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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
  • Collective dynamic modes of microconfined ferroelectric liquid crystals

    Publication Year: 2001 , Page(s): 488 - 493
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (912 KB) |  | HTML iconHTML  

    The dielectric properties of the ferroelectric liquid crystal 4-oetyloxy-4-(2-methylbutyloxy)carbonyl-phenylbenzoate in different confinements have been investigated. While the molecular dynamic processes are not influenced by the micro-porous confinement, the collective relaxation processes are strongly affected by restricted geometry. Changes of shape, dispersion and frequency of the relaxation processes caused by confinement were observed. The Goldstone mode present in the bulk ferroelectric liquid crystal is not observed in the porous materials. The reason for the disappearance of the Goldstone mode depends on the structure, pore size and surface interactions in confinement 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)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2472 KB) |  | HTML iconHTML  

    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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  • 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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  • Determination of the order parameter of 4-(trans-4'-n-heptyl-cyclohexyl)isothiocyanato-benzene by means of dielectric relaxation spectroscopy

    Publication Year: 2001 , Page(s): 381 - 384
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (384 KB) |  | HTML iconHTML  

    Studies of the dielectric relaxation were made for the isotropic and nematic phases of 4-(trans-4'-n-heptylcyclohexyl)isothiocyanatobenzene, (C7H 15-CyHx-Ph-N=C=S) (7CHBT) in the frequency range from 100 kHz to 1 GHz. In the nematic phase two relaxation processes were recorded for the dielectric permittivity component measured parallel to the molecular orientation (director n&oarr;) and three relaxation processes for the perpendicular permittivity component. The elementary contributions to the total dielectric absorption are found to be of the Debye-type. The strength of the nematic potential and the nematic order parameter as a function of temperature were estimated. The results obtained were compared with the predictions of the Maier-Saupe theory View full abstract»

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  • The influence of dipolar species on charge carrier transport in a linear polysilicon

    Publication Year: 2001 , Page(s): 432 - 441
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    Effect of polar substituents and polar dopants on the transport of charge carriers in poly[methyl(phenyl)silanediyl] (PMPSI) was studied. The transport in undoped PMPSI can be explained within the theory of disordered polarons which postulates that the temperature and field dependence of the charge carrier mobility contain contributions both from the dynamic disorder, i.e. the polaron barrier, and from the environment-dependent static disorder. Polar moieties, chemically attached to the main polymer chain, give rise to a decrease of the on-chain mobility, due to the formation of local electronic polarization states. On the macroscopic level, these moieties and polar dopants give rise to a decrease of the drift (hopping) mobility due to a broadening of the distribution of the density of transport states as a consequence of the electrostatic interaction of the charge carrier with the dipole View full abstract»

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  • On the applicability of the GOK model for TSC relaxation

    Publication Year: 2001 , Page(s): 469 - 471
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (248 KB) |  | HTML iconHTML  

    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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  • Energy criterion in interacting cluster systems

    Publication Year: 2001 , Page(s): 352 - 358
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (812 KB) |  | HTML iconHTML  

    The high-frequency fractional power law of relaxation, seen in a wide range of materials, yields a constant ratio of the macroscopic energy lost per radian to the energy stored in the system, in the corresponding frequency range. For almost two decades, the above energy criterion has been supposed to imply the existence of similar microscopic properties which determine the observed power-law exponent. Here, a rigorous formulation of the energy-criterion argument is proposed in the frame of a new probabilistic approach to derive the Havriliak-Negami (HN) and Kohlraush-Williams-Watts (KWW) responses. In this approach the commonly observed macroscopic laws are related to the microscopic scenario of relaxation, and the energy-criterion interpretation is applied to the physical basis of the relation. The presented considerations reinforce the physical significance of the empirically found forms of relaxation, and open a new line of analysis of relaxation phenomena View full abstract»

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  • Electrical relaxation in iron-containing glasses

    Publication Year: 2001 , Page(s): 442 - 446
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (532 KB) |  | HTML iconHTML  

    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
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (720 KB) |  | HTML iconHTML  

    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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  • 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)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (776 KB) |  | HTML iconHTML  

    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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  • A molecular dynamics study of lead-bismuth-silicate glasses

    Publication Year: 2001 , Page(s): 385 - 389
    Cited by:  Patents (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (648 KB) |  | HTML iconHTML  

    We present the results of molecular dynamics (MD) simulations of the structure of ternary lead-bismuth-silicate glasses of compositions xPbO(0.3-x)Bi1.50.7SiO2, x=0.06, 0.15, 0.24, and their totally reduced forms, i.e. xPb(0.3-x)Bi0.7SiO2, x=0.06, 0.15, 0.24 systems. The simulations have been performed in the microcanonical (NVE) ensemble, using two-body interaction potentials. The results can be summarized as follows. With increasing PbO content in unreduced xPbO(0.3-x)Bi1.50.7SiO2 glasses, the Pb-O and Bi-O first pair distribution function (PDF) peaks become sharper, and the fraction of strained 2 and 3 member Si-O-Si-O- rings decreases significantly. In the case of reduced xPb(0.3-x)Bi0.7SiO2 glasses, similarly as in reduced binary lead-silicate and bismuth-silicate glasses, a strong tendency to agglomeration of neutral atoms occurs. The metallic phase is composed of Pb-Bi alloy. The agglomeration tendency increases with increasing Pb content View full abstract»

