Thermally Stimulated Depolarization Research Articles

Study of ionic impurity mobility in quartz crystals by impedance and thermionic current measurements

Defects, notably interstitial impurities, are responsible for degradation of resonator performance with time. In order to study the mobility of ionic impurities, we have measured thermionic currents as a function of temperature by the thermally stimulated depolarization (TSD) method. We have observed several current maxima; each peak is due to the displacement of an impurity family from a given site and is characterized by its activation energy. Making impedance measurements to complete these results, we find energies of about 1 eV. We have studied quartz crystals doped with a given impurity in order to identify the nature of the impurities responsible for some current peaks. This study confirms that the TSD method is very sensitive.

Thermally stimulated current study of space charge formation and contact effects in metal-Polyethylene Terephthalate film-metal systems. II. Influence of polarization conditions

The influence of the polarization conditions on the space charge formation in Metal-Insulator-Metal systems obtained by vacuum deposition of aluminum electrodes on both faces of thin Polyethylene Terephthalate (PET) films has been investigated by using the Thermally Stimulated Depolarization Current (TSDC) method in a wide range of poling temperatures, poling times and applied field strengths, emphasizing the effects of the presence of Schottky barriers at the Al-PET interfaces after heat treatment under helium. TSDC spectra of PET films ranging in thickness from 1.5 to 12 μm have been interpreted on the basis of the extended electronic band model described in a previous paper. Different values of activation energies, corresponding to distinct processes occurring during the space charge relaxation, have been determined, allowing a clear relationship between dipolar orientation and electronic detrapping to be evidenced. The height of the interfacial potential barriers between aluminum and PET has also been estimated.

Thermally stimulated current study of space charge formation and contact effects in metal-Polyethylene Terephthalate film-metal systems. I. Generalities and theoretical model

The Thermally Stimulated Depolarization Current (TSDC) method has been used to emphasize the important role played by the nature of the aluminum-polyester contact on the electrical properties of Metal-Insulator-Metal systems involving thin Polyethylene Terephthalate films (PET) used in capacitors. A progressive change of initially ohmic contacts into blocking ones upon heat treatment has been shown to be responsible for current reversals observed in the space charge region of the TSDC profiles. The use of an electronic band model allowed us to account for the nature and properties of the space charge accumulated in films ranging in thickness from 1.5 to 12 μm. Heterogeneity and retrapping effects have been put forward to explain the difference in behavior observed from ultrathin (1.5 μm thick) to thin films (12 μm thick). It has been shown that the existence of a significant gradient in density of localized states along the thickness of the film gives rise to a significant potential difference between the two vacuum deposited electrodes.

A novel polar polymer via romp

AbstractWe have synthesised poly(2,3‐bis(trifluoromethyl)norbornadiene) (PBTFMND) via ring‐opening metathesis polymerisation (ROMP) to yield a glassy, highly polar polymer. The high trans polymer is ∼92% tactic and the high cis polymer is ∼75% tactic but the type of tacticity cannot be determined by NMR techniques. Thermally Stimulated Depolarisation (TSD) measurements give relaxed susceptibilities as high as 45 for the high trans material but as low as 3 for the high cis material. These data suggest that both the trans and cis materials are syndiotactic. The high trans material can be poled to yield a maximum polarisation of about 20 mC m−2 and a pyroelectric coefficient of 6 μC m−2. Though this is less than that of PVDF, the low room temperature permittivity and loss of PBTFMND results in a pyroelectric figure of merit comparable with that of PVDF.

