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Dielectrics and Electrical Insulation, IEEE Transactions on

Issue 3 • Date Jun 2001

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Displaying Results 1 - 25 of 47
  • AC conductivity of Bi-Sr-Ca-Cu-O glasses

    Publication Year: 2001 , Page(s): 426 - 428
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    The results of AC electric conductivity measurements in Bi-Sr-Ca-Cu-O glasses are reported. Two components of the total conductivity were observed, and the activation energies of both processes was determined. Small polaron hopping between copper ions in a different valency state CuI-CuII is one process. We believe that the second conductivity component is CuI ion diffusion View full abstract»

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  • Dielectric relaxation in photochromically doped polymeric matrices studied by optical waveguide technique

    Publication Year: 2001 , Page(s): 507 - 511
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    Optical waveguide methods and, comparatively, optical absorption measurements are used to study dielectric relaxation of polystyrene (PS) thin films doped with spiropyran (SP) at optical frequencies. The time variation in the position and intensity of guided modes is connected with changes in the real and imaginary part of the dielectric function of the film at different wavelengths of the incident light, and reflects dynamic photochromic processes in the polymer matrix. The differences in the decay patterns recorded by the two methods are related to aggregate formation between colored species of the parent SP View full abstract»

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  • Synthesis, structure and conduction of a novel radical cation salt, (ET)5Dy(NCS)6NO3.C2H5 OH

    Publication Year: 2001 , Page(s): 429 - 431
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    A new radical cation salt (ET)5Dy(NCS)6No 3.C2H5OH based on a complex dysprosium anion was prepared by electrochemical oxidation of bis (ethylenedithio)tetrathiafulvalene (ET) in a chlorobenzene-ethanol solution. Its crystal structure and conducting properties were studied. The salt has a layered crystal structure with a new type of packing of the radical cation layer, which is called ω type. Its electrical properties show that this salt is a semiconductor View full abstract»

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  • Dielectric properties of holmium oxide films

    Publication Year: 2001 , Page(s): 447 - 453
    Cited by:  Papers (1)
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    Results of dielectric studies of electron-beam deposited holmium oxide thin films, examined in metal/insulator/metal (MIM) structures, are reported. The frequency domain characteristics of the capacitance, dielectric loss and complex impedance have been estimated from the time domain measurements of the charging and discharging currents. The influence of the voltage on the dielectric characteristics at 430 K has been tested. Experimental results clearly show that the dielectric response in the frequency range from 100 kHz to 20 Hz comes from the insulating film of Ho2O3 as well as from metal-insulator interfaces. The capacitance and resistance of Ho2 O3 film and Al-Ho2O3 regions have been determined View full abstract»

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  • Limiting losses in dielectrics

    Publication Year: 2001 , Page(s): 345 - 351
    Cited by:  Papers (1)
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    Examination of a wide range of experimental data relating to `low-loss' dielectric materials reveals the little acknowledged fact that their loss at high frequencies (kHz to GHz) and low temperatures (typically 100 to 200 K) is weakly or very weakly dependent on frequency, what we call `flat loss', and is likewise weakly dependent on temperature. Moreover, the absolute value of the loss tangent tan δ, for a wide range of materials, falls in the relatively narrow range 0.001 to 0.1, although some cases of lower loss ~10-5 to 10-4 are known. Examples of such behavior are given. An explanation of this hitherto apparently not recognized behavior, which is not understood in terms of any accepted mechanism, is proposed in terms of screening of dipoles by other dipoles or by point charges. The principal feature is a constant loss per reversal of polarization, independent of the frequency of reversals, arising from the delayed screening process. The magnitude of the resulting flat loss depends on the dipolar species density, while the power-law index of the frequency dependence depends on the ratio of energy lost per reversal to energy stored in the polarization. The theory of this phenomenon explains the observed behavior and provides a basis for understanding of the residual losses View full abstract»

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  • Kinetics of photochemical reactions in condensed phases. What can be borrowed from methods of dielectric physics?

