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Sample records for dielectric relaxation behaviour

  1. Dielectric Relaxation, Modulus Behaviour and Conduction Mechanism in NdAlO3 Ceramics

    NASA Astrophysics Data System (ADS)

    Sakhya, Anup Pradhan; Dutta, Alo; Sinha, T. P.

    2015-10-01

    The dielectric property of neodymium aluminate, NdAlO3 ceramic, synthesized by the solid state reaction method is investigated. The Rietveld refinement of the room temperature x-ray diffraction pattern suggests the rhombohedral crystal structure with R-3c space symmetry of the system. The dielectric relaxation is observed in the temperature range from 313 K to 523 K and in the frequency range from 580 Hz to 1.1 MHz as a gradual decrease in the real part ( ɛ') of the dielectric constant and as a broad peak in the imaginary part ( ɛ″) of the dielectric constant. The complex impedance plane plot confirms the existence of both the grain and grain-boundary contributions to the relaxation and is analysed by an electrical equivalent circuit consisting of a resistance and a constant-phase element. The temperature dependence of both the grain and grain-boundary resistances follow the Arrhenius law with activation energy of 0.3 eV and 0.34 eV, respectively. The room temperature Raman spectrum confirms the rhombohedral phase of the system. Photoluminescence measurements show a red band at around 682 nm due to the transition from the 4I9/2 ground state to the 4F9/2 excited state.

  2. Dielectric Relaxation of Hexadeutero Dimethylsulfoxide

    NASA Astrophysics Data System (ADS)

    Betting, H.; Stockhausen, M.

    1999-11-01

    The dielectric relaxation parameters of the title substance (DMSO-d6) in its pure liquid state are determined from meas-urements up to 72 GHz at 20°C in comparison to protonated DMSO. While the relaxation strengths do not differ, the relax-ation time of DMSO-d 6 is significantly longer (21.3 ps) than that of DMSO (19.5 ps).

  3. Dielectric relaxation time spectroscopy.

    PubMed

    Paulson, K S; Jouravleva, S; McLeod, C N

    2000-11-01

    A new mathematical method is developed to recover the permittivity relaxation spectrum of living tissue from measurements of the real and imaginary parts of the impedance. Aiming to derive information about electrical properties of living tissue without the prior selection of any impedance model, the procedure calculates the relaxation time distribution. It provides new characteristic independent parameters: time constants, their distribution, and the amplitudes of the associated dispersion. As the beta-dispersion is the most important in the area of electrical impedance spectroscopy of tissue, the paper gives an estimate of the essential frequency range to cover the whole relaxation spectrum in that area. Results are presented from both simulation and known lumped--constant element circuit. PMID:11077745

  4. Dielectric relaxations in aliphatic polyesters

    NASA Astrophysics Data System (ADS)

    Sen, Sudeepto

    2001-07-01

    The dielectric technique was used to study the relaxation processes of five linear aliphatic polyesters. The polyesters studied were poly (ethylene succinate/adipate) or PESA, poly (trimethylene succinate/adipate) or PTSA, poly (butylene succinate/adipate) or PBSA, poly (ethylene succinate) or PES, and poly (ethylene adipate) or PEA. Three of the polyesters were copolymers (PESA, PTSA, and PBSA), and the remaining two (PES and PEA) were homopolymers. Two of the five were amorphous (PESA and PTSA), and the remaining three (PBSA, PES, and PEA) were semicrystalline. All the five polyesters were synthesized in the laboratory using a poly-condensation reaction between a series of aliphatic diols and diesters. The succinic and adipic groups in the copolymers are in equimolar amounts. The polymers were characterized by differential scanning calorimetry and density measurements. Elemental analysis done on the polymers confirmed that their compositions matched theoretical estimates. The relaxation processes were studied dielectrically using an IMASS time domain dielectric spectrometer (TDS) and an HP 4284A LCR meter. Together they allowed a frequency range from 0.001 Hz to 1 MHz. Typically in the subglass region, good data were obtained between 0.01 Hz and 100 kHz. In the glass transition region, good data were occasionally available over the entire range. Two relaxation processes were detected in the subglass temperature region for all the polymers, and in the case of the copolymers PTSA and PBSA, they were also well resolved. Both the processes showed Arrhenius behavior with modest activation energies characteristic of subglass processes in general. They also progressively merged with increasing temperature, which implies a lower activation energy for the faster process which is consistent with the current understanding of relaxation phenomena. The glass transition region of all the polymers also showed a merging of the dominant alpha relaxation with the subglass

  5. Dielectric behaviour of polycarbonate

    NASA Astrophysics Data System (ADS)

    El-Shabasy, M.; Riad, A. S.

    1996-05-01

    The dielectric constant and the dielectric loss of polycarbonate are investigated in the frequency range 30-10 5 Hz and at temperature from 297 to 365 K. The frequency dependence of the impedance spectra plotted in the complex plane shows semicircles. The system could be represented by an equivalent circuit of a bulk resistance in series with a parallel surface resistance-capacitance combination. The Cole-Cole diagrams have been used to determine the molecular relaxation time τ. The temperature dependence of τ is expressed by a thermally activated process. Analysis of the AC conductivity reveals semiconducting features based predominantly on a hopping mechanism.

  6. Dielectric polarization evolution equations and relaxation times

    SciTech Connect

    Baker-Jarvis, James; Riddle, Bill; Janezic, Michael D.

    2007-05-15

    In this paper we develop dielectric polarization evolution equations, and the resulting frequency-domain expressions, and relationships for the resulting frequency dependent relaxation times. The model is based on a previously developed equation that was derived using statistical-mechanical theory. We extract relaxation times from dielectric data and give illustrative examples for the harmonic oscillator and derive expressions for the frequency-dependent relaxation times and a time-domain integrodifferential equation for the Cole-Davidson model.

  7. Dielectric relaxation of gamma irradiated muscovite mica

    SciTech Connect

    Kaur, Navjeet; Singh, Mohan; Singh, Lakhwant; Awasthi, A.M.; Lochab, S.P.

    2015-03-15

    Highlights: • The present article reports the effect of gamma irradiation on the dielectric relaxation characteristics of muscovite mica. • Dielectric and electrical relaxations have been analyzed in the framework of dielectric permittivity, electric modulus and Cole–Cole formalisms. • The frequency dependent electrical conductivity has been rationalized using Johnsher’s universal power law. • The experimentally measured electric modulus and conductivity data have been fitted using Havriliak–Negami dielectric relaxation function. - Abstract: In the present research, the dielectric relaxation of gamma irradiated muscovite mica was studied in the frequency range of 0.1 Hz–10 MHz and temperature range of 653–853 K, using the dielectric permittivity, electric modulus and conductivity formalisms. The dielectric constants (ϵ′ and ϵ′′) are found to be high for gamma irradiated muscovite mica as compared to the pristine sample. The frequency dependence of the imaginary part of complex electric modulus (M′′) and dc conductivity data conforms Arrhenius law with single value of activation energy for pristine sample and two values of activation energy for gamma irradiated mica sample. The experimentally assessed electric modulus and conductivity information have been interpreted by the Havriliak–Negami dielectric relaxation explanation. Using the Cole–Cole framework, an analysis of real and imaginary characters of the electric modulus for pristine and gamma irradiated sample was executed which reflects the non-Debye relaxation mechanism.

  8. Dielectric relaxation of high-k oxides

    PubMed Central

    2013-01-01

    Frequency dispersion of high-k dielectrics was observed and classified into two parts: extrinsic cause and intrinsic cause. Frequency dependence of dielectric constant (dielectric relaxation), that is the intrinsic frequency dispersion, could not be characterized before considering the effects of extrinsic frequency dispersion. Several mathematical models were discussed to describe the dielectric relaxation of high-k dielectrics. For the physical mechanism, dielectric relaxation was found to be related to the degree of polarization, which depended on the structure of the high-k material. It was attributed to the enhancement of the correlations among polar nanodomain. The effect of grain size for the high-k materials' structure mainly originated from higher surface stress in smaller grain due to its higher concentration of grain boundary. PMID:24180696

  9. Dielectric relaxation in a protein matrix

    SciTech Connect

    Pierce, D.W.; Boxer, S.G.

    1992-06-25

    The dielectric relaxation of a sperm whale ApoMb-DANCA complex is measured by the fluorescence dynamic Stokes shift method. Emission energy increases with decreasing temperature, suggesting that the relaxation activation energies of the rate-limiting motions either depend on the conformational substrate or different types of protein motions with different frequencies participate in the reaction. Experimental data suggest that there may be relaxations on a scale of <100 ps. 61 refs., 7 figs., 2 tabs.

  10. Dielectric relaxation and birefringence study of 7.O5O.7 dimeric liquid crystal compound

    NASA Astrophysics Data System (ADS)

    Bhattacharjee, Debanjan; Paul-Choudhury, Sandip; Alapati, Parameswara Rao; Bhattacharjee, Ayon

    2016-05-01

    Measurement of dielectric relaxation and birefringence phenomenon of dimeric liquid crystal compound with the dependence of temperature was reported in this paper. Homogeneous (HG) and homeotropic (HT) alignment of the cell are introduced to investigate the dielectric relaxation, activation energy and birefringence. Cole-Cole plots analyzed the dielectric relaxation of the dimeric compound. The observed Cole-Cole plots were semi-circular, and the relaxation mechanism obeys the non-Debye type of relaxation behaviour. Slater's perturbation equations have been used to analysis the activation energy of the compound. The birefringence of the compound has positively anisotropy and thin prism mechanism was used to study the anisotropy of the compound.

  11. Anomalous relaxation and dielectric response

    NASA Astrophysics Data System (ADS)

    Goychuk, Igor

    2007-10-01

    It is shown that all the known experimental (quasi)stationary dielectric response functions of glassy media can be derived from a standard generalized Langevin description of overdamped torsional dipole oscillators in trapping potentials with random orientations under some minimal assumptions. The non-Markovian theory obeys the fluctuation-dissipation theorem and the Onsager regression theorem. Moreover, it displays no aging on the time scale of the dielectric response, all in assumption of local thermal (quasi)equilibrium. Aging might come from jumping among metastable traps. It occurs on a quite different time scale which is not related to the principal dielectric response. We put the old phenomenological theory of Cole and Cole, Davidson and Cole, and others on a firm basis within a stochastic, thermodynamically consistent approach.

  12. Dielectric relaxation characteristics of muscovite mica

    NASA Astrophysics Data System (ADS)

    Kaur, Navjeet; Singh, Lakhwant; Singh, Mohan; Awasthi, A. M.; Kumar, Jitender

    2014-04-01

    In the present work, the dielectric relaxation phenomenon in muscovite mica has been studied over the frequency range 0.1 Hz-10 MHz and in the temperature range of 653-853K, using the dielectric permittivity, electric modulus and conductivity formalisms. The values of the activation energy obtained from electric modulus and conductivity data are found to be nearly similar, suggesting that same types of charge carriers are involved in the relaxation mechanism. This type of study will explore the potential of this material for various applications in electrical engineering.

  13. Dielectric relaxation and defect analysis of Ta2O5 thin films

    NASA Astrophysics Data System (ADS)

    Ezhilvalavan, S.; Shiahn Tsai, Ming; Yuen Tseng, Tseung; Shiahn Tsai, Ming

    2000-05-01

    The presence of defects in thin-film dielectrics often leads to dielectric relaxation as a function of frequency, in which the dielectric constant decreases and the loss tangent increases with increasing frequency. Dielectric relaxation results in charge storage capacity reduction under dynamic random access memory operating conditions. In this work, the dielectric relaxation behaviour of dc reactive sputtered Ta2O5 thin film was investigated. Using dielectric dispersion measurements as a function of frequency (100 Hz≤f≤10 MHz) and temperature (27 °C≤T≤150 °C), we determined the dielectric relaxation and defect quantity of the films and propose an equivalent circuit on the basis of complex capacitance, admittance and impedance spectral studies.

  14. Dielectric secondary relaxations in polypropylene glycols.

    PubMed

    Grzybowska, K; Grzybowski, A; Zioło, J; Paluch, M; Capaccioli, S

    2006-07-28

    Broadband dielectric measurements of polypropylene glycol of molecular weight M(w)=400 g / mol (PPG 400) were carried out at ambient pressure over the wide temperature range from 123 to 353 K. Three relaxation processes were observed. Besides the structural alpha relaxation, two secondary relaxations, beta and gamma, were found. The beta process was identified as the true Johari-Goldstein relaxation by using a criterion based on the coupling model prediction. The faster gamma relaxation, well separated from the primary process, undoubtedly exhibits the anomalous behavior near the glass transition temperature (T(g)) which is reflected in the presence of a minimum of the temperature dependence of the gamma-relaxation time. We successfully applied the minimal model [Dyre and Olsen, Phys. Rev. Lett. 91, 155703 (2003)] to describe the entire temperature dependence of the gamma-relaxation time. The asymmetric double-well potential parameters obtained by Dyre and Olsen for the secondary relaxation of tripropylene glycol at ambient pressure were modified by fitting to the minimal model at lower temperatures. Moreover, we showed that the effect of the molecular weight of polypropylene glycol on the minimal model parameters is significantly larger than that of the high pressure. Such results can be explained by the smaller degree of hydrogen bonds formed by longer chain molecules of PPG at ambient pressure than that created by shorter chains of PPG at high pressure. PMID:16942189

  15. Lithium-induced dielectric relaxations in potassium tantalate ceramics

    NASA Astrophysics Data System (ADS)

    Tkach, A.; Almeida, A.; Agostinho Moreira, J.; Espinha, A.; Chaves, M. R.; Perez de la Cruz, J.; Vilarinho, P. M.

    2011-08-01

    This work reports the effect of lithium doping on the dielectric and polar properties of potassium tantalate. Experimental data were obtained in K1-xLixTaO3 ceramics with x = 0, 0.02, 0.05 and 0.10 by measuring both the dielectric permittivity from 102 to 108 Hz, and polarization under an ac electric field driven at 2.5 Hz, for temperatures from 10 to 300 K. The dielectric permittivity exhibits all the relaxations reported for K1-xLixTaO3 single crystals. Two dielectric relaxations observed at 40-125 K are ascribed to the individual hopping by 90° and 180° of dipoles created by the off-centre Li ions. Another relaxation observed at 100-200 K is related to 180°-flips of Li pairs for x = 0.02 and of polar clusters of interacting Li ions for x = 0.05 and 0.10. In addition to that, an additional relaxation not reported before is presented at 135-235 K for x = 0.10 and attributed to 90°-reorientation of Li polar clusters. Both the change from an Arrhenius to a Vogel-Fulcher dependence with increasing lithium content, and the emergence of slim P (E) hysteresis loops around the relaxation temperatures show that the relaxation dynamics in K1-xLixTaO3 can be understood if a crossover from a dipolar glass to a relaxor-like behaviour is assumed.

  16. Dielectric relaxation in proteins: the computational perspective.

    PubMed

    Simonson, Thomas

    2008-07-01

    In photoexcitation and electron transfer, a new dipole or charge is introduced, and the structure is adjusted. This adjustment represents dielectric relaxation, which is the focus of this review. We concentrate on a few selected topics. We discuss linear response theory, as a unifying framework and a tool to describe non-equilibrium states. We review recent, molecular dynamics simulation studies that illustrate the calculation of dynamic and thermodynamic properties, such as Stokes shifts or reorganization free energies. We then turn to the macroscopic, continuum electrostatic view. We recall the physical definition of a dielectric constant and revisit the decomposition of the free energy into a reorganization and a static term. We review some illustrative continuum studies and discuss some difficulties that can arise with the continuum approach. In conclusion, we consider recent developments that will increase the accuracy and broaden the scope of all these methods. PMID:18443919

  17. Dielectric Relaxation of Molecular Dipolar Rotors

    NASA Astrophysics Data System (ADS)

    Clarke, L.; Horansky, R.; Hinderer, T.; Price, J.; Nunez, J.; Khuong, T.; Garcia-Garibay, M.; Horinek, D.; Kottas, G.; Varaska, N.; Magnera, T.; Michl, J.

    2003-03-01

    Molecular rotors, molecules with a rotational degree of freedom about a single bond, are a fundamental element of nanoscale machinery. We study dipolar rotors arranged into either three-dimensional crystalline arrays or surface mounted to form two-dimensional films. Through dielectric relaxation experiments, we probe fundamental rotor attributes such as torsional barriers, polarization, and dipole-dipole interactions. We have measured the dielectric response of chloromethylsilyl rotors, surface mounted on fused silica, at frequencies in the kHz range and temperatures from 4 to 300 K, and find an inhomogeneous system, where the intrinsic barrier to rotation in the vapor phase has been modified by surface interactions. Using computer simulations, we have studied both thermally activated and driven rotors. We discuss work towards experimental realization of more homogeneous systems.

  18. Dielectric Relaxation and Rheological Behavior of Supramolecular Polymeric Liquid

    SciTech Connect

    Lou, Nan; Wang, Yangyang; Li, Xiaopeng; Li, Haixia; Wang, Ping

    2013-01-01

    A model self-complementary supramolecular polymer based on thymine and diamidopyridine triple hydrogen-bonding motifs has been synthesized, and its dielectric and rheological behavior has been investigated. The formation of supramolecular polymers has been unequivocally demonstrated by nuclear magnetic resonance, electrospray ionization mass spectrometry with traveling wave ion mobility separation, dielectric spectroscopy, and rheology. The dynamical behaviors of this associating polymer generally conform to those of type-A polymers, with a low-frequency chain relaxation and a high-frequency relaxation visible in both rheological and dielectric measurements. The dielectric chain relaxation shows the ideal symmetric Debye-like shape, resembling the peculiar features of hydrogen-bonding monoalcohols. Detailed analysis shows that there exists a weak decoupling between the mechanical terminal relaxation and dielectric Debye-like relaxation. The origin of the Debye-like dielectric relaxation is further discussed in the light of monoalcohols.

  19. Dielectric relaxation of CdO nanoparticles

    NASA Astrophysics Data System (ADS)

    Tripathi, Ramna; Dutta, Alo; Das, Sayantani; Kumar, Akhilesh; Sinha, T. P.

    2016-02-01

    Nanoparticles of cadmium oxide have been synthesized by soft chemical route using thioglycerol as the capping agent. The crystallite size is determined by X-ray diffraction technique and the particle size is obtained by transmission electron microscope. The band gap of the material is obtained using Tauc relation to UV-visible absorption spectrum. The photoluminescence emission spectra of the sample are measured at various excitation wavelengths. The molecular components in the material have been analyzed by FT-IR spectroscopy. The dielectric dispersion of the material is investigated in the temperature range from 313 to 393 K and in the frequency range from 100 Hz to 1 MHz by impedance spectroscopy. The Cole-Cole model is used to describe the dielectric relaxation of the system. The scaling behavior of imaginary part of impedance shows that the relaxation describes the same mechanism at various temperatures. The frequency-dependent electrical data are also analyzed in the framework of conductivity and electrical modulus formalisms. The frequency-dependent conductivity spectra are found to obey the power law.

  20. Investigating low frequency dielectric properties of a composite using the distribution of relaxation times technique

    SciTech Connect

    Tuncer, Enis

    2006-01-01

    The distribution of relaxation times approach, a less frequently employed dielectric data analysis technique, is utilized to better understand the relaxation characteristics of composites consisting of metal-coated, hollow glass spheres dispersed in a paraffin wax matrix. The dielectric properties of the composite samples are measured by means of impedance spectroscopy in the frequency range 0.1mHz to 10 MHz. The application of a mixture law is not appropriate for the analysis of the frequency-dependent properties of the considered system on this broad frequency range. However, utilization of the distribution of relaxation times procedure to study the dielectric behaviour shows clear trends in the mixtures' relaxation spectra. Relaxation processes of the paraffin wax and those specific to the composites are found from the extracted distribution of relaxation times spectra. The influence of the filler concentration, q, on the dielectric properties is examined; a relaxation with a narrow distribution at intermediate frequencies becomes broad with the addition of the filler. This relaxation, in the form of the low-frequency-dispersions (also known as constant phase angle) phenomenon, dominates the dielectric properties of the composites with high bead concentration, q > 0:15. The variation in dielectric properties of individual samples whose bead concentrations q are nominally the same is discussed in terms of possible microstructural variations.

  1. Investigating low-frequency dielectric properties of a composite using the distribution of relaxation times technique

    SciTech Connect

    Tuncer, Enis; Bowler, Nicola; Youngs, I. J.; Lymer, K. P.

    2006-01-01

    The distribution of relaxation times approach, a less frequently employed dielectric data analysis technique, is utilized to better understand the relaxation characteristics of composites consisting of metal-coated, hollow glass spheres dispersed in a paraffin wax matrix. The dielectric properties of the composite samples are measured by means of impedance spectroscopy in the frequency range 0.1 mHz to 10 MHz. The application of a mixture law is not appropriate for the analysis of the frequency-dependent properties of the considered system on this broad frequency range. However, utilization of the distribution of relaxation times procedure to study the dielectric behaviour shows clear trends in the mixtures' relaxation spectra. Relaxation processes of the paraffin wax and those specific to the composites are found from the extracted distribution of relaxation times spectra. The influence of the filler concentration, q, on the dielectric properties is examined; a relaxation with a narrow distribution at intermediate frequencies becomes broad with the addition of the filler. This relaxation, in the form of the low-frequency-dispersions (also known as constant phase angle) phenomenon, dominates the dielectric properties of the composites with high bead concentration, q>0.15. The variation in dielectric properties of individual samples whose bead concentrations q are nominally the same is discussed in terms of possible microstructural variations.

  2. Identification of Structural Relaxation in the Dielectric Response of Water

    NASA Astrophysics Data System (ADS)

    Hansen, Jesper S.; Kisliuk, Alexander; Sokolov, Alexei P.; Gainaru, Catalin

    2016-06-01

    One century ago pioneering dielectric results obtained for water and n -alcohols triggered the advent of molecular rotation diffusion theory considered by Debye to describe the primary dielectric absorption in these liquids. Comparing dielectric, viscoelastic, and light scattering results, we unambiguously demonstrate that the structural relaxation appears only as a high-frequency shoulder in the dielectric spectra of water. In contrast, the main dielectric peak is related to a supramolecular structure, analogous to the Debye-like peak observed in monoalcohols.

  3. Ultra-Slow Dielectric Relaxation Process in Polyols

    NASA Astrophysics Data System (ADS)

    Yomogida, Yoshiki; Minoguchi, Ayumi; Nozaki, Ryusuke

    2004-04-01

    Dielectric relaxation processes with relaxation times larger than that for the structural α process are reported for glycerol, xylitol, sorbitol and their mixtures for the first time. Appearance of this ultra-slow process depends on cooling rate. More rapid cooling gives larger dielectric relaxation strength. However, relaxation time is not affected by cooling rate and shows non-Arrhenius temperature dependence with correlation to the α process. It can be considered that non-equilibrium dynamic structure causes the ultra-slow process. Scale of such structure would be much larger than that of the region for the cooperative molecular orientations for the α process.

  4. Identification of Structural Relaxation in the Dielectric Response of Water.

    PubMed

    Hansen, Jesper S; Kisliuk, Alexander; Sokolov, Alexei P; Gainaru, Catalin

    2016-06-10

    One century ago pioneering dielectric results obtained for water and n-alcohols triggered the advent of molecular rotation diffusion theory considered by Debye to describe the primary dielectric absorption in these liquids. Comparing dielectric, viscoelastic, and light scattering results, we unambiguously demonstrate that the structural relaxation appears only as a high-frequency shoulder in the dielectric spectra of water. In contrast, the main dielectric peak is related to a supramolecular structure, analogous to the Debye-like peak observed in monoalcohols. PMID:27341258

  5. Dielectric relaxations investigation of a synthesized epoxy resin polymer

    NASA Astrophysics Data System (ADS)

    Jilani, Wissal; Mzabi, Nissaf; Gallot-Lavallée, Olivier; Fourati, Najla; Zerrouki, Chouki; Zerrouki, Rachida; Guermazi, Hajer

    2015-04-01

    A diglycidylether of bisphenol A (DGEBA) epoxy resin was synthesized, and cured with 3,3'-diaminodiphenyl sulfone (DDS) at a curing temperature of 120 °C. The relaxation properties of the realized polymers were studied by two complementary techniques: dielectric relaxation spectroscopy (DRS), in the temperature range 173-393K and in the frequency interval 10-1-106 Hz, and thermally stimulated depolarization current (TSDC) with a windowing polarization process. Current-voltage (I-V) measurements were also carried out to study interfacial relaxations. Dielectric data were analyzed in terms of permittivity and electric modulus variations. Three relaxation processes ( γ, β and α) have been identified. They were found to be frequency and temperature dependent and were interpreted in terms of the Havriliak-Negami approach. Relaxation parameters were determined by fitting the experimental data. The temperature dependence of the relaxation time was well fitted by the Arrhenius law for secondary relaxations, while the Vogel-Fulcher-Tamann model was found to better fit the τ( T) variations for α relaxation. We found τ 0 = 4.9 10-12 s, 9.6 10-13 s and 1.98 10-7 s for γ, β and α relaxations, respectively. The obtained results were found to be consistent with those reported in the literature. Due to the calculation of the low-frequency data of dielectric loss by the Hamon approximation, the Maxwell-Wagner-Sillars (MWS) relaxation was highlighted.

