Thermally Stimulated Discharge Current Measurements Research Articles

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.

Investigation of thermally stimulated charge relaxation mechanism in SiO2 filled polycarbonate nanocomposites

Abstract The thermally stimulated charge relaxation properties of polycarbonate (PC) filled with SiO2 nanofiller were studied by means of thermally stimulated discharge current (TSDC). The nanocomposite samples were further characterized by UV–vis spectroscopy, scanning electron microscopy, energy dispersive X-ray spectra, and differential scanning calorimetry (DSC) techniques to investigate the dispersion of nanofillers in polymer matrix and glass transition temperature. All pristine and nanocomposites samples of thickness about 25 μm were prepared using solution mixing method. The suitable weight percentage of SiO2 nanofillers has been chosen to prevent the nonuniform dispersion. TSDC measurement of PC (Pristine) and PC+ (7% SiO2) shows the single peak, while TSDC characteristic of other nanocomposites are showing two peaks. The higher temperature TSDC peak of pristine and nanocomposites samples is originated due to the charge relaxation from shallower and deeper trapping sites, however, low temperature...

Relaxation investigations in polysulfone: Thermally stimulated discharge current and dielectric spectroscopy

The temperature and electric field dependence of dielectric relaxation have been investigated in amorphous polysulfone (PSF) samples using thermally stimulated discharge current (TSDC) and AC dielectric measurement. All measurements were performed on solution grown thin films of thickness 50 μm. The nature of relaxation mechanisms in amorphous PSF is discussed on the basis of TSDC and dielectric measurement results. The comparative studies of dielectric properties with TSDC indicated a strong resemblance between the two techniques. Polysulfone (PSF) films are characterized by two TSDC peaks, i.e. β peak at 348 K and α peak at 470 K. The depolarization current for the β peak increases linearly with poling field. The peak obtained at lower temperature (i.e. β peak) is associated with dipolar relaxation and the other one obtained at high temperature (i.e. α peak), which appears due to the α relaxation.

Effects of charge trapping in gamma irradiated and accelerated aged low-density polyethylene

The effects of gamma irradiation in air and accelerated aging of low-density polyethylene (LDPE) were studied through dielectric loss (tan δ) analysis in the temperature range from 25 to 325 K and using thermally stimulated discharge current (TSDC) measurements. The radiation-induced oxidation was observed using IR spectroscopy. The influence of radiation dose and accelerated aging on the intensities and the positions of the γ and β dielectric relaxation maxima were correlated with maxima of TSDC measurements, and found to be strongly dependent upon the changes in the microstructure of the amorphous phase and on the surface of the crystallites induced by oxidation and crosslinking.

Thermally stimulated discharge current and DC resistivity of ethylene propylene rubberwith various Pb concentrations

DC resistivity of extruded ethylene propylene rubber (EPR) samples with various Pb concentration have been measured under wet conditions as a function of electrical field at selected temperatures in a range from 20 to 100°C. The temperature and electrical field coefficients of resistivity have been calculated. Thermally stimulated discharge current (TSDC) has also been measured and a broad positive peak has been observed for three EPR samples. It has been found that the resistivity of EPR is not sensitive to the Pb concentration within the range of 0 to 5 parts per hundred base resin (phr). The results show that the resistivity of EPR varies non-linearly with both temperature and electrical field. The temperature coefficient of resistivity α of EPR has been measured to be ∼0.1 K−1 for all the samples with various Pb concentration. The electrical field coefficient of resistivity β of EPR at room temperature is small and increases with temperature. Increasing Pb content increases slightly the electrical field coefficient β of resistivity. Based on a space charge limited conduction model, the trap depth of EPR has been estimated. TSDC measurements indicate that doping with Pb increases both the density of charge carriers and the number of deep traps simultaneously. The broad TSDC peak reveals that there must be a distribution rather than just a single value of the trap depth.

Charge trapping and dielectric relaxations of gamma irradiated radiolytically oxidized highly oriented LDPE

The influence of gamma irradiation in air on the effects of charge trapping in highly oriented LDPE has been studied through dielectric loss (tan δ) analysis in the temperature range from 25 to 325 K and using thermally stimulated discharge current (TSDC) measurements. The radiation induced oxidation was observed using IR spectroscopy. The intensity and the position of the γ and β dielectric relaxation maxima were correlated with maxima of TSDC measurements. It was found that the positions of the relaxation peaks are strongly dependent upon the changes in the microstructure of the amorphous phase and on the surface of the crystallites induced by orientation and gamma irradiation.

Relaxation processes in aromatic polyimide

Electrical conduction in non-conjugated insulating polymers such as Kapton(R) films was studied as a function of temperature, T (15–500 K) and electric field F (⩽16 kV cm−1). The time dependent isothermal transient currents (ITC) were also studied at different temperatures (15 K<T<500 K). Thermally stimulated discharge current (TSDC) studies were carried out as a function of initial poling conditions. A distinct change in conduction mechanism as a function of T was observed at T⩾300 K from DC conductivity, ITC and TSDC measurements. The origin of this behaviour is discussed in terms of transition of dipolar at low T to space charge mechanism at high T which can be attributed to carrier trapping and release of charge carriers from the trap states. The effective barrier energy, Δ, for transport and hopping parameter λ(T) are estimated for Kapton on the basis of these studies. The results obtained for Kapton suggest that, for T<Tg at low or moderate fields, the transient currents are essentially governed by dipolar relaxation mechanisms.

