Thermally Stimulated Depolarization Current Peak Research Articles

Quantitative trap analysis of grafting-modified polypropylene based on thermally stimulated depolarization current

• MMA-grafted PP is prepared with enhanced DC resistivity and more deep traps. • Trap characteristics of MMA-grafted PP based on TSDC is quantitatively analyzed. • MMA deepens the inherent PP trap depth and introduces a new deep trap of 1.8 eV. In this paper, the thermally stimulated depolarization current (TSDC) spectrum of methyl methacrylate (MMA)-grafted polypropylene is quantitatively analyzed by our TSDC peak separating algorithm. The separated trap peaks and extracted trap parameters are verified to be effective and credible by the experimental peak-separating method based on thermo-cleaning. The trap analysis on pristine and MMA-grafted polypropylene is carried out and indicates that grafting MMA can introduce a new high-depth trap peak at about 1.8 eV, meanwhile the intrinsic trap of polypropylene is deepened. This work would provide an opportunity to advance the understanding of trap characteristics in grafting-modified polypropylene.

A method for the calculation the activation energies of thermally stimulated depolarization current peaks: Application in polyvinylidene fluoride/graphene nanocomposites

A simple method is presented for the calculation of the activation energies of first order peaks of Thermally Stimulated Depolarization Current (TSDC). Three equations are derived, which relate the activation energy of the relaxation process, to three characteristic temperatures of the TSDC thermographs, which correspond to the peak temperature TM, and the half of the peak current temperatures T1, T2 (T1<T2). Each equation gives an expression of the activation energy as a function of two out of the three characteristic temperatures of the TSDC peak, assuming typical values of activation energy in the range 0.2–2.0 eV. The proposed equations were compared with other methods based on the same characteristic temperatures, in pristine PVDF and PVDF with 1wt% graphene samples at a temperature range where the MWS relaxation takes place. In PVDF-graphene samples, the MWS peak was found to consist of two overlapping mechanisms.

Thermally stimulated depolarization current measurements on degraded lead zirconate titanate films

AbstractCharge transport mechanisms governing DC resistance degradation in ferroelectric films are influenced by defects, particularly oxygen vacancies. This paper demonstrates that oxygen vacancies migrate in lead zirconate titanate (PZT) films under a DC bias field and contribute to resistance degradation. Model PZT thin films were developed in which the concentration and distribution of oxygen vacancies were controlled via (a) changing the dopant type and concentration from 1%–4% Mn (acceptor) to 1%–4% Nb (donor) or (b) annealing undoped PZT films at varying partial pressures of PbO. The presence of associated (immobile) and dissociated (mobile) oxygen vacancies was distinguished by thermally stimulated depolarization current (TSDC) measurements. The impact of mobile oxygen vacancies on local defect chemistry and associated charge transport mechanisms was explored by electron energy loss spectroscopy (EELS). For Mn‐doped PZT films, following resistance degradation, TSDC studies revealed only one depolarization peak with an activation energy of 0.6–0.8 eV; this peak was associated with ionic space charge presumably due to migration of oxygen vacancies. The magnitude of the depolarization current peak increased with increasing degradation times. A similar depolarization current peak attributed to the existence of mobile oxygen vacancies was also observed for undoped and Nb‐doped PZT films; the magnitude of this peak decreased as the Nb or PbO contents in PZT films increased. An additional TSDC peak associated with polaron hopping between Ti3+ and Ti4+ was found in both Nb‐doped PZT films and undoped PZT films annealed under low PbO partial pressure. Degraded Nb‐doped samples exhibited a chemical shift in the TiL2,3 peak to lower energy losses and the appearance of shoulders on the t2g and eg peaks, implying a reduction of Ti cations in regions near the cathode.

Electrical polarization phenomena, dielectric relaxations and structural transitions in a relaxor-ferroelectric terpolymer investigated with electrical probing techniques

Dielectric Relaxation Spectroscopy (DRS) and Thermally Stimulated Depolarization Current (TSDC) measurements were employed to study dielectric-relaxation processes, structural transitions and electric-polarization phenomena in poly(vinylidenefluoride-trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE)) terpolymer films. Results from DRS confirm the existence of two separate dispersion regions related to a para-to-ferroelectric phase transition and to the glass transition. The dipolar TSDC peak correlates with the loss peak of the α relaxation that represents the glass transition. The electric polarization calculated from the dipolar TSDC peak (glass transition) shows a non-linear electric-field dependence and saturates at high electric poling fields. As the observed behaviour is essentially the same as that of the electric polarization obtained from direct polarization-versus-electric-field hysteresis measurements, TSDC experiments are also suitable for studying the polarization in relaxor-ferroelectric polymers. A saturation polarization of 44 mC m−2 was found for an electric field of 190 MV m−1.