  6. Dielectric relaxation measurement and analysis of restricted water structure in rice kernels

    NASA Astrophysics Data System (ADS)

    Yagihara, Shin; Oyama, Mikio; Inoue, Akio; Asano, Megumi; Sudo, Seiichi; Shinyashiki, Naoki

    2007-04-01

    Dielectric relaxation measurements were performed for rice kernels by time domain reflectometry (TDR) with flat-end coaxial electrodes. Difficulties in good contact between the surfaces of the electrodes and the kernels are eliminated by a TDR set-up with a sample holder for a kernel, and the water content could be evaluated from relaxation curves. Dielectric measurements were performed for rice kernels, rice flour and boiled rice with various water contents, and the water amount and dynamic behaviour of water molecules were explained from restricted dynamics of water molecules and also from the τ-β (relaxation time versus the relaxation-time distribution parameter of the Cole-Cole equation) diagram. In comparison with other aqueous systems, the dynamic structure of water in moist rice is more similar to aqueous dispersion systems than to aqueous solutions.

  7. Dielectric relaxation in monoclinic hydroxyapatite: Observation of hydroxide ion dipoles

    NASA Astrophysics Data System (ADS)

    Horiuchi, N.; Wada, N.; Nozaki, K.; Nakamura, M.; Nagai, A.; Yamashita, K.

    2016-02-01

    We prepared monoclinic hydroxyapatite (HAp) ceramics and measured their dielectric properties. The dielectric dispersion that was observed in the monoclinic HAp consisted of two different relaxations and could be expressed by a summation of two Debye-like relaxations. One relaxation was ascribed to the reorientational motions of OH- ions. The temperature dependence of the relaxation time obeyed the Arrhenius equation. The relaxation time decreased with temperature but decreased discontinuously at 483 K, the monoclinic-hexagonal phase transition temperature of HAp. Correspondingly, the activation energy changed from 0.74 eV for the monoclinic phase to 0.43 eV for the hexagonal phase. The results suggest that the mobility of the OH- ions increases discontinuously with the phase transition to hexagonal HAp. However, critical phenomena, such as critical slowing down, were not observed.

  8. Ultraslow dielectric relaxation process in supercooled polyhydric alcohols

    NASA Astrophysics Data System (ADS)

    Yomogida, Yoshiki; Minoguchi, Ayumi; Nozaki, Ryusuke

    2006-04-01

    Complex permittivity was obtained on glycerol, xylitol, sorbitol and sorbitol-xylitol mixtures in the supercooled liquid state in the frequency range between 10μHz and 500MHz at temperatures near and above the glass transition temperature. For all the materials, a dielectric relaxation process was observed in addition to the well-known structural α and Johari-Goldstein β relaxation process [G. P. Johari and M. Goldstein, J. Chem. Phys. 53, 2372 (1970)]. The relaxation time for the new process is always larger than that for the α process. The relaxation time shows non-Arrhenius temperature dependence with correlation to the behavior of the α process and it depends on the molecular size systematically. The dielectric relaxation strength for the new process shows the effect of thermal history and decreases exponentially with time at a constant temperature. It can be considered that a nonequilibrium dynamics causes the new process.

  9. Dynamic Analyses of Polymer Surface using Dielectric Relaxation

    NASA Astrophysics Data System (ADS)

    Ishii, Masashi

    A new dielectric relaxation measurement technique for analyses of polymer surface was developed. In this technique, in order to maintain the original surface, probing electrodes were placed away from the sample, and a liquid to stabilize the surface was filled in the space between the sample and the electrodes. From difference of dielectric relaxation between a bare polyimide and gold-coated polyimide, the surface of polyimide was characterized. The surface dielectric relaxation spectrum at room temperature depended on the liquid species: The Debye relaxation was obtained for ethanol, while multiple-relaxation was observed for ultrapure water. A thermal activation process of the polyimide surface was investigated using temperature-controlled ultrapure water, and it was found that the surface transited from the multiple-relaxation to the Debye relaxation at ∼95°C. In the Debye relaxation condition, the surface can be characterized with a capacitance independent of the liquid species. The capacitance estimated at 110 pF provided a characteristic curve of the polyimide surface. A surface model was proposed to explain the thermal activation process.

  10. Dielectric relaxations and dielectric response in multiferroic BiFeO{sub 3} ceramics

    SciTech Connect

    Hunpratub, Sitchai; Thongbai, Prasit; Maensiri, Santi; Yamwong, Teerapon; Yimnirun, Rattikorn

    2009-02-09

    Single-phase multiferroic BiFeO{sub 3} ceramics were fabricated using pure precipitation-prepared BiFeO{sub 3} powder. Dielectric response of BiFeO{sub 3} ceramics was investigated over a wide range of temperature and frequency. Our results reveal that the BiFeO{sub 3} ceramic sintered at 700 deg. C exhibited high dielectric permittivity, and three dielectric relaxations were observed. A Debye-type dielectric relaxation at low temperatures (-50 to 20 deg. C) is attributed to the carrier hopping process between Fe{sup 2+} and Fe{sup 3+}. The other two dielectric relaxations at the temperature ranges 30-130 deg. C and 140-200 deg. C could be due to the grain boundary effect and the defect ordering and/or the conductivity, respectively.

  11. Alternating-current conductivity and dielectric relaxation of bulk iodoargentate

    SciTech Connect

    Duan, Hai-Bao Yu, Shan-Shan; Zhou, Hong

    2015-05-15

    Graphical abstract: The electric modulus shows single dielectric relaxation process in the measured frequency range. - Highlights: • The conduction mechanism is described by quantum mechanical tunneling model. • The applications of dielectric modulus give a simple method for evaluating the activation energy of the dielectric relaxation. • The [Ag{sub 2}I{sub 4}]{sup 2−}1-D chain and [Cu(en){sub 2}]{sup 2+} cation column form the layered stacks by hydrogen bond interactions. - Abstract: An inorganic-organic hybrid compound Cu(en){sub 2}Ag{sub 2}I{sub 4} (en = ethylenediamine) (1) was synthesized and single crystal structurally characterized. Along the [001] direction, the inorganic parts form an infinite 1-D chain and [Cu(en){sub 2}]{sup 2+} cations are separated by inorganic chain. The electrical conductivity and dielectric properties of 1 have been investigated over wide ranges of frequency. The alternating-current conductivities have been fitted to the Almond–West type power law expression with use of a single value of S. It is found that S values for 1 are nearly temperature-independent, which indicates that the conduction mechanism could be quantum mechanical tunneling (QMT) model. The dielectric loss and electric modulus show single dielectric relaxation process. The activation energy obtained from temperature-dependent electric modulus compare with the calculated from the dc conductivity plots.

  12. Dielectric relaxation of electrolyte solutions using terahertz transmission spectroscopy

    NASA Astrophysics Data System (ADS)

    Asaki, M. L. T.; Redondo, A.; Zawodzinski, T. A.; Taylor, A. J.

    2002-05-01

    We use terahertz (THz) transmission spectroscopy to obtain the frequency dependent complex dielectric constants of water, methanol, and propylene carbonate, and solutions of lithium salts in these solvents. The behavior of the pure solvents is modeled with either two (water) or three (methanol and propylene carbonate) Debye relaxations. We discuss the effects of ionic solvation on the relaxation behavior of the solvents in terms of modifications to the values of the Debye parameters of the pure solvents. In this way we obtain estimates for numbers of irrotationally bound solvent molecules, the numbers of bonds broken or formed, and the effects of ions on the higher-frequency relaxations.

  13. Relaxation dynamics of amorphous dibucaine using dielectric studies

    NASA Astrophysics Data System (ADS)

    Sahra, M.; Jumailath, K.; Thayyil, M. Shahin; Capaccioli, S.

    2015-06-01

    Using broadband dielectric spectroscopy the molecular mobility of dibucaine is investigated in the supercooled liquid and gassy states, over a wide temperature range for some test frequencies. Above the glass transition temperature Tg, the presence of structural α- relaxation peak was observed due to the cooperative motions of the molecule and upon cooling frozen kinetically to form the glass. The secondary relaxation process was perceivable below Tg due to localized motions. The peak loss frequency of α-relaxation process shows non-Arrhenius behavior and obeys Vogel-Fulcher-Tammann equation over the measured temperature range whereas the β- process shows Arrhenius behavior.

  14. Rotational Mobility in a Crystal Studied by Dielectric Relaxation Spectroscopy

    ERIC Educational Resources Information Center

    Dionisio, Madalena S. C.; Diogo, Herminio P.; Farinha, J. P. S.; Ramos, Joaquim J. Moura

    2005-01-01

    A laboratory experiment for undergraduate physical chemistry courses that uses the experimental technique of dielectric relaxation spectroscopy to study molecular mobility in a crystal is proposed. An experiment provides an excellent opportunity for dealing with a wide diversity of important basic concepts in physical chemistry.

  15. Dielectric relaxation of α -tocopherol acetate (vitamin E)

    NASA Astrophysics Data System (ADS)

    Kaminski, K.; Maslanka, S.; Ziolo, J.; Paluch, M.; McGrath, K. J.; Roland, C. M.

    2007-01-01

    Dielectric loss spectra are reported for α -tocopherol acetate (an isomer of vitamin E) in the supercooled and glassy states. The α -relaxation times, τα , measured over a 190° range of temperatures, T , at pressures, P , up to 400MPa can be expressed as a single function of TV3.9 ( V is specific volume, measured herein as a function of T and P ). At ambient pressure, there is no dynamic crossover over eight decades of measured τα . The relaxation spectra above the glass transition temperature Tg show ionic conductivity and an excess wing on the high-frequency flank of the α -relaxation loss peak. Temperature-pressure superpositioning is valid for the α process; moreover, the peak shape is constant (stretch exponent equal to 0.65). However, application of pressure changes the shape of the dielectric spectrum at higher frequencies due to the shift of the excess wing to form a resolved peak. Additionally, another relaxation process, absent at atmospheric pressure, emerges on the high-frequency side of the α -process. We propose that this new peak reflects a more compact conformation of the α -tocopherol acetate molecule. Drawing on the coupling model, the experimentally determined relaxation times, activation energy, and activation volume for the Johari-Goldstein process are compared to values calculated from the properties of the α relaxation. The agreement is generally satisfactory, at least for T

  16. Dielectric relaxations on erythrocyte membrane as revealed by spectrin denaturation.

    PubMed

    Ivanov, I T; Paarvanova, B

    2016-08-01

    We studied the effect of spectrin denaturation at 49.5°C (TA) on the dielectric relaxations and related changes in the complex impedance, Z*, complex capacitance, C*, and dielectric loss curve of suspensions containing human erythrocytes, erythrocyte ghost membranes (EMs) and Triton-X-100 residues of EMs. The loss curve prior to, minus the loss curve after TA, resulted in a bell-shaped peak at 1.5MHz. The changes in the real and imaginary components of Z* and C* at TA, i.e., ΔZre, ΔZim, ΔCre and ΔCim, calculated in the same way, strongly varied with frequency. Between 1.0 and 12MHz the -ΔZim vs ΔZre, and ΔCim vs ΔCre plots depicted semicircles with critical frequencies, fcr, at 2.5MHz expressing recently reported relaxation of spectrin dipoles. Between 0.02 and 1.0MHz the -ΔZim vs ΔZre plot exhibited another relaxation whose fcr mirrored that of beta relaxation. This relaxation was absent on Triton-X-shells, while on erythrocytes and EMs it was inhibited by selective dissociation of either attachment sites between spectrin and bilayer. Considering above findings and inaccessibility of cytosole to outside field at such frequencies, the latter relaxation was assumed originating from a piezoelectric effect on the highly deformable spectrin filaments. PMID:27071054

  17. Dielectric relaxation of thin films of polyamide random copolymers.

    PubMed

    Taniguchi, Natsumi; Fukao, Koji; Sotta, Paul; Long, Didier R

    2015-05-01

    We investigate the relaxation behavior of thin films of a polyamide random copolymer, PA66/6I, with various film thicknesses using dielectric relaxation spectroscopy. Two dielectric signals are observed at high temperatures, the α process and the relaxation process due to electrode polarization (the EP process). The relaxation time of the EP process has a Vogel-Fulcher-Tammann type of temperature dependence, and the glass transition temperature, T(g), evaluated from the EP process agrees very well with the T(g) determined from the thermal measurements. The fragility index derived from the EP process increases with decreasing film thickness. The relaxation time and the dielectric relaxation strength of the EP process are described by a linear function of the film thickness d for large values of d, which can be regarded as experimental evidence for the validity of attributing the observed signal to the EP process. Furthermore, there is distinct deviation from this linear law for thicknesses smaller than a critical value. This deviation observed in thinner films is associated with an increase in the mobility and/or diffusion constant of the charge carriers responsible for the EP process. The α process is located in a higher-frequency region than the EP process at high temperatures but merges with the EP process at lower temperatures near the glass transition region. The thickness dependence of the relaxation time of the α process is different from that of the EP process. This suggests that there is decoupling between the segmental motion of the polymers and the translational motion of the charge carriers in confinement. PMID:26066192

  18. Dielectric relaxation of thin films of polyamide random copolymers

    NASA Astrophysics Data System (ADS)

    Taniguchi, Natsumi; Fukao, Koji; Sotta, Paul; Long, Didier R.

    2015-05-01

    We investigate the relaxation behavior of thin films of a polyamide random copolymer, PA66/6I, with various film thicknesses using dielectric relaxation spectroscopy. Two dielectric signals are observed at high temperatures, the α process and the relaxation process due to electrode polarization (the EP process). The relaxation time of the EP process has a Vogel-Fulcher-Tammann type of temperature dependence, and the glass transition temperature, Tg, evaluated from the EP process agrees very well with the Tg determined from the thermal measurements. The fragility index derived from the EP process increases with decreasing film thickness. The relaxation time and the dielectric relaxation strength of the EP process are described by a linear function of the film thickness d for large values of d , which can be regarded as experimental evidence for the validity of attributing the observed signal to the EP process. Furthermore, there is distinct deviation from this linear law for thicknesses smaller than a critical value. This deviation observed in thinner films is associated with an increase in the mobility and/or diffusion constant of the charge carriers responsible for the EP process. The α process is located in a higher-frequency region than the EP process at high temperatures but merges with the EP process at lower temperatures near the glass transition region. The thickness dependence of the relaxation time of the α process is different from that of the EP process. This suggests that there is decoupling between the segmental motion of the polymers and the translational motion of the charge carriers in confinement.

  19. Dielectric and specific heat relaxations in vapor deposited glycerol.

    PubMed

    Kasina, A; Putzeys, T; Wübbenhorst, M

    2015-12-28

    Recently [S. Capponi, S. Napolitano, and M. Wübbenhorst, Nat. Commun. 3, 1233 (2012)], vapor deposited glasses of glycerol have been found to recover their super-cooled liquid state via a metastable, ordered liquid (MROL) state characterized by a tremendously enhanced dielectric strength along with a slow-down of the relaxation rate of the structural relaxation. To study the calorimetric signature of this phenomenon, we have implemented a chip-based, differential AC calorimeter in an organic molecular beam deposition setup, which allows the simultaneous measurement of dielectric relaxations via interdigitated comb electrodes and specific heat relaxation spectra during deposition and as function of the temperature. Heating of the as-deposited glass just above the bulk Tg and subsequent cooling/reheating revealed a step-wise increase in cp by in total 9%, indicating unambiguously that glycerol, through slow vapour deposition, forms a thermodynamically stable glass, which has a specific heat as low as that of crystalline glycerol. Moreover, these glasses were found to show excellent kinetic stability as well as evidenced by both a high onset-temperature and quasi-isothermal recovery measurements at -75 °C. The second goal of the study was to elucidate the impact of the MROL state on the specific heat and its relaxation to the super-cooled state. Conversion of "MROL glycerol" to its "normal" (ordinary liquid, OL) state revealed a second, small (∼2%) increase of the glassy cp, a little gain (<10%) in the relaxed specific heat, and no signs of deviations of τcal from that of normal "bulk" glycerol. These findings altogether suggest that the MROL state in glycerol comprises largely bulk-type glycerol that coexist with a minor volume fraction (<10%) of PVD-induced structural anomalies with a crystal-like calorimetric signature. Based on the new calorimetric findings, we have proposed a new physical picture that assumes the existence of rigid polar clusters (RPCs

  20. Dielectric relaxation of NdMnO{sub 3} nanoparticles

    SciTech Connect

    Saha, Sujoy Chanda, Sadhan; Dutta, Alo; Sinha, T.P.

    2013-11-15

    Graphical abstract: (a) TEM image of particle distribution of NMO. (b) HRTEM image of a single NMO particle under 4,000,000× magnification. (c) SAED pattern of a single NMO nanoparticle. - Highlights: • NdMnO{sub 3} nanoparticles are synthesized by sol–gel process. • TEM micrograph shows a granular characteristic with an average particle size of ∼50 nm. • HRTEM is consistent with the spacing between the (2 0 0) planes of the orthorhombic NdMnO{sub 3}. • Band gap is found to be 4.4 eV. • Cole–Cole model has been used to explain the dielectric relaxation in the material. • The activation energy of the material is found to be ∼0.43 eV. - Abstract: The neodymium manganate (NdMnO{sub 3}) nanoparticles are synthesized by the sol–gel process. The phase formation and particle size of the sample are determined by X-ray diffraction analysis and transmission electron microscopy. The band gap of the material is obtained by UV–visible absorption spectroscopy using Tauc relation. Dielectric properties of the sample have been investigated in the frequency range from 42 Hz to 1 MHz and in the temperature range from 303 K to 573 K. The dielectric relaxation peaks are observed in the frequency dependent dielectric loss spectra. The Cole–Cole model is used to explain the dielectric relaxation mechanism of the material. The complex impedance plane plot confirms the existence of both the grain and grain-boundary contribution to the relaxation. The temperature dependence of both grain and grain-boundary resistances follow the Arrhenius law with the activation energy of 0.427 and 0.431 eV respectively. The frequency-dependent conductivity spectra follow the power law.

  1. Novel gigahertz frequency dielectric relaxations in chitosan films.

    PubMed

    Kumar-Krishnan, Siva; Prokhorov, Evgen; Ramírez, Marius; Hernandez-Landaverde, Martín A; Zarate-Triviño, Diana G; Kovalenko, Yu; Sanchez, Isaac C; Méndez-Nonell, Juan; Luna-Bárcenas, Gabriel

    2014-11-21

    Molecular relaxations of chitosan films have been investigated in the wide frequency range of 0.1 to 3 × 10(9) Hz from -10 °C to 110 °C using dielectric spectroscopy. For the first time, two high-frequency relaxation processes (in the range 10(8) to 3 × 10(9) Hz) are reported in addition to the low frequency relaxations α and β. These two relaxation processes are related to the vibrations of OH and NH2/NH3(+), respectively. The high-frequency relaxations exhibit Arrhenius-type dependencies in the temperature range 10 °C to 54 °C with negative activation energy; this observation is traceable to hydrogen bonding reorientation. At temperatures above the glass transition temperature (54 °C), the activation energy changes from negative to positive values due to breaking of hydrogen bonding and water loss. Upon cooling in a sealed environment, the activation energies of two relaxation processes are nearly zero. FTIR and XRD analyses reveal associated structural changes upon heating and cooling. These two new high-frequency relaxation processes can be attributed to the interaction of bound water with OH and NH2/NH3(+), respectively. A plausible scenario for these high-frequency relaxations is discussed in light of impedance spectroscopy, TGA, FTIR and XRD measurements. PMID:25254949

  2. Dielectric relaxations of collagen and elastin in the dehydrated state

    NASA Astrophysics Data System (ADS)

    Samouillan, V.; Lamure, A.; Lacabanne, C.

    2000-05-01

    The dielectric properties of collagen and elastin, two major components of connective tissues that greatly differ in their secondary structure, were investigated in the air-dried state and at high temperatures (100-220°C). Two techniques were used to study the dielectric relaxations of both proteins: thermally stimulated currents (TSC), an isochronal spectrometry running at variable temperature, analogous to a low frequency spectroscopy (10 -3-10 -2 Hz) and dynamic dielectric spectroscopy (DDS), performed isothermally with the frequency varying from 10 -2 to 10 6 Hz. A main relaxation mode is evidenced by the two techniques for collagen and elastin, located at 90°C and 145°C, respectively, at 10 -3 Hz. The combination of TSC and DDS experiments and the determination of the activation parameters of the relaxation times give information on the molecular mobility of the proteins, in the glassy state and in the liquid state. Major differences between the relaxation behavior of elastin and collagen have been discussed with the fragility concept of Angell and correlated with the structure of both proteins.

  3. Dynamic Relaxational Behaviour of Hyperbranched Polyether Polyols

    NASA Astrophysics Data System (ADS)

    Navarro-Gorris, A.; Garcia-Bernabé, A.; Stiriba, S.-E.

    2008-08-01

    Hyperbranched polymers are highly cascade branched polymers easily accessible via one-pot procedure from ABm type monomers. A key property of hyperbranched polymers is their molecular architecture, which allows core-shell morphology to be manipulated for further specific applications in material and medical sciences. Since the discovery of hyperbranched polymer materials, an increasing number of reports have been published describing synthetic procedures and technological applications of such materials, but their physical properties have remained less studied until the last decade. In the present work, different esterified hyperbranched polyglycerols have been prepared starting from polyglycerol precursors in presence of acetic acid, thus generating functionalization degree with range from 0 to 94%. Thermal analysis of the obtained samples has been studied by Differential Scanning Calorimetry (DSC). Dielectric Spectroscopy measurements have been analyzed by combining loss spectra deconvolution with the modulus formalism. In this regard, all acetylated polyglycerols exhibited a main relaxation related to the glass transition (α process) and two sub-glassy relaxations (β and γ processes) which vanish at high functionalization degrees.

  4. Low temperature dielectric relaxation study of aqueous solutions of diethylsulfoxide

    NASA Astrophysics Data System (ADS)

    Gabrielyan, Liana; Markarian, Shiraz; Lunkenheimer, Peter; Loidl, Alois

    2014-11-01

    In the present work, dielectric spectra of mixtures of diethylsulfoxide (DESO) and water are presented, covering a concentration range of 0.2-0.3 molar fraction of DESO. The measurements were performed at frequencies between 1Hz and 10MHz and for temperatures between 150 and 300K. It is shown that DESO/water mixtures have strong glass-forming abilities. The permittivity spectra in these mixtures reveal a single relaxation process. It can be described by the Havriliak-Negami relaxation function and its relaxation times follow the Vogel-Fulcher-Tammann law, thus showing the typical signatures of glassy dynamics. The concentration dependence of the relaxation parameters, like fragility, broadening, and glass temperature, are discussed in detail.

  5. Complex electric modulus and dielectric relaxation of nanocrystalline zinc ferrite

    NASA Astrophysics Data System (ADS)

    Choudhury, S.; Sinha, M.; Mandal, M. K.; Pradhan, S. K.; Meikap, A. K.

    2015-06-01

    We report the complex electric modulus and dielectric relaxation studies of nanocrystalline zinc ferrite. The dielectric constant exhibits strong temperature dependence at higher temperature and lower frequencies and this has been analyzed in terms of electric modulus vector. The real part of complex impedance has also been modeled by an ideal equivalent circuit consisting of grain and grain boundary resistances and capacitances. The metallic electrode and semiconductor junction forms Schottky diode, whose parameters like built in voltage and space charge density have been extracted from the capacitance-voltage characteristics.

  6. Subterahertz dielectric relaxation in lead-free Ba(Zr,Ti)O3 relaxor ferroelectrics

    PubMed Central

    Wang, D.; Bokov, A. A.; Ye, Z.-G.; Hlinka, J.; Bellaiche, L.

    2016-01-01

    Relaxors are complex materials with unusual properties that have been puzzling the scientific community since their discovery. The main characteristic of relaxors, that is, their dielectric relaxation, remains unclear and is still under debate. The difficulty to conduct measurements at frequencies ranging from ≃1 GHz to ≃1 THz and the challenge of developing models to capture their complex dynamical responses are among the reasons for such a situation. Here, we report first-principles-based molecular dynamic simulations of lead-free Ba(Zr0.5Ti0.5)O3, which allows us to obtain its subterahertz dynamics. This approach reproduces the striking characteristics of relaxors including the dielectric relaxation, the constant-loss behaviour, the diffuse maximum in the temperature dependence of susceptibility, the substantial widening of dielectric spectrum on cooling and the resulting Vogel–Fulcher law. The simulations further relate such features to the decomposed dielectric responses, each associated with its own polarization mechanism, therefore, enhancing the current understanding of relaxor behaviour. PMID:27040174

  7. Subterahertz dielectric relaxation in lead-free Ba(Zr,Ti)O3 relaxor ferroelectrics

    NASA Astrophysics Data System (ADS)

    Wang, D.; Bokov, A. A.; Ye, Z.-G.; Hlinka, J.; Bellaiche, L.

    2016-04-01

    Relaxors are complex materials with unusual properties that have been puzzling the scientific community since their discovery. The main characteristic of relaxors, that is, their dielectric relaxation, remains unclear and is still under debate. The difficulty to conduct measurements at frequencies ranging from ~=1 GHz to ~=1 THz and the challenge of developing models to capture their complex dynamical responses are among the reasons for such a situation. Here, we report first-principles-based molecular dynamic simulations of lead-free Ba(Zr0.5Ti0.5)O3, which allows us to obtain its subterahertz dynamics. This approach reproduces the striking characteristics of relaxors including the dielectric relaxation, the constant-loss behaviour, the diffuse maximum in the temperature dependence of susceptibility, the substantial widening of dielectric spectrum on cooling and the resulting Vogel-Fulcher law. The simulations further relate such features to the decomposed dielectric responses, each associated with its own polarization mechanism, therefore, enhancing the current understanding of relaxor behaviour.