    Publication Year: 2001 , Page(s): 543 - 548
    Cited by:  Patents (1)
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    Methods, commonly used to analyze relaxations in dielectrics in the time domain, have been adapted to study kinetics of chemical reactions in solids. In particular, the effect of distributed parameters on the reaction kinetics was taken into consideration. Simple methods, allowing for a straightforward determination of the kinetic parameters, have been put forward and applied to interpret experimental results obtained on a series of crown ethers, with a photoactive azobenzene moiety incorporated in the molecules, dispersed in polymer matrices View full abstract»

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  • Behavior of the discrete energy states

    Publication Year: 2001 , Page(s): 461 - 468
    Cited by:  Papers (1)
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    A study comparing composite thermally stimulated current (TSC) curves that usually are measured by the single heating method, and partial curves from repeated heating and cooling processes, is reported. For this purpose, both the auto-separation (As) and reconstruction (Re) methods are necessary. The former enables us to separate accurately composite curves obtained by one heating process into several TSC curves with a single relaxation process. The latter enables us to reconstruct TSC curves from partial curves obtained by repeated heating and cooling, even if they had no observed peak. Both methods apply a theory, using the fundamental element that was defined originally to be the smallest quantity and a coordinate determined arbitrarily on the measured TSC curves. The current type of charge compensation equation that makes accurate RC procedure possible was first proposed. From detailed analysis, it was confirmed that an electron trap and a hole trap are produced simultaneously in a naphthacene doped anthracene single crystal. Analysis suggests that repeated heating and cooling influences both trap sites and that the indirect transport mechanisms via discrete state-to-state charge transfer processes is not negligible View full abstract»

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  • Dielectric spectroscopy of chemically stabilized pericardium tissue at sub-zero temperatures

    Publication Year: 2001 , Page(s): 527 - 530
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    In this paper dielectric spectroscopy is used as a tool for the investigation of crosslinking processes in chemically modified collageneous tissues. Measurements in the frequency range of 10-1 to 107 Hz and at temperatures 180, 200 and 220 K have been performed for collageneous porcine pericardium tissues, crosslinked with glutaraldehyde (GA) and dimethyl suberimidate (DMS) reagents for exposure times ranging from 15 min to 2 h. The dielectric loss spectra allowed detection of a shift of the main relaxation process to lower frequencies upon GA or DMS treatment. The observed increase of relaxation times can be interpreted as a result of the crosslinking-induced changes in dipolar polarization of collagen bound water as well as in water-assisted polarization of polar sidegroups in collagen polypeptide chains. It has been found that the relaxation time reaches a maximum value after 1 h of chemical treatment for both reagents. This result can support earlier findings, which have shown that the major part of crosslinks in collagen is created over the first hour of the chemical modification View full abstract»

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  • Time-of-flight ion mobility measurements in epoxy-amine systems during curing

    Publication Year: 2001 , Page(s): 572 - 576
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    The technique based on the time-of-flight (TOF) concept was proposed for determination of ion mobility in epoxy resins under isothermal curing conditions. This study extends our earlier investigations on this subject. Ionic conductivity dc measurements also were carried out in order to gain better understanding of the evolution of the ionic conductivity and mobility. The experiments have been performed for selected epoxy-amine systems that gellify and vitrify: diglycidyl ether of bisphenol A (DGEBA) with 4,4'-methylenebis [3-chloro-2,6-diethylaniline] (MCDEA) and for reacting medium that gellify only: diglycidyl ether of 1,4-butanediol (DGEBD) with 4,9-dioxa-1,12-dodecane diamine (4D). The differences found between the time dependency of the ionic conductivity and mobility during curing are explained by the decrease of the concentration of ionic charge carriers during the reaction. We conclude that the decrease of the ionic charge carrier density during the reaction, limits the applicability of the basic assumption of electrical techniques for reaction monitoring, that the ionic conductivity is related directly to the medium viscosity View full abstract»

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  • Electrical conduction of thin 1,4-cis-polybutadiene films