Determining the activation energy of amorphous SrTiO3 film based on thermally stimulated depolarization current

Thermally stimulated depolarization current (TSDC) was investigated on amorphous SrTiO3 film to study the internal polarization mechanism. Three TSDC peaks were observed around 240K, 270K and 320K, respectively. By comparing the experiment results with the theoretical characteristics of three polarization mechanisms, the first peak was assigned to dipole polarization and the second peak was consistent with ionic polarization. The origin of the third peak was ascribed to the trap charge depolarization, since it exhibited a typical linear relation between poling field and square of peak temperatures. In addition, the second peak vanished after the sample had been treated by heating treatment to remove the absorbed water, indicating that the second peak arose from the absorbed water. For the absorbed water, the activation energy of ionic polarization activation energy and ionic conductance are approximately equal, which suggests that ionic polarization charge could turn to be ionic conductance with increasing field.

Crystallinity effect on the structural relaxation of polyethylene naphtalate (PEN) by TSDC and DSC experiments

The effect of physical ageing process on the electrical and thermal properties of amorphous and semi-crystalline PEN was investigated by means of the thermally stimulated depolarization currents (TSDC) and the differential scannig calorimetry (DSC). The TSDC measurements revealed a significant decrease in the mobility of the molecular chains in the amorphous PEN (PENa), aged at a temperature Tg-10K (Tg is the glass transition temperature). This mobility is directly related to the polarisation corresponding to the main relaxation of the material. This phenomenon was also observed in the case of biaxially stretched PEN (PENbiax). However, it is much less important in this case. The calorimetric technique (DSC) showed, in the case of PENa, that the effect of ageing is particularly important when the ageing time increases with a maximum effect for ageing temperature equal to Tg-10 K. In the other side, no effect was observed on the semi crystalline PENbiax by the DSC technique unlike the TSDC technique. These results confirm again the high resolving power of this latter. Also, the effect of crystallinity on the structural relaxation of PEN was highlighted and is summeryzed as following : firstly, we have observed a decrease in the TSDC peak's intensity of the α-relaxation and in the recovery enthalpy of the structural relaxation when the crystallinity rate increases. Secondly, an increase in the activation energy Δh* with the increase in the crystallinity rate and a decrease in the limit fictive temperature T'f were observed.

The origin of thermally stimulated depolarization currents in multiferroic CuCrO2

We have measured the thermally stimulated depolarization currents (TSDC) of multiferroic CuCrO2. We observe a sharp peak near the antiferromagnetic ordering temperature TN ∼ 24 K, below which the material becomes ferroelectric. In addition, we observe three other peaks above TN at ∼50, 120, and 150 K, when the poling is done at a higher temperature than TN. These peaks are not related to exotic kinds of ferroelectricity. Using the poling field dependence of TSDC, the origins of the first two peaks are ascribed to the relaxation of defect dipoles and to space charge relaxation due to the release of trapped charges, respectively. Upon polishing, the peaks observed at 120 and 150 K disappear, suggesting a surface defect origin. Moreover, using temperature and frequency dependent dielectric measurements, we find Maxwell–Wagner type dielectric relaxation. In connection with the mechanism of one of the TSDC peaks, we suggest a Schottky barrier formation to explain the dielectric relaxation.

Dipole defects in BeO

Thermally Stimulated Depolarization Currents (TSDC) technique was applied to study the effects of thermal treatments and gamma irradiation in the formation, aggregation and destruction processes of dipole defects in beryllium oxide (BeO). In this work, a TSDC dipole peak was observed at 350 K that was assigned to impurity-vacancy complexes. The TSDC peak presents a linear dependence with the Polarization Voltage (VP), typical behaviour of defects with dipole origin. Thermal treatments of 1 h were performed between 400 and 900 °C and a decay in the peak intensity was observed. After the gamma irradiation of the thermal treated samples a restoration tendency of the TSDC peak was observed.