  8. Dielectric Relaxations in Polypropylene-Polyamide Compatibilized Blends

    NASA Astrophysics Data System (ADS)

    Laredo, Estrella; Grimau, Mario; Sánchez, Freddy; Bello, Alfredo; Gómez, Marian; Marco, Carlos

    2003-03-01

    The dielectric relaxations in semicrystalline nylon-6,PA, and its blends with polypropylene, and polypropylene grafted with maleic anhydride are studied by broad band dielectric spectroscopy (BBDS) (10-2<= ν <= 3× 10^6 Hz) for temperatures from 133 to 433 K. The BBDS spectrum consists for the homopolymer and the blends of low temperature relaxations γ and β, which intensities vary oppositely with the water level. At higher temperatures the α relaxation is on the high temperature tail of a frequency independent peak which disappears as the sample is dryed. This peak is associated to the existence of a phase transition occurring in the water clusters present in these samples. The glass transition mode presents important differences if observed during the experimental run taken with increasing temperatures (wet sample) or during the runs recorded while the temperature decreases(dry samples). As the water content in the material is changing during the temperature sweep, the initially water plasticized material is rigidized by the drying procedure and a new α peak appears at higher temperature which corresponds to the Tg of the dry PA. At still higher temperatures there is an additional relaxation, α ^', probably associated to chain motions in the crystalline phase. The precise determination of the relaxation parameters for the different modes is presented.

  9. The mechanism of the dielectric relaxation in water.

    PubMed

    Popov, Ivan; Ishai, Paul Ben; Khamzin, Airat; Feldman, Yuri

    2016-05-18

    Although relating to the same system, the interpretations of the water spectra from Raman and Dielectric spectroscopy present independent pictures of the nature of water. We show that in the overlap region of the two methods it is possible to combine these views into a coherent concept of what drives the dynamic features of water. In this work, we develop the idea that the dielectric relaxation in water is driven by the migration of defects through the H-bond network, leading to a Debye-like peak in the lower frequencies. The deviation from the Debye law in the higher sub-THz frequencies is traced to a global fluctuation of the same H-bond network, clearly evident in the Raman Spectra. By incorporating these two views, a mathematical formalism is presented that can aptly explicate the dielectric spectra of liquid water. PMID:27148837

  10. Probing the dynamics of amyloidogenic peptides by dielectric relaxation spectroscopy

    NASA Astrophysics Data System (ADS)

    Barry, Donald; Prifti, Fioleda; Stroe, Izabela

    2010-03-01

    Fibrillar amyloidogenic structures have been considered for a long time indicators of neurodegenerative diseases. However, it has been proposed recently that amyloid oligomers are in fact the cytotoxic form and more importantly, they exhibit dynamics which differ from the fibrillar form due to the structure of water around these molecular structures. Here, we report dielectric relaxation measurements of non-amyloidogenic and amyloidogenic peptides in deionized water as a function of time and concentration. Our preliminary data show that the dielectric relaxation time of mixtures of deionized water and amyloidogenic peptides is a sensitive indicator of a transition state dominated by soluble oligomers to one characterized by the formation of large fibrils. Over time, this transition shifts the dielectric signal towards large relaxation time values, similar to those in bulk-like water as more molecules are liberated when small oligomers form fibrils. This is in agreement with recent theoretical models.footnotetextF. Despa et al., J. Biol. Phys. (2008) 34, 577 and references herein.

  11. Anomalous dielectric relaxation of water confined in graphite oxide

    SciTech Connect

    Yu, Ji; Tian, Yuchen; Gu, Min; Tang, Tong B.

    2015-09-28

    Nonmonotonic thermal dependence of dielectric relaxation of water has been observed in hydrated graphite oxide (GO). Graphite oxide prepared via Hummers method then imbued with specific water contents were characterized, with {sup 13}C and {sup 1}H nuclear magnetic resonance spectroscopies, X-ray photoelectron spectroscopy, ambient- and variable-temperature X-ray diffractometries, as well as thermogravimetric analysis. Pressed pellets provided with either conducting or blocking electrodes yielded dielectric loss, which was shown to originate from dielectric relaxation of the confined water. Three relaxation processes were observed in impedance spectroscopy. Our previous work has identified two different types of water in GO, namely, intercalated water and water in inter-grain voids. P{sub 1} expresses the reorientation of water confined inside inter-grain voids, and P{sub 2}, the rotation of intercalated water molecules confined in interlayers. The present work reveals a new process P{sub 3}, which also relates to intercalated water. It slows down with temperature, and this apparent anomaly is explained by the decrease in water content and consequent narrowing of interlayer spacing in graphite oxide, as confirmed by characterization techniques. The present study should contribute to our understanding of surface water dynamics.

  12. Studies of Amyloidogenic Peptide Dynamics by Dielectric Relaxation Spectroscopy

    NASA Astrophysics Data System (ADS)

    Prifti, Fioleda; Barry, Donald; Stroe, Izabela

    2010-03-01

    Recent theoretical studiesfootnotetextF. Despa et al., J. Biol. Phys. (2008) 34, 577 show that amyloidogenic peptides associate to form oligomers through long-range hydrophobic attractions. When peptides aggregate in larger composites, their hydrophobic patches are buried inside the newly formed amyloidogenic assembly. This gradually changes their interactions with the surrounding water molecules. The various amyloidogenic structures can then be differentiated based on the partition of the interface water and the dielectric signal of water. Here, we present dielectric relaxation spectroscopy measurements of amyloidogenic (human IAPP and Aβ (1-42)) and non-amyloidogenic (rat IAPP and Aβ (1-42) scrambled) peptides over a frequency range of 10-3 to 10^7 Hz, at different concentrations (5-100 μM), and over a large incubation time interval (0-220 h). In comparing the dielectric response of the amyloidogenic and non-amyloidogenic peptides, we find that it varies from peptide to peptide. Our experimental results also reveal a shift in the dielectric response as a function of time and concentration for each peptide. We attribute these variations in the dielectric signal to structural changes that affect the surrounding and cage water associated with the amyloid aggregates. Our results are in agreement with theoretical predictions.

  13. Dielectric and specific heat relaxations in vapor deposited glycerol

    SciTech Connect

    Kasina, A. E-mail: wubbenhorst@fys.kuleuven.be; Putzeys, T.; Wübbenhorst, M. E-mail: wubbenhorst@fys.kuleuven.be

    2015-12-28

    Recently [S. Capponi, S. Napolitano, and M. Wübbenhorst, Nat. Commun. 3, 1233 (2012)], vapor deposited glasses of glycerol have been found to recover their super-cooled liquid state via a metastable, ordered liquid (MROL) state characterized by a tremendously enhanced dielectric strength along with a slow-down of the relaxation rate of the structural relaxation. To study the calorimetric signature of this phenomenon, we have implemented a chip-based, differential AC calorimeter in an organic molecular beam deposition setup, which allows the simultaneous measurement of dielectric relaxations via interdigitated comb electrodes and specific heat relaxation spectra during deposition and as function of the temperature. Heating of the as-deposited glass just above the bulk T{sub g} and subsequent cooling/reheating revealed a step-wise increase in c{sub p} by in total 9%, indicating unambiguously that glycerol, through slow vapour deposition, forms a thermodynamically stable glass, which has a specific heat as low as that of crystalline glycerol. Moreover, these glasses were found to show excellent kinetic stability as well as evidenced by both a high onset-temperature and quasi-isothermal recovery measurements at −75 °C. The second goal of the study was to elucidate the impact of the MROL state on the specific heat and its relaxation to the super-cooled state. Conversion of “MROL glycerol” to its “normal” (ordinary liquid, OL) state revealed a second, small (∼2%) increase of the glassy c{sub p}, a little gain (<10%) in the relaxed specific heat, and no signs of deviations of τ{sub cal} from that of normal “bulk” glycerol. These findings altogether suggest that the MROL state in glycerol comprises largely bulk-type glycerol that coexist with a minor volume fraction (<10%) of PVD-induced structural anomalies with a crystal-like calorimetric signature. Based on the new calorimetric findings, we have proposed a new physical picture that assumes the

  14. Modeling of the dielectric relaxation in eukaryotic cells

    NASA Astrophysics Data System (ADS)

    Salou, P.; Mejdoubi, A.; Brosseau, C.

    2009-06-01

    There are two major objectives to the present work. The first objective is to study the influence of the frequency of the oscillating electrical field and membrane conductivity on the dielectric relaxation (β-dispersion resulting from the buildup of charge at cell membranes due to the Maxwell-Wagner-Sillars interfacial polarization) of simple core-shell structural models of biological cells. The characteristic frequency, relaxation strength, and effective conductivity are explicitly computed, via finite element simulations, as a function of surface fraction of inclusion and shape. The second objective of this work is to determine the electric potential distribution inside and outside several cell models and comment on the relevance of these numerical expectations to many aspects of cellular transformation.

  15. Dielectric relaxation study of mixtures of alkyl methacrylates and 1-alcohols using time-domain reflectometry

    NASA Astrophysics Data System (ADS)

    Sivagurunathan, P.; Dharmalingam, K.; Ramachandran, K.; Prabhakar Undre, B.; Khirade, P. W.; Mehrotra, S. C.

    2006-05-01

    Dielectric relaxation measurements on alkyl methacrylates (methyl methacrylate, ethyl methacrylate and butyl methacrylate) with 1-alcohols (1-propanol, 1-pentanol, 1-heptanol, 1-octanol and 1-decanol) have been carried out using time-domain reflectometry (TDR) over the frequency range 10 MHz to 20 GHz at 303 K for different concentrations of alcohols. The dielectric parameters, namely the static dielectric constant (ɛ0), the dielectric constant at microwave frequencies (ɛ∞) and the relaxation time (τ) were determined. The Kirkwood correlation factor, which contains information regarding solute-solvent interaction and corresponding structural information, the excess permittivity and the excess inverse relaxation time were also determined. The values of the static dielectric constant and the relaxation time increase with the percentage of alkyl methacrylates in the alcohol, whereas the static dielectric constant decreases and the relaxation time increases with an increase in the alkyl chain length of both the methacrylates and the alcohols.

  16. Multi-Relaxation Temperature-Dependent Dielectric Model of the Arctic Soil at Positive Temperatures

    NASA Astrophysics Data System (ADS)

    Savin, I. V.; Mironov, V. L.

    2014-11-01

    Frequency spectra of the dielectric permittivity of the Arctic soil of Alaska are investigated with allowance for the dipole and ionic relaxation of molecules of the soil moisture at frequencies from 40 MHz to 16 GHz and temperatures from -5 to +25°С. A generalized temperature-dependent multi-relaxation refraction dielectric model of the humid Arctic soil is suggested.

  17. Dielectric relaxation and hopping conduction in reduced graphite oxide

    NASA Astrophysics Data System (ADS)

    Wei, Guidan; Yu, Ji; Gu, Min; Tang, Tong B.

    2016-06-01

    Graphite oxide reduced by sodium borohydride was characterised and its electrical conduction investigated with impedance spectroscopy. Thermal dependence of electrical modulus (instead of permittivity, its inverse) was calculated from complex impedance spectra, an approach that prevents any peak in dielectric loss (imaginary component) from being swarmed by large dc conductivity. Two loss peaks appeared at each tested frequency, in a sample of either degree of reduction. The set of weaker peak should arise from the relaxation of some polar bonds, as proposed earlier by us. The stronger loss peaks may correspond to the hopping of conduction electrons; variable range hopping is also consistent with the observed thermal dependence of conductivity. However, nearer ambient temperature there is a change in mechanism, to band transport, with an activation energy of fairly similar values as derived from both loss peaks and conductivity.

  18. Study of dielectric relaxation process in nanocomposite of Li{sub 2}O−SiO{sub 2} nanoglass-CuO nanoparticles

    SciTech Connect

    Saha, Dhriti Ranjan Chakravorty, Dipankar

    2014-04-24

    Dielectric behaviour of a nanocomposite consisting of 23Li{sub 2}O⋅77SiO{sub 2} nanoglass within the pores of compacted CuO nanoparticles was studied. Real and imaginary parts of dielectric permittivity of the material were measured over the temperature range 313 to 363 K. The results indicated a relaxation behaviour. The data were explained by a space charge polarization model developed in the case of a laminar conductor. The activation energy of the relaxation process was in close agreement with that of lithium ion conduction in the nanoglass.

  19. Dielectric relaxation of PrFeO3 nanoparticles

    NASA Astrophysics Data System (ADS)

    Saha, Sujoy; Chanda, Sadhan; Dutta, Alo; Sinha, T. P.

    2016-08-01

    PrFeO3 (PFO) nanoceramic is synthesized by a sol-gel reaction technique. Thermogravimetric study of the as prepared gel is performed to get the lowest possible calcination temperature of PFO nanoparticles. The Rietveld refinement of the powder X-ray diffraction (XRD) pattern shows that the sample crystallizes in the orthorhombic (Pnma) phase at room temperature. The particle size of the sample is determined by scanning electron microscopy. The vibrational properties of the samples are studied by Raman spectroscopy at an excitation wavelength of 488 nm to substantiate the XRD results. Group-theoretical study is performed to assign the different vibrational modes of the sample in accordance with structural symmetry. Dielectric spectroscopy is applied to investigate the ac electrical properties of PFO at various temperatures between 313 and 473 K and in a frequency range of 42 Hz-1.1 MHz. The modified Cole-Cole equation is used to describe the experimental dielectric spectra. The frequency-dependent conductivity spectra are found to follow the power law. The temperature dependent dc conductivity is found to obey the Arrhenius law with an activation energy of 0.280 eV. An analysis of the real and imaginary parts of impedance is performed, assuming a distribution of relaxation times as confirmed by Cole-Cole plot.

  20. Dielectric Relaxation of Materials that Form Ultra-Stable Glasses

    NASA Astrophysics Data System (ADS)

    Richert, Ranko

    2015-03-01

    Physical vapor deposition of glass forming materials onto substrates at temperatures around 0.8 Tg produces glasses of high density and low enthalpy. Using interdigitated electrode cells as substrates, such stable glasses can be studied by dielectric spectroscopy in situ. This technique is applied to monitor the dynamics of stable films upon their conversion to the ordinary supercooled liquid state. The dielectric loss during transformation indicates that the softening proceeds by a growth front mechanism and generates the ordinary liquid state without forming intermediates. The same technique is also used to assess the residual dynamics of the stable glassy state. We observe that processes such as the Johari-Goldstein beta relaxation are strongly suppressed in this stable state, consistent with the relatively low fictive temperature of these glassy states. coauthors: Hai-Bin Yu, Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85278; Michael Tylinski, and Mark D. Ediger, Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706.

  1. Analysis of conductivity and dielectric spectra of Mn0.5Zn0.5Fe2O4 with coupled Cole-Cole type anomalous relaxations

    NASA Astrophysics Data System (ADS)

    Kumar, N. S. K.; Shahid, T. S.; Govindaraj, G.

    2016-05-01

    Most of the crystalline materials seldom show a well-defined dielectric loss peak due to domination of dc conductivity contribution, but effects of loss peaks are seen at high frequencies. Ac electrical data of nano-crystalline Mn0.5Zn0.5Fe2O4 synthesised by chemical co-precipitation method show such behaviour. Properly combined and formulated conduction and dielectric relaxation functions are required for such materials. Cole-Cole type relaxation function in the combined conduction and dielectric process is formulated for complex resistivity ρ*(ω), complex permittivity ε*(ω), complex conductivity σ*(ω) and complex electric modulus M*(ω). Conduction and dielectric relaxation are linked to Jonscher's idea of 'pinned dipole' and 'free dipole' to understand the relaxation dynamics. The physical parameters of 'pinned dipole' and 'free dipole' formalism are unique for all representations like ρ*(ω), ε*(ω), σ*(ω) and M*(ω). 'Pinned dipole' relaxation time τc related to conduction process and 'free dipole' relaxation time τd related to dielectric process show Arrhenius behaviour with the same activation energy. Correlation of dc conductivity σc with τc and τd indicates the coupled dynamics of 'pinned dipole' and 'free dipole'. Time-temperature scaling of conduction and dielectric relaxation reveals that the mechanism of coupled dynamics of 'pinned dipole' and 'free dipole' is temperature independent. Hopping of charge carriers with dynamics of disordered cation distribution of host matrix generates a coupled conduction and dielectric relaxation in Mn0.5Zn0.5Fe2O4.

  2. High temperature dielectric relaxation anomaly of Y3+ and Mn2+ doped barium strontium titanate ceramics

    NASA Astrophysics Data System (ADS)

    Yan, Shiguang; Mao, Chaoliang; Wang, Genshui; Yao, Chunhua; Cao, Fei; Dong, Xianlin

    2014-10-01

    Relaxation like dielectric anomaly is observed in Y3+ and Mn2+ doped barium strontium titanate ceramics when the temperature is over 450 K. Apart from the conventional dielectric relaxation analysis method with Debye or modified Debye equations, which is hard to give exact temperature dependence of the relaxation process, dielectric response in the form of complex impedance, assisted with Cole-Cole impedance model corrected equivalent circuits, is adopted to solve this problem and chase the polarization mechanism in this paper. Through this method, an excellent description to temperature dependence of the dielectric relaxation anomaly and its dominated factors are achieved. Further analysis reveals that the exponential decay of the Cole distribution parameter n with temperature is confirmed to be induced by the microscopic lattice distortion due to ions doping and the interaction between the defects. At last, a clear sight to polarization mechanism containing both the intrinsic dipolar polarization and extrinsic distributed oxygen vacancies hopping response under different temperature is obtained.

  3. Interconversion of mechanical and dielectrical relaxation measurements for dicyclohexylmethyl-2-methyl succinate.

    PubMed

    Díaz-Calleja, R; Garcia-Bernabé, A; Sanchis, M J; del Castillo, L F

    2005-11-01

    A comparison between results of dielectrical relaxation and dynamic mechanical spectroscopies is carried out for the alpha-relaxation of the ester dicyclohexyl methyl-2-methyl succinate (DCMMS). The results for the dielectric permittivity and the shear modulus measurements are presented according to the empirical Havriliak-Negami (HN) equation. By using the time-temperature principle a master curve in each case was obtained for several temperatures. The comparative analysis presented here is based on the assumption of a relationship between rotational and shear viscosities. The former one is associated to the dielectrical relaxation, whereas the latter is associated to mechanical relaxation. Both viscosities are not necessarily equal in general, and we assume that the difference between them is an important factor to appropriately compare the dielectrical and mechanical results. PMID:16383609

  4. Magnetic relaxation behaviour in Pr2NiSi3

    NASA Astrophysics Data System (ADS)

    Pakhira, Santanu; Mazumdar, Chandan; Ranganathan, R.

    2016-05-01

    Time dependent isothemal remanent magnetizatin (IRM) behaviour for polycrystalline compound Pr2NiSi3 have been studied below its characteristic temperature. The compound undergoes slow magnetic relaxation with time. Along with competing interaction, non-magnetic atom disorder plays an important role in formation of non-equilibrium glassy like ground state for this compound.

  5. Anomalous dielectric nonlinearity and dielectric relaxation in xBST-(1- x) (LMT-LNT) ceramics

    NASA Astrophysics Data System (ADS)

    Liu, Cheng; Liu, Peng

    2011-11-01

    xwt%Ba0.6Sr0.4TiO3-(1- x)wt%[0.4La (Mg0.5Ti0.5)O3-0.6(La0.5Na0.5)TiO3] ( x=0.30, 0.40, 0.50, 0.60, 0.70, 0.80, 0.90, 0.95) ceramics were prepared via a traditional solid-state reaction route. Interesting anomalous dielectric nonlinearity (ADN)—permittivity increased with dc bias electric field ( E-field), and low-temperature dielectric relaxation (LTDR) behaviors—were observed within a x range of 0.30˜0.70 for the first time. Based on our experimental facts, it was suggested that the LTDR was originated from a charge-associated process between electron-oxygen vacancy pairs during a thermal stimulation, while the ADN was related with a metastable state of polarized nano-regions (PNRs).

  6. Dielectric relaxations of small carbohydrate molecules in the liquid and glassy states

    SciTech Connect

    Noel, T.R.; Ring, S.G.; Whittam, M.A.

    1992-06-25

    Dielectric relaxations of several vitreous and liquid monosaccharides were measured at 100 - 10{sup 5} Hz and -100 to 150 {degrees}C. Depending upon the molecule, one or two relaxations were observed. Primary alcohol moieties on the monosaccharide conferred higher activation energies than those without, such as xylitol and glucitol. 19 refs., 7 figs., 2 tabs.

  7. Anomalous dielectric relaxation in lithium-potassium tantalate crystals

    NASA Astrophysics Data System (ADS)

    Doussineau, P.; Farssi, Y.; Frénois, C.; Levelut, A.; Toulouse, J.; Ziolkiewicz, S.

    1994-08-01

    In order to describe the unusual dielectric properties observed in Ki{1-χ}Li{χ}TaO3. crystals a new approchh is proposed. The dynamical Glauber theory, previously applied to spinglasses, is modifiéd by the introduction of the spectral distribution of the random interactions between the dipoles associated with the Li+ ions. Moreover, the dipole corrélations are taken into account by the Onsager réaction field. As a result, the calculated dielectric constant reproduces well the unusual features of the Argand diagrams and, in particular, their finite slope at low frequencies and infinite slope at high frequencies (strophoidal shape). The temperature dépendance of some parameters shows, however, the limits of a spin-glass type model in describing the collective behaviour of randomly distributed dipoles in a highly polarizable medium. Une nouvelle approche est présentée qui permet de décrire les propriétés diélectriques particulières de cristaux mixtes de Ki{1-χ}Li{χ}TaO3. Elle s'appuie sur la théorie dynamique de Glauber, déjà utilisée pour les verres de spins, et modifiée par l'introduction d'une distribution spectrale spécifique aux interactions aléatoires des dipôles électriques associés aux ions Li+. En outre, les corrélations entre dipôles sont prises en compte par le champ de réaction d'Onsager. II s'ensuit que la constante diélectrique complexe ainsi calculée reproduit fidèlement les particularités des diagrammes d'Argand, telles que la pente finie aux basses fréquences et la pente infinie aux hautes fréquences (forme strophoïdale). La dépendance en température de certains paramètres déterminés par le calcul montre les limites de l'analogie avec les verres de spins et met en évidence le rôle d'un réseau très polarisable dans le comportement collectif d'une assemblée de dipôles électriques.

  8. Low temperature dielectric relaxation and charged defects in ferroelectric thin films

    SciTech Connect

    Artemenko, A.; Payan, S.; Rousseau, A.; Arveux, E.; Maglione, M.; Levasseur, D.; Guegan, G.

    2013-04-15

    We report a dielectric relaxation in BaTiO{sub 3}-based ferroelectric thin films of different composition and with several growth modes: sputtering (with and without magnetron) and sol-gel. The relaxation was observed at cryogenic temperatures (T < 100 K) for frequencies from 100 Hz up to 10 MHz. This relaxation activation energy is always lower than 200 meV and is very similar to the relaxation that we reported in the parent bulk perovskites. Based on our Electron Paramagnetic Resonance (EPR) investigation, we ascribe this dielectric relaxation to the hopping of electrons among Ti{sup 3+}-V(O) charged defects. Being dependent on the growth process and on the amount of oxygen vacancies, this relaxation can be a useful probe of defects in actual integrated capacitors with no need for specific shaping.

  9. Dielectric behaviour of Zn substituted Cu nano-ferrites

    NASA Astrophysics Data System (ADS)

    Parashar, Jyoti; Saxena, V. K.; Jyoti; Bhatnagar, Deepak; Sharma, K. B.

    2015-11-01

    Herein, the dielectric properties such as permittivity (real part ε‧ and imaginary part ε‧‧) and dielectric loss tangent (tan δ) are reported for Zn substituted Cu ferrites (Cu1-xZnxFe2O4; 0≤x≤1) composite using the sol-gel auto-combustion method. The variations of real and imaginary part of dielectric constant, tan δ and AC conductivity (σac) are studied at room temperature in the frequency range of 100 Hz-120 MHz. The real part of dielectric constant decrease with increasing frequency and the imaginary part (ε‧‧) varies with frequency showing the characteristic peak for each sample. The relation of tan δ with frequency shows relaxation spectra. Further, the σac tended to increase with increase in frequency. The variation in dielectric constant may be explained on the basis of space charge polarization, according to Maxwell and Wagner two-layer model. The dielectric constant and tan δ as a function of temperature are also studied with different temperatures ranging from 323 K to 583 K.

