3 nanofiller. Thermally stimulated discharge current (TSDC) and transient discharging current study presented the dipolar and interfacial type of relaxations.

Depolarization current relaxation process of insulating dielectrics after corona poling under different charging conditions

As an insulating dielectric, polyimide is favorable for the application of optoelectronics, electrical insulation system in electric power industry, insulating, and packaging materials in space aircraft, due to its excellent thermal, mechanical and electrical insulating stability. The charge storage profile of such insulating dielectric is utmost important to its application, when it is exposed to electron irradiation, high voltage corona discharge or other treatments. These treatments could induce changes in physical and chemical properties of treated samples. To investigate the charge storage mechanism of the insulating dielectrics after high-voltage corona discharge, the relaxation processes responsible for corona charged polyimide films under different poling conditions were analyzed by the Thermally Stimulated Discharge Currents method (TSDC). In the results of thermal relaxation process, the appearance of various peaks in TSDC spectra provided a deep insight into the molecular status in the dielectric material and reflected stored space charge relaxation process in the insulating polymers after corona discharge treatments. Furthermore, the different space charge distribution status under various poling temperature and different discharge voltage level were also investigated, which could partly reflect the influence of the ambiance condition on the functional dielectrics after corona poling.

Measurement of thermally stimulated discharge current (TSDC) for detection of thyroid-stimulating hormone (TSH) in human blood

TSDC was measured in human blood sample with different level of TSH. The origin of TSDC could be explained on the basis of bioelectret effect in biological sample, which is interpreted by fundamental concepts of bioelectret state in biopolymers. The concept of thermal analysis of blood gives the basis of TSDC peaks. The nature of the TSDC peaks and their relation to the physicochemical transformations and the interphase interactions in these systems are discussed. It is observed that the position of TSDC peak is different for different level of TSH. The activation energy, charge released, and peak current were observed to decrease with TSH contents in human blood. The increase of TSH nonpolar salt in human blood is associated with the decrease of charge carriers due to denaturation or hydration of protein with temperature. It is noted that TSDC can be suitable diagnostics of TSH in human blood.

Characterisation and optimisation of the d 33 coefficient of cellular PP films

Piezoelectric polymer cellular films have been studied since 1986. In recent years, they have improved the potential applications due to materials progress. Cellular polypropylene (PP) polymers are characterised by its high piezoelectric coefficient d 33 in comparison with other piezoelectric materials such as ceramics. One of the advantages of these films is their elasticity and flexibility. This study is based on the optimisation of the activation process and characterisation results of polymer cellular films. Samples were made of a commercially available PP film which was modified by a thermal biaxial stretching. Coefficient d 33 was measured by a quasi-static method and the frequency characterisation was made for validating all characterisations and their relations. Transducer coefficients around 700 pC/N were obtained with polymer cellular PP films with silver coating electrodes, activated by corona discharge. An approximation of the surface charge density in the polymer voids was obtained with a mathematical model. Thermal stability was checked by thermally stimulated discharge currents (TSDCs) showing a relationship between the TSDC and the coefficient d 33. Time stability was determined after 3000 h ageing, and finally was obtained a resonance frequency by interferometry measurement.

Synthesis and characterization of polymethyl methacrylate with double electro-optic molecules thin film and its application

Polymethyl methacrylate (PMMA) with double electro-optic (EO) molecules was synthesized. One kind of chromophoric groups, hydroxyethyl carbazole, reacted with PMMA by a chemical method to form poly(methacrylic acid ethyl carbazole ester). Another small nonlinear optical molecule (NOL), 4–6-alkoxy-4′-cyano-biphenyl (6OCB), was mixed into the polymers by a physical method to further improve EO properties. The structure of the material was characterized and the effect on EO coefficient of different mixing proportions was investigated. Photoconductive properties and the orientation stability were studied. Experimental results showed that the enhanced EO coefficient was 44.8pm/V when the mixing proportion was 20wt%. Thermally stimulated discharge current (TSDC) testing curves were obtained, which confirmed the existence of two depolarization processes. Thin films formed by this polymer material were used to detect terahertz (THz) radiation. The detecting efficiency and the spectrum sensitivity were enhanced largely compared with ZnTe crystal. It can be concluded that this polymer material is a very good candidate for THz application.

Analysis of thermally stimulated processes in new phenanthroline derivatives suitable for optoelectronic devices

Thermally stimulated processes have been studied in thin films of phenanthroline derives to describe the states that had been localized. Ultraviolet Photoelectron Spectroscopy had checked out before thin films of new pyrrolo[l,2-a][l,10] phenanthroline derivatives [1], in order to further applications in optoelectronic devices. The investigated compounds have an electronic band structure which is due to the substituent (R=NO2, Cl) induced transformations of molecular orbitals. Thermally stimulated discharge currents (TSDC) attested dipolar and charge transport mechanisms. Each TSDC peak has been assigned to elementary processes that are different utilizing in addition dielectric spectroscopy (DES), and the mean trap depths have been approximated from thermally stimulated luminescence (TSL) curves.