    Publication Year: 2001 , Page(s): 406 - 410
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    This work contains results on the internal structure and dc conduction of 1,4-cispolybutadiene. X-ray and thermally stimulated depolarization (TSD) studies have been a source of information on phase transitions in the investigated material. The conduction measurements have been performed on thin films of thickness varying from 1 to 10 μm. Gold and aluminum have been applied as electrodes. The temperature range changed from 13 to 325 K. The investigated material was 1,4-cis polybutadiene of the Philips Petroleum Co, It contained 96% cis and 4% of the trans form of polybutadiene. It was observed that the internal structure of the polymer had a strong influence on its electrical properties. Electric conduction resulted from non-activated or thermally activated hopping with some contribution of the Poole-Frenkel effect. Electrode contact phenomena, such as thermionic emission and field emission (tunneling), are very likely responsible for charge carrier injection into the investigated material. The obtained activation energies range from 0.002 to N 0.3 eV View full abstract»

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  • On the applicability of the GOK model for TSC relaxation

    Publication Year: 2001 , Page(s): 469 - 471
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    Basic theoretical models for thermally stimulated relaxation phenomena, due to the many parameters involved, are usually too complex to be applied to the analysis of experimental data. For many years, the general order kinetics (GOK) model was used as a `first approach' analysis of thermoluminescence (TL) glow curves. In this paper similar equations are derived for thermally stimulated current (TSC) measurements. The new formula has approximately the same range of applicability as the GOK model for TL, but depends on more parameters View full abstract»

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  • Thermally stimulated currents in cured resin of electrostatic powder coating

    Publication Year: 2001 , Page(s): 531 - 537
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    Thermally stimulated currents (TSC) were observed for commercial powder paints partially cured at different temperatures and different times. A higher temperature band between the two TSC bands observed in the cured paints shifted with regularity towards the high temperature side, depending on the cure temperature and time. Activation energies for the cure processes were derived from phenomenological analysis of this TSC peak shift on the basis of a simple model View full abstract»

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  • Complex dynamics of hydrogen bonded self-assembling polymers

    Publication Year: 2001 , Page(s): 365 - 372
    Cited by:  Patents (2)
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    Supramolecular polymers, which are non-covalently bonded and formed by self association of di or trifunctional monomers exhibit, by virtue of quadruple hydrogen bonds, many of the properties of normal high molecular weight polymers, e.g. a dynamic rubber plateau. We focus on the molecular and cooperative dynamics of self-assembled linear polymers and networks, studied by broadband dielectric relaxation spectroscopy (DRS) in the frequency range from 10-2 to 106 Hz. The DRS analysis was backed up by dynamic mechanical and rheological experiments. In the high temperature region two loss processes (α and α*) show up, the relaxation times of which obey the Vogel-Fulcher-Tammann (VFT) law. The dielectric α process is related to the dynamic glass-rubber transition and is slightly faster than the corresponding mechanical α process. A slower (high-temperature) α* relaxation is identified as chemical, corresponding to the mean lifetime of the hydrogen bonded linkages in the supramolecular chains. Its relaxation time τα* was found to be 1 to 2 decades larger than the terminal flow relaxation time, indicating that the relaxation of an entire chain is dominated by the joint dynamics of many hydrogen bonds. The β relaxation, observed in both DRS and dynamic mechanical analysis (DMA) at temperatures below Tg, arises from the local junction dynamics of hydrogen bonded units in the glassy state. Details of the temperature dependence and the shape of the loss peaks of the α and α* relaxations will be discussed in terms of temporary physical networks and cooperativity View full abstract»

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  • Dielectric relaxation of chiral octylocyanobiphenyl in racemate sample