Polarization and space charge analysis in thermally poled PVDF

The spatial distribution of the polarization and space charge in thermally poled poly (vinylidene fluoride) is studied using the laser intensity modulation method. Injected space charge, localized near the electrode polymer interface, tends to prevent the formation of uniform polarization in the polymer bulk. The actual amount of charge existing in the poled specimen is determined using hysteresis measurements and thermally stimulated discharge current (TSDC) measurements. By using the peak cleaning technique and by measuring the pyroelectric current during the cooling of the specimen, the contribution of depolarization current and space charge detrapping to the TSDC measurement is considered. From hysteresis measurements a relaxation process was observed around 65°C which was related to the dipolar relaxation in the crystalline phase known as the αc relaxation. A significant increase of the TSDC at temperatures higher than 130°C was observed meaning that the dipolar charge and the space charge are very stable up to high temperature. In this temperature range, the pyroelectric current is significant. Two relaxation processes were identified for a polarizing temperature lower than 120°C. One is centred around the polarizing temperature and is related to space charge release. The second is related to dipole relaxation in the crystalline phase. The position of the last peak is determined by interaction between the dipoles and the internal electric field, resulting from the charge stored in the sample. We propose to call this as the αcρ interaction. The higher temperature of the dipolar peak was identified as 86°C with an activation energy of 0.52±0.04 eV.

Charge trapping in gamma irradiated low-density polyethylene

The influence of gamma irradiation in two different atmospheres, air and distilled water on charge trapping in LDPE has been studied through dielectric loss (tan δ) analysis in the temperature range from 25 to 325 K and using thermally stimulated discharge current (TSDC) measurements. The radiation induced oxidation was observed using IR spectroscopy. The intensity and the position of the γ and β dielectric relaxation maxima were correlated with maxima of TSDC measurements, and found to be strongly dependent upon the changes in the microstructure of the amorphous phase and on the surface of the crystallites induced by oxidation and crosslinking.

Thermal step and TSDC measurement in PVC

The space charge behavior of some polyvinylchloride (PVC) samples with different molecular microstructures, obtained through chemical modification of PVC has been analyzed by means of the thermal step (TS) and the thermally stimulated discharge current (TSDC) techniques. The magnitude of the space charge distribution has been shown to be lower as the degree of chemical modification increases. Combining the TS and the TSDC methods allowed us to study minority carriers, which could not be observed by a single TS measurement.

Antistatic process of dielectric thin films using low pressure discharge plasma

By using space charge density distribution measurement and TSDC (Thermally Stimulated Discharge Current) measurement, space and surface charge behavior of a corona-charged Polypropylene(PP) and Polyethylene(PE) thin film was studied. The Effect of an antistatic process using a low pressure discharge plasma and charge elimination process dipping in city water was examined. In order to study the mechanisms of the antistatic process, the composition of the sample surface was analyzed by X-ray photoelectron spectroscopy.It was observed that plasma surface processing enhanced the charge elimination performance for both PP and PE films. Charge accumulation in/on plasma processed PE films were much smaller than that of untreated ones. XPS analysis of those samples suggested the existence of carbonyl, car☐yl and amino groups on the surface of the plasma processed sample. In particular, a large amount of the amino group was found on the surface of the sample processed in nitrogen.

A relation between the space charge distribution and TSDC spectrum of corona charged PTFE thin films

A space charge density distribution measuring system based on a PPP (piezoelectrically induced pressure pulse wave) method was constructed. The pressure pulse wave is generated by a pulse-driven piezoelectric PVDF (polyvinylidene fluoride) thin film used as a piezoelectric pulse generator. A thin aluminum plate is used as a shield electrode to electrically separate the pressure pulse generator and the sample holder. This thin shield electrode reduces attenuation and dispersion of the pressure pulse wave compared to the former system. The spatial resolution of the system is estimated to be about 7 μm, based on the PPP response to a sheet charge that is artificially placed on a dielectric thin film. Using space charge distribution measurements and TSDC (thermally stimulated discharge current) measurements, the charge behavior of the corona-charged PTFE Teflon TM (polytetrafluoroethylene) thin films was studied.

Analysis of the thermally stimulated discharge current around glass-rubber transition temperature in polyethylene terephthalate

The nature of the thermally stimulated discharge current (TSDC) for polyethylene terephthalate samples in the temperature range from room temperature to above glass-rubber transition temperature of the amorphous phase is analyzed. The well conditioning of the sample is strictly necessary in order to have a good reproducibility and accuracy of results. A main peak was observed whose maximum temperature moves towards a lower value with the decreasing of the amount of charge that flows through the sample during polarization. The peak position changes as well, if the sample is polarized in air or in oxygen and the nature of change is more important in the case of oxygen. The shape of the peak is complex and at least four shoulders have been identified around 85, 90, 105, and 125 °C using the cleaning technique. The activation energy tends to increase with repetition of the TSDC runs, in the glass-rubber transition temperature range, in the case when the cleaning technique is used for the peaks separation. For the conditioned samples, there is a good agreement between the experimental results and the analytical expression of the current, particularly in the region where it reaches a maximum, and so relevant values for the characteristic parameters of the peak are determined. The time interval of the short circuiting of the sample, at room temperature, before the TSDC measurement, strongly influences the initial rise of the current and consequently the parameters of the peak. A possible redistribution of the internal field arising from the injected charge, the heterocharge, and the existing charge in the sample as received, has been put forward to account for the experimental evidences. The conclusion is that the current is mainly determined by the space-charge released from the traps that are likely continuously distributed in energy. For the stated polarization conditions, the charge is released from the shallow traps with an activation energy in the range 0.23–0.32 eV and a concentration of ∼1018/m3. The dipolar charge is of little importance.