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  • Polymorphism of righthanded octyloxycyanobiphenyl

    Publication Year: 2001 , Page(s): 522 - 526
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (632 KB) |  | HTML iconHTML  

    Polymorphism of the octyloxycyanobiphenyl isomer 4-(1(S)-methylheptyloxy)-4'cyanobiphenyl (8OCB) was studied by means of adiabatic calorimetry, infrared spectroscopy and polarizing microscopy. Two crystalline phases, C1 and C2, were identified and their thermodynamic parameters measured. A monotropic system of the metastable C1 and stable C2 crystals was obtained. Far infrared absorption and polarizing microscopy textures are discussed View full abstract»

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  • Thermally stimulated currents in cured resin of electrostatic powder coating

    Publication Year: 2001 , Page(s): 531 - 537
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (728 KB) |  | HTML iconHTML  

    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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  • Real-time crystallization and melting of poly(n-octadecyl methacrylate) induced by temperature and pressure. A dielectric spectroscopy investigation

    Publication Year: 2001 , Page(s): 359 - 364
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (760 KB) |  | HTML iconHTML  

    We have studied the crystallization and melting of poly(n-octadecyl methacrylate) (PNODMA) by performing temperature and pressure jump experiments from the melt to the final semicrystalline state. The evolution of the crystallization process is studied in real time by recording the changes in the dielectric spectrum. The single α process in the melt upon crystallization looses intensity and a new slower α' process appears, reflecting the dynamics of the restricted amorphous phase. The effect of pressure on increasing the crystallization temperature is stronger than the increase of the melt glass transition temperature, i.e. dTc/dP≈2.3Tg m/dP. The isothermal/isobaric crystallization experiments induced by T and P jumps give rise, respectively, to stretched exponential and to typical nucleation and growth kinetics of the Avrami type. The different crystallization kinetics induced by T and P reflect the `paradoxical' situation of increasing mobility with increasing pressure. From the equivalence of the dynamics we concluded that undercooling of 1 K corresponds to an overpressure of 20 MPa, i.e. δT/δP≈50 WGPa 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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  • Influence of temperature and pressure on the dynamics of glass formers explored by dielectric spectroscopy

    Publication Year: 2001 , Page(s): 395 - 400
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (708 KB) |  | HTML iconHTML  

    The dynamics of the epoxy compound polyphenyl-glycidyl-ether-coformaldehyde was investigated by wideband dielectric spectroscopy (10-2 to 1010 Hz) by varying either pressure or temperature. The measurements were undertaken in two different conditions: under isobaric condition (atmospheric pressure) varying temperature down to the supercooled and glassy phases and under isothermal conditions by changing the pressure from 0.1 to 270 MPa. The analysis of the structural relaxation time behavior either varying the temperature or the pressure was found to agree well with a previously derived expression for τ(T, P) based on a cooperative model. In particular it was found that with a unique set of parameters it is possible to describe the 2-dimensional surface τ(T, P) over a wide range of temperature and pressure. This result agrees well with the observed independence of the fragility in both isothermal and isobaric conditions View full abstract»

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  • On dielectric data analysis. Using the Monte Carlo method to obtain relaxation time distribution and comparing non-linear spectral function fits

    Publication Year: 2001 , Page(s): 310 - 320
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1248 KB) |  | HTML iconHTML  

    In this paper, we present a technique for analyzing dielectric response data in the frequency domain, χ(ω)=ε(ω)-ε=ε'(ω)-ε-iε(ω). We use a predistribution of relaxation times and reconstruct the original data by single Debye relaxations using a box constraint, least squares algorithm. The resulting relaxation times τ(Di) and their amplitudes Δεi,, yield the relaxation time spectrum, where i is equal or less than the number of data points. Two different predistributions of relaxation times are considered, log-uniform and adaptive. The adaptive predistribution is determined by the real part of the dielectric susceptibility χξ', and it allows for the increase of the number of effective relaxation times used in the fitting procedure. Furthermore, since the number of unknowns is limited to the number of data points, the Monte Carlo technique is introduced. In this way, the fitting procedure is repeated many times with randomly selected relaxation times, and the number of relaxation times treated in the procedure becomes continuous. The proposed method is tested for `ideal' and measured data. Finally, the method is compared with a nonlinear curve fitting by a spectral function which consists of three contributions, i.e. the Havriliak-Negami relaxation polarization, low frequency dispersion and de conductivity. It has been found that more information can be obtained from a particular data set if it is compared with a nonlinear curve fitting procedure. The method also can be used instead of the Kramers-Kronig transformation View full abstract»