Structural and thermal properties of swift heavy ion beam irradiated polycarbonate/zinc oxide nanocomposites

Polycarbonate (PC)/Zinc oxide (ZnO) nanocomposite films were prepared by a solution mixing method and irradiated by Swift heavy ion at various ions fluences ranging from 1 × 1011 to 3 × 1013. The surface morphological, structural, and thermal properties of untreated and irradiated PC/ZnO nanocomposite films were investigated by various characterizations techniques such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry, Thermogravimetric (TG) and Thermally stimulated discharge current (TSDC). The XRD pattern reveals that the average crystallite size and percentage of crystallinity decreases with increase of ion fluences. TSDC measurement is an evidence of different type of relaxation process. The activation energy released charge and charge carrier mobility for α-relaxation peak decreases, while relaxation time and peak current increase. TG measurement shows thermal stability and mass loss decreases with ions fluences. FTIR spectra reveal the position of different bonds in PC and nanocomposite films. The glass transition temperature of nanocomposites is observed to be decreases with ion fluences.

Dielectric relaxation behavior of C5+ (70 MeV) swift heavy ion irradiated polyetheretherketone (PEEK) using TSDC technique

The dielectric relaxation characteristics of polyetheretherketone (PEEK) irradiated with C5+ (70 MeV) ion, have been investigated in the temperature range 60–230° as a function of poling temperature TP (50, 100, 150, and 200°C), poling field EP (200, 300, 400, and 500 kV/cm), and storage time ts (2, 24, 48, and 120 h), using thermally stimulated discharge current (TSDC) technique. The TSDC spectra show a prominent maximum around glass transition temperature (Tg ∼ 143°C) named as α-peak. This peak is attributed to the movement of ketone dipoles linked with the main chain. It is observed that the magnitude of α-peak increases with the increase in poling temperature and poling field. The peak current and area under the α-peak are found to be diminished with the increase of storage time ts for electrets. The β-peak (space charge peak) is absent in irradiated PEEK samples as compared to pristine PEEK samples. The results obtained, in the present studies, are compared with the results on pristine samples. The activation energies and pre-exponential factor for PEEK samples determined using Bucci plot method.

Thermally stimulated discharge conductivity study of zinc oxide thermoelectrets

The present work deals with transmission electron microscopy (TEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and thermally stimulated discharge current (TSDC) study of inorganic metal oxide (ZnO) nanoparticles and its thermoelectrets. The thermoelectrets were prepared by applying different electric polarizing field (E P) at constant polarizing temperature (T P), for constant polarization time (t p). The TSDC study was carried out in the temperature region of 313–473 K. It was observed that the conductivity of ZnO samples increases with the increase in temperature and polarizing field. The dependence of TSDC data on polarizing agents, i.e. field and temperature shows Arrhenius type of behviour and is explained on the basis of variable range hopping mechanism.

Thermally stimulated discharge current (TSDC) characteristics in β-phase PVDF–BaTiO3 nanocomposites

β-phase polyvinylidene fluoride (PVDF)–BaTiO3 nanocomposite samples have been prepared by solution mixing method. XRD data represent that the crystallinity of PVDF decreases with increase in loading level of BaTiO3 nanoparticles. DSC curve represents that the melting point of PVDF is lightly affected by loading concentration of BaTiO3. The morphology and microstructure of PVDF and PVDF embedded by BaTiO3 nanofillers were investigated by using inverted contrast microscopy (ICM) and scanning electron microscopy (SEM). FTIR interferrometry is proven that PVDF and BaTiO3 are not chemically interacting; therefore, interaction of BaTiO3 is van der Waals type of interaction. The thermally stimulated discharge current (TSDC) of PVDF and PVDF–BaTiO3 nanocomposites sample was characterized by single peak. The observed TSDC peak is discussed on the basis of dipolar and interfacial polarization.

The effect of bismuth oxide polymorph forms on degradation processes in ZnO varistors

Abstract The behavior of a ZnO–Bi 2 O 3 binary system and ZnO-based varistors under a biasing electric field and temperature was investigated. Both types of samples were exposed to aging with 50 μA DC at 115 °C for 22 h. The degradation effect of DC biasing was manifested by a drop of varistor voltage as well as the presence of peaks in the thermally stimulated discharge current (TSDC) spectra. It was found that the TSDC generation is related to a particular form of the Bi 2 O 3 in ceramics. Activation energies of the thermally stimulated responses ranged from 0.01 eV to 0.17 eV. In the high temperature range, the peaks attributable to degradation were found in the TSDC current when the Bi-rich inter-granular phase formed agglomerates and the Bi 2 O 3 was in its β- or defective γ- variety. When Bi 2 O 3 was in an α-form, well-crystallized γ-form, or an amorphous form, none of the high temperature TSDC maximums were identified. Under a DC bias, the varistor voltage returned to its starting value when the samples were cooled to room temperature. However, passing the current in the opposite direction by reversing the bias from positive to negative exhibited a persistent drop of the varistor voltage.