    Publication Year: 2001 , Page(s): 377 - 380
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    The complex electric permittivity of racemate of chiral octyloxycyanobiphenyl (8*OCB) molecules has been studied in the frequency range 0.1 Hz to 0.1 MHz and over a wide temperature range. On cooling the isotropic liquid phase is easily supercooled and below 30 K transforms into glass. On heating a corresponding glass-liquid transition was observed. The dielectric α-relaxation found in supercooled liquid conforms to the Vogel-Fulcher-Tamman equation for the average relaxation time. The Kohlrausch-Williams-Watts function was used to describe the spectral line shape. The molecular dynamics and electric properties of 8*OCB were compared with those of an 8*OCB sample with linear molecules View full abstract»

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  • Molecular dynamics of grafted PBLG in the swollen and dried state

    Publication Year: 2001 , Page(s): 390 - 394
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    We describe a novel experimental approach based on the use of solid electrodes to prepare capacitor arrangements with a thickness in the order of 10 nm containing layers of grafted polymers. It enables study of the molecular dynamics in ultrathin grafted layers of e.g. poly(y-benzyl-L-glutamate) (PBLG) by means of dielectric spectroscopy. The results of our method are compared to those obtained by evaporating the upper electrode on the polymer film and to measurements on the bulk material. In the bulk, two relaxation processes are observed which are assigned to fluctuations of the helical main chain as a whole (chopstick motion) and to fluctuations of the polar side groups. The latter are found to be broadened and to be slowed down in the grafted layer, while the chopstick motion is, depending on the thickness of the grafted layer, two orders of magnitude faster compared with the bulk. This is presumably due to a higher order in the grafted layer. The dielectric dispersion Δε of the side chain motion can be described by assuming free fluctuations of these chains, whereas the model of Wang and Pecora (1980) has been applied for the chopstick motion. After swelling the grafted polymer layer, the side chain fluctuation becomes faster, while the chopstick motion is not influenced View full abstract»

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  • Electrical conductivity in thin layers of chitosan and chitosan acetate

    Publication Year: 2001 , Page(s): 411 - 412
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    The present work is concerned with experimental results on the electrical conductivity of chitosan and chitosan acetate in the temperature range 20 to 325 K, and a broad range of electric field strength. The thickness of the layers was ~15 μm. The influence of the internal structure on electrical properties was observed. The mechanism of the electrical conductivity was controlled by the Poole-Frenkel effect with contribution of hopping or tunneling from deep traps View full abstract»

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  • Effect of water inclusions on charge transport and polarization in porous media

    Publication Year: 2001 , Page(s): 454 - 460
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (984 KB) |  | HTML iconHTML  

    Wideband dielectric spectroscopy measurements (100 Hz to 10 GHz) were carried out on different microporous systems (including sintered glass filters, sandstone and carbonate rocks) saturated with brine (electrolytic water solution) and a hydrocarbon oil at different relative fractions. Three main contributions were singled out in the dielectric spectra: low frequency dispersion (LFD) effects (<100 kHz) related to long range ionic transport and dependent on the connectivity of the water phase; Maxwell-Wagner-Sillars (MWS) polarization effects (100 kHz to 1 GHz), essentially controlled by the shape of the water inclusions; and high-frequency effects (>1 GHz) due to short-range ion transport and related to specific pore surface. For each analyzed system, oil-wet (o-W) and water-wet (w-w) samples were obtained by chemical treatment of the pore surfaces. Systematic differences were observed in the electrical response on varying wettability (and so the respective distribution of the fluids in the pore space). Parameters such as the loss tangent value, the strength and the exponent of the LFD power law, as well as the characteristic time and strength of the MWS relaxation were good indicators of wettability. Results were discussed by using some standard models that account for the pore wettability effects on dielectric spectra. A new method for wettability determination of reservoir rocks from both laboratory and borehole electric measurements was presented View full abstract»

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  • Revised approach to dielectric relaxation of TMACAB crystals near the ferroelectric phase transition