TSDC and DSC Study of Effects of Physical Aging on Polybutylene Terephthalate (PBT)

The impact of the physical aging process on the electrical and thermal properties of semicrystalline polybutylene terephthalate (PBT) was investigated by means of thermally stimulated depolarization currents (TSDC) and differential scanning calorimetry (DSC). The TSDC technique was used to study the relaxation modes of PBT in the temperature range −50° to + 120°C. The obtained spectra revealed two peaks located at temperature maxima of 45° and 93°C. The peak appearing at 45°C corresponds to the dielectric manifestation of the glass transition phenomenon (α-relaxation). The aim of this work is to study the effect of physical aging on this relaxation. The recording of TSDC peaks of aged PBT at different temperatures for different times revealed a reduction in their intensities and their shift towards higher temperatures when the aging becomes significant. This result can be explained by the diminution of molecular chain mobility, which is directly related to the area under the peak representing the polarization of the sample. This result was confirmed by DSC measurements, which revealed the growth and the shift of the peak, which is superimposed on the jump of the heat capacity, located around 38°C and characteristic of the glass transition, towards higher temperatures where aging becomes significant.

Thermally stimulated depolarization current measurements in cubic and tetragonal yttria-stabilized zirconia

Abstract Thermally stimulated depolarization current (TSDC) measurements were performed on 3 mol% and 8 mol% yttria stabilized zirconia ceramics (3YSZ and 8YSZ), in order to observe defect associations. Several TSDC peaks were observed, and the characteristics suggested that the peaks were attributed to space charge polarization due to long range migration of oxygen vacancies and electric dipole polarization due to trimeric defect association of Y at Zr site (Y Zr ') and oxygen vacancy (Vo). The activation energies for the dipole polarizations were different between 3YSZ and 8YSZ. The difference was caused by the difference of the structure of defect association. In addition, in 3YSZ, peaks with high activation energy of 1.24 eV were observed. The high activation energy suggests the presence of oxygen migration across Y–Y edges, in other word, indicating that Y–Y pairs exist in 3YSZ.

Evaluation of thermal stability of electro-optic polymer by thermally stimulated depolarization current measurement

The thermal relaxation process of electro-optic (EO) polymers, Disperse Red 1 (DR1)/poly(methyl methacrylate) (PMMA) guest/host polymer and side-chain copolymer DR1–PMMA (PMMA-co-DR1), was studied using thermally stimulated depolarization current (TSDC) measurement. For the guest/host polymer, two TSDC peaks were identified at temperatures of −50 °C (β-peak) and around 100 °C (α-peak) due to dipolar depolarization. It was also suggested that the α-peak is ascribed to disordering of guest DR1 molecules together with randomization of the main body of the PMMA. For the side-chain copolymer, a simple relaxation process of the side-chain DR1 was observed in contrast with the guest/host polymer. Analyzing the TSDC, we estimated the activation energy and relaxation times, and discussed the relaxation mechanisms. Results showed that the TSDC method is available for evaluating the thermal stability of EO polymer.

Study of an initial transient relaxation in XLPE cable insulation by TSDC and PEA

Space charge profiles in electrets of cable XLPE insulation have been determined by pulsed electroacustic method (PEA). A single positive peak close to the cathode, which decreases with annealing time, is observed. Typically, thermally stimulated depolarization currents (TSDC) of those electrets show heteropolar peaks initially. A new transient homopolar peak emerges in TSDC profiles at 99°C with annealing at high temperatures. No direct correlation can be established between PEA and TSDC results, since the case of the largest value of the maximum of this TSDC peak corresponds to the smallest charge peak observed in PEA profile. The transient behavior is explained by means of charge trapped on crystals surfaces due to the differences between the conductivities of amorphous and crystalline phases. The homoplar peak is associated with dipolar contaminants located in the interlamellar amorphous phase, which are reoriented by the field produced by charge trapped on crystal surfaces, during the TSDC discharges. Detrapping of charge trapped on crystal surfaces occurs when lamellae melt, which contributes homopolarly to the current. Both contributions result in the peaks observed in the TSDC discharge.

Thermally stimulated current in low‐density polyethylene/MgO nanocomposite. On the mechanism of its superior dielectric properties

AbstractPolymer nanocomposites are attracting attention as emerging insulating materials. We measured the thermally stimulated depolarization current (TSDC) in low‐density polyethylene (LDPE)/MgO nanocomposites while varying measuring such parameters as the temperature increase rate and the intensity of the applied electric field. A TSDC peak that spreads over a wide temperature range from 0 °C to 60 °C was observed in all samples. As the amount of MgO nanofiller increases, the TSDC peak height decreases. Furthermore, by adopting a partial heating method, the wide TSDC peak was resolved into several component peaks. Among them, the peak at about 12 °C was found not to appear in the base LDPE. Analysis of its initial rising portion indicated that the 12 °C peak had a fairly large energy depth of about 2 eV. These results indicate that charge carriers tend to be captured more strongly after the addition of MgO nanofillers. If these captured charge carriers induce homocharge layers in the vicinity of the electrodes, further space charge formation would be suppressed. This seems to explain the fact that the amount of space charge is smaller in nanocomposites with a proper addition of MgO than in the base LDPE. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 176(3): 1–7, 2011; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21136