Study of the Denaturation Process in Albumin−Urea Solutions by Means of the Thermally Stimulated Depolarization Currents Technique

The dielectric relaxation of bovine serum albumin (BSA) aqueous solution was studied in various stages of urea denaturation by means of the thermally stimulated depolarization currents (TSDC) technique. A large variation of urea concentration was utilized (0−4 M). Special attention was given for concentrations between 0.006 and 0.050 M, which are comparable to those measured in normal and uremic human serum. The TSDC spectrum consists of two main bands in the temperature range 100−300 K: (1) a broad low-temperature band (A) with two maxima at about 128 and 142 K, which are attributed to the (re)orientation mechanisms of bulk and hydration water molecules, respectively, and (2) an intense band (B), whose position varies in the range between 230 and 245 K and which is attributed to the (re)orientation of protein macromolecules. Two peaks of lower intensity (B1 and B2) are resolved in the rising part of band B and are most likely due to relaxation mechanisms of the side chains of BSA. The activation energies for the last three mechanisms depend on urea concentration, and this fact might be attributed to the conformational changes of BSA upon denaturation. It is of interest to note that the macromolecules' activation energies depend drastically on the concentration of urea up to 0.05 M.

Study of the Denaturation Process in Albumin−Urea Solutions by Means of the Thermally Stimulated Depolarization Currents Technique

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionStudy of the Denaturation Process in Albumin−Urea Solutions by Means of the Thermally Stimulated Depolarization Currents TechniqueA. Vassilikou-Dova, S. Grigorakis, P. Varotsos, A. Kapetanaki, and D. KoutsikosCite this: J. Phys. Chem. 1996, 100, 21, 9196Publication Date (Web):May 23, 1996Publication History Published online23 May 1996Published inissue 1 January 1996https://doi.org/10.1021/jp9609545Copyright © 1996 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views160Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (108 KB) Get e-Alerts

Water electret relaxation at dispersed silica surfaces

The behavior of water adsorbed at highly dispersed silica surfaces at low temperatures has been studied by thermally stimulated depolarization (TSD) and quantum chemical methods. Three relaxation maxima of the TSD spectra are observed without high-temperature treatment of the samples, and are interpreted as connected with uni-, bi- and tridimensional water clusters. Dynamic simulation of different relaxation processes of water molecules, which bind to silica surfaces directly or through hydrogen bonds with other adsorbed molecules, shows that the relaxation time decreases as the water cluster grows. The activation energy of rotation is a maximum for molecules with donor-acceptor bonds Si←OH 2 in the complexes ▪.

Dielectric Properties and Dynamic Simulation of Water Bound to Titania/Silica Surfaces

Water adsorbed on titania/silica (TS) surfaces has been studied by dielectric spectroscopy (DS) in the 3-10 MHz frequency range at T = 120-300 K, thermally stimulated depolarization (TSD) at the same temperatures, 1 H NMR, and quantum chemical methods. The TSD spectra ofTS have only one relaxation maximum after sample heating at 400 K. The activation energies of depolarization (TSD) and polarization (DS) decrease at TiO 2 content increasing in TS. According to the TSD, DS, and 1 H NMR data, water adsorbed on the TS surfaces essentially in the interface region forms more weakly bound clusters than on the silica surfaces. Simulation of vibrational-rotational relaxation of the water molecules attached to the TS surfaces shows that the activation energy of rotation is a maximum for the molecules having donor-acceptor bonds, Me-OH 2 (Me = Si, Ti), in the complexes HO-Me-OH 2 + mH 2 O and it is minimum for one water molecule linked to the Ti-O(H)-Si bridge through a hydrogen bond.

Wettability and thermally stimulated depolarisation current spectra of naturally aged silicone rubber insulators

AbstractInvestigations are reported on high‐ and low‐temperature vulcanized silicone rubber composite insulators that were exposed to service for three, nine and eleven years under industrial or marine pollution conditions. Wetting angles and thermally stimulated depolarization (TSD) current spectra were measured. Microscopic observations of selected insulator surfaces were carried out as well. The prolonged services cause gradual and inhomogeneous losses of hydrophobicity on surfaces and inside of insulator housing materials. It is shown that there exists a correlation between the measured TSD current spectra and the wettability changes. In addition, the spectra also allow to predict an ability to support a process of hydrophobicity recovery at a housing surface. It seems that TSD measurements may be applied as a complementary test method during performance assessment of silicone rubber composite insulators.