  10. Gamma-radiation-induced dielectric relaxation characteristics of layered crystals of phlogopite mica

    NASA Astrophysics Data System (ADS)

    Kaur, Navjeet; Singh, Mohan; Singh, Lakhwant; Awasthi, A. M.; Kumar, Jitender

    2013-12-01

    In the present investigation, the influence of gamma irradiation on the dielectric relaxation characteristics of phlogopite mica was studied over the frequency range of 0.1 Hz-10 MHz and in the temperature range of 593-813 K by measuring the dielectric permittivity, electric modulus and conductivity. By comparing the dielectric spectra obtained for pristine and irradiated samples, it was observed that gamma irradiation significantly enhances the dielectric constants (ɛ‧ and ɛ″) of phlogopite mica because of the production of defects and lattice disorder by the gamma irradiation. The values of the activation energy for pristine and irradiated mica (determined from the electric modulus and the conductivity) were found to be substantially similar, suggesting that the same types of charge carriers are involved in the relaxation mechanism. The experimentally measured electric modulus and conductivity data could be well interpreted by the Havriliak-Negami dielectric relaxation function. The scaling of the electric-modulus spectra of both pristine and irradiated mica results in a master curve, which indicates that the relaxation mechanism is independent of temperature. Cole-Cole plots were also employed to analyze the non-Debye relaxation mechanism. This research will boost the reader's interest concerning the emerging contributions of irradiation and materials such as mica in electrical engineering.

  11. Dielectric relaxations and alternating current conductivity in manganese substituted cobalt ferrite

    SciTech Connect

    Kolekar, Y. D.; Sanchez, L. J.; Ramana, C. V.

    2014-04-14

    Manganese (Mn) substituted cobalt ferrites (CoFe{sub 2-x}Mn{sub x}O{sub 4}, referred to CFMO) have been synthesized by the solid state reaction method and their dielectric properties and ac conductivity have been evaluated as a function of applied frequency and temperature. X-ray diffraction measurements indicate that CFMO crystallize in the inverse cubic spinel phase with a lattice constant ∼8.38 Å. Frequency dependent dielectric measurements at room temperature obey the modified Debye model with relaxation time of 10{sup −4} s and spreading factor of 0.35(±0.05). The frequency (20 Hz–1 MHz) and temperature (T = 300–900 K) dependent dielectric constant analyses indicate that CFMO exhibit two dielectric relaxations at lower frequencies (1–10 kHz), while completely single dielectric relaxation for higher frequencies (100 kHz–1 MHz). The dielectric constant of CFMO is T-independent up to ∼400 K, at which point increasing trend prevails. The dielectric constant increase with T > 400 K is explained through impedance spectroscopy assuming a two-layer model, where low-resistive grains separated from each other by high-resistive grain boundaries. Following this model, the two electrical responses in impedance formalism are attributed to the grain and grain-boundary effects, respectively, which also satisfactorily accounts for the two dielectric relaxations. The capacitance of the bulk of the grain determined from impedance analyses is ∼10 pF, which remains constant with T, while the grain-boundary capacitance increases up to ∼3.5 nF with increasing T. The tan δ (loss tangent)-T also reveals the typical behavior of relaxation losses in CFMO.

  12. Dielectric Relaxation Behavior of Poly(acrylonitrile-co-methacrylonitrile) Microcapsules Dispersed in a Silicone Matrix

    NASA Technical Reports Server (NTRS)

    Park, Taigyoo; OBrien, Emmett; Lizotte, Jeremy R.; Glass, Thomas E.; Ward, Thomas C.; Long, Timothy E.; Leo, Donald J.

    2006-01-01

    The dielectric relaxation behavior of poly(acrylonitrile-co-methacrylonitrile) dispersed in a cured polydimethyl siloxane (PDMS) matrix as microcapsules was investigated over multiple thermal cycles and at varying concentrations. The copolymer microcapsules contained an isopentane core. In the PDMS matrix this copolymer displayed a pronounced relaxation signal at temperatures above the glass transition of the copolymers due to Maxwell-Wagner-Sillars (MWS) relaxation. The mechanism of MWS relaxation interpreted by the Havriliak-Negami and Kohlrausch-Williams-Watts relaxation functions was found to be very similar to previous studies of neat polyacrylonitrile and its copolymer. The activation energy of the relaxation decreased over successive thermal cycling coincident with a decreasing strength of the relaxation. These observations were attributed to the decreasing concentration of nitrile groups due to intramolecular cyclizations.

  13. The relaxation of a prolate leaky dielectric drop in a uniform DC electric field

    NASA Astrophysics Data System (ADS)

    Khair, Aditya; Lanauze, Javier; Walker, Lynn

    2015-11-01

    We quantify the relaxation of a prolate leaky dielectric drop upon removal of a uniform DC electric field. Experiments consisting of a castor oil drop suspended in a silicone oil are compared against boundary integral simulations that account for transient charging of the interface. Charge relaxation causes a marked asymmetry in the drop evolution during deformation and relaxation. In particular, during relaxation a prolate to oblate shape transition is observed before the drop recovers its equilibrium spherical shape. Furthermore, the high field strengths utilized in the experiments yield a fast drop relaxation in comparison with the transient development towards the steady deformation. The storage and release of capacitive energy and capillary energy is then quantified during deformation and relaxation, respectively. Finally, we present computational results for a drop that does not relax back to its initial spherical shape upon removal of the field; rather, the drop breaks up.

  14. Dielectric relaxation, resonance and scaling behaviors in Sr3Co2Fe24O41 hexaferrite

    PubMed Central

    Tang, Rujun; Jiang, Chen; Qian, Wenhu; Jian, Jie; Zhang, Xin; Wang, Haiyan; Yang, Hao

    2015-01-01

    The dielectric properties of Z-type hexaferrite Sr3Co2Fe24O41 (SCFO) have been investigated as a function of temperature from 153 to 503 K between 1 and 2 GHz. The dielectric responses of SCFO are found to be frequency dependent and thermally activated. The relaxation-type dielectric behavior is observed to be dominating in the low frequency region and resonance-type dielectric behavior is found to be dominating above 108 Hz. This frequency dependence of dielectric behavior is explained by the damped harmonic oscillator model with temperature dependent coefficients. The imaginary part of impedance (Z″) and modulus (M″) spectra show that there is a distribution of relaxation times. The scaling behaviors of Z″ and M″ spectra further suggest that the distribution of relaxation times is temperature independent at low frequencies. The dielectric loss spectra at different temperatures have not shown a scaling behavior above 108 Hz. A comparison between the Z″ and the M″ spectra indicates that the short-range charges motion dominates at low temperatures and the long-range charges motion dominates at high temperatures. The above results indicate that the dielectric dispersion mechanism in SCFO is temperature independent at low frequencies and temperature dependent at high frequencies due to the domination of resonance behavior. PMID:26314913

  15. Dielectric relaxation, resonance and scaling behaviors in Sr3Co2Fe24O41 hexaferrite.

    PubMed

    Tang, Rujun; Jiang, Chen; Qian, Wenhu; Jian, Jie; Zhang, Xin; Wang, Haiyan; Yang, Hao

    2015-01-01

    The dielectric properties of Z-type hexaferrite Sr3Co2Fe24O41 (SCFO) have been investigated as a function of temperature from 153 to 503 K between 1 and 2 GHz. The dielectric responses of SCFO are found to be frequency dependent and thermally activated. The relaxation-type dielectric behavior is observed to be dominating in the low frequency region and resonance-type dielectric behavior is found to be dominating above 10(8) Hz. This frequency dependence of dielectric behavior is explained by the damped harmonic oscillator model with temperature dependent coefficients. The imaginary part of impedance (Z″) and modulus (M″) spectra show that there is a distribution of relaxation times. The scaling behaviors of Z″ and M″ spectra further suggest that the distribution of relaxation times is temperature independent at low frequencies. The dielectric loss spectra at different temperatures have not shown a scaling behavior above 10(8) Hz. A comparison between the Z″ and the M″ spectra indicates that the short-range charges motion dominates at low temperatures and the long-range charges motion dominates at high temperatures. The above results indicate that the dielectric dispersion mechanism in SCFO is temperature independent at low frequencies and temperature dependent at high frequencies due to the domination of resonance behavior. PMID:26314913

  16. Dielectric and conductivity relaxation in AgI doped silver selenite superionic glasses

    SciTech Connect

    Deb, B.; Ghosh, A.

    2010-10-15

    Non-Debye relaxation in superionic AgI-Ag{sub 2}O-SeO{sub 2} glasses has been investigated as a function of frequency and temperature. The experimental data have been analyzed in the framework of complex dielectric permittivity and complex electric modulus formalisms. The dielectric permittivity data have been well interpreted using the Havriliak-Negami function. The electric modulus data have been analyzed by invoking Kohlrausch-Williams-Watts function and various parameters describing the relaxation mechanism have been obtained. The temperature and compositional variation in relaxation times and the activation energy, obtained from dielectric permittivity as well as from electric modulus data, have been compared. The low value of stretched exponential parameter implies a highly nonexponential nature of relaxation and is attributed to the correlated ionic motion. The values of the stretched exponential parameter are observed to be independent of temperature as well as composition. Different scaling formalisms have been applied to understand the temperature and compositional dependence of the relaxation mechanism. The scaling of dielectric loss spectra and electric modulus spectra results in master curves, which signifies that the relaxation mechanism is independent of temperature as well as composition.

  17. Acoustic and relaxation behaviors of polydimethylsiloxane studied by using brillouin and dielectric spectroscopies

    NASA Astrophysics Data System (ADS)

    Lee, Byoung Wan; Ko, Jae-Hyeon; Park, Jaehoon; Shin, Dong-Myeong; Hwang, Yoon-Hwae

    2016-04-01

    The temperature dependences of the acoustic properties and the dielectric relaxation times of polydimethylsiloxane were investigated by using high-resolution Brillouin and broadband dielectric spectroscopies. The longitudinal sound velocity showed a large increase upon approaching the glass transition temperature while the acoustic absorption coefficient exhibited a maximum at ~263 K. Comparison of these results with previous ultrasonic data revealed a substantial frequency dispersion of the acoustic properties of this silicone-based elastomer. The relaxation times derived from the acoustic absorption peaks were consistent with the temperature dependence of the dielectric relaxation time of the structural a process, indicating a strong coupling between the acoustic waves and the segmental motions of the main chains.

  18. Investigation of crystalline morphology in poly (ether ether ketone) using dielectric relaxation spectroscopy

    SciTech Connect

    Kalika, D.S.; Krishnaswamy, R.K.

    1993-12-31

    The relaxation behavior of poly (ether ether ketone) [PEEK] has been investigated using dielectric relaxation spectroscopy; the glass-rubber ({alpha}) relaxation and a sub-glass ({beta}) relaxation were examined for the amorphous material and both cold-crystallized and melt-crystallized specimens. Analysis of the data using the Cole-Cole modification of the Debye equation allowed determination of the dielectric relaxation strength and relaxation broadening parameter for both transitions as a function of material crystallization history. The crystallized specimens displayed a positive offset in isochronal loss temperature for both the {alpha} and {beta} relaxations, with the {alpha} relaxation broadened significantly. The measured dipolar response was interpreted using a three-phase morphological model encompassing a crystalline phase, a mobile amorphous phase, and a rigid amorphous phase. Determination of phase fractions based on dipolar mobilization across the glass-rubber relaxation revealed a finite rigid amorphous phase fraction for both the cold-crystallized specimens which was relatively insensitive to thermal history and degree of crystallinity (W{sub RAP}40.20).

  19. Difference and similarity of dielectric relaxation processes among polyols

    NASA Astrophysics Data System (ADS)

    Minoguchi, Ayumi; Kitai, Kei; Nozaki, Ryusuke

    2003-09-01

    Complex permittivity measurements were performed on sorbitol, xylitol, and sorbitol-xylitol mixture in the supercooled liquid state in an extremely wide frequency range from 10 μHz to 500 MHz at temperatures near and above the glass transition temperature. We determined detailed behavior of the relaxation parameters such as relaxation frequency and broadening against temperature not only for the α process but also for the β process above the glass transition temperature, to the best of our knowledge, for the first time. Since supercooled liquids are in the quasi-equilibrium state, the behavior of all the relaxation parameters for the β process can be compared among the polyols as well as those for the α process. The relaxation frequencies of the α processes follow the Vogel-Fulcher-Tammann manner and the loci in the Arrhenius diagram are different corresponding to the difference of the glass transition temperatures. On the other hand, the relaxation frequencies of the β processes, which are often called as the Johari-Goldstein processes, follow the Arrhenius-type temperature dependence. The relaxation parameters for the β process are quite similar among the polyols at temperatures below the αβ merging temperature, TM. However, they show anomalous behavior near TM, which depends on the molecular size of materials. These results suggest that the origin of the β process is essentially the same among the polyols.

  20. In-Vivo Like Studies of the hIAPP Amyloid Precursors Using Dielectric Relaxation Spectroscopy

    NASA Astrophysics Data System (ADS)

    Hirai, Yusuke; Mahommed Assiri, Reem; Barry, Donal; Despa, Florin; Stroe, Izabela

    2013-03-01

    Recent studies show that the amyloid formation in Type II diabetic disease involves aggregation of monomers of the human islet amyloid polypeptide (hIAPP) into oligomers, protofibrils, and fibrils. Here we present data showing that Dielectric Relaxation Spectroscopy is a very sensitive technique to detect the hIAPP precursors. We measured the dielectric response of amyloidogenic hIAPP and non-amyloidogenic rIAPP as a function of frequency (10-3 Hz to 107 Hz), temperature (193K to 283K), and incubation time (0-120 h). To mimic in-vivo like conditions, the proteins were measured in bovine serum albumin. Our results show that the dielectric signal of amyloidogenic hIAPP shifts towards the dielectric signal of the background, as predicted by theoretical calculations. No similar shift is observed for the non-amyloidogenic rIAPP. In addition, the dielectric signal of both the hIAPP and the rIAPP shows two relaxation processes over the measured temperature range. We used two Havrilik-Negami functions plus conductivity to fit the two relaxation processes we determined the relaxation time for both processes and calculated the corresponding activation energies. This work was supported by the Kalenian Award.

  1. Dielectric relaxation of normothermic and hypothermic rat corneas.

    PubMed

    Marzec, E; Sosnowski, P; Olszewski, J; Krauss, H; Bahloul, K; Samborski, W; Krawczyk-Wasielewska, A

    2015-02-01

    This paper aims at the presentation of the results of in vitro research on the dielectric properties of the cornea specimen collected from the rats subjected to in vivo hypothermia. The average values of the relative permittivity and dielectric loss are about 40% higher for the hypothermic cornea than those for the normothermic tissue at the same water content of 12% for both samples and at 25°C. Whereas, at 50°C this effect of increase in the dielectric properties of the hypothermic cornea when compared to the normothermic one is observed clearly only in the relative permittivity of about 19%. In the temperature range of 25-50°C, the activation energy of conductivity associated with the release of loosely bound water takes the average values of 45kJ/mol and 30kJ/mol for the normothermic and hypothermic corneas, respectively. The study provided information on dielectric polarization and conductance mechanisms in the cornea which may be helpful in interpreting clinical results of human cornea examination, currently obtained by means of such electrodiagnostic methods as conductive keratoplasty, electroretinography or electrooculography. PMID:25308935

  2. Conduction mechanism and dielectric relaxation in high dielectric KxTiyNi1-x-yO

    NASA Astrophysics Data System (ADS)

    Jana, Pradip Kumar; Sarkar, Sudipta; Karmakar, Shilpi; Chaudhuri, B. K.

    2007-10-01

    Complex impedance spectroscopic study has been made to elucidate the conductivity mechanism and dielectric relaxations in a low loss giant dielectric (ɛ'˜104) KxTiyNi1-x-yO (KTNO) system with x =0.05-0.30 and y =0.02 over a wide temperature range (200-400K). Below ambient temperature (300K), dc conductivity follows variable range hopping mechanism. The estimated activation energy for dielectric relaxation is found to be higher than the corresponding polaron hopping energy, which is attributed to the combined effect of K-doped grains and highly disordered grain boundary (GB) contributions in KTNO. Observed sharp fall of ɛ' below ˜270K is ascribed to the freezing of charge carriers. Comparatively lower value of relaxation time distribution parameter β of KTNO than that of the CaCu3Ti4O12 (CCTO) system reveals more disorder in KTNO. It is also found that KTNO is structurally more stable compared to the CCTO system, both having giant ɛ' value.

  3. Alternating current conductivity and dielectric relaxation of PANI:PVDF composites

    NASA Astrophysics Data System (ADS)

    Saïdi, Sami; Mannaî, Aymen; Bouzitoun, Mouna; Belhadj Mohamed, Abdellatif

    2014-04-01

    In this work, PANI:PVDF composites films were prepared with different PANI contents (p = 1, 2, 3, 4 and 5%). The resulting films were dried at various temperatures such as 30, 90 and 120 °C. The alternating current mechanisms and dielectric relaxation and of PANI:PVDF films were studied using complex impedance spectroscopy over a wide range of temperature (303-453 K) and a frequency range (1 kHz to 1 MHz). We found that the ac conductivity in PANI:PVDF composite is governed by correlated barrier hopping (CBH) model. In dielectric loss modulus study, two relaxation processes were identified. The first peak was associated to Maxwell Wagner-Sillas (MWS) relaxation whereas the second one which obtained at higher frequency was attributed to the αc relaxation. For PANI:PVDF film which dried at 30 °C, the MWS relaxation appears only at higher temperature. The temperature dependence of αc relaxation was suitably fitted according to Vogel Flucher Temman model whereas MWS relaxation follows Arrhenius type behavior. The effect of drying temperature on microstructure and phase crystallization of PVDF in the composites was carried out using atomic force microscopy (AFM) and Fourier transform infrared (FTIR) spectroscopy. These results were used to find a reasonable correlation between microstructure and electrical properties.

  4. Dielectric relaxation of barium strontium titanate and application to thin films for DRAM capacitors

    NASA Astrophysics Data System (ADS)

    Baniecki, John David

    This thesis examines the issues associated with incorporating the high dielectric constant material Barium Strontium Titanate (BSTO) in to the storage capacitor of a dynamic random access memory (DRAM). The research is focused on two areas: characterizing and understanding the factors that control charge retention in BSTO thin films and modifying the electrical properties using ion implantation. The dielectric relaxation of BSTO thin films deposited by metal-organic chemical vapor deposition (MOCVD) is investigated in the time and frequency domains. It is shown that the frequency dispersion of the complex capacitance of BSTO thin films can be understood in terms of a power-law frequency dependence from 1mHz to 20GHz. From the correspondence between the time and frequency domain measurements, it is concluded that the power-law relaxation currents extend back to the nano second regime of DRAM operation. The temperature, field, and annealing dependence of the dielectric relaxation currents are also investigated and mechanisms for the observed power law relaxation are explored. An equivalent circuit model of a high dielectric constant thin film capacitor is developed based on the electrical measurements and implemented in PSPICE. Excellent agreement is found between the experimental and simulated electrical characteristics showing the utility of the equivalent circuit model in simulating the electrical properties of high dielectric constant thin films. Using the equivalent circuit model, it is shown that the greatest charge loss due to dielectric relaxation occurs during the first read after a refresh time following a write to the opposite logic state for a capacitor that has been written to the same logic state for a long time (opposite state write charge loss). A theoretical closed form expression that is a function of three material parameters is developed which estimates the opposite state write charge loss due to dielectric relaxation. Using the closed form

  5. Study of relaxation and transport processes by means of AFM based dielectric spectroscopy

    SciTech Connect

    Miccio, Luis A.

    2014-05-15

    Since its birth a few years ago, dielectric spectroscopy studies based on atomic force microscopy (AFM) have gained a growing interest. Not only the frequency and temperature ranges have become broader since then but also the kind of processes that can be studied by means of this approach. In this work we analyze the most adequate experimental setup for the study of several dielectric processes with a spatial resolution of a few nanometers by using force mode AFM based dielectric spectroscopy. Proof of concept experiments were performed on PS/PVAc blends and PMMA homopolymer films, for temperatures ranging from 300 to 400 K. Charge transport processes were also studied by this approach. The obtained results were analyzed in terms of cantilever stray contribution, film thickness and relaxation strength. We found that the method sensitivity is strongly coupled with the film thickness and the relaxation strength, and that it is possible to control it by using an adequate experimental setup.

  6. Dielectric Relaxation of Rare Earth Ordered Double Perovskite Oxide Ba2ErTaO6

    NASA Astrophysics Data System (ADS)

    Mukherjee, Rajesh; Dutta, Alo; Sinha, T. P.

    2016-01-01

    The electrical properties of rare-earth based ordered double perovskite oxide barium erbium tantalate, Ba2ErTaO6 synthesized by solid-state reaction method are investigated. The x-ray diffraction pattern of the sample shows cubic Fm3m phase at room temperature with ordering of the B cations. Fourier transform infrared spectrum shows two primary phonon modes of the sample at around 350 cm-1 and 600 cm-1. The dielectric relaxation of the sample is investigated in the frequency range from 50 Hz to 1.1 MHz and in the temperature range from 303 K to 673 K. Electric modulus and electrical impedance data are fitted to the Cole-Cole equation. The frequency dependent conductivity spectra follow the power law. Summerfield scaling is used to explain the conduction mechanism. The scaling behavior of the imaginary part of the impedance spectra suggests that the relaxation shows the same mechanism at various temperatures. The complex impedance plane plots show that the relaxation (conduction) mechanism in this material is mainly due to grain boundary effect for all temperatures and grain effect for low temperature. The relaxation frequency corresponding to dielectric loss is found to obey Arrhenius law with activation energy of 0.50 eV. The values of activation energy indicate that the dielectric relaxation and the conduction mechanism are due to adiabatic small polaronic hole hopping mechanism.

  7. Compressibility and Dielectric Relaxation of Mixtures of Water with Monohydroxy Alcohols.

    PubMed

    Dzida, Marzena; Kaatze, Udo

    2015-09-24

    Isentropic compressibility data and principal dielectric relaxation times, mostly for normal alcohols and for mixtures of monohydroxy alcohols with water, are evaluated and compared to one another. It is found that the microdynamics of the liquids, as reflected by the dielectric relaxation times, can be generally explained in the light of a defect diffusion model. Within the framework of that model, the principal relaxation time is predominantly controlled by the local concentration of hydrogen bonding sites. The alkyl groups of the alcohols are shown to have a 2-fold influence by reducing the concentration of the H-bonding sites and by also contributing to the activation enthalpy of relaxation. The effect of alkyl groups on the compressibility is quite different. The compressibility of methanol exceeds that of water by a substantial amount. Within the series of normal alcohols, in correspondence with the behavior of normal alkanes, the liquids become less compressible with increasing alkyl chain length. Relative molal shifts Bκ and Bd of the compressibility and dielectric relaxation time, respectively, of dilute solutions of alcohols in water are consistent with the behavior of aqueous solutions of other organic solutes. The Bd values increase with hydrophobic character of the solute (ΔBd = 0.045 (mol/kg)(-1) for an additional methyl group per solute molecule or organic ion), whereas Bκ decreases (ΔBκ = -0.012 (mol/kg)(-1)). Reduced orientational mobility combined with decreased compressibility appears to be characteristic of hydration shells around hydrophobic solutes. PMID:26335254

  8. Investigation of the dielectric relaxation and the transport properties of porous silicates containing humidity

    NASA Astrophysics Data System (ADS)

    Papathanassiou, A. N.

    2000-07-01

    The dielectric relaxation responses of pelite, which is a porous silicate sediment containing a low content of inherent humidity, were identified and characterized by employing the experimental scheme of the thermally stimulated depolarization current (TSDC) spectroscopy. Comparative experiments were performed on dry samples. The elementary responses that compose the dielectric spectrum were recorded by applying certain sampling techniques. The dielectric relaxation spectrum consists of two low-temperature mechanisms, which are related to different modes of relaxation of water molecules. A third one is probably produced by permanent dipoles consisting of point defects in the calcium participant. Three relaxation mechanisms were sampled within the intermediate temperature region and were strongly affected by the outgassing of the pore network. They correspond to polarization processes occurring in the multi-layer shell of humidity over the surface the solid aggregates. At higher temperatures, two mechanisms were traced: the first is related to the homogeneous polarization of the specimen as charge carriers migrate within conducting territories until they are trapped at internal boundaries and the latter is described as a long-distance conduction mechanism which is enhanced by the presence of humidity. The activation energy profiles of the above-mentioned relaxation mechanisms were obtained from the analysis of the experimental signals of the thermal sampling and the partial heating schemes.

  9. Dynamics of glass-forming liquids. XIV. A search for ultraslow dielectric relaxation in glycerol

    NASA Astrophysics Data System (ADS)

    Richert, Ranko

    2010-08-01

    A recent dielectric study of various polyalcohols reported on the general occurrence of an ultraslow process with Debye type character in hydrogen bonded liquids [R. Bergman, H. Jansson, and J. Swenson, J. Chem. Phys. 132, 044504 (2010)], whereas previous work suggested that such behavior is specific to monoalcohols only. Clarifying this issue is highly relevant for assessing models aimed at rationalizing these modes that are slower than the primary structural relaxation and associated with a single time constant. To this end, the dielectric relaxation of glycerol is measured at different electrode distances with high accuracy. In this manner, electrode polarization can be separated from the dielectric signals intrinsic in the supercooled liquid. In the frequency range below the loss peak frequency ωmax of the α-process, only dc-conductivity is required to understand the dielectric properties of supercooled glycerol within a margin of ɛ″≈±0.1 and thus no indication of an ultraslow peak is found. More quantitatively, any dielectric Debye like mode located around 10-5ωmax would need to have an amplitude smaller than 0.4% of that of the primary dielectric process to be consistent with the present findings, in contrast to previous claims of >50%.

  10. Applications and Implications of Fractional Dynamics for Dielectric Relaxation

    NASA Astrophysics Data System (ADS)

    Hilfer, R.