    Publication Year: 2001 , Page(s): 481 - 484
    Cited by:  Papers (1)
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    This paper presents results on statistical investigations of dielectric relaxation data of the mixed crystal [N(CH3)3 H]3Sb2(1-x)Bi2xCl9 (x=0, 0.07, 0.33) (TMACAB) in the frequency range 107 to 10 9 Hz. The most characteristic property observed at temperatures close to the ferroelectric phase transition is the non-Debye dielectric contribution of ferroelectric active dipoles exhibiting the two power law `universal' relaxation response. This contribution does not appear in the paraelectric phase and its appearance is observed in the region in which the random process of formation of one phase into another originates. The observed behavior commonly is assumed to reflect the relaxation response of randomly-sized order clusters, considered as precursors of the ferroelectric domains. Using the idea of order clusters we reveal the relaxation mechanism underlying the investigated dielectric response of TMACAB crystals. We also discuss the influence of temperature and stoichiometry on the dielectric response View full abstract»

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  • Relaxation of excitons and charge carriers in polymers

    Publication Year: 2001 , Page(s): 321 - 328
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    In this paper various aspects of relaxation of optically generated excitations in random organic solids are discussed. Examples are spectral diffusion of excitons in organic glasses, or conjugated polymers, involving energy transfer within an inhomogeneously broadened dense manifold of chromophores, and charge carrier transport in random photoconductors. After an outline of the concept of time dependent random walks within an energetically and spatially disordered array of hopping sites, recent results on charge and exciton transport in π-conjugated systems such as conjugated polymers will be presented. The main emphasis will be on site-selective methods. Site selectivity, achieved by means of a spectrally tunable excitation source, is an unique opportunity to identify a subensemble of excitations which will be able to undergo subsequent relaxation probed by time-dependent spectroscopy View full abstract»

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  • Coupling model explanation of salient dynamic properties of glass-forming substances

    Publication Year: 2001 , Page(s): 329 - 344
    Cited by:  Papers (1)
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    Most of the important and general dynamic properties of structural glass-forming substances have been classified into twelve different categories in a recent review. Within the same property in each category, by examining a large number of glass-formers, a pattern of variation is found which correlates with the departure of the structural relaxation of the glass-former from exponential decay or the quantity 1-β, where β is the fractional exponent in the Kohlrausch expression exp[-(t/τ)β], that well describes the time dependence of the structural at relaxation. The correlation of the patterns or trends with 1-β suggests that the salient dynamic properties, or phenomenology, of glass-forming substances, all are governed by the non-exponential nature of the structural relaxation, i.e. the quantity 1-β. Therefore, a theory or model capable of relating the structural relaxation time τ to 1-β has the potential of explaining most, if not all, of the salient dynamic properties of glass-forming substances. The coupling model of the author has this relation. In this accompanying paper we show the coupling model can either explain or interpret all these properties View full abstract»

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  • The orientational order in nematic liquid crystals from birefringence measurements

    Publication Year: 2001 , Page(s): 512 - 515
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    Various methods of order parameter determination from optical measurements are compared. Measurement results of birefringence and refractive index of liquid-crystalline 4'-pentyloxy-4-cyanobiphenyl (OCB) in the nematic phase are reported. Using these data, the polarizability anisotropy was calculated for both Vuks and Neugebauer local field models. Polarizabilities calculated in this way were applied to determine Δα (polarizability anisotropy in the case of perfect orientation) using either Haller's or Subramhanyam's normalization procedures. These procedures enabled the calculation of the orientation order parameter. Polarizabilities calculated using both local field models and both normalization procedures have been compared. The values of polarizability anisotropy for both local electric field models differ significantly (⩽30%). No criterion is known to decide which value is correct. To avoid the determination of uncertain α i and Δα values, a simple procedure was used for evaluation of S, based solely on birefringence measurement. This procedure gave very reasonable results View full abstract»

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  • Electrical relaxation in iron-containing glasses