Vulcanization influence on tsd currents and wettability of room temperature vulcanized silicone rubber hv insulator coatings

AbstractThis paper deals with the Thermally Stimulated Depolarization (TSD) current and contact angle measurements on Room Temperature Vulcanized (RTV) silicone rubber High‐Voltage (HV) insulator coatings taken recently by Dr. S. M. Gubanski and Dr. M.‐S. E. Wang.

On the nature of the thermally stimulated depolarization currents in MgO:Li

Two peaks at around 245 and 280 K are observed in the thermally stimulated depolarization (TSD) spectra of MgO:Li quenched in static air from temperatures above 1100 K. They are related to the ionization of [Li] 0 centers which are induced by this oxidizing quenching. The sample-thickness and applied-voltage dependences of the TSD results indicate, contrary to the previously proposed model based on Maxwell-Wagner polarization processes, that both peaks are due to the blocking character of the contracts at the sample-electrode interfaces.

Mobilité des impuretés ioniques dans le quartz

In order to produce very high quality oscillators of quartz, crystals which include a minimum of impurities are necessary. «Sweeping» is used in industry to purify synthetic crystals. An electric field is applied to a quartz sample at a given temperature to move ionic impurities nearer to the electrodes. After a lapse of time, the crystal is cooled and the field is removed and subsequently the extremities are either cut off or removed by polishing. The technique T.S.D. (Thermally Stimulated Depolarization) is used to better know the effects of «sweeping». Current densities are measured as a function of temperature. Two qualities of quartz, furnished by the S.I.C.N. (Societe Industrielle de Combustible Nucleaire a Annecy) have been studied. Samples, purified or not, cut either perpendicular to the Z axis or to the Y axis, were extracted from various places in the crystal. The results obtained vary according to the origin of the studied samples and their treatment. In order to determine the influence of different parameters which occur at the time of «sweeping», we varied the intensity of the applied tension and the polarization time. Effects on the measurements of the thermoionic current were observed for a high quality sample

Negative thermally stimulated currents in ice

Using precision equipment of our own design, we measured thermally stimulated currents (TSCs) in pure crystalline ice and crystalline ice doped with HCl or NH4OH. The conditions for heterocharge and homocharge decay under thermally stimulated depolarization (TSD) were studied. The role of proton relaxation during the formation of an electret state of the ice was determined.

Dielectric studies of molecular mobility in hydrated zeolites

We report on detailed investigations of the dielectric relaxation mechanisms in a Na-13X zeolite by means of the method of thermally-stimulated depolarization currents (TSDC) over a wide range of temperatures, 77–300 K, and water content, 0.020–0.566 w w . Interest is mainly focused on quantitatively characterizing the effects of water on the motion of ions and the reduction of the mobility of water molecules in the confined pore geometry. Five distinct relaxation processes were identified. Three of them were attributed to motions of ions, namely, in the order of increasing temperature, local jumps of ions in the supercages, a Maxwell-Wagner effect and d.c. conductivity. The remaining two processes, present in the samples only for water content higher than a critical one for the completion of the first hydration layer, about 0.30, were ascribed to the reorientation of water molecules in the supercages and the small β-cages, respectively. The reduction of the mobility of water molecules was much stronger in the β-cages than in the supercages.

Thermally stimulated depolarization of ellipsoidal particles in an insulating medium

The equations governing thermally stimulated depolarization (TSD) processes in a suspension of ellipsoidal particles in an insulating matrix, which exhibits Maxwell-Wagner type polarization, have been obtained from the Sillars-Van Beek formalism. A first-order TSD process is obtained when all particles are identical and arranged with one of their principal axes parallel to the electric field. For a random distribution of particle shapes, sizes and orientations, the TSD peak is wider than a first-order one. The dependence of the depolarization processes on the physical properties of the matrix and the embedded particles is shown for different particle size distributions.