Dielectric relaxation in polyvinylidenefluoride–polysulfone blends

Abstract Dielectric properties of polymer blend of polyvinylidenefluoride (PVDF) and polysulfone (PSF) of different wt. % have been studied to understand the molecular motion and their relaxation behavior in the frequency range of 100 Hz to 10 kHz at different temperatures between 30 and 190 °C. The dielectric constant of the blend decreased with frequency and increased with the increasing temperature and PSF content in the blend. The magnitude of dielectric loss also increased with increase in temperature and PSF content. The observed characteristic has been consistently explained in terms of dipolar motions and the plasticization effect brought about by blending of PSF with PVDF. At constant frequency and temperature, the blend follows a linear relationship between logarithm of their dielectric constant and different ratios of blend. The appearance of a peak for each concentration in dielectric loss suggests the presence of relaxing dipoles in the blend. In addition of PSF with PVDF, the peak shifts toward higher frequency side suggesting the speed up the relaxation process. AC dielectric data is also combined with thermally stimulated depolarization current (TSDC) data which is generally studied for low-frequency dielectric properties of polymers blends so as to produce the results in a wide frequency range. The glass transition temperature ( T g ) of the blend was studied by differential scanning calorimetric technique (DSC), the T g was compared and correlated with TSDC peak. The blend samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) to study the formation of blend and micro structural properties of the materials. The shifting of peak toward lower diffraction angle side confirms the reduction in particle size with increasing amorphous content in the blend.

Modeling of thermally stimulated depolarization current (TSDC) using dipole–dipole interaction concept

The study of thermally stimulated depolarization current (TSDC) using the dipole–dipole interaction model is describedin this work. The dipole–dipole interaction model (DDIM) determines the TSDC peak successfully since it gives significant peak parameters (i.e. activation energy ( ${\bf \textit{E}}$ ) and pre-exponential factor ( ${\boldsymbol\tau}_{{\bf 0}})$ ) in addition to the dipole–dipole interaction strength parameter ( ${\bf \textit{d}}_{{\bf i}})$ . Application of this model to study the peak parameters of some polymeric systems is presented.

Correlation Between Resistance Degradation and Thermally Stimulated Depolarization Current in Acceptor (Mg)‐Doped BaTiO3 Submicrometer Fine‐Grain Ceramics

Thermally stimulated depolarization current (TSDC) of acceptor (Mg)‐doped BaTiO3 ceramics was analyzed for submicrometer fine grain specimens. For a fixed condition of polarization field (EP) and polarization time (tP), the TSDC associated with an oxygen vacancy relaxation showed two peaks with relaxation temperatures (Tm) under low polarization temperature (TP) conditions. It is inferred that the TSDC peak of the lower Tm is due to the relaxation of a distributed space charge within a grain and has a short relaxation time constant (τ0), and the higher Tm is due to the long‐range relaxation across grain boundaries with a larger time constant, τ0. The onset condition for resistance degradation can be correlated with the breaking point of TP, at which the TSDC peak changes from in‐grain relaxation to across‐grain boundary relaxation. The breaking point of TP and the time to degradation systematically decreased with the increase of acceptor concentration. Such behavior can be correlated with the decrease of TP, Tm, τ0, and little change of activation energy of relaxation, which is due to the increase of concentration.

Polarization and microstructural effects of ceramic hydroxyapatite electrets

To provide bioelectrets with controlled electrical energy, the polarization and relaxation characteristics of hydroxyapatite (HA) ceramic electrets were investigated in terms of poling conditions and microstructures. HA electrets were prepared between 250 and 500 °C for 5–120 min under a 5 kV cm−1 dc electrical field. Poling conditions and grain size of HA ceramics significantly influenced the thermally stimulated depolarization current (TSDC) spectra and charge storage (Q). Under a poling field of 5 kV cm−1, varying the poling temperature from 250 to 500 °C drastically shifted the TSDC peak temperature from 250 to 620 °C and increased Q from 0.5 to 45 μC cm−2. The change in the average grain size from 2 to 11 μm increased the Q value from 15 to 60 μC cm−2 with a negligible shift in the TSDC peak position. The measured difference of the TSDC peak shapes and positions, as well as the Q values, was theoretically due to the four polarization states with different activation energies (Edr) of dipole relaxation and the pre-exponential factor of relaxation times (τ0). The dependences on the poling conditions and grain size indicated that the four states were due to the orientation polarization of absorbed water (state 1), the localizations of displaced protons around PO43− and OH− in the grains (states 2 and 3), and the localization of displaced protons in the grain boundaries (state 4).