    This article summarizes briefly the presentation given by the author at the NATO Advanced Research Workshop on "Broadband Dielectric Spectroscopy and its Advanced Technological Applications", held in Perpignan, France, in September 2011. The purpose of the invited presentation at the workshop was to review and summarize the basic theory of fractional dynamics (Hilfer, Phys Rev E 48:2466, 1993; Hilfer and Anton, Phys Rev E Rapid Commun 51:R848, 1995; Hilfer, Fractals 3(1):211, 1995; Hilfer, Chaos Solitons Fractals 5:1475, 1995; Hilfer, Fractals 3:549, 1995; Hilfer, Physica A 221:89, 1995; Hilfer, On fractional diffusion and its relation with continuous time random walks. In: Pekalski et al. (eds) Anomalous diffusion: from basis to applications. Springer, Berlin, p 77, 1999; Hilfer, Fractional evolution equations and irreversibility. In: Helbing et al. (eds) Traffic and granular flow'99. Springer, Berlin, p 215, 2000; Hilfer, Fractional time evolution. In: Hilfer (ed) Applications of fractional calculus in physics. World Scientific, Singapore, p 87, 2000; Hilfer, Remarks on fractional time. In: Castell and Ischebeck (eds) Time, quantum and information. Springer, Berlin, p 235, 2003; Hilfer, Physica A 329:35, 2003; Hilfer, Threefold introduction to fractional derivatives. In: Klages et al. (eds) Anomalous transport: foundations and applications. Wiley-VCH, Weinheim, pp 17-74, 2008; Hilfer, Foundations of fractional dynamics: a short account. In: Klafter et al. (eds) Fractional dynamics: recent advances. World Scientific, Singapore, p 207, 2011) and demonstrate its relevance and application to broadband dielectric spectroscopy (Hilfer, J Phys Condens Matter 14:2297, 2002; Hilfer, Chem Phys 284:399, 2002; Hilfer, Fractals 11:251, 2003; Hilfer et al., Fractional Calc Appl Anal 12:299, 2009). It was argued, that broadband dielectric spectroscopy might be useful to test effective field theories based on fractional dynamics.

  11. Dielectric relaxation in weakly ergodic dilute dipole systems

    NASA Astrophysics Data System (ADS)

    Lerner, Shimon E.; Mierzwa, Michal; Paluch, Marian; Feldman, Yuri; Ishai, Paul Ben

    2013-05-01

    We introduce a method for calculating dipole correlations in systems containing hopping processes exhibiting weak ergodicity breaking. Modeled after the original Kirkwood-Fröhlich theory, the new method provides a bridge extending Fröhlich's insights from the realm of rigid dipoles into weakly non-ergodic fluctuating virtual dipolar entities. Relevant for the investigation of any system containing transport processes, it provides a testable parameter derived primarily from the static dielectric parameters. Three examples of systems including porous silicon, porous glass, and ferroelectric crystals are brought to demonstrate the model's versatility, including direct confirmation of Fröhlich's original idea.

  12. Dielectric relaxation in weakly ergodic dilute dipole systems.

    PubMed

    Lerner, Shimon E; Mierzwa, Michal; Paluch, Marian; Feldman, Yuri; Ishai, Paul Ben

    2013-05-28

    We introduce a method for calculating dipole correlations in systems containing hopping processes exhibiting weak ergodicity breaking. Modeled after the original Kirkwood-Fröhlich theory, the new method provides a bridge extending Fröhlich's insights from the realm of rigid dipoles into weakly non-ergodic fluctuating virtual dipolar entities. Relevant for the investigation of any system containing transport processes, it provides a testable parameter derived primarily from the static dielectric parameters. Three examples of systems including porous silicon, porous glass, and ferroelectric crystals are brought to demonstrate the model's versatility, including direct confirmation of Fröhlich's original idea. PMID:23742487

  13. The effects of different additives on the dielectric relaxation and the dynamic mechanical properties of urethane dimethacrylate.

    PubMed

    Mohsen, N M; Craig, R G; Filisko, F E

    2000-03-01

    The polymer-filler interaction of a dental composite was examined by dielectric measurements to determine how a non-compatible inorganic phase modifies the molecular behaviour of the polymer chains and how modification of this phase by silanation can affect these molecular behaviours. Urethane dimethacrylate (UDMA) monomer and zirconia-silica (ZS) powder were used as organic and inorganic phases, respectively. 3-Acryloxypropyltrimethoxysilane (MAPM) and 4-aminobutyltriethoxysilane (ABTE) were used as silanating coupling agents. The components of the composite were mixed in different ratios after treating the filler with from 0 to 30 times the minimum uniform coverage with the silane, then the composite was made into thin films. The dielectric spectra of five replicas for each filler-monomer ratio were measured, and three replicas were measured for each silane and for each amount of silane used to treat the filler. Increasing the filler concentration in the composites decreased the intensity of Tan(delta)epsilon for the alpha- and beta-relaxations, where the beta-relaxations also became broader and the alpha-relaxations were totally obstructed. The alpha-relaxations were shifted to higher temperatures, while the beta-relaxations were shifted to lower temperatures. Filler treatment with small amounts of MAPM shifted the alpha-relaxations to higher temperatures; they were shifted back to lower temperatures when the filler was treated with large amounts of silane. Filler treatment with large amounts of ABTE (30-fold) caused an extra peak to emerge in the high-temperature region. It can be concluded that increasing filler concentration restricts the mobility of the main chains and decreases the thickness of the surface layer, while allowing more movement of the local chains. Filler treatment with MAPM was shown to be a compatible coupling agent with the ZS and the UDMA systems. Such compatibility was observed through the effectiveness of the chemical linkage of the

  14. Grains and grain boundaries contribution to dielectric relaxations and conduction of Bi5Ti3FeO15 ceramics

    NASA Astrophysics Data System (ADS)

    Rehman, Fida; Li, Jing-Bo; Zhang, Jia-Song; Rizwan, Muhammad; Niu, Changlei; Jin, Hai-Bo

    2015-12-01

    Dielectric relaxation behaviors of Aurivillius Bi5Ti3FeO15 ceramics were investigated in a wide range of frequency and temperature via dielectric and impedance spectroscopies. We distinguished two dielectric relaxations using the combination of impedance and modulus analysis. Resistance of the grain boundary was found to be much larger than grains, whereas capacitance was at the same level. The kinetic analysis of dielectric data was carried out to evaluate the contributions of microstructure and defects to the relaxation and conduction. The possible relaxation-conduction mechanism in the ceramics was discussed. The results enable deep understanding of microstructure-defect-relaxation behaviors in Bi5Ti3FeO15 ceramics.

  15. Molecular dynamics in polymers, polymer networks, and model compounds by dielectric relaxation spectroscopy

    NASA Astrophysics Data System (ADS)

    Fitz, Benjamin David

    Segmental dynamics are investigated in model compounds, polymers, and network-forming polymers. Two aspects of these materials are investigated: (1) the role of molecular structure and connectivity on determining the characteristics of the segmental relaxation, and (2) monitoring the variations in the segmental dynamics during network-forming chemical reactions. We quantify the most important aspects of the dynamics: the relaxation shape, the relaxation strength, the relaxation time, and the temperature dependencies of these properties. Additionally, two general segmental dynamics issues of interest are the length-scale and the homogeneous/heterogeneous aspects. A judicious choice of network-forming polymer provides for the determination of an upper bound on the length-scale. A comparison of relaxation characteristics between dynamic light scattering (measuring density fluctuations) and dielectric relaxation spectroscopy (measuring segmental dipolar reorientation) provides one evaluation of the heterogeneity issue. Dipole dynamics in small molecule model compounds show the influence of molecular connectivity on the cooperative molecular response associated with the glass transition. A rigid, nonpolar, cyanate ester network is shown to develop an anomalous relaxation process during crosslinking. A specific local mode of motion is assigned. Additionally, the main relaxation becomes extraordinarily broad during the course of the network formation, due to markedly increased segmental rigidity and loss of configurational entropy.

  16. Resolving environmental microheterogeneity and dielectric relaxation in fluorescence kinetics of protein

    NASA Astrophysics Data System (ADS)

    Rolinski, Olaf J.; McLaughlin, Damien; Birch, David J. S.; Vyshemirsky, Vladislav

    2016-06-01

    The fluorescence intensity decay of protein is easily measurable and reports on the intrinsic fluorophore-local environment interactions on the sub-nm spatial and sub-ns temporal scales, which are consistent with protein activity in numerous biomedical and industrial processes. This makes time-resolved fluorescence a perfect tool for understanding, monitoring and controlling these processes at the molecular level, but the complexity of the decay, which has been traditionally fitted to multi-exponential functions, has hampered the development of this technique over the last few decades. Using the example of tryptophan in HSA we present the alternative to the conventional approach to modelling intrinsic florescence intensity decay in protein where the key factors determining fluorescence decay, i.e. the excited-state depopulation and the dielectric relaxation (Toptygin and Brand 2000 Chem. Phys. Lett. 322 496–502), are represented by the individual relaxation functions. This allows quantification of both effects separately by determining their parameters from the global analysis of a series of fluorescence intensity decays measured at different detection wavelengths. Moreover, certain pairs of the recovered parameters of tryptophan were found to be correlated, indicating the influence of the dielectric relaxation on the transient rate of the electronic transitions. In this context the potential for the dual excited state depopulation /dielectric relaxation fluorescence lifetime sensing is discussed.

  17. Resolving environmental microheterogeneity and dielectric relaxation in fluorescence kinetics of protein

    NASA Astrophysics Data System (ADS)

    Rolinski, Olaf J.; McLaughlin, Damien; Birch, David J. S.; Vyshemirsky, Vladislav

    2016-09-01

    The fluorescence intensity decay of protein is easily measurable and reports on the intrinsic fluorophore-local environment interactions on the sub-nm spatial and sub-ns temporal scales, which are consistent with protein activity in numerous biomedical and industrial processes. This makes time-resolved fluorescence a perfect tool for understanding, monitoring and controlling these processes at the molecular level, but the complexity of the decay, which has been traditionally fitted to multi-exponential functions, has hampered the development of this technique over the last few decades. Using the example of tryptophan in HSA we present the alternative to the conventional approach to modelling intrinsic florescence intensity decay in protein where the key factors determining fluorescence decay, i.e. the excited-state depopulation and the dielectric relaxation (Toptygin and Brand 2000 Chem. Phys. Lett. 322 496–502), are represented by the individual relaxation functions. This allows quantification of both effects separately by determining their parameters from the global analysis of a series of fluorescence intensity decays measured at different detection wavelengths. Moreover, certain pairs of the recovered parameters of tryptophan were found to be correlated, indicating the influence of the dielectric relaxation on the transient rate of the electronic transitions. In this context the potential for the dual excited state depopulation /dielectric relaxation fluorescence lifetime sensing is discussed.

  18. Fitting the excess wing in the dielectric α-relaxation of propylene carbonate

    NASA Astrophysics Data System (ADS)

    Hilfer, R.

    2002-03-01

    A novel fitting function for the complex frequency-dependent dielectric susceptibility is introduced and compared against other fitting functions for experimental broadband dielectric loss spectra of propylene carbonate taken from Schneider et al (Schneider U, Lunkenheimer P, Brand R and Loidl A 1999 Phys. Rev. E 59 6924). The fitting function contains a single stretching exponent similar to the familiar Cole-Davidson or Kohlrausch stretched exponential fits. It is compared to these traditional fits as well as to the Havriliak-Negami susceptibility and a susceptibility for a two-step Debye relaxation. The results for the novel fit are found to give superior agreement.

  19. Dielectric relaxation of ethylene carbonate and propylene carbonate from molecular dynamics simulations

    SciTech Connect

    Chaudhari, Mangesh I.; You, Xinli; Pratt, Lawrence R.; Rempe, Susan B.

    2015-11-24

    Ethylene carbonate (EC) and propylene carbonate (PC) are widely used solvents in lithium (Li)-ion batteries and supercapacitors. Ion dissolution and diffusion in those media are correlated with solvent dielectric responses. Here, we use all-atom molecular dynamics simulations of the pure solvents to calculate dielectric constants and relaxation times, and molecular mobilities. The computed results are compared with limited available experiments to assist more exhaustive studies of these important characteristics. As a result, the observed agreement is encouraging and provides guidance for further validation of force-field simulation models for EC and PC solvents.

  20. Analysis of the dielectric relaxation during crystallization of glassy polymer PEKK

    NASA Astrophysics Data System (ADS)

    Dendzik, Zbigniew; Gburski, Zygmunt

    1997-06-01

    The dielectric (alpha) relaxation occurring during isothermal crystallization of a glassy polymer PEKK has been recently measured in real time as crystallization proceeds. We use these new experimental data and the SchOnhals-Schlosser model to interpretation of the dielectric loss line shape of PEKK during crystallization. Once the crystallization proceeds, the values of the intramolecular diffusional hindrance parameter (alpha) , slightly decrease. Relatively fast, internal diffusion along polymer chain becomes a bit more hindered as a result of environmental change creates by crystallization process. Contrary, the intermolecular correlation parameter (kappa) is very sensitive to the crystallization process.

  1. Study of dielectric relaxation at room temperature of the composite (100-x) LCMO/(x) BTO

    NASA Astrophysics Data System (ADS)

    Khan, Momin Hossain; Pal, Sudipta; Bose, Esa

    2013-02-01

    The frequency dependent complex impedance and dielectric behavior of (100-x) La0.7Ca0.3MnO3 (LCMO)/(x) BaTiO3 (BTO) has been investigated at room temperature (300K). Separate contributions from various factors such as bulk effect, grain boundary and interface effect have been established by fitting the cole-cole function of real and imaginary part of complex impedance. Dielectric data were well fitted in the frequency domain with modified Curie-Von Schweider (CS) functions. Both formalisms support a non-Debye relaxation process in the composites.

  2. Dielectric relaxation studies of methyl cellulose with phenol derivatives in non-polar solvents using time domain reflectometry

    NASA Astrophysics Data System (ADS)

    Mohan Kumar, P.; Malathi, M.; Khirade, P. W.

    2009-11-01

    Dielectric relaxation measurements of methyl cellulose with substituted phenols p-cresol, m-cresol and o-cresol mixture in different non-polar solvents CCl 4, benzene and 1,4-dioxan for different concentrations over the frequency range of 10 MHz-20 GHz at 303 K have been carried out using Time Domain Reflectometry (TDR). Dielectric parameters such as static permittivity ( ε0) and relaxation time ( τ) were determined and discussed to yield information on the molecular structure and dynamics of the mixture. The dielectric constant and relaxation time were found to be high for methyl cellulose with p-cresol in CCl 4 compared with the other mixtures.

  3. Effect of oxygen vacancy on the dielectric relaxation of BaTiO3 thin films in a quenched state

    NASA Astrophysics Data System (ADS)

    Yao, Sheng-Hong; Yuan, Jin-Kai; Gonon, Patrice; Bai, Jinbo; Pairis, Sébastien; Sylvestre, Alain

    2012-05-01

    A thermal treatment below the crystallization temperature followed by rapid cooling down was adopted onto as-deposited BaTiO3 (BTO) amorphous films to freeze the microstructure activated at annealed temperature. A large increase of dielectric constant from 19 to 329 was observed at 0.1 Hz for the BTO film annealed at 600 °C for 60 min. Subsequently, three separated dielectric relaxations were exploited as a function of the frequency and temperature. Such dielectric responses were analyzed in terms of the activation energy. The evolution of oxygen vacancy with temperature can be invoked as being responsible for the observed dielectric relaxations.

  4. Dielectric relaxation and resonance in relaxor ferroelectric K1-xLixTaO3

    NASA Astrophysics Data System (ADS)

    Pattnaik, R. K.; Toulouse, J.

    1999-09-01

    Polar regions are shown to mediate a strong coupling between polarization and strain in the paraelectric phase of the mixed ferroelectric K1-xLixTaO3 (KLT) and KTa1-xNbxO3 resulting in a field-induced piezoelectric response. The coupling is shown to result in a resonance in the dielectric spectrum of the crystals. In KLT, polar nanoregions can reorient via 180° (π relaxation) or 90° (π/2 relaxation) rotations. While the π relaxation is of no consequence, the π/2 relaxation has a strong influence on the overall character of the resonance. In addition to providing a mechanism for loss and degradation of the quality factor, this relaxation alters the character of the resonance as the two cross. Experimental results from dielectric spectroscopy above and below this crossover are presented and discussed. A simple theoretical Debye model involving the electrostrictive polarization-strain coupling is presented and the calculated spectrum is shown to reproduce the experimental spectrum. The parameters derived from the model are discussed. Most significantly, the electrostrictive coefficient of KLT is found to be 100 times larger than that of BaTiO3, and is due to the presence of polar nanoregions.

  5. Effects of pH on dielectric relaxation of montmorillonite, allophane, and imogolite suspensions

    SciTech Connect

    Ishida, Tomoyuki; Makino, Tomoyuki

    1999-04-01

    Dielectric measurements were performed on montmorillonite, allophane, and imogolite suspensions under various pH conditions, using time domain reflectometry over the frequency range 10 kHz--20 GHz. A dielectric relaxation peak due to bound water could be observed for all the clays. Allophane has two peaks, indicating that its peaks are very similar to those of silica-alumina gels. Although imogolite has a similar chemical composition, only one peak was found. The relaxation strength of montmorillonite is greater than that of the other two clays. For all the clays, the relaxation strength depended on the pH. A change in the relaxation strength according to a change in pH is explained in terms of the different network structures of the clay particles. It is suggested that bound water influences the network structure formation. In montmorillonite, a great relaxation process detected at low frequency is caused by surface polarization of counterions. The change in measure of the structural unit with the pH, identified from Schwartz`s theory, has a tendency similar to that postulated by other experimental techniques, and surface charge densities identified are close to those estimated from CEC.

  6. Influence of lanthanum doping on the dielectric, ferroelectric and relaxor behaviour of barium bismuth titanate ceramics

    NASA Astrophysics Data System (ADS)

    Kumar, Sunil; Varma, K. B. R.

    2009-04-01

    Barium lanthanum bismuth titanate (Ba1-(3/2)xLaxBi4Ti4O15, x = 0-0.4) ceramics were fabricated using the powders synthesized via the solid-state reaction route. X-ray powder diffraction analysis confirmed the above compositions to be monophasic and belonged to the m = 4 member of the Aurivillius family of oxides. The effect of the partial presence of La3+ on Ba2+ sites on the microstructure, dielectric and relaxor behaviour of BaBi4Ti4O15 (BBT) ceramics was investigated. For the compositions pertaining to x <= 0.1, the dielectric constant at both room temperature and in the vicinity of the temperature of the dielectric maximum (Tm) of the parent phase (BBT) increased significantly with an increase in x while Tm remained almost constant. Tm shifted towards lower temperatures accompanied by a decrease in the magnitude of the dielectric maximum (ɛm) with an increase in the lanthanum content (0.1 < x <= 0.4). The dielectric relaxation was modelled using the Vogel-Fulcher relation and a decrease in the activation energy for frequency dispersion with increasing x was observed. The frequency dispersion of Tm was found to decrease with an increase in lanthanum doping, and for compositions corresponding to x >= 0.3, Tm was frequency independent. Well-developed P(polarization)-E(electric field) hysteresis loops were observed at 150 °C for all the samples and the remanent polarization (2Pr) was improved from 6.3 µC cm-2 for pure BBT to 13.4 µC cm-2 for Ba0.7La0.2Bi4Ti4O15 ceramics. Dc conductivities and associated activation energies were evaluated using impedance spectroscopy.

  7. Ion transport and dielectric relaxation studies in nanocrystalline Ce 0.8Ho 0.2O 2-δ material

    NASA Astrophysics Data System (ADS)

    Baral, Ashok Kumar; Sankaranarayanan, V.

    2009-06-01

    The ac electrical conductivity and dielectric relaxation properties of nanocrystalline 20 mol% Ho doped ceria (Ce 0.8Ho 0.2O 2-δ) prepared by citrate auto ignition method, were studied in the temperature range 300-550 °C. The conductivity behaviour showed the absence of any precipitation of Ho inside the grains, even though it has the tendency of forming a C-type structure similar to Ho 2O 3 in association with oxygen vacancies. The frequency spectra of electric modulus M″ exhibits a single relaxation peak corresponding to relaxation reorientation of oxygen vacancy around the Ho +3 ions in the cubic nanostructured material. The migration of oxygen ions in the nanocrystalline Ce 0.8Ho 0.2O 2-δ material takes place through hopping and the migration energy and association energy of oxygen vacancies in the long range order motion are found to be 1.02 and 0.24 eV, respectively.

  8. Dielectric spectroscopy for probing the relaxation and charge transport in polypyrrole nanofibers

    NASA Astrophysics Data System (ADS)

    Banerjee, Somik; Kumar, A.

    2011-06-01

    Conductivity relaxation and charge transport mechanisms in polypyrrole (PPy) nanofibers synthesized using a micellar polymerization technique with varying surfactant concentration has been investigated by dielectric relaxation spectroscopy. TEM micrographs depict that the increasing surfactant concentration leads to the reduction of the nanofiber diameter. X-ray diffraction studies show that domain length in the PPy nanofibers decreases with decreasing fiber diameter whereas the strain caused due to dislocations and point defects increases. The permittivity spectra reveal that the relaxation mechanism in PPy nanofibers are dominated by hopping of trapped charges. Two relaxation peaks in the impedance spectra are attributed to the two-phase structure in the PPy nanofibers; the lower frequency peak is ascribed to the phase of oxidized repeat units and the higher frequency peak to the reduced repeat units of PPy nanofibers. The occurrence of relaxation peaks at different frequencies in the impedance and modulus spectra indicates a non-Debye relaxation with a wide distribution of relaxation times. The ac conductivity has been interpreted as a power law of frequency. The decrease of the parameter s with increasing temperature indicates that correlated barrier hopping is the dominant charge transport mechanism. Existence of polarons as major charge carriers has been confirmed by the low values of polaron binding energy.

  9. Dielectric relaxation study of binary mixture of sulfolane and N,N-dimethylformamide in benzene solution using microwave absorption data

    NASA Astrophysics Data System (ADS)

    Singh, Dalip; Thakur, Nagesh; Sharma, D. R.

    2012-12-01

    The dielectric constant (ɛ') and dielectric loss (ɛ″) for dilute solutions of the binary mixture of different molar concentrations of sulfolane and DMF in benzene solution has been measured at 9.885 GHz and different temperatures (25, 30, 35, 40°C) by using standard microwave techniques. Following the single frequency concentration variational method, the dielectric relaxation time (τ) and dipole moment (μ) have been calculated. It is found that dielectric relaxation process can be treated as the rate process, just like the viscous flow. The presence of solute-solute molecular associations in benzene solution has been proposed. Energy parameters (Δ H ɛ, Δ F ɛ, Δ S ɛ) for dielectric relaxation process of binary mixture at 50% mole fraction in benzene at 25, 30, 35, and 40°C have been calculated and compared with the corresponding energy parameters (Δ H η, Δ F η, Δ S η) for the viscous flow.

  10. High-frequency dielectric behaviour of erbium substituted Ni-Zn ferrites

    NASA Astrophysics Data System (ADS)

    Kumar, K. Vijaya; Reddy, A. Chandra Shekhar; Ravinder, D.

    2003-07-01

    Dielectric properties such as dielectric constant ( ɛ') and dielectric loss tangent (tan δ) of mixed Ni-Zn-Er ferrites have been measured at room temperature in the frequency range 1-13 MHz using a HP 4192A impedance analyser. Plots of dielectric constant ( ɛ') versus frequency show a normal dielectric behaviour of spinel ferrites. The frequency dependence of dielectric loss tangent (tan δ) is found to be abnormal, giving a peak at certain frequency for all mixed Ni-Zn-Er ferrites. A qualitative explanation is given for the composition and frequency dependence of the dielectric constant and dielectric loss tangent. Plot of dielectric constant versus temperature has shown a transition near the Curie temperature for all the samples of Ni-Zn-Er ferrites. On the basis of these results an explanation for the dielectric mechanism in Ni-Zn-Er ferrites is suggested.

  11. Dielectric Investigation of Parylene D Thin Films: Relaxation and Conduction Mechanisms.

    PubMed

    Mokni, M; Kahouli, A; Jomni, F; Garden, J-L; André, E; Sylvestre, A

    2015-09-01

    Parylene is a generic name indicating a family of polymers with the basic chemical structure of poly-p-xylylene. Parylene N and Parylene C are the most popular for applications. Curiously, Parylene D (poly( dichloro-p-xylylene), (C8H6Cl2)) was forgotten for applications. This report is the consequence of a later availability of a commercial dimer of Parylene D and also to the recent advent of fluorinated Parylenes allowing extending applications at higher temperatures. In our work, from a dielectric analysis, we present the potentialities of Parylene D for applications particularly interesting for integration in organic field-effect transistors. Dielectric and electrical properties, macromolecular structures, and dynamics interaction with electric field as a function of frequency and temperature are studied in 5.8 μm thick Parylene D grown by chemical vapor deposition. More exactly, the dielectric permittivity, the dissipation factor, the electrical conductivity, and the electric modulus of Parylene D were investigated in a wide temperature and frequency ranges from -140 to +350 °C and from 0.1 Hz to 1 MHz, respectively. According to the temperature dependence of the dielectric permittivity, Parylene D has two different dielectric responses. It is retained as a nonpolar material at very low temperature (like Parylene N) and as a polar material at high temperature (like parylene C). The dissipation factor shows the manifestation of two relaxations mechanisms: γ and β at very low and high temperatures, respectively. The γ relaxation is assigned to the local motions of the C-H end of the chains when the cryogenic temperature range is approached. A broad peak in tan δ is assigned to the β relaxation. It corresponds to rotational motion of some polar C-Cl groups. For temperature above 260 °C a mechanism of Maxwell-Wagner-Sillars polarization at the amorphous/crystalline interfaces was identified with two activation energies of Ea1 = 2.12 eV and Ea2 = 3.8 e

  12. Role of Cu additive on the dielectric relaxation of Se75Te25 and Se85Te15 glassy alloys

    NASA Astrophysics Data System (ADS)

    Sharma, J.; Kumar, S.

