Thermally stimulated discharge current

Conductivity Direct current measurement, Dielectric measurement, Thermally Stimulated Discharge (TSD) method A—>C 46-49... 

TSD experiments are performed using the measuring circuit shown in Figure 5.1. The experimental method is schematically drawn in Figure 5.28. The sample is heated to polarisation temperature (Tp), at time t an electrical field (B,) starts to polarise the sample. After a certain polarisation time (tpl) the temperature is decreased to T the polarisation is then frozen in. At temperature T (i.e. at time t,) the electrical field (E ) is removed and a small depolarisation current effect is measured. If this depolarisation effect has been vanished conpletely, the temperature is to increased linearly as a function of time and the thermally stimulated discharge current is recorded. 

The electronic and atomic polarisation can not be frozen-in and cause the small depolarisation current after removing of the electrical field at time t2. Thus, the measured discharge current is the sum of dipole and space charge relaxation effects. The exponential relation between the relaxation times of these effects and the temperature makes it possible to shorten the discharge time drastically by thermal stimulation. 

The theory describing space charge depolarisation processes is conqplicated [38]. Equations like 5.39 describe the thermally stimulated discharge currents but contain more unknown variables which are depending of ... 

The principal characteristics of the triboelectret state in polymers recorded experimentally are i) the efficient surface charge density (ESCD) value and ii) the thermally stimulated depolarization (TSD) current spectrum, i.e. the discharge current dependence of the electret on its heating temperature. The analysis of TSD spectra helped to estimate the parameters of the triboelectret state, including the homo- to heterocharge relation in a dielectric, activation energy of the charge relaxation processes, relaxation time and others. 

Shallow traps can, after being filled at lower temperatures by an electrical current, be thermally emptied by heating the crystal, and they then lead to an increase in the dark current. Figure 8.41 gives as an example the thermally-stimulated discharge current from the traps in an anthracene crystal whose electron traps were previously filled at a lower temperature the crystal was thus charged at a low temperature. The corresponding experiment was carried out with the same crystal also... 

Glass transition K By thermally stimulated discharge currents 223 (38)... 

Note that thermally stimulated current spectroscopy cannot be applied to conductive materials with a resistance smaller than lO Q/m thickness. In addition, the presence of space charges in the sample can produce artefacts. For solid samples the upper temperature limit of measurement is the onset of flow, which presents itself as a large current discharge. This discharge is due to the sample behaving like a battery and draining the charges accumulated at the surfaces. 

Finally, temperature modulated thermally stimulated current analysis has been applied to study dielectric materials via the separation of reversible pyroelectric effects from nonreversing thermally stimulated discharges. 

ES, resonance electrostatic method FO, forced oscillation dynamic-mechanical analysis FV, free vibration TP, torsion pendulum TSC, thermally stimulated discharge current measurement D, dielectric VR, vibrating reed. 

Thermally stimulated discharge experiments were also done on PS samples with different stereochemistry and placement of the phenyl groups along the chain (51). All PS samples showed 5 current maxima but they are not always... 

Myslinski, P. and Kryszewski, M. (1987) The effect of crystalline structure on the thermally stimulated discharge current in isotactic polypropylene, Acta... 

ASD amorphous solid dispersions, TW-TSDC thermal-windowing thermally stimulated discharge current... 

Saxena Pooja, Gaur Mulayam Singh, Shukla Prashant, et al. Relaxation investigations in polysulfone Thermally stimulated discharge current and dielectric spectroscopy. J. Electrostat. 66 no. 11-12 (2008) 584-588. 

The previous section reviewed the advances of what may be termed the classical technique of dielectric spectroscopy, which has, as its modes of operation, measurements either at constant temperature or at constant frequency. Recently a technique which does not operate with these restrictions has been developed, particularly by van Tumhout This technique is variously termed thermally stimulated discharge (TSD) or thermally stimulated current (TSC). In its simplest form a material in the form of a disc with electrodes in intimate contact on opposite faces is heated to some forming temperature Tf. At this stage the sample is polarized by applying a strcsng electrostatic field ( 30 kV/cm) for an extended period. All polarization processes which are active at, or below the tenqjerature Tf and within the time the fidd has been on, will contribute to an overall polarization the material within the field is polarized. If the field were now removed at the temperature Tf, the polarization could be disdiarged as in the step response technique of the previous section. However, in TSD the temperature is reduced to some value < Tf with the field still on. Any polarization process which is non-active at but active between and Tf has thereby been frozen-in at T < Tg, even when the field is removed as in the TSD tech-... 

Other methods for the determination of carrier mobility include holographic time of flight (HTOF) and extraction current transients [67, 68]. The density of traps may be estimated with near-IR optical absorption in the case of Cgo-sensitized PVK systems [69] or can be estimated from thermally stimulated discharge current measurements [70]. 

Qrou and Gultinger [486] applied the method of ionk thermal currents to a polarized electret which is discharged by the thermally stimulated discharge current technique and showed a method of calculation of dipok relaxation times and their activation energies. Perimsn and Meunkr [487], van Tumhout [488], and several others (489,490) have used it to analyze the electret effect quantitatively. 

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