Evaluation of the dielectric parameters from TSDC spectra: application to polymeric systems

Abstract

The Thermally Stimulated Discharge Current (TSDC) technique is widely used for the study of main and secondary dielectric relaxations in polymers. The TSD current is described by different equations that can be arranged in a unique three-parameters (the activation energy W, A and B) general form. The physical meaning of A and B depends on the origin of the discharge currents. In this paper a method is proposed to obtain these parameters by fitting the experimental data with the analytical expression of the current, in the range around the maximum. Simulations were carried out to underline the relative importance of the parameters. A method is proposed for the decomposition of experimentally determined complex bands into a limited number of elementary peaks, each of them characterized by average values for W and B. The errors resulting from different approximations used in the analytical current expression or by the utilization of various expressions for the relaxation time are analyzed. The method is applied for the analysis of the TSDC spectra in the glass-rubber transition temperature regions of PET and PMMA, yielding several peaks characterized by narrow distributions of W (∆W ≈ ± 0.06 eV).

Thermally stimulated depolarization current and dielectric spectroscopy used to study dipolar relaxations and trap level distribution in PMMA polymer

“…It has been reported in literature that the lower limit of τ 0 value (~10 −13 s) was obtained in the ideal situation when the measured quantity (TSDC current) is determined only by dipoles [20]. However, in several TSDC studies with the use of the thermal sampling technique (such as WP) much smaller values for τ 0 were reported [37,38].…”

“…Many attempts have been made in order to elucidate the origin of complex TSDC peaks. They are based on the behavior of the TSDC peaks as a function of the polarization parameters [8,20,21]. Several methods were used to decompose the experimental complex bands into limited number of elementary peaks [18,22].…”

Comparative dielectric studies of segmental mobility in novel polyurethanes

“…A typical TSDC experiment [35] consists of the polarization of the dielectric material at a sufficiently high temperature T p (polarization temperature) by applying an electric field E p (polarizing field) for time t p (isothermal polarization time). In the next step, the temperature of the sample is lowered, with a controlled rate and with the electric field applied, to T 0 << T p , at which the non-equilibrium state of the system is 'frozen-in'.…”

“…The relaxation time τ (T) and the corresponding parameters (E, τ 0 ) were determined for each TS peak directly from the whole-curve graphical integration method (details in ref. [35]). The high values observed for the α peak, in particular in its central region, and the shape of the E(T max ) dependence are characteristic of the α relaxation, in agreement with TS results in other polymers [19][20][21]23].…”

Polyethylene crosslinked in different media: structural changes versus dielectric behaviour

“…The same is obviously true for the depolarization process, where carrier drift now occurs under the added complication of local electric fields. Charge trapping in crystalline polymers has been the subject of many previous works and these effects are attributed to different structural defects [17][18][19][20][21][22][23][24][25][26][27][28][29]. Fleming has considered the formation of the ''cavity'' traps in the amorphous regions of the polymer [20][21][22].…”