    2010-07-01

    The effect of Cu additive on the dielectric relaxation of two binary Se-Te glassy systems, comparing the properties of a-Se75Te25, a-Se85Te15 and a-Se75Te15Cu10 alloys has been reported. The temperature and frequency dependence of dielectric parameters in Glassy Se75Te25, Se85Te15 and Se75Te15Cu10 alloys are studied by measuring capacitance and dissipation factor in the frequency range (1 kHz-5 MHz) and temperature range (300-350 K). A Debye like relaxation of dielectric behavior has been observed. A comprehensive study on the relaxation mechanism revealed that the presence of grains and grain boundaries across the pallet thickness is the basic relaxation process. A detailed analysis shows that the observed dielectric loss is in agreement with the Guintini's theory of dielectric dispersion based on two electron hopping over a potential barrier and is applicable in the present case. Dielectric constant (ɛ’), dielectric loss (ɛ”), loss tangent (δ) and capacitive reactance (Xc) are found highly frequency and temperature dependent. Dependence of these dielectric parameters over the metallic impurity Cu, has also been found in the present glassy system and has been discussed in terms of electronegativity difference between the elements used in making the aforesaid glassy system.

  13. Probing the subglass relaxation behavior in model heterocyclic polymer networks by dielectric spectroscopy

    NASA Astrophysics Data System (ADS)

    Kramarenko, V. Yu.; Ezquerra, T. A.; Privalko, V. P.

    2001-11-01

    The subglass relaxation (β) in model heterocyclic polymer networks (HPNs) with a controlled ratio of trimerized mono- and diisocyanates was characterized by dielectric spectroscopy in the frequency domain. The β relaxation in the investigated HPNs follows the Arrhenius law with unusually low values of the preexponential factor (10-17<τβ0<10-15 s). However, little influence of the local environment, as characterized by the network density, on the apparent activation energies ΔEβ is observed. This fact, combined with their fairly low absolute values (50.4-58.3 kJ/mol), were considered as typical of a noncooperative relaxation in loosely packed regions of a glassy quasilattice. Both the intensity and dielectric strength of the β relaxation in HPNs increase with increasing apparent network density (i.e., with lower ratios of linear and network structures in the system, L/N). This effect was explained by a model assuming that the total, composition-invariant, free volume available was distributed between densely packed domains comprising linear, two-arm isocyanurate heterocycles (ISHs) and loosely packed, three-arm ISHs, which form continuous, three-dimensional network structures. The experimental data for HPNs confirm Ngai's correlation between the logarithm of the secondary β-relaxation time and the Kohlrausch-Williams-Watts stretching exponent for the primary α relaxation. It is suggested that the absence of conjugated bonds within isocyanurate heterocycles makes them sufficiently flexible to allow for specific conformational transitions, like the ``chair-boat-chair'' transition in the structurally similar cyclohexyl ring.

  14. Non-Debye dipoles and their relaxation dynamics for the description of dielectric spectra

    NASA Astrophysics Data System (ADS)

    Govindaraj, G.

    2016-05-01

    Non-Debye dipole idea is introduced in terms of Debye dipole for the description of relaxation polarization process and dielectric loss spectra. The dipoles ∑m=1n{G0,G,G 1, G 2} m are designated as dielectric dipole relaxors, associated with molecule, where G0 is Debye dipole moment, G=(1-gd)G0, G1=gdG0, G2=(2-gd)G0 are non-Debye dipole moments in terms of G0, the fraction gd lies 0relaxation functions are obtained for non-Debye dipole G1=G0-G and G2=G0+G. The fraction, 0dielectric loss spectra of glass-former glycerol [C3H5(OH)3]. The present model predicts the existence of two internal degrees of freedom of molecular motions in glycerol in terms of two Debye dipoles and corresponding non-Debye dipoles for structural relaxation. Both the non-Debye dipole relaxation contributes for dielectric loss and are identified as α relaxation time (τd)1 and secondary process β relaxation time (τd)2. The non-Debye dipole strength for α and β processes are (gd)1 and (gd)2 and they show a temperature dependence. Existence of non-Debye dipole process is established in various systems by compiling the loss data based on the proposed model.

  15. AC Conductivity and Dielectric Relaxation Behavior of Sb2S3 Bulk Material

    NASA Astrophysics Data System (ADS)

    Abd El-Rahman, K. F.; Darwish, A. A. A.; Qashou, Saleem I.; Hanafy, T. A.

    2016-04-01

    The Sb2S3 bulk material was used for next-generation anode for lithium-ion batteries. Alternative current (AC) conductivity, dielectric properties and electric modulus of Sb2S3 have been investigated. The measurements were carried out in the frequency range from 40 Hz to 5 MHz and temperature range from 293 K to 453 K. The direct current (DC) conductivity, σ DC, shows an activated behavior and the calculated activation energy is 0.50 eV. The AC conductivity, σ AC, was found to increase with the increase of temperature and frequency. The conduction mechanism of σ AC was controlled by the correlated barrier hopping model. The behavior of the dielectric constant, ɛ', and dielectric loss index, ɛ'', reveal that the polarization process of Sb2S3 is dipolar in nature. The behavior of both ɛ' and ɛ'' reveals that bulk Sb2S3 has no ferroelectric or piezoelectric phase transition. The dielectric modulus, M, gives a simple method for evaluating the activation energy of the dielectric relaxation. The calculated activation energy from M is 0.045 eV.

  16. AC Conductivity and Dielectric Relaxation Behavior of Sb2S3 Bulk Material

    NASA Astrophysics Data System (ADS)

    Abd El-Rahman, K. F.; Darwish, A. A. A.; Qashou, Saleem I.; Hanafy, T. A.

    2016-07-01

    The Sb2S3 bulk material was used for next-generation anode for lithium-ion batteries. Alternative current (AC) conductivity, dielectric properties and electric modulus of Sb2S3 have been investigated. The measurements were carried out in the frequency range from 40 Hz to 5 MHz and temperature range from 293 K to 453 K. The direct current (DC) conductivity, σ DC, shows an activated behavior and the calculated activation energy is 0.50 eV. The AC conductivity, σ AC, was found to increase with the increase of temperature and frequency. The conduction mechanism of σ AC was controlled by the correlated barrier hopping model. The behavior of the dielectric constant, ɛ', and dielectric loss index, ɛ'', reveal that the polarization process of Sb2S3 is dipolar in nature. The behavior of both ɛ' and ɛ'' reveals that bulk Sb2S3 has no ferroelectric or piezoelectric phase transition. The dielectric modulus, M, gives a simple method for evaluating the activation energy of the dielectric relaxation. The calculated activation energy from M is 0.045 eV.

  17. Rehydration of dehydrated CaFe-L(ayered)D(ouble)H(ydroxide) followed by thermogravimetry, X-ray diffractometry and dielectric relaxation spectroscopy

    NASA Astrophysics Data System (ADS)

    Bugris, V.; Haspel, H.; Kukovecz, Á.; Kónya, Z.; Sipiczki, M.; Sipos, P.; Pálinkó, I.

    2013-07-01

    In this contribution the rehydration process of a dehydrated CaFe-LDH is described with the combination of thermogravimetric (TG), X-ray diffraction (XRD) and dielectric relaxation spectroscopic (DRS) measurements. Dehydration was followed by TG and the major steps were identified. For studying the rehydration procedure the dehydrated samples were treated in the 6-97% relative humidity range at several preset vapour contents at 298 K. For equilibration 72 h were allowed. Then, the XRD diffractograms and the DRS spectra were registered and the thermal behaviour of the partially rehydrated samples was also studied. From these measurements the various forms of water molecules interacting with the LDH were deduced and their relaxation behaviour in the rehydration procedure is described.

  18. Dielectric relaxations of polyether-based polyurethanes containing ionic liquids as antistatic agents.

    PubMed

    Tsurumaki, Akiko; Bertasi, Federico; Vezzù, Keti; Negro, Enrico; Di Noto, Vito; Ohno, Hiroyuki

    2016-01-28

    Dielectric properties of polyurethanes containing poly(propylene oxide) (PO) and poly(ethylene oxide) (EO) units are discussed, along with the results of direct current (DC) measurements and broadband electrical spectroscopy (BES) studies. The dielectric properties of polyether-containing polyurethanes (PUs) are compared to those of PUs containing 1000 ppm of ionic liquids (ILs) as antistatic agents. The effects of the chemical environment of these ILs, including anion-fixed polymers (PU-AF), cation-fixed polymers (PU-CF), and a simple mixture of IL with the PUs (PU-IL), are compared and discussed on the basis of ion mobility. DC measurements suggest that the charge current is attributed not only to the electrode polarization but also to continuous dielectric relaxation. BES studies elucidate that both fast and slow relaxations are taking place in EO-rich domains in pristine PU and PU-AF. The activation energies of the slow relaxation and of the ionic conductivity are similar, suggesting that the ionic conductivity of these materials is attributed to the ion exchange reaction in EO/ion complexes. In contrast, only fast relaxations are observed in the domains mostly comprised of ion-depleted EO in the PUs containing "free" anions, i.e., PU-CF and PU-IL. This suggests that [Tf2N](-) ligands are weakly interacting with the EO chains and contribute effectively to the ion conduction. Thus, enhanced ionic conductivity is observed in PU-CF and PU-IL, yielding sufficient antistatic effects. Taking into account its long shelf life, arising from the lack of IL bleed-out, PU-CF is concluded to be the most promising candidate. PMID:26700822

  19. Ray Tracing to Predict Optical Behaviour of Shock Compressed Dielectrics

    NASA Astrophysics Data System (ADS)

    Tear, Gareth R.; Proud, William G.

    2015-06-01

    In order to investigate the optical response of dielectric materials under shock compression, a characteristics model has been combined with a three dimensional optical ray tracing model. A general biaxial optical model is used along with a first order photoelastic model which couples the characteristics component to the optical component. This optical model is three dimensional and as such can be used to investigate small deviations from the perfect one dimensional shock wave which is typically assumed in plate impact experiments. A detailed description of the model will be presented, and comparison to available literature as well as recent experiments on the optical behaviour of shock compressed a-cut calcite and a-cut sapphire. The authors would like to thank Dr D E Eakins and Dr D J Chapman for fruitful discussions. The Institute of Shock Physics acknowledges the continued support of AWE and Imperial College London.

  20. On the nonlinear variation of dc conductivity with dielectric relaxation time

    NASA Astrophysics Data System (ADS)

    Johari, G. P.; Andersson, Ove

    2006-09-01

    The long-known observations that dc conductivity σdc of an ultraviscous liquid varies nonlinearly with the dielectric relaxation time τ, and the slope of the logσdc against logτ plot deviates from -1 are currently seen as two of the violations of the Debye-Stokes-Einstein equation. Here we provide a formalism using a zeroth order Bjerrum description for ion association to show that in addition to its variation with temperature T and pressure P, impurity ion population varies with a liquid's equilibrium dielectric permittivity. Inclusion of this electrostatic effect modifies the Debye-Stokes-Einstein equation to log(σdcτ )=constant+logα, where α is the T and P-dependent degree of ionic dissociation of an electrolytic impurity. Variation of a liquid's shear modulus with T and P would add to the nonlinearity of σdc-τ relation, as would a nonequivalence of the shear and dielectric relaxation times, proton transfer along the hydrogen bonds, or occurrence of another chemical process. This is illustrated by using the data for ultraviscous acetaminophen-aspirin liquid.

  1. Effect of organo-clay on the dielectric relaxation response of silicone rubber

    NASA Astrophysics Data System (ADS)

    Gharavi, N.; Razzaghi-Kashani, M.; Golshan-Ebrahimi, N.

    2010-02-01

    Dielectric elastomers are light weight, low-cost, highly deformable and fast response smart materials capable of converting electrical energy into mechanical work or vice versa. Silicone rubber is a well-known dielectric elastomer which is used as actuator, and in order to enhance the efficiency of this smart material, compounding of silicone rubber with various fillers can be carried out. The effect of organically modified montmorillonite (OMMT) nano-clay on improvement of dielectric properties, actuation stress and its relaxation response was considered in this study. OMMT was dispersed in room temperature vulcanized (RTV) silicone rubber, and a composite film was cast. Using an in-house actuation set-up, it was shown that the actuation stress for a given electric field intensity is higher for composites than that for pristine silicone rubber. Also, the time-dependent actuation response of the samples was evaluated, and it was shown that the characteristic relaxation time of the actuation stress for composites is less than for the pristine rubber as a result of OMMT addition.

  2. Some physical chemical concepts relevant to coal science. [Dielectric relaxation studies of water present in coals

    SciTech Connect

    Neumann, R.M.

    1984-09-01

    This report discusses approaches to understanding certain physical and physical chemical properties of low-rank coals from a molecular perspective. Dielectric relaxation measurements are described which have identified two distinct modes of water incorporation in lignite. The theoretical aspects of dielectric relaxation are presented along with the experimental details. The need for performing vapor pressure measurements on lignite-water vapor equilibrium systems is examined. In recent years, many researchers have attempted to understand the macromolecular network in coal by means of techniques useful for studying bulk polymers. Here, the underlying theoretical ideas are presented for dynamic mechanical relaxation and rubber elasticity. Researchers have drawn inferences, from the measurement of viscoelastic properties of coals, about the molecular nature of the crosslinking in the organic network. Their conclusions are critically examined and suggestions are made as to how the experimental procedures might be improved. The interpretation of the temperature dependence of slag viscosity is a particularly vexing problem. Here, it is suggested that the theoretical methods used to describe the viscosity of molten glasses may be useful as a point of departure in characterizing slag viscosities. Finally, a brief outline of the Hildebrand theory of liquid-liquid miscibility is presented; the ideas relevent to understanding supercritical solvent extraction of coals in terms of the Hildebrand solubility parameter are discussed. 28 references, 22 figures.

  3. Dielectric relaxation time of bulk water at 136-140 K, background loss and crystallization effects

    NASA Astrophysics Data System (ADS)

    Johari, G. P.

    2005-04-01

    Dielectric relaxation time, τ, of ultraviscous bulk water has been determined by analyzing its loss tangent, tanδ, data, which had been measured on heating the vapor-deposited amorphous solid water and hyperquenched glassy water in our earlier studies. [Johari, Hallbrucker, and Mayer, J. Chem. Phys. 95, 2955 (1991); 97, 5851 (1992)]. As for glasses and liquids generally, the measured tanδ of water is the sum of a frequency-independent background loss and a frequency-dependent relaxational loss. A two-frequency method is provided for determining the background loss and used for obtaining the relaxational part of tanδ. After considering the structural relaxation and crystal-nuclei growth effects, τ for water has been determined. At 136±1K, it is 2.5±0.6s when a single relaxation time is (untenably) assumed, and 42±14s when a distribution of relaxation times, a characteristic of viscous liquids, is assumed, with Davidson-Cole distribution parameter of 0.75. Structural relaxation time of ˜70s for water at 136K, which was originally estimated from the DSC endotherm [Johari, Hallbrucker, and Mayer, Nature (London) 330, 552 (1987)], has been revised to ˜33s. Temperature dependence of τ could not be determined because ultraviscous water crystallizes too rapidly to cubic ice containing stacking faults and intergranular water. The study demonstrates that water is a liquid over the 136-155K range, thus removing the basis for a recent contention on its state.

  4. Temperature dependence anomalous dielectric relaxation in Co doped ZnO nanoparticles

    SciTech Connect

    Ansari, Sajid Ali; Nisar, Ambreen; Fatma, Bushara; Khan, Wasi; Chaman, M.; Azam, Ameer; Naqvi, A.H.

    2012-12-15

    Graphical abstract: Display Omitted Highlights: ► We prepared Co doped ZnO by facile gel-combustion method. ► Studied temperature dependent dielectric properties in detail. ► Relaxation time shifts toward the higher temperature as increase in Co content. ► SEM analysis shows formation and agglomeration of nanoparticles. ► Dielectric constants, loss and ac conductivity increases with rise in temperature. ► The dielectric constant, loss and ac conductivity decreases as Co ion increases. -- Abstract: We have reported temperature and frequency dependence of dielectric behavior of nanocrystalline Zn{sub 1−x}Co{sub x}O (x = 0.0, 0.01, 0.05 and 0.1) samples prepared by gel-combustion method. The synthesized samples were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM) and LCR-meter, respectively. The XRD analysis reveals that ZnO has a hexagonal (wurtzite) crystal structure. The morphology and size of the nanoparticles (∼10–25 nm) were observed by SEM for 5% Co doped ZnO sample. In dielectric properties, complex permittivity (ε{sup *} = ε′ − jε″), loss tangent (tan δ) and ac conductivity (σ{sub ac}) in the frequency range 75 kHz to 5 MHz were analyzed with temperature range 150–400 °C. The experimental results indicate that ε′, ε″, tan δ and σ{sub ac} decreases with increase in frequency and temperature. The transition temperature as obtained in dispersion curve of dielectric constant shifts toward higher temperature with increase Co content.

  5. Dielectric relaxation in ytterbium- and lead-doped calcium fluoride crystals

    NASA Astrophysics Data System (ADS)

    Stef, Marius; Nicoara, Irina; Stef, Florica

    2013-04-01

    YbF3-doped and 1 mol% PbF2 co-doped CaF2 crystals were grown by vertical Bridgman method using a shaped graphite furnace in vacuum. Dielectric spectra and optical absorption spectra were measured in order to study the influence of Pb2+ ions on the charge compensating defects formation. The influence of Pb2+ ions on the various charge compensating defects depend on the YbF3 concentration. For low YbF3 concentrations the influence is stronger than for concentrations higher than 1 mol% YbF3. Dielectric relaxation in double doped (Yb,Pb):CaF2 crystals in order the study the charge compensating defects formation was not reported before.

  6. Extended dielectric relaxation scheme for fluid transport simulations of high density plasma discharges

    NASA Astrophysics Data System (ADS)

    Kwon, Deuk-Chul; Song, Mi-Young; Yoon, Jung-Sik

    2014-10-01

    It is well known that the dielectric relaxation scheme (DRS) can efficiently overcome the limitation on the simulation time step for fluid transport simulations of high density plasma discharges. By imitating a realistic and physical shielding process of electric field perturbation, the DRS overcomes the dielectric limitation on time step. However, the electric field was obtained with assuming the drift-diffusion approximation. Although the drift-diffusion expressions are good approximations for both the electrons and ions at high pressure, the inertial term cannot be neglected in the ion momentum equation for low pressure. Therefore, in this work, we developed the extended DRS by introducing an effective electric field. To compare the extended DRS with the previous method, two-dimensional fluid simulations for inductively coupled plasma discharges were performed. This work was supported by the Industrial Strategic Technology Development Program (10041637, Development of Dry Etch System for 10 nm class SADP Process) funded by the Ministry of Knowledge Economy (MKE, Korea).

  7. Dielectric and relaxation properties of poly(o-anisidine)/graphene nanocomposite

    NASA Astrophysics Data System (ADS)

    Sangamithirai, D.; Narayanan, V.; Stephen, A.

    2016-05-01

    Poly(o-anisidine)/graphene (POA/GR) nanocomposite was synthesized via chemical oxidative polymerization of o-anisidine in the presence of graphene sheets in acidic medium. The electrical properties of the nanocomposite are studied using AC impedance spectroscopic technique. It has been found that the room temperature electrical conductivity value enhanced from 1.28 × 10-6 S cm-1 to 4.47 × 10-4 S cm-1 on addition of 10 wt % of graphene into the polymer. An analysis of real and imaginary parts of dielectric permittivity reveals that both ɛ` and ɛ״ increases with the decrease of frequency at all temperature levels. Frequency dependence of dielectric loss (tan δ) spectrum indicates that hopping frequency increases with temperature and the relaxation time decreases from 2.67 × 10-5 to 7.28 × 10-6 sec.

  8. Low temperature dielectric and conductivity relaxation studies on magnetoelectric Pb(Fe2/3W1/3)O3

    NASA Astrophysics Data System (ADS)

    Matteppanavar, Shidaling; Shivaraja, I.; Rayaprol, Sudhindra; Angadi, Basavaraj

    2016-05-01

    The single phase perovskite Pb(Fe2/3W1/3)O3 [PFW] was synthesized by modified low - temperature (sintering at 850°C) solid-state reaction. Rietveld refinement ofroom temperature (RT) X-ray diffraction (XRD) and neutron diffraction (ND) patterns of the samples confirm the single phase formation with cubic structure (Pm-3m). Surface morphology of the compounds was studied by Scanning electron microscope (SEM) and average grain size was estimated to be ˜2 µm. The RT dielectric properties of PFW ceramic are studied as a function of frequency from 100 - 1MHz. The temperature dependent (120 - 293K) dielectric properties were studied at few selected frequencies. We found the frequency dependent dielectric constant shows increasing trend with increase in temperature from 120 - 293K, with minimum dielectric loss. The frequency dependence of dielectric loss shows a maximum in between 10 Hz and 1 kHz, confirms the extrinsic phenomena like interfacial polarization due to space charge accumulation at grain boundaries. Impedance spectroscopy is used to study the electrical behaviour of PFW in the frequency range from 100 to 1MHz and in the temperature range from 120 - 293 K. The frequency-dependent electrical data are analysed by impedance formalisms and shows the relaxation (conduction) mechanism in the sample. We suggest this low temperature sintered PFW is a suitable candidate for the multilayer ceramic capacitorsandrelated negative temperature coefficient of resistance type (NTCR) behavior like that of semiconductors.

  9. Dielectric relaxation behavior of poly(acrylonitri1e-co-methacrylonitrile) microcapsules dispersed in a silicone matrix

    NASA Technical Reports Server (NTRS)

    Park, Taigyoo; O'Brien, Emmett; Lizotte, Jeremy R.; Glass, Thomas E.; Ward, Thomas C.; Long, Timothy E.; Leo, Donald J.

    2006-01-01

    The dielectric relaxation behavior of poly(acry1onitrile-co-methacrylonitrile) dispersed in a cured polydimethyl siloxane (PDMS) matrix as microcapsules was investigated over multiple thermal cycles and at varying concentrations. The copolymer microcapsules contained an isopentane core. In the PDMS matrix this copolymer displayed a pronounced relaxation signal at temperatures above the glass transition of the copolymers due to Maxwell-Wagner-Sillars (MWS) relaxation. The mechanism of MWS relaxation interpreted by the Havriliak-Negami and Kohlrausch-Williams-Watts relaxation functions was found to be very similar to previous studies of neat polyacrylonitrile and its copolymer. The activation energy of the relaxation decreased over successive thermal cycling coincident with a decreasing strength of the relaxation. These observations were attributed to the decreasing concentration of nitrile groups due to intramolecular cyclizations.

  10. Studies of structural, optical, dielectric relaxation and ac conductivity of different alkylbenzenesulfonic acids doped polypyrrole nanofibers

    NASA Astrophysics Data System (ADS)

    Hazarika, J.; Kumar, A.

    2016-01-01

    Polypyrrole (PPy) nanofibers doped with alkylbenzenesulfonic acids (ABSA) have been synthesized using interfacial polymerization method. HRTEM studies confirm the formation of PPy nanofibers with average diameter ranging from 13 nm to 25 nm. Broad X-ray diffraction peak in 2 θ range 20-23.46° reveals amorphous structure of PPy nanofibers. The ordering or crystallinity of polymer chains increases, while their interplanar spacing (d) and interchain separation (R) decreases for short alkyl chain ABSA doped PPy nanofibers. FTIR studies reveal that short alkyl chain ABSA doped PPy nanofibers show higher value of "effective conjugation length". PPy nanofibers doped with short alkyl chain ABSA dopant exhibit smaller optical band gap. TGA studies show enhanced thermal stability of short alkyl chain ABSA doped PPy nanofibers. Decrease in dielectric permittivity ε ‧ (ω) with increasing frequency suggests presence of electrode polarization effects. Linear decrease in dielectric loss ε ″ (ω) with increasing frequency suggests dominant effect of dc conductivity process. Low value of non-exponential exponent β (<1) reveals non-Debye relaxation of charge carriers. Scaling of imaginary modulus (M ″) reveals that the charge carriers follow the same relaxation mechanism. Moreover, the charge carriers in PPy nanofibers follow the correlated barrier hopping (CBH) transport mechanism.

  11. Effect of magnesium ions on dielectric relaxation in semidilute DNA aqueous solutions

    NASA Astrophysics Data System (ADS)

    Grgičin, D.; Dolanski Babić, S.; Ivek, T.; Tomić, S.; Podgornik, R.