    Publication Year: 2001 , Page(s): 442 - 446
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    Glasses with composition 70 mol%(SiO2, B2O 3, P2O5, TeO2)-15 mol% Fe 2O3-15 mol%(BaO, CaO) were prepared by the conventional melt quenching technique. The electrical relaxation of these glasses has been studied in the frequency range 20 to 105 Hz. The small polaron hopping between iron ions in a different valence state Fe2+ to Fe3+ is found to be the principal conduction mechanism. The ratio of Fe2+ ions to the total iron content, C=Fe2+/Fetot, is one of the factors determining the electrical conductivity. The glass former has a minor influence on dc conductivity, except of TeO2 glass where conductivity is three order of magnitude higher than those of other glasses. The ac conductivity as a function frequency is divided into two domains, a dc plateau, followed by a power law in frequency. These two regions are well distinguished in the complex plot of electric modulus where all data points for different temperatures reside on the single plot. The results are discussed in the frame of the Hunt theory of dielectric relaxation in glasses containing mobile charge carriers View full abstract»

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  • Aging effects in pure and doped barium titanate ceramics

    Publication Year: 2001 , Page(s): 500 - 506
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    Ferroelectric properties of 9% mol (Hf,Zr)-doped BaTiO3 ceramics have been studied by comparison with those of pure tetragonal BaTiO3 ceramics. The addition of doping ions lead to a shift of the rhombohedral to orthorhombic and orthorhombic to tetragonal transition temperatures above 0°C, and to a decrease of tetragonal to cubic (ferroelectric to paraelectric) transition temperature from 122°C to 95°C on heating and from 120°C to 85°C on cooling. In pure tetragonal ceramics at room temperature, aging develops by a thermally activated process, leading to a linear dependence of the relative permittivity and dielectric loss on the logarithm of time. In the case of doped ceramics, the experiments showed a decreasing reversed-S dependence of capacitance and tan δ on the logarithm of time, suggesting that dielectric aging in these materials is related with defect diffusion. It was concluded that in doped BaTiO3 ceramics the aging mechanisms depend on the crystalline symmetry, which influences the twinning process and the domain-wall dynamics. Aging of (Hf,Zr)-doped BaTiO3 ceramics depends on temperature and the phase symmetry, which imposes the twinning rate and the rearrangement speed of ferroelectric domains minimizing the elastic energy of the lattice View full abstract»

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  • Measuring the frequency dependent polarizability of colloidal particles from dielectrophoretic collection data

    Publication Year: 2001 , Page(s): 566 - 571
    Cited by:  Papers (4)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (744 KB) |  | HTML iconHTML  

    In a non-uniform ac electric field, dipole forces cause polarizable particles to experience ponderomotive forces. The particle velocity is a function of the dielectric properties of the particle, the suspending medium, particle volume and the electric field gradient. Measurement of the collection rate of particles can be used to estimate their dielectric polarizability. In this work we have measured the collection rate of sub-micrometer particles collecting at the edges of a planar interdigitated electrode array. The Fokker-Planck equation was used to simulate the spatial and temporal accumulation of particles at the electrodes. The experimental data shows that the collection rate decreases with increasing frequency of the applied field, in agreement with the predicted frequency-dependent reduction in the effective polarizability of the particles. Numerical simulations are in broad agreement with experimental results View full abstract»

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  • Thermal aging phenomena in chitosan-related pharmaceutical systems

    Publication Year: 2001 , Page(s): 555 - 558
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    Results are presented of detection of thermal aging in the chitosan/ketoprofen acid (KTA) system, using low-frequency dielectric spectroscopy. Aging leads to substantial changes of the low frequency dielectric properties of the system. In order to identify the reasons for the detected aging, near infra-red (NIR) Raman spectra and distribution of molecular weights as well as direct measurements of water content were carried out. The additional measurements suggest that water desorption is mainly responsible for the detected aging phenomena. Formation of a charge transfer complex between the anionic carbonyl group of KTA and the cationic NH3+ group of chitosan, has also been detected View full abstract»

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Aims & Scope

IEEE Transactions on Dielectrics and Electrical Insulation contains topics concerned with dielectric phenomena and measurements with development and characterization of gaseous, vacuum, liquid and solid electrical insulating materials and systems.

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