Effect of Acceptor (Mg) Concentration on the Resistance Degradation Behavior in Acceptor (Mg)‐Doped BaTiO3 Bulk Ceramics: II. Thermally Stimulated Depolarization Current Analysis

Thermally stimulated depolarization current (TSDC) of acceptor (Mg)‐doped BaTiO3 ceramics was analyzed with different acceptor concentrations for coarse‐grained specimens with uniform grain sizes. In all specimens, the increase of the polarization temperature (TP) for a fixed condition of polarization field (EP) and polarization time (tP) increased TSDC peak associated with an oxygen vacancy (VO••) relaxation. When the acceptor concentration is increased, both TP to generate same magnitude of TSDC and the relaxation temperature (Tm) of the TSDC peak systematically decreased. On the other hand, the activation energy of the oxygen vacancy relaxation showed roughly constant values of ∼0.9 eV, irrespective of acceptor concentration. Such behavior can be explained by a decrease in the relaxation time constant (τ0), which is in turn associated with the shape of oxygen vacancy profile in the specimen after polarization. The decrease of TP, Tm, τ0, and the little change of activation energy from the TSDC data with the increase of acceptor concentration implies an increase in the oxygen vacancy concentration C(VO••). The experimentally observed behavior of C(VO••) vs acceptor concentration could be explained by the defect chemical model, and from these results, the acceptor ionization energy EA was estimated to be about 1.0 eV.

Effect of Blending with Polysulfone on Thermally Stimulated Discharge Behavior of Polyvinylidenefluoride Films

Thermally stimulated depolarization current (TSDC) have been undertaken on solution grown foil samples of polyvinylidenefluoride (PVDF)-polysulfone (PSF) blends as a function of the polarizing temperature, applied field, and polysulfone weight percentage in the blend. The TSDC thermograms of pure PVDF and PSF shows two peaks whereas the blend composition of the two polymers shows a single peak at around 170–190°C. The magnitude of the TSDC peak current increases and the peak current position shifted toward the lower temperature side as the polysulfone weight percentage in the blends was increased. The peak temperature of blend samples is higher than the dipolar peak (β peak) of PVDF samples and does not vary with change in polarizing field. This indicates that this peak may be due to dipoles. At the same time, the peak shifts towards higher temperatures with increase in polarizing temperature, which shows the behavior of space charge peak. This contradiction may be explained on the basis of induced dipoles. It seems that the charge originating from the bulk of the samples gets trapped in the deeper traps during polarization, and thus form induced dipoles. Afterward these induced dipoles get aligned in the polarizing field. It can be explained on the basis that either the dipolar peak gets covered by the space charge peak, or its contribution to the total polarization is very small.

Thermally Stimulated Current in Low-density Polyethylene/MgO Nanocomposite -On the Mechanism of its Superior Dielectric Properties-

Recently polymer nanocomposite has been attracting much attention as an emerging insulating material. In this paper, we measured thermally stimulated depolarization current (TSDC) in low-density polyethylene (LDPE)/MgO nanocomposite by changing measuring parameters such as the temperature increasing rate and the intensity of electric field applied. As a result, a TSDC peak that spreads over a wide temperature range from 0°C to 60°C was observed in all the samples. As the amount of MgO nano-filler increases, the TSDC peak height decreases. Furthermore, by adopting a partial heating method, the wide TSDC peak was resolved into several component peaks. Among them, the peak at around 12°C was found not to appear in the base LDPE. By analyzing its initial rising portion, the 12-°C peak was assumed to have a fairly deep energy depth of about 2 eV. These results indicate that charge carriers tend to be captured more strongly by the addition of MgO nano-fillers. If these captured charge carriers induce homocharge layers in the vicinity of the electrodes, further formation of space charge would be suppressed. This seems to explain the fact that the amount of space charge is smaller in the nanocomposite with a proper addition of MgO than in the base LDPE.