    2013-11-01

    The effect of magnesium ion Mg2+ on the dielectric relaxation of semidilute DNA aqueous solutions has been studied by means of dielectric spectroscopy in the 100 Hz-100 MHz frequency range. de Gennes-Pfeuty-Dobrynin semidilute solution correlation length is the pertinent fundamental length scale for sufficiently low concentration of added salt, describing the collective properties of Mg-DNA solutions. No relaxation fingerprint of the DNA denaturation bubbles, leading to exposed hydrophobic core scaling, was detected at low DNA concentrations, thus indicating an increased stability of the double-stranded conformation in Mg-DNA solutions as compared to the case of Na-DNA solutions. Some changes are detected in the behavior of the fundamental length scale pertaining to the single molecule DNA properties, reflecting modified electrostatic screening effects of the Odijk-Skolnick-Fixman type. All results consistently demonstrate that Mg2+ ions interact with DNA in a similar way as Na1+ ions do, their effect being mostly describable through an enhanced screening.

  12. Optically activated sub-millimeter dielectric relaxation in amorphous thin film silicon at room temperature

    SciTech Connect

    Rahman, Rezwanur; Ohno, Tim R.; Taylor, P. C.; Scales, John A.

    2014-05-05

    Knowing the frequency-dependent photo-induced complex conductivity of thin films is useful in the design of photovoltaics and other semi-conductor devices. For example, annealing in the far-infrared could in principle be tailored to the specific dielectric properties of a particular sample. The frequency dependence of the conductivity (whether dark or photo-induced) also gives insight into the effective dimensionality of thin films (via the phonon density of states) as well as the presence (or absence) of free carriers, dopants, defects, etc. Ultimately, our goal is to make low-noise, phase-sensitive room temperature measurements of the frequency-dependent conductivity of thin films from microwave frequencies into the far-infrared; covering, the frequency range from ionic and dipole relaxation to atomic and electronic processes. To this end, we have developed a high-Q (quality factor) open cavity resonator capable of resolving the complex conductivity of sub-micron films in the range of 100–350 GHz (0.1–0.35 THz, or 0.4–1 meV). In this paper, we use a low-power green laser to excite bound charges in high-resistivity amorphous silicon thin film. Even at room temperature, we can resolve both the dark conductivity and photo-induced changes associated with dielectric relaxation and possibly some small portion of free carriers.

  13. Dielectric relaxation and alternating current conductivity of lanthanum, gadolinium, and erbium-polyvinyl alcohol doped films

    NASA Astrophysics Data System (ADS)

    Hanafy, Taha A.

    2012-08-01

    Fourier transform infrared (FTIR) spectrum dielectric constant, ɛ', loss tangent, tan(δ), electric modulus, M*, and ac conductivity, σac, of pure polyvinyl alcohol (PVA) as well as La-, Gd-, and Er-PVA doped samples have been carried out. The dielectric properties have been studied in the temperature and frequency ranges; 300-450 K and 1 kHz-4 MHz, respectively. FTIR measurements reveal that La3+, Gd3+, and Er3+ ions form complex configuration within PVA structure. Two relaxation processes, namely, ρ and α were observed in pure PVA sample. The first process is due to the interfacial or Maxwell-Wagner-Sillers polarization. The second one is related to the micro-Brownian motion of the main chains. For doped PVA samples, α-relaxation process splits into αa and αc. This splitting is due to the segmental motion in the amorphous (αa) and crystalline (αc) phases of PVA matrix. Electric modulus analysis was discussed to understand the mechanism of the electrical transport process. The behavior of ac conductivity for all PVA samples indicates that the conduction mechanism is correlated barrier hopping.

  14. State of water in starch-water systems in the gelatinization temperature range as investigated using dielectric relaxation spectroscopy

    NASA Astrophysics Data System (ADS)

    Motwani, Tanuj

    Starch-water interactions occurring during gelatinization are critical for developing a mechanistic understanding of the gelatinization process. The overall goal of this project was to investigate the state of water in starch-water systems in the gelatinization temperature range using dielectric relaxation spectroscopy. In the first part of the project, the dielectric response of native wheat starch-water slurries was measured at seven different starch concentrations between 5--60% starch (w/w) in the frequency range of 200 MHz--20 GHz at 25°C. The deconvolution of the dielectric spectra using the Debye model revealed presence of up to three relaxation processes. The relaxation time range of what were considered to be the high, intermediate and low frequency relaxations were 4--9 ps, 20--25 ps and 230--620 ps, respectively. The high frequency relaxation was observed at all starch concentrations, while the intermediate and low frequency relaxation were only observed at starch concentrations of 10% and above, and 30% and above, respectively. The high frequency relaxation was attributed to bulk water, while the intermediate and low frequency relaxations were attributed to rotationally restrained water molecules present in the starch-water system. To investigate the state of water in the gelatinization temperature range, the dielectric response, gelatinization enthalpy and water absorption by 10%, 30% or 50% starch slurries were measured after heating the slurries to different end temperatures between 40--90°C for 30 min. The high frequency relaxation time for 10% starch slurry dropped significantly (P<0.001) upon heating up to 60°C. For 30% and 50% starch slurries, high frequency relaxation times were not significantly influenced (P>0.159) by heating up to 80°C. The intermediate and low frequency relaxation times were not significantly influenced (P>0.712) by heating for all starch concentrations. Also, the amount of water associated with the three relaxations was

  15. Low frequency ac conduction and dielectric relaxation in pristine poly(3-octylthiophene) films

    NASA Astrophysics Data System (ADS)

    Singh, Ramadhar; Kumar, Jitendra; Singh, Rajiv K.; Rastogi, Ramesh C.; Kumar, Vikram

    2007-02-01

    The ac conductivity σ(ω)m, dielectric constant ɛ'(ω) and loss ɛ''(ω) of pristine poly(3-octylthiophene) (P3OT) films (thickness ~ 20 μm) have been measured in wide temperature (77 350 K) and frequency (100 Hz 10 MHz) ranges. At low temperatures, σ(ω)m can be described by the relation σ(ω)m = Aωs, where s is ~ 0.61 at 77 K and decreases with increasing temperature. A clear Debye-type loss peak is observed by subtracting the contribution of σdc from σ(ω)m. The frequency dependence of conductivity indicates that there is a distribution of relaxation times. This is confirmed by measurement of the dielectric constant as a function of frequency and temperature. Reasonable estimates of various electrical parameters such as effective dielectric constant (ɛp), phonon frequency (νph), Debye temperature (θD), polaron radius (rp), small-polaron coupling constant (\\Upsilon ), effective polaron mass (mp), the density of states at the Fermi level N(EF), average hopping distance (R) and average hopping energy (W) from dc conductivity measurements suggest the applicability of Mott's variable range hopping model in this system.

  16. Comment on ``Study of dielectric relaxations of anhydrous trehalose and maltose glasses'' [J. Chem. Phys. 134, 014508 (2011)

    NASA Astrophysics Data System (ADS)

    Kaminski, K.; Wlodarczyk, P.; Paluch, M.

    2011-10-01

    Very recently Kwon et al. [H.-J. Kwon, J.-A. Seo, H. K. Kim, and Y. H. Hwang, J. Chem. Phys. 134, 014508 (2011)] published an article on the study of dielectric relaxation in trehalose and maltose glasses. They carried out broadband dielectric measurements at very wide range of temperatures covering supercooled liquid as well as glassy state of both saccharides. It is worth to mention that authors have also applied a new method for obtaining anhydrous glasses of trehalose and maltose that enables avoiding their caramelization. Four relaxation processes were identified in dielectric spectra of both saccharides. The slower one was identified as structural relaxation process the next one, not observed by the others, was assigned as Johari-Goldstein (JG) β-relaxation, while the last two secondary modes were of the same nature as found by Kaminski et al. [K. Kaminski, E. Kaminska, P. Wlodarczyk, S. Pawlus, D. Kimla, A. Kasprzycka, M. Paluch, J. Ziolo, W. Szeja, and K. L. Ngai, J. Phys. Chem. B 112, 12816 (2008)]. In this comment we show that the authors mistakenly assigned the slowest relaxation process as structural mode of disaccharides. We have proven that this relaxation process is an effect of formation of thin layer of air or water between plate of capacitor and sample. The same effect can be observed if plates of capacitor are oxidized. Thus, we concluded that their slowest mode is connected to the dc conduction process while their β JG process is primary relaxation of trehalose and maltose.

  17. Dielectric and conducting behaviour of polycrystalline holmium octa-molybdate

    NASA Astrophysics Data System (ADS)

    Want, Basharat; Zahoor Ahmad, Bhat; Bhat, Bilal Hamid

    2014-09-01

    Polycrystalline holmium octa-molybdate spherulites have been obtained by using gel diffusion technique and characterized by different physio-chemical techniques. The surfaces of these spherulites are composed of nano-rod with an average diameter of about 80 nm. At room temperature the initial crystal structure is triclinic, space group P1. Thermal studies suggested a phase transition occurring in holmium octa-molybdate crystals at about 793 K. The electrical properties of the system have been studied as a function of frequency and temperature in the ranges of 20 Hz-3 MHz and 290-570 K, respectively. A giant dielectric constant and two loss peaks have been observed in the permittivity formalism. The conducting behaviour of the material is also discussed. The conductivity was found to be 1572 μ Ω-1 m-1 at room temperature and 3 MHz frequency. The conductivity of the polycrystalline material was attributed to the fact that it arises due to the migration of defects on the oxygen sub-lattice. Impedance studies were also performed in the frequency domain to infer the bulk and grain boundary contributions to the overall electric response of the material. The electrical responses have been attributed to the grain, grain-boundary, and interfacial effects.

  18. Dielectric relaxation study of the dynamics of monosaccharides: D-ribose and 2-deoxy-D-ribose

    NASA Astrophysics Data System (ADS)

    Kaminski, K.; Kaminska, E.; Wlodarczyk, P.; Paluch, M.; Ziolo, J.; Ngai, K. L.

    2008-08-01

    The dielectric loss spectra of two closely related monosaccharides, D-ribose and 2-deoxy-D-ribose, measured at ambient and elevated pressures are presented. 2-deoxy-D-ribose and D-ribose are respectively the building blocks of the backbone chains in the nucleic acids DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). Small differences in the structure between D-ribose and 2-deoxy-D-ribose result in changes of the glass transition temperature Tg, as well as the dielectric strength and activation enthalpy of the secondary relaxations. However, the frequency dispersion of the structural α-relaxation for the same relaxation time remains practically the same. Two secondary relaxations are present in both sugars. The slower secondary relaxation shifts to lower frequencies with increasing applied pressure, but not the faster one. This pressure dependence indicates that the slower secondary relaxation is the important and 'universal' Johari-Goldstein β-relaxation of both sugars according to one of the criteria set up to classify secondary relaxations. Additional confirmation of this conclusion comes from good agreement of the observed relaxation time of the slower secondary relaxation with the primitive relaxation time calculated from the coupling model. All the dynamic properties of D-ribose and 2-deoxy-D-ribose are similar to the other monosaccharides, glucose, fructose, galactose and sorbose, except for the much larger relaxation strength of the α-relaxation of the former compared to the latter. The difference may distinguish the chemical and biological functions of D-ribose and 2-deoxy-D-ribose from the other monosaccharides.

  19. Mechanism of the typical relaxation process at low frequency based on dielectric measurements of water absorbed in porous titanium dioxide

    NASA Astrophysics Data System (ADS)

    Gao, Xin; Wang, Qiang; Sun, Gang; Li, Chenxi; Hu, Lin

    2016-02-01

    Dielectric spectroscopy is a valuable tool in physics, chemistry, biophysics, and materials science. However, there is still an argument about the typical relaxation process at low frequency, which is always masked by electrode polarization. Low-frequency dielectric measurements of water absorbed in porous titanium dioxide have been performed. The experimental results show that typical polarization at low frequency is caused by space-charge polarization. A model is proposed to explain the experimental results, which indicates that the electric field in the sample is close to 0. An effective circuit is given, and the calculation gives similar dielectric spectra to those measured in experiments, which confirms the physical model.

  20. State of water in perfluorosulfonic acid membranes studied by microwave dielectric relaxation spectroscopy

    NASA Astrophysics Data System (ADS)

    Lu, Zijie

    The physical state of water in perfluosulfonic acid membranes (e.g., Nafion 117 and Flemion SH150) has been studied by the water sorption isotherms, DSC, 2H NMR, and microwave dielectric relaxation spectroscopy. Different water states have been discriminated in these membranes: (1) the first few water molecules upon absorption from water vapor (lambda ˜ 3, where lambda denotes the number of water molecules per sulfonic acid group) are tightly bound to the sulfonic acid group to form the first hydration water; (2) beyond this water content, water molecules form the second hydration layer of the sulfonic acid group. The amount of this water increases with water content, but reaches a constant value at higher water contents. The microwave DRS measurements showed a relaxation time of about 30 ps for this type of water; (3) the free water, locating at the center of the ion cluster regions where the ion-water interaction is negligible, is present when lambda ≥ 6. The free water, with relaxation time tau ≈ 8 ps at 25°C, shows the characteristic dynamics of bulk water; and (4) finally, as water content increases further, water molecules start to be associated with the perfluorinated side chains and even with the fluorocarbon backbone. A much longer relaxation time, tau ≈ 90 ps, is observed for this part of water due to the hydrophobic confinement by the polymer. Microwave DRS measurements showed markedly different dynamics, i.e., negligible activation enthalpy and large negative activation entropy, for the dielectric relaxation of this type of water. The presence of the hydrophobically confined water is found to correspond to the clustering of water and to the appearance of the freezing water in these membranes. The equivalent weight (EW) of the PSA membrane has been found to have considerable influence on the dielectric response of the membranes. Flemion SH150, which has an EW value of 909, shows higher static permittivity than Nafion 117, which has an EW of 1100

  1. A new application of the nonlinear dielectric method for studying relaxation processes in liquids

    NASA Astrophysics Data System (ADS)

    Górny, M.; Ziolo, J.; Rzoska, S. J.

    1996-12-01

    The measurement setup for studying changes of electric permittivity induced in liquids by a strong electric field nonlinear dielectric effect, (NDE) is presented. The construction is based on the idea of frequency modulation of an LC generator (with an inductance L and a capacitance C in resonant circuit), proposed by Malecki [J. Chem. Soc. Faraday Trans. II 72, 104 (1976)]. The strong electric field is applied in the form of rectangular pulses (typically 1-4 ms). The setup enables measurements in a broad range of frequencies (80 kHz-12 MHz) and contains a new calibrating system, minimizing the influence of systematic error on the measured NDE values. We also indicate menthol as a standard, reference liquid in NDE studies. New applications of the NDE technique for studying relaxation processes in critical solution are also presented. They are based on the time resolved analysis of NDE decay after switching off the strong electric field.

  2. Confined liquid crystaline 5CB in 2D Thermodynamic Space - Preliminary Dielectric Relaxation Study

    NASA Astrophysics Data System (ADS)

    Pawlus, S.; Osinska, J.; Rzoska, S. J.; Kralj, S.; Cordoyiannis, G.

    Results of preliminary broadband dielectric spectroscopy studies in a wide range of temperatures and pressures range for a mixture of rod-like liquid crystalline 4-cyano-4-pentylalkylbiphenyl (5CB) and hydrophilic silica spheres (Aerosil 300) are shown. Pretransitional anomaly, observed previously in the bulk 5CB, has been found. Temperature dynamics of the mixture was investigated with via the DC conductivity σ, coupled to the reorientational relaxation. The derivative based analysis of electric conductivity showed a clear non-Arrhenius dynamics and indicated the anomalous increase of the fragility strength coefficient on approaching the isotropic-nematic transition. Pressure investigations of the solidification from the nematic phase showed the increase of the transition temperature on pressuring but with unusual increasing of dT NS /dP coefficient.

  3. The role of temperature on dielectric relaxation and conductivity mechanism of dark conglomerate liquid crystal phase

    NASA Astrophysics Data System (ADS)

    Yildiz, Alptekin; Canli, Nimet Yilmaz; Özdemir, Zeynep Güven; Ocak, Hale; Eran, Belkız Bilgin; Okutan, Mustafa

    2016-03-01

    In this study, dielectric properties and ac conductivity mechanism of the bent-core liquid crystal 3‧-{4-[4-(3,7-Dimethyloctyloxy)benzoyloxy]benzoyloxy}-4-{4-[4-[6-(1,1,3,3,5,5,5-heptamethyltrisiloxan-1yl)hex-1-yloxy]benzoyloxy]benzoyloxy}biphenyl (DBB) have been analyzed by impedance spectroscopy measurements at different temperatures. According to the polarizing microscopy results, DBB liquid crystal compound exhibits a dark conglomerate mesophase (DC[*] phase) which can be identified by the occurrence of a conglomerate of domains with opposite chirality. The chiral domains of this low-birefringent mesophase become more visible by rotating the polarizer. The variation of the real (ε‧) and imaginary (ε″) parts of dielectric constant with angular frequency and Cole-Cole curves of DBB have been analyzed. The fitting results for dispersion curves at different temperatures revealed that DBB system exhibits nearly Debye-type relaxation except for 125 °C. Moreover, it has been determined that while the relaxation frequencies shift to higher frequencies as the temperature increases from 25 °C to 125 °C, the peak intensities remarkably decrease with increasing temperature. According to Cole-Cole plot and phase angle versus frequency curve, it has been determined that DBB LC may have a possibility of utilizing as a super-capacitor at room temperature. Furthermore, it has been found that the conductivity mechanism of the DBB alters from Correlated Barrier Hoping (CBH) model to Quantum Tunneling Model (QMT) with in increasing temperature at high frequency region. In terms of CBH model, optical band gaps at 25 °C and 75 °C temperatures have also been calculated. Finally, activation energies for some selected angular frequencies have also been calculated.

  4. The effects of moisture on the dielectric relaxation of urethane dimethacrylate polymer and composites.

    PubMed

    Mohsen, N M; Craig, R G; Filisko, F E

    2001-04-01

    Dielectric characterization evaluated the influence of sorbed moisture on urethane dimethacrylate (UDMA) polymer matrix and unsilanated and silanated zirconia-silica (ZS)-filled UDMA composites. The moisture content (MC) of samples tested ranged from 0 to 7.32% with maximum values for UDMA, silanated and unsilanated ZS-filled UDMA were 3.72, 6.0 and 7.32%, respectively. Dielectric spectra were measured from 0.053 to 100 kHz and from -180 to 180;C. Small MC stiffened the polymers, which was shown by a shift of beta-peaks to higher temperatures, a decrease in the half width of bands and an increase in the change of activation energies. Higher MC resulted in water plasticizing the polymer by shifting the beta-peaks to lower temperatures. Maximum water sorption restricted the motion of the polymer chains and the b-peaks shifted to higher temperatures. Further, increasing MC shifted the a-relaxation to lower temperatures in both UDMA and composites. However, in composites with unsilanated ZS, a new relaxation occurred at high temperatures and low frequencies which was attributed to Maxwell-Wagner-Sillars (MWS) polarization. Thus, in UDMA, water occurs as fragments that form non-freezing clusters. However, in unsilanated ZS-UDMA composites, bulk water can exist at the polymer-filler interface and form disordered structures of ice at low temperatures which can evaporate at high temperatures. Silanated ZS-UDMA composites function similarly to UDMA at low MC but are more plasticized at high temperatures. PMID:11350592

  5. Insights into cation exchange selectivity of a natural clinoptilolite by means of dielectric relaxation spectroscopy

    NASA Astrophysics Data System (ADS)

    Rodríguez-Fuentes, Gerardo; Devautour-Vinot, Sabine; Diaby, Sekou; Henn, François

    2011-09-01

    Purified natural clinoptilolite from the Tasajeras deposit, Cuba, and some of its metal exchanged forms are studied, at the dehydrated state, by means of dielectric relaxation spectroscopy (DRS) using two different modus operandi: complex impedance spectroscopy and dielectric dynamic thermal analysis. Data analysis yields the determination of the extra-framework cation (EFC) population into the various possible crystallographic sites of the zeolitic framework as well as of the activation energy characterizing the localized hopping mechanism of EFC. First, it is shown that the DRS responses obtained here match well with the previous reported data, which were previously localized EFCs in positions close to M1 and M2 sites when the clinoptilolite is modified to almost homoionic form. From this outcome, it can be concluded that all EFCs are in the same crystallographic situation regarding solvation or, in other terms, that no steric effect can be taken into account to explain cationic selectivity. Second, based on the assumption that the activation energy for EFC hopping is directly connected to the EFC/framework interaction and on simple thermodynamics consideration, we show this interaction does not govern the EFC exchange reaction. So, it is emphasized that EFC/H2O interaction is the key factor for cation exchange selectivity.

  6. Electrical conduction and dielectric relaxation in p-type PVA/CuI polymer composite

    PubMed Central

    Makled, M.H.; Sheha, E.; Shanap, T.S.; El-Mansy, M.K.

    2012-01-01

    PVA/CuI polymer composite samples have been prepared and subjected to characterizations using FT-IR spectroscopy, DSC analysis, ac spectroscopy and dc conduction. The FT-IR spectral analysis shows remarkable variation of the absorption peak positions whereas DSC illustrates a little decrease of both glass transition temperature, Tg, and crystallization fraction, χ, with increasing CuI concentration. An increase of dc conductivity for PVA/CuI nano composite by increasing CuI concentration is recoded up to 15 wt%, besides it obeys Arhenuis plot with an activation energy in the range 0.54–1.32 eV. The frequency dependence of ac conductivity showed power law with an exponent 0.33 < s < 0.69 which predicts hopping conduction mechanism. The frequency dependence of both dielectric permittivity and dielectric loss obeys Debye dispersion relations in wide range of temperatures and frequency. Significant values of dipole relaxation time obtained which are thermally activated with activation energies in the range 0.33–0.87 eV. A significant value of hopping distance in the range 3.4–1.2 nm is estimated in agreement with the value of Bohr radius of the exciton. PMID:25685462

  7. Analysis of gene mutation in plant cell wall by dielectric relaxation

    NASA Astrophysics Data System (ADS)

    Roig, Frédéric; Dantras, Eric; Grima-Pettenatti, Jacqueline; Lacabanne, Colette

    2012-07-01

    Arabidopsis Thaliana is a plant composed mainly of cellulose and lignin. Geneticists need techniques able to make differences at the molecular level between modified plants (DML6, CAD C/D) and non-modified ones. Thermo-stimulated current (TSC) analysis is a promising route to identify gene mutations. For the non-modified plant, at low temperatures, TSC thermograms highlight three dielectric relaxation modes. From -150 to -110 °C, γCellulose is attributed to CH2OH and-OH groups of cellulose. Between -110 and -80 °C, βLignin is detected. From -80 to -40 °C, βCellulose is characteristic of the molecular mobility of glycosidic linkages. For the CAD C/D modified plants, only γCellulose and βLignin are observed; due to analogous enthalpy values, those modes have the same molecular origin as in the non-modified plant. So, the βLignin mode is associated with the molecular mobility of the lignin-OH groups. The CAD C/D gene mutation changes the chemical structure of lignin, which promotes hydrogen bonds in the network and inhibits molecular mobility of glucosidic rings. It is also interesting to note that the DML6 gene mutation induces a higher cooperativity of this βCellulose relaxation than in wild vegetal composites. In fact, this mutation promotes molecular mobility of glycosidic rings thanks to β1-4 glycosidic linkages.

  8. The order parameter model of liquids and glasses with applications to dielectric relaxation

    NASA Astrophysics Data System (ADS)

    Lesikar, Arnold V.; Moynihan, Cornelius T.

    1980-08-01

    The order parameter model is generalized to describe systems whose equilibrium states depend on other intensive variables, e.g., electric field E, in addition to temperature T and pressure P. The set of order parameters required to specify the state of a liquid or glass is shown to form an abstract Euclidean vector space in the vicinity of a particular equilibrium state. The results of relaxational experiments are then connected with geometric relations in this space of order parameters. Thermodynamic stability requires that certain angles in this space have real values. This leads to thermodynamic stability conditions (TSC's), which include the well known Prigogine-Defay condition for systems with intensive variables T and P and analogs of it for systems with other sets of intensive variables. The order parameter model is applied to dielectric relaxation, and its predictions are tested against available data. It is shown that the addition of E as an intensive variable requires at least one more order parameter to specify the state of the system than the number needed when T and P are the only intensive variables.

  9. Scaling behaviour of relaxation dependencies in metaloxide superconductors

    NASA Technical Reports Server (NTRS)

    Sidorenko, A. S.; Panaitov, G. I.; Gabovich, A. M.; Moiseev, D. P.; Postnikov, V. M.

    1990-01-01

    Superconducting glass state has been investigated in different types of metaloxide ceramics, Y-Ba-Cu-O, Bi-Sr-Ca-Cu-O, Ba-Pb-Bi-O, using the highly sensitive SQUID magnetometer. The analysis of long-time relaxation processes of thermoremanent magnetization m(sup trm) (+) = M(sub o) - Slnt displayed scaling dependence of the decay rate S = -dM/dlnt on quantity of trapped magnetic flux M(sub o): 1gs = 31g M(sub o) - observed universal dependence S is approximately M(sup 3) (sub o) seems to one of the features of superconducting glass state in metaloxide ceramics.

  10. Comment on "Study of dielectric relaxations of anhydrous trehalose and maltose glasses" [J. Chem. Phys. 134, 014508 (2011)].