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  • Dielectric and UV spectrophotometric study of physicochemical effects of ionizing radiation on mammalian macromolecular DNA

    Publication Year: 2001 , Page(s): 549 - 554
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    The purpose of this work was the comparative investigation of physicochemical effects induced by γ and α radiation on the thermal denaturation dynamics of native macromolecular calf thymus DNA, combining dielectric relaxation spectroscopy (DRS) and UV thermal transition spectrophotometry (TTS), while the apparent molecular weight (MW) distribution of the DNA macromolecules was measured by pulse field gel electrophoresis (PFGE). A DNA thermal stability enhancement over the non-irradiated samples was observed at radiation doses <10 Gy for γ rays and 32 Gy for α particles, attributed to the development of intra and/or intermolecular DNA-DNA interactions, whereas at higher irradiation doses, the expected decrease of thermal stability was observed. Moreover, in all studied cases, the recorded conductivity changes were found to precede by 2 to 3°C those of UV TTS absorbance changes, a fact indicative of a multi-stage process for DNA thermal transition. Finally, the displacement of the low dose region limit towards higher doses in the case of α particles, confirm earlier results attesting higher yields of DNA strand breaks induced by γ rays compared to α particles View full abstract»

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  • Collective and molecular modes in ferroelectric and antiferroelectric liquid crystals

    Publication Year: 2001 , Page(s): 477 - 480
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (340 KB) |  | HTML iconHTML  

    A new 4-(1-methylheptyloxycarbonyl)phenyl4'-octyloxybiphenyl-4-carboxylate (MHPOBC) analog exhibiting ferroelectric and antiferroelectric properties has been studied by dielectric and electro-optic methods. Dielectric measurements were performed using a gold coated cell, thickness 23 μm. In the ferroelectric SmC* phase a pronounced Goldstone mode was found, whereas in the antiferroelectric SmC*A phase two dielectric relaxation processes have been observed. It has been shown that collective processes, like soft mode and Goldstone mode, show non-Arrhenius behavior. The measurements of spontaneous polarization were performed by means of the reversal current method using a cell of thickness 7 μm coated with indium-tin oxide (ITO) layers. Temperature dependencies of spontaneous polarization are discussed in terms of the mean-field model View full abstract»

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  • AC conductivity of Bi-Sr-Ca-Cu-O glasses

    Publication Year: 2001 , Page(s): 426 - 428
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (280 KB) |  | HTML iconHTML  

    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
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (608 KB) |  | HTML iconHTML  

    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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  • Glass transition of an epoxy resin. A wideband dielectric investigation

    Publication Year: 2001 , Page(s): 373 - 376
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (436 KB) |  | HTML iconHTML  

    The dynamics of an epoxy resin, poly(phenyl glycidyl ether-co-formaldehyde), has been investigated in the supercooled and glassy phases by wideband dielectric spectroscopy (10-2 to 3×109 Hz) and compared with that of the previously investigated epoxy resin, diglycidyl ether of bisphenol-A. The temperature evolution of the dynamics of the system is monitored through the characteristic parameters of the relaxations, namely the relaxation times, the relaxation strengths and the shape parameters. Two transition regions are revealed: the glass transition and the split between structural and fast secondary relaxation, where the onset of the structural relaxation is located also View full abstract»

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  • DC conductivity of metal/DLC/Si/metal heterostructures

    Publication Year: 2001 , Page(s): 418 - 421
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (468 KB) |  | HTML iconHTML  

    Electrical conduction of metal/DLC/silicon/metal heterostructures has been investigated, Both DLC/p-Si and DLC/n-Si systems shows rectifying properties. The current-voltage (I-V) characteristics of the heterostructures can be described well by the simplified diode equation with the ideality factor between 21.2 and 3.25, decreasing with increasing temperature. The directive tendency of I-V characteristics is independent of the type of silicon substrate. A simple qualitative band model of DLC/Si junction is proposed View full abstract»

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  • Dielectric response of cyanobiphenyl in the low frequency region

    Publication Year: 2001 , Page(s): 401 - 405
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (492 KB) |  | HTML iconHTML  

    Dielectric measurement of liquid crystal materials with the cyanobiphenyl group, in different phases, are described. Measurements were carried out from 10-4 Hz to 104 Hz. In both isotropic and nematic phases a linear increase of ΔC'=C'-C and C" with decreasing frequency is observed at f⩽0.1 Hz. C' and C" represent the complex capacitance, C is the capacitance at high f. Below 0.1 Hz such behavior is not significant in the area where saturation is noticed. A similar dependence of solid and smectic phases is obtained, but all plots are shifted towards the low frequencies range. Linear slopes of log ΔC' and log C" vs. log f have been determined in order to evaluate fractal exponents of the dispersion laws. A very weak temperature dependence of these exponents has been noticed. The frequency of maximum loss tangent depends clearly on the temperature. This maximum shifts to higher frequencies with an increase in temperature. Results obtained have been compared with theoretical predictions of the literature models by numerical adjustment of the data 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
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (460 KB) |  | HTML iconHTML  

    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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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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