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Dielectric Relaxation (dielectric + relaxation)
Terms modified by Dielectric Relaxation Selected AbstractsDielectric Relaxation in CaO,Bi2O3,B2O3 GlassesINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 2010Koushik Majhi Glasses in the system CaO,Bi2O3,B2O3 (in molar ratio) have been prepared using melt-quenching route. Ion transport characteristics were investigated for this glass using electric modulus, ac conductivity and impedance measurements. The ac conductivity was rationalized using Almond,West power law. Dielectric relaxation has been analyzed based on the behavior of electric modulus behavior. The activation energy associated with the electrical relaxation determined from the electric modulus spectra was found to be 1.76 eV, close to that the activation energy for dc conductivity (1.71 eV) indicating that the same species took part in both the processes. The stretched exponent , (0.5,0.6) is invariant with temperature for the present glasses. [source] Dielectric Relaxation in Layer-Structured SrBi2,xNdxNb2O9 Ceramics (x=0, 0.05, 0.2, 0.35)JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2007Lin Sun SrBi2,xNdxNb2O9 (x=0, 0.05, 0.2, 0.35) ceramics were synthesized by the traditional solid-state sintering method. X-ray diffraction analysis showed that single-phase-layered perovskites were obtained for all compositions. The substitution of Nd3+ for Bi3+ induced a relaxor behavior of frequency dispersion for Nd-doped SrBi2Nb2O9. The parameter of frequency dispersion ,Tm, which is the Tm between 1 kHz and 1 MHz, increases from 0°C for x=0 to 13°C for x=0.35, and the degree of relaxor behavior , increases from 0.96 for x=0 to 2.02 for x=0.35. The temperature of the maximum dielectric constant Tm decreases linearly with an increase in the Nd content (x). [source] Structure, Ionic Conduction and Dielectric Relaxation in a Novel Fast Ion Conductor, Na2Cd(SO4)2.CHEMINFORM, Issue 18 2007Diptikanta Swain Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Dielectric relaxation in ferroelectric TlInS2 layered crystals within metastable chaotic stateCRYSTAL RESEARCH AND TECHNOLOGY, Issue 6 2007entürk Abstract The results of investigations low frequency dielectric relaxation in layered ferroelectric TlInS2 crystals are presented. The measurements were performed in the temperature range of 180-230 K and in the frequency range of 5 kHz,1 MHz. Two different relaxation processes were observed in mentioned temperature interval. The crystal has "slow" and "fast" relaxation mechanisms in low and high frequency region, respectively. The presence of two different relaxation mechanisms in TlInS2 is discussed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Dielectric Relaxation in CaO,Bi2O3,B2O3 GlassesINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 2010Koushik Majhi Glasses in the system CaO,Bi2O3,B2O3 (in molar ratio) have been prepared using melt-quenching route. Ion transport characteristics were investigated for this glass using electric modulus, ac conductivity and impedance measurements. The ac conductivity was rationalized using Almond,West power law. Dielectric relaxation has been analyzed based on the behavior of electric modulus behavior. The activation energy associated with the electrical relaxation determined from the electric modulus spectra was found to be 1.76 eV, close to that the activation energy for dc conductivity (1.71 eV) indicating that the same species took part in both the processes. The stretched exponent , (0.5,0.6) is invariant with temperature for the present glasses. [source] Dielectric relaxation and crystallization of ultraviscous melt and glassy states of aspirin, ibuprofen, progesterone, and quinidineJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 5 2007G.P. Johari Abstract Molecular relaxation in ultraviscous melt and glassy states of aspirin, ibuprofen, progesterone, and quinidine has been studied by dielectric spectroscopy. The asymmetric relaxation spectra is characterized by the Kohlrausch distribution parameter of 0.46,±,0.02 for aspirin to 0.67,±,0.02 for progesterone. The dielectric relaxation time varies with the temperature, T, according to the Vogel,Fulcher,Tammann Equation, log10(,0),=,AVFT,+,[BVFT/(T,,,T0)], where AVFT, BVFT, and T0 are empirical constants. The extrapolated ,0 at calorimetric glass-softening temperature is close to the value expected. The equilibrium permittivity, ,0, is lowest for ibuprofen which indicates an antiparallel orientation of dipoles in its liquid's hydrogen-bonded structure. A decrease in ,0 with time shows that ultraviscous aspirin, progesterone, and quinidine begin to cold-crystallize at a relatively lower temperature than ibuprofen. ,0 of the cold-crystallized phases are, 4.7 for aspirin at 290 K, 2.55 for ibuprofen at 287 K, 2.6 for progesterone at 320 K, and 3.2 for quinidine at 375 K. It is argued that hydrogen-bonding, the Kohlrausch parameter, extent of localized motions and the long-range diffusion times all determine the physical and chemical stability of an amorphous pharmaceutical during storage. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 96: 1159,1175, 2007 [source] Dielectric relaxation in ferroelectric TlInS2 layered crystals within metastable chaotic stateCRYSTAL RESEARCH AND TECHNOLOGY, Issue 6 2007entürk Abstract The results of investigations low frequency dielectric relaxation in layered ferroelectric TlInS2 crystals are presented. The measurements were performed in the temperature range of 180-230 K and in the frequency range of 5 kHz,1 MHz. Two different relaxation processes were observed in mentioned temperature interval. The crystal has "slow" and "fast" relaxation mechanisms in low and high frequency region, respectively. The presence of two different relaxation mechanisms in TlInS2 is discussed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Dielectric properties of thermosetting material nanocompositesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007Newton Luiz Dias Filho Abstract The dieletric relaxation properties of thermosetting material nanocomposites based on spherosilicate nanoplatforms were studied from room temperature to 170°C, varying the frequency from 10 to 1000 KHz. Permittivity (,,), dielectric loss (,,), and activation energy (Ea) were calculated. The results of dielectric relaxation were confirmed by those of the final properties. The dielectric loss amplitude decreases with increasing ODPG content until about 70,73 wt % and slightly increases at higher ODPG content. This means that the increasing of the ODPG content in the composite samples decreases the number of pendants groups and/or increases crosslink density, causing decreased motion of organic tethers, and subsequently decreasing of the dipolar mobility. The results of apparent activation energy, fracture toughness and tensile modulus mechanical properties show the same profile with respect to ODPG content, in the sense that they exhibit maxima around 70 wt % ODPG. For the ODPG/MDA composites, this formulation of 70 wt % ODPG containing excess of amine is not composition where the highest crosslinked density is reached. This implies that the best mechanical properties and Ea are provided by some degree of chain flexibility. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [source] Dielectric studies of molecular motions in amorphous solid and ultraviscous acetaminophenJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 10 2005G.P. Johari Abstract The dielectric permittivity and loss spectra of glassy and ultraviscous states of acetaminophen have been measured over the frequency range 10 Hz,0.4 MHz. The relaxation spectra show an asymmetric distribution of times expressed in terms of the Kohlrausch exponent, ,, which remains constant at 0.79,±,0.02 over the 305,341 K range. The dielectric relaxation time increases on cooling according to the Vogel,Fulcher,Tammann equation. However, the values of the parameters are considerably different from the values deduced from earlier work by other researchers using the heat capacity of ultraviscous acetaminophen and relating it to its molecular mobility. The calorimetric glass softening temperature of 296 K obtained from differential scanning calorimetry is close to the value measured from dielectric relaxation. The equilibrium permittivity of ultraviscous acetaminophen decreases on heating like that of a normal dipolar liquid, as anticipated from the Curie law. But, its value decreases rapidly with time when it begins to crystallize. The equilibrium permittivity of this crystal phase is ,3.1 at 300 K and increases with temperature, which indicates a partial, orientational-disordering of its structure. The results show limitations of the procedures used in the modeling of the kinetics of molecular motions, that is, estimating physical stability, using thermodynamic considerations based on thermal analyses of the amorphous solid phase of acetaminophen. © 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:2207,2223, 2005 [source] Effect of Multiwall Carbon Nanotubes on Electrical and Dielectric Properties of Yttria-Stabilized Zirconia CeramicJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2006Sui-Lin Shi MWCNT/3Y-TZP (3 mol% yttria-stabilized tetragonal polycrystalline zirconia) composites with different multiwall carbon nanotube (MWCNT) contents were prepared by the spark plasma sintering technique. The effect of MWCNT addition on the electrical and dielectric properties of the composites at room temperature was studied. The experimental results showed that the DC conductivity of the composites demonstrated a typical percolation behavior with a very low percolation threshold between 1.0 and 2.0 wt% MWCNT content, and the dielectric constant was greatly increased when the MWCNT concentration was close to the percolation threshold, which was attributed to dielectric relaxation, the space charge polarization effect, and the percolation effect. [source] Anomalous charge relaxation in channels of pentacene-based organic field-effect transistors: a charge transient spectroscopy studyPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 10 2006I. Thurzo Abstract Two types of Si/SiO2/pentacene organic field-effect