Thermally stimulated current in glass‐laminated unsaturated polyester resins

AbstractExperimental results are reported on the electrical properties of glass‐laminated unsaturated polyester (UP) resins. Measurements of the poling current as a function of temperature reveal two different activated processes. Above 50°C the activation energy is 160 kJ/mol and has been associated with ionic condition, possibly by protons, while at lower temperatures (below −70°C) the activation energy is very low (less than 40 kJ/mol) and is associated with dipole relaxation. It is concluded that the laminated UP resin undergoes a phase transformation between low and high temperatures, which gives rise to a completely different electrical response. This phase transformation can be associated with the glass transition of UP resin phase. In view of the low activation energy, giving rise to a polarization peak, it is concluded that the low temperature range (glassy state) favors strictly localized motions of charges—most likely electrons. At higher temperatures, the behavior corresponds to d.c. conductivity and is associated with extended motions of charge carriers with limitations at contacts and at internal barriers. According to the air gap measurements, the pronounced dip found in the temperature dependence of the poling current (in the range from 20 to −30°C) may be due to separation of conduction and dipole relaxation current. Thermally stimulated depolarization (TSD) current measurements reveal the presence of high internal fields due to space charges accumulated at the phase boundaries of glass fibers.

Thermally stimulated depolarization of poly(ether block amide) copolymer

Phase segregation in poly(ether block amide) copolymer has been studied by thermally stimulated depolarization (TSD). Well-defined, complex and partial phase segregation were observed depending on the molecular mass of each segment of the copolymer. A new glass transition peak appeared were broadened. Soft-segment component poly(tetramethylene glycol) (PTMG), with a lower molecular mass, was found to be completely amorphous. No additional Maxwell-Wagner-Sillers (MWS) effect peak at the phase boundaries was detected.

Polarisation of CdF2 by blocking electrodes. II. The effect of passing currents

For pt.I see J. Phys. C, vol.14, p.4357, (1981). Thermally stimulated depolarisation (TSD) currents and charging and discharging currents at room temperature were obtained with graphite-contacted CdF2. The results and scrutiny of published TSD data show that, besides the known impurity-complex and point defect space-charge polarisation, the currents are caused by charge carriers trapped at Cd colloids segregated below the contact surface and by the electrochemical potential which Cd and accumulation fluorine entail.

Multiplicity of dielectric-relaxation times of dispersed ice microcrystals. Time dependence

This work deals with a detailed study of the multiplicity of relaxation times of the dielectric relaxation of water molecules in dispersed ice microcrystals at different stages of evolution with time, by means of the thermally stimulated depolarization (TSD) current method. Independently of the stage of evolution, the relaxation mechanism is multiple due to a continuous distribution of both the activation energyW and the pre-exponential factorτ0. A linear relationship exists betweenW and lnτ0, the socalled compensation law. With advancing evolution the distribution becomes broader, while the relaxation process becomes faster. The compensation temperature is, on the contrary, independent of the stage of evolution. Some aspects of the dielectric-relaxation mechanism in ice emulsions are discussed in the light of these results.

Multiplicity of dielectric relaxation times of dispersed ice microcrystals

The multiplicity of relaxation times of the dielectric relaxation of water molecules in dispersed ice microcrystals has been studied by means of the thermally stimulated depolarization (TSD) current method. Using several experimental techniques offered by the TSD method we have shown that the relaxation mechanism is characterized by a continuous distribution of relaxation times with both the activation energy.W and the pre-exponential factorτ0 in the Arrhenius equation being distributed parameters. A linear relationship has been found to exist betweenW and lnτ0. The dielectric behaviour of ice emulsions has been found to resemble strongly in some aspects that of HF-doped ice and ice samples with high concentrations of crystal imperfections. The multiplicity of relaxation times has been explained by the interaction of intrinsic ionic defects with water molecules.