transistors (OFET) with bottom Au-source (S) and , drain (D) electrodes were examined by charge transient spectroscopy (QTS), applying pulsed bias ,UDS to the channel of an OFET with floating gate electrode. The transient charge Q (t ), flowing through the channel after the removal of the bias pulse, was processed at a constant temperature by a three-channel correlator yielding the signal ,Q = Q (t1) , 3/2Q (2t1) + 1/2Q (4t1), the scanned delay t1 being related to the trailing edge of the bias pulse. Most of the QTS spectra were characterized by peaks of ,Q (t1) with FWHM corresponding to discrete time constants ,m , t1m, while scanning t1 from 2 ,s to 0.1 s. The common feature of the QTS spectra was a linear dependence of the peak height ,Qm on ,UDS for both polarities of the latter, thereby resembling what is expected for dielectric relaxation (polarization). Some devices showed anomalous (reversed) sign of the signal with respect to the polarity of ,UDS, or even features like transitions from the correct sign to the reversed one. In order to customize the anomalies, a model is presented which ignores injection of excess charge carriers and takes into account two contributions to the total transient charge: a/space charge of intrinsic charge carriers piled up at the blocking Au-electrodes during the pulse, relaxing with the dielectric relaxation time ,D = ,0,r/, (, being conductivity of the organics); b/orientation of molecular dipoles (,dip) in the relaxing electric field of the space charge. It is the dipolar component that is responsible for the anomalous charge flow direction manifested by the signal reversal. The origin of the permanent dipole moment of the otherwise non-polar pentacene molecules may be either attached excess or missing atoms (vacancies) of the defect molecules [J. E. Northrup and M. L. Chabinyc, Phys. Rev. B 68, 041202 (2003)]. In cases of non-blocking contacts the dipolar relaxation would lead to QTS peaks of correct sign, to be distinguished from possibly non-negligible contribution of the dielectric relaxation in the semiconductor. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Relaxation behavior of conductive carbon black reinforced EPDM microcellular vulcanizatesPOLYMER ENGINEERING & SCIENCE, Issue 7 2007S.P. Mahapatra Dynamic mechanical analysis and dielectric relaxation spectra of conductive carbon black reinforced microcellular EPDM vulcanizates were used to study the relaxation behavior as a function of temperature (,90 to +100°C) and frequency (0.01,105 Hz). The effect of filler and blowing agent loadings on dynamic mechanical and dielectric relaxation characteristics has been investigated. The effect of filler and blowing agent loadings on glass transition temperature was marginal for all the composites (Tg value was in the range of ,39 to ,35°C), which has been explained on the basis of relaxation dynamics of polymer chains in the vicinity of fillers. Strain-dependent dynamical parameters were evaluated at dynamic strain amplitudes of 0.07,5%. The nonlinearity in storage modulus has been explained based on the concept of filler,polymer interaction and interaggregate attraction (filler networking) of carbon black. The variation in real and complex part of impedance with frequency has been studied as a function of filler and blowing agent loading. Additionally, the effect of crosslinking on the dielectric relaxation has also been reported. POLYM. ENG. SCI., 47:984,995, 2007. © 2007 Society of Plastics Engineers [source] Influence of the cross-linking density on the main dielectric relaxation of poly(methyl acrylate) networksPOLYMER ENGINEERING & SCIENCE, Issue 10 2005J.M. Meseguer Dueñas A series of polymer networks of varying cross-linking density was prepared by copolymerization of methyl acrylate and ethyleneglycol dimethacrylate. The aim of this work is to study the influence of cross-linking on the conformational mobility of the polymer chains using dielectric relaxation spectroscopy (DRS) in the temperature range of the main dielectric relaxation. As expected, the temperature range in which glass transition takes place became wider with increasing crosslinking density. DRS results were analyzed using the Havriliak-Negami equation. Master Cole-Cole arcs could be drawn for all the networks. The arcs become more symmetric as cross-linking density increases, as a consequence of the different effect of cross-links on large and small scale mobility. The conformational mobility that produces the main relaxation is drastically reduced when the cross-linking density increases what reduces the relaxation strength, but it also gives a qualitative change of behavior, as shown by the temperature dependence of the relaxation strength. In the loosely cross-linked networks the relaxation strength decreases monotonously as temperature increases, as in the main dielectric relaxation of linear polymers. Nevertheless, in highly cross-linked networks the curve of relaxation strength against temperature presents a maximum. POLYM. ENG. SCI., 45:1336,1342, 2005. © 2005 Society of Plastics Engineers [source] | |||||||||||||||||||||||||