    PubMed

    Kaminski, K; Wlodarczyk, P; Paluch, M

    2011-10-28

    Very recently Kwon et al. [H.-J. Kwon, J.-A. Seo, H. K. Kim, and Y. H. Hwang, J. Chem. Phys. 134, 014508 (2011)] published an article on the study of dielectric relaxation in trehalose and maltose glasses. They carried out broadband dielectric measurements at very wide range of temperatures covering supercooled liquid as well as glassy state of both saccharides. It is worth to mention that authors have also applied a new method for obtaining anhydrous glasses of trehalose and maltose that enables avoiding their caramelization. Four relaxation processes were identified in dielectric spectra of both saccharides. The slower one was identified as structural relaxation process the next one, not observed by the others, was assigned as Johari-Goldstein (JG) β-relaxation, while the last two secondary modes were of the same nature as found by Kaminski et al. [K. Kaminski, E. Kaminska, P. Wlodarczyk, S. Pawlus, D. Kimla, A. Kasprzycka, M. Paluch, J. Ziolo, W. Szeja, and K. L. Ngai, J. Phys. Chem. B 112, 12816 (2008)]. In this comment we show that the authors mistakenly assigned the slowest relaxation process as structural mode of disaccharides. We have proven that this relaxation process is an effect of formation of thin layer of air or water between plate of capacitor and sample. The same effect can be observed if plates of capacitor are oxidized. Thus, we concluded that their slowest mode is connected to the dc conduction process while their β JG process is primary relaxation of trehalose and maltose. PMID:22047271

  11. Dielectric relaxation in ionic liquid/dipolar solvent binary mixtures: A semi-molecular theory

    NASA Astrophysics Data System (ADS)

    Daschakraborty, Snehasis; Biswas, Ranjit

    2016-03-01

    A semi-molecular theory is developed here for studying dielectric relaxation (DR) in binary mixtures of ionic liquids (ILs) with common dipolar solvents. Effects of ion translation on DR time scale, and those of ion rotation on conductivity relaxation time scale are explored. Two different models for the theoretical calculations have been considered: (i) separate medium approach, where molecularities of both the IL and dipolar solvent molecules are retained, and (ii) effective medium approach, where the added dipolar solvent molecules are assumed to combine with the dipolar ions of the IL, producing a fictitious effective medium characterized via effective dipole moment, density, and diameter. Semi-molecular expressions for the diffusive DR times have been derived which incorporates the effects of wavenumber dependent orientational static correlations, ion dynamic structure factors, and ion translation. Subsequently, the theory has been applied to the binary mixtures of 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]) with water (H2O), and acetonitrile (CH3CN) for which experimental DR data are available. On comparison, predicted DR time scales show close agreement with the measured DR times at low IL mole fractions (xIL). At higher IL concentrations (xIL > 0.05), the theory over-estimates the relaxation times and increasingly deviates from the measurements with xIL, deviation being the maximum for the neat IL by almost two orders of magnitude. The theory predicts negligible contributions to this deviation from the xIL dependent collective orientational static correlations. The drastic difference between DR time scales for IL/solvent mixtures from theory and experiments arises primarily due to the use of the actual molecular volume ( Vmol dip ) for the rotating dipolar moiety in the present theory and suggests that only a fraction of Vmol dip is involved at high xIL. Expectedly, nice agreement between theory and experiments appears when experimental

  12. Stress relaxation and recovery behaviour of composite orthodontic archwires in bending.

    PubMed

    Zufall, S W; Kusy, R P

    2000-02-01

    The viscoelastic behaviour of prototype composite orthodontic archwires was evaluated using a bend stress relaxation test. Archwires having 10 different volume fractions of reinforcement were subjected to constant bending radii in a water bath at 37 degrees C for time periods of up to 90 days. The wires were subsequently released and left unconstrained for the same testing conditions. Creep-induced changes in the unconstrained bending radii of the wires were measured at specific times during both phases (stress relaxation and recovery) of the test. The statistical analysis showed that stress relaxation behaviour was strongly correlated with the archwire reinforcement level. The final relaxation varied, with decreasing reinforcement, from 2 to 8 per cent. Archwire recovery was not correlated with reinforcement level, and revealed a final viscous loss of only 1 per cent. The relaxed elastic moduli in bending of the composite wires were similar to the elastic moduli in bending of several conventional orthodontic archwire materials. Losses that were associated with the viscoelastic behaviour varied with decreasing reinforcement level from 1.2 to 1.7 GPa. Because these modulus losses were minimal, each archwire retained sufficient resilience to be applicable to the early and intermediate stages of orthodontic treatment. PMID:10721240

  13. Effect of polarization on dielectric behaviour of PET/0.8PHB polymer liquid crystals

    SciTech Connect

    Yarramaneni, Sridharbabu; Sharma, Anu; Quamara, J. K.

    2014-04-24

    Dielectric constant and loss behaviour of pristine and polarized samples of Poly (p-hydroxybenzoic acid-co-ethylene terephthalate) polymer liquid crystals were studied at continuous temperatures ranging from 20 °C to 250 °C, polarized at potentials 500V and 2000V with high precision d.c. power supply. Dielectric constant appears to be almost linearly dependent in the lower temperature region and is independent in the higher temperature region. Dielectric loss becomes approximately ten times lower at higher temperatures.

  14. Effect of polarization on dielectric behaviour of PET/0.8PHB polymer liquid crystals

    NASA Astrophysics Data System (ADS)

    Yarramaneni, Sridharbabu; Sharma, Anu; Quamara, J. K.

    2014-04-01

    Dielectric constant and loss behaviour of pristine and polarized samples of Poly (p-hydroxybenzoic acid-co-ethylene terephthalate) polymer liquid crystals were studied at continuous temperatures ranging from 20 °C to 250 °C, polarized at potentials 500V and 2000V with high precision d.c. power supply. Dielectric constant appears to be almost linearly dependent in the lower temperature region and is independent in the higher temperature region. Dielectric loss becomes approximately ten times lower at higher temperatures.

  15. Dielectric relaxation spectroscopy of heteronuclear cobalt(II)-copper(II) complex of 1-phenyl-3-methyl-5-pyrazolone

    NASA Astrophysics Data System (ADS)

    Masoud, Mamdouh S.; Ali, Alaa E.; Mohamed, Rabah H.; Mostafa, M. Abd El Zaher

    2005-12-01

    A bright green CoCu(PMP)(OH) 2(H 2O) 2 complex was synthesized. Its structure was elucidated and characterized by different spectroscopic techniques. Both cobalt and copper atoms attain tetrahedral geometry. The complex was investigated by the dielectric relaxation spectroscopy. The dielectric parameters are discussed in terms of temperature and frequency changes. The conductivity of the complex decreased as the temperature increased in the temperature range 30-100 °C, while above this temperature range stepwise increase in the conductivity was observed.

  16. Investigation of dielectric and electrical behaviour of nanocrystalline Zn1-xMnxO (x=0 to 0.10) semiconductors synthesized by mechanical alloying

    NASA Astrophysics Data System (ADS)

    Choudhury, S.; Sain, S.; Mandal, M. K.; Pradhan, S. K.; Meikap, A. K.

    2016-07-01

    The results on the measurement of electric and dielectric behaviour and capacitance-voltage characteristics of Zn1-xMnxO (x=0 to 0.10) nanocrystalline semiconductors are reported. Direct current conductivity increases with the increase Mn concentration and its thermal behavior can be explained by adiabatic polaronic hopping model. The alternating current conductivity obeys a power law of temperature and frequency. The temperature exponent p strongly depends on Mn concentration. The temperature dependence of frequency exponent s suggests that the overlapping large polaron conduction model is the appropriate conduction mechanism for the investigated samples. The interfacial boundaries and grain contribution to the dielectric properties can be identified by the analysis of complex impedance. Relaxation behaviour of the samples can be explained from the analysis of the electric modulus. Formation of Schottky diode can be described from capacitance-voltage characteristic of the samples and different diode parameters can be extracted from it.

  17. Dielectric relaxation in a new double perovskite oxide Ho 2MgZrO 6

    NASA Astrophysics Data System (ADS)

    Mahato, Dev K.; Dutta, Alo; Sinha, T. P.

    2012-01-01

    A new double perovskite oxide holmium magnesium zirconate Ho 2MgZrO 6 (HMZ) was prepared by solid state reaction technique. The crystal structure has been determined by powder X-ray diffraction which shows monoclinic phase at room temperature with cell parameters a = 9.3028 ± 0.0030 Å, b = 5.2293 ± 0.0008 Å, c = 4.4009 ± 0.0009 Å, β = 103.3746 ± 0.0166°. An analysis of complex permittivity with frequency was carried out assuming a distribution of relaxation times. The frequency dependent electrical data are analyzed in the framework of conductivity and electric modulus formalisms. At the high temperature range, conductivity data satisfy the variable range hopping (VRH) model. In this regime, the conductivity of sample obeys Mott's T1/4 law, characteristic of VRH. High temperature data indicates the formation of thermally activated small polarons. The scaling behaviour of imaginary part of electric modulus suggests that the relaxation describes the same mechanism at various temperatures.

  18. Dielectric relaxation of 4:1 v/v methanol-ethanol to 90 kbar

    NASA Astrophysics Data System (ADS)

    Mishima, Osamu; Whalley, Edward

    1986-03-01

    The effect of pressure on dielectric relaxation in a 4:1 v/v methanol-ethanol mixture has been measured in the range -44 -+22 °C to a maximum pressure of 90 kbar using a tungsten-carbide anvil apparatus. Graphs of the complex capacitance in the complex plane are not semicircles, but are approximately skewed arcs. The frequencies of maximum loss were fitted to a general quadratic in the deviations of the pressure and the reciprocal temperature from a reference pressure and temperature near the middle of the field, and apparent activation enthalpies and volumes were calculated. The model in which molecules are represented by spheres of radius a immersed in a medium of viscosity η predicts that the quantity fmη/T, where fm is the frequency of maximum loss and T the temperature, is independent of temperature and pressure. Its value changes relatively little with temperature but changes by three orders of magnitude in the range 0-70 kbar at 21 °C. Our theories of the transport properties of fluids at very high pressures are therefore quite inadequate. As much of the interior of the earth is made of such fluids, our small understanding of them limits our understanding of the earth's interior.

  19. Dielectric relaxation of alkyl chains in graphite oxide and n-alkylammonium halides

    NASA Astrophysics Data System (ADS)

    Ai, Xiaoqian; Tian, Yuchen; Gu, Min; Yu, Ji; Tang, Tong B.

    2016-05-01

    The dynamic of n-alkylammonium halides and n-alkylammonium cations (n = 12, 14, 16, 18) intercalated in graphite oxide (GO) have been investigated with complex impedance spectroscopy. X-ray diffraction, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, elemental analysis and thermogravimetry served to characterize the materials. The intercalated alkylammonium cations distributes as monolayers (when n = 12, 14 or 16) or bilayers (when n = 18), with their long axis parallel to GO layers, and with cations of headgroups bonded ionically to C-O- groups of GO; backbones of the confined molecules remain free. All halides and intercalation compounds suffer dielectric loss at low temperature. Arrhenius plots of the thermal dependence of the loss peaks, which are asymmetric, produce apparent activation energies that rise with increasing n. Ngai's correlated-state model helps to correct for effects of dipole-dipole interaction, leading to virtually identical values for actual activation energy of 110 meV ± 5%; the values are also almost the same as the barrier energy for internal rotation in the alkyl macromolecule. We conclude that the relaxation of the alkylammonium cations arises not from C3 reorientation of the CH3 at its headgroup, but from small-angle wobbling around its major axis, an intrinsic motion.

  20. Supercooled water's thermodynamic behaviour and a conflict between Arrhenius relaxation and configurational entropy

    NASA Astrophysics Data System (ADS)

    Johari, G. P.

    2000-03-01

    The increase in the time- and temperature-dependent heat capacity, Cp, in the glass-liquid transition range of water has been investigated using earlier data [G.P. Johari, A. Hallbrucker, E. Mayer, Nature 330 (1987) 552], new computation of the manner of Cp increase in the glass-liquid transition range and theoretical views. The investigation shows that the temperature dependence of structural relaxation time of water in the 136-148 K range remains non-Arrhenius, like the dielectric relaxation time [G.P. Johari, J. Chem. Phys. 105 (1996) 7079] and the self-diffusion coefficient [R.C. Smith, B.D. Kay, Nature 398 (1999) 788]. Theoretical reasons for the broadening of the heat-capacity endotherm are given and verified by computation. Analysis shows that for an Arrhenius-type relaxation-dynamics, the configurational entropy of a liquid will remain constant on its cooling, which violates the consequences of the third law of thermodynamics. When the relaxation time is taken as 10 2 s at Tg and as 10 -14 s at infinite temperature for analysing a liquid's relaxation [K. Ito, C.T. Moynihan, C.A. Angell, Nature 398 (1999) 492; R. Richert, C.A. Angell, J. Chem. Phys. 108 (1998) 9016], the Arrhenius energy becomes unjustifiably proportional to the Tg of a liquid. In its glass transition features, water is not as analogous with molten silica as is believed.

  1. Hysteresis behaviour of low-voltage organic field-effect transistors employing high dielectric constant polymer gate dielectrics

    NASA Astrophysics Data System (ADS)

    Kim, Se Hyun; Yun, Won Min; Kwon, Oh-Kwan; Hong, Kipyo; Yang, Chanwoo; Choi, Woon-Seop; Eon Park, Chan

    2010-11-01

    Here, we report on the fabrication of low-voltage-operating pentacene-based organic field-effect transistors (OFETs) that utilize crosslinked cyanoethylated poly(vinyl alcohol) (CR-V) gate dielectrics. The crosslinked CR-V-based OFET could be operated successfully at low voltages (below 4 V), but abnormal behaviour during device operation, such as uncertainty in the field-effect mobility (μ) and hysteresis, was induced by the slow polarization of moieties embedded in the gate dielectric (e.g. polar functionalities, ionic impurities, water and solvent molecules). In an effort to improve the stability of OFET operation, we measured the dependence of μ and hysteresis on dielectric thickness, CR-V crosslinking conditions and sweep rate of the gate bias. The influence of the CR-V surface properties on μ, hysteresis, and the structural and morphological features of the pentacene layer grown on the gate dielectric was characterized and compared with the properties of pentacene grown on a polystyrene surface.

  2. Effects of swift heavy ion irradiation on dielectric relaxation and conduction mechanism in Ba0.90Sr0.10TiO3

    NASA Astrophysics Data System (ADS)

    Mohan, C. R. K.; Dey, Ranajit; Patel, Shiv P.; Pandey, R. K.; Sharma, M. P.; Bajpai, P. K.

    2016-04-01

    The effects of 100 MeV O8+ ion beam irradiation on the structural and dielectric behavior of Ba0.90Sr0.10TiO3 ceramics have been analyzed. Ion irradiation does not change the crystalline structure, however the tetragonal distortion increases. The low frequency dielectric dispersion especially at high temperatures increases significantly after ion irradiation. The dielectric relaxation phenomenon has been probed through complex impedance and electric modulus approaches. The observed dielectric relaxation has distributed relaxation times and is a thermally activated process. Ion irradiation enhances the cationic disordering. The contributions of grains and grains boundaries towards impedance have been separated. It is inferred that the grain boundaries become more resistive due to ion irradiation and is associated to oxygen vacancies annihilation. Ion irradiation also decreases the bulk ferroelectric polarization demonstrating that the surface or near surface modifications may tune the bulk properties in polar dielectrics.

  3. The evolution of antipredator behaviour following relaxed and reversed selection in Alaskan threespine stickleback fish

    PubMed Central

    Wund, Matthew A.; Baker, John A.; Golub, Justin L.; Foster, Susan A.

    2015-01-01

    Changing environments, whether through natural or anthropogenic causes, can lead to the loss of some selective pressures (‘relaxed selection’) and possibly even the reinstatement of selective agents not encountered for many generations (‘reversed selection’). We examined the outcome of relaxed and reversed selection in the adaptive radiation of the threespine stickleback fish, Gasterostues aculeatus L., in which isolated populations encounter a variety of predation regimes. Oceanic stickleback, which represent the ancestral founders of the freshwater radiation, encounter many piscivorous fish. Derived, freshwater populations, on the other hand, vary with respect to the presence of predators. Some populations encounter native salmonids, whereas others have not experienced predation by large fish in thousands of generations (relax-selected populations). Some relax-selected populations have had sport fish, including rainbow trout, Oncorhynchus mykiss, introduced within the past several decades (reverse-selected). We examined the behavioural responses of stickleback from three populations of each type to simulated attacks by trout and birds to determine whether relaxed and reversed selection has led to divergence in behaviour, and whether this divergence was predator specific. Fish from trout-free populations showed weak responses to trout, as predicted, but these responses were similar to those of oceanic (ancestral) populations. Fish from populations that co-occur with trout, whether native or introduced, showed elevated antipredator responses, indicating that in freshwater, trout predation selects for enhanced antipredator responses, which can evolve extremely rapidly. Comparison of laboratory-reared and wild-caught individuals suggests a combination of learned and genetic components to this variation. Responses to a model bird flyover were weakly linked to predation environment, indicating that the loss of predation by trout may partially influence the

  4. Finite-element modeling method for the study of dielectric relaxation at high frequencies of heterostructures made of multilayered particle

    NASA Astrophysics Data System (ADS)

    Fourn, Cédric; Lasquellec, Sophie; Brosseau, Christian

    2007-12-01

    There has been much recent interest in how morphological descriptors may affect the electromagnetic wave transport in particulate composite mediums. In this work, we present results of finite-element simulations that model the permittivity of two-dimensional (or cross sections of infinite three-dimensional parallel, infinitely long, identical, circular cylinders, where the properties and characteristics are invariant along the perpendicular cross-sectional plane) three-phase heterostructures made of a multilayered discoidal particle. While strictly valid only in a direct current situation, our analysis can be extended to treat electric fields that oscillate with time provided that the wavelengths and attenuation lengths associated with the fields are much larger than the microstructure dimension in order that the homogeneous (effective medium) representation of the composite structure makes sense. From simulations over a range of parameters, our analysis evaluates the effect of the surface fraction of inclusion, the conductivity, and thickness (relative to the particle radius) of the particle conductive coating on the effective complex permittivity of isotropic heterostructures in which the filler particles have a core-shell structure. Four main effects are found. First, the importance of the surface fraction of inclusion on the effective complex permittivity at high frequencies (from microwave to infrared) is illustrated over a broad range of coating thicknesses and conductivities. Second, the encapsulation phase (metallic coating) conductivity is identified as the key property controlling the dielectric relaxation due to interfacial polarization. Third, a simple parametrization of the high-frequency effective permittivity spectrum allowed us to obtain a reliable modelization of the Debye-type relaxation processes. From the least-squares fit of the effective complex permittivity data, we extract information on these relaxation processes, i.e., relaxation

  5. Collective dynamic dipole moment and orientation fluctuations, cooperative hydrogen bond relaxations, and their connections to dielectric relaxation in ionic acetamide deep eutectics: Microscopic insight from simulations.

    PubMed

    Das, Suman; Biswas, Ranjit; Mukherjee, Biswaroop

    2016-08-28

    The paper reports a detailed simulation study on collective reorientational relaxation, cooperative hydrogen bond (H-bond) fluctuations, and their connections to dielectric relaxation (DR) in deep eutectic solvents made of acetamide and three uni-univalent electrolytes, lithium nitrate (LiNO3), lithium bromide (LiBr), and lithium perchlorate (LiClO4). Because cooperative H-bond fluctuations and ion migration complicate the straightforward interpretation of measured DR timescales in terms of molecular dipolar rotations for these conducting media which support extensive intra- and inter-species H-bonding, one needs to separate out the individual components from the overall relaxation for examining the microscopic origin of various timescales. The present study does so and finds that reorientation of ion-complexed acetamide molecules generates relaxation timescales that are in sub-nanosecond to nanosecond range. This explains in molecular terms the nanosecond timescales reported by recent giga-Hertz DR measurements. Interestingly, the simulated survival timescale for the acetamide-Li(+) complex has been found to be a few tens of nanosecond, suggesting such a cation-complexed species may be responsible for a similar timescale reported by mega-Hertz DR measurements of acetamide/potassium thiocyanate deep eutectics near room temperature. The issue of collective versus single particle relaxation is discussed, and jump waiting time distributions are determined. Dependence on anion-identity in each of the cases has been examined. In short, the present study demonstrates that assumption of nano-sized domain formation is not required for explaining the DR detected nanosecond and longer timescales in these media. PMID:27586932

  6. Role of α-relaxation on crystallization of amorphous celecoxib above T(g) probed by dielectric spectroscopy.

    PubMed

    Dantuluri, Ajay K R; Amin, Aeshna; Puri, Vibha; Bansal, Arvind K

    2011-06-01

    In the present study, the role of α-relaxation toward isothermal crystallization of amorphous celecoxib was studied using dielectric spectroscopy (DES). The dielectric response of the α-relaxation was measured as a function of frequency (10⁻¹ to 10⁶ Hz), isothermally at every 4 K interval in the range of 303.15 to 443.15 K. The dielectric loss spectrum at each temperature was analyzed using the Havriliak Negami (HN) equation to extract the characteristic relaxation time, τ(HN). Two Vogel-Fulcher-Tammann (VFT) functions were required for representing the temperature dependence of τ(HN) across the temperature range of study. The VFT fit parameters obtained from the two regions varied drastically pointing toward the underlying differences in the dynamics of relaxation above and below the crossover. Later, in situ isothermal crystallization experiments were performed at 363.15, 368.15, 373.15, and 378.15 K. The conversion rate, obtained from the normalized dielectric strength, was modeled using the Avrami model, which indicated the possibility of different crystallization mechanism at higher crystallization temperatures. HN shape parameters, α(HN) and product of α(HN) and β(HN), were analyzed during the course of crystallization to understand the dynamics of amorphous phase when crystallites were being evolved. HN shape parameters indicated α-like motions were affected, whereas β-like remained unaffected by the crystallization temperature. Characteristic crystallization time, τ(cr), obtained from Avrami fits, showed Arrhenius type of temperature dependence (R² = 0.999). A plot between log τ(cr) and log τ(HN) show a linear regression with R² of 0.997 indicating the direct correlation between these two phenomena. However, the coupling coefficient was found to be varying within the temperature range of study, indicating tendency of crystallization to be more diffusion controlled at higher crystallization temperatures. With different crystalline solid

  7. Molecular Relaxations in Supercooled Liquid and Glassy States of Amorphous Quinidine: Dielectric Spectroscopy and Density Functional Theory Approaches.

    PubMed

    Schammé, Benjamin; Mignot, Mélanie; Couvrat, Nicolas; Tognetti, Vincent; Joubert, Laurent; Dupray, Valérie; Delbreilh, Laurent; Dargent, Eric; Coquerel, Gérard

    2016-08-01

    In this article, we conduct a comprehensive molecular relaxation study of amorphous Quinidine above and below the glass-transition temperature (Tg) through broadband dielectric relaxation spectroscopy (BDS) experiments and theoretical density functional theory (DFT) calculations, as one major issue with the amorphous state of pharmaceuticals is life expectancy. These techniques enabled us to determine what kind of molecular motions are responsible, or not, for the devitrification of Quinidine. Parameters describing the complex molecular dynamics of amorphous Quinidine, such as Tg, the width of the α relaxation (βKWW), the temperature dependence of α-relaxation times (τα), the fragility index (m), and the apparent activation energy of secondary γ relaxation (Ea-γ), were characterized. Above Tg (> 60 °C), a medium degree of nonexponentiality (βKWW = 0.5) was evidenced. An intermediate value of the fragility index (m = 86) enabled us to consider Quinidine as a glass former of medium fragility. Below Tg (< 60 °C), one well-defined secondary γ relaxation, with an apparent activation energy of Ea-γ = 53.8 kJ/mol, was reported. From theoretical DFT calculations, we identified the most reactive part of Quinidine moieties through exploration of the potential energy surface. We evidenced that the clearly visible γ process has an intramolecular origin coming from the rotation of the CH(OH)C9H14N end group. An excess wing observed in amorphous Quinidine was found to be an unresolved Johari-Goldstein relaxation. These studies were supplemented by sub-Tg experimental evaluations of the life expectancy of amorphous Quinidine by X-ray powder diffraction and differential scanning calorimetry. We show that the difference between Tg and the onset temperature for crystallization, Tc, which is 30 K, is sufficiently large to avoid recrystallization of amorphous Quinidine during 16 months of storage under ambient conditions. PMID:27391029

  8. Dielectric relaxation in sodium bis(2-ethylhexyl)sulfosuccinate--water--decane microemulsions near the percolation temperature threshold

    SciTech Connect

    Feldman, Y.; Kozlovich, N.; Nir, I.; Garti, N. )

    1995-01-01

    The frequency scaling parameters [ital m], [ital p], and [ital u], as well as the stretched parameters in the time window [beta], provide information about the microstructure and dynamics of the system. The analysis of their temperature dependence shows the existence of spatial, temporal, and energetic disorder associated with anomalous diffusion of charge carriers in the percolation clusters. On the basis of a detailed analysis of the time relaxation data spectrum, the molecular dynamic mechanism of dielectric polarization in the percolation region was suggested.

  9. Relaxation behavior in model compounds of poly(aryl-ether-ketone-ketone) as revealed by dielectric spectroscopy

    NASA Astrophysics Data System (ADS)

    Ezquerra, T. A.; Zolotukhin, M.; Privalko, V. P.; Baltá-Calleja, F. J.; Nequlqueo, G.; García, C.; de la Campa, J. G.; de Abajo, J.

    1999-05-01

    The relaxation behavior of a series of ether-ketone oligomers, considered as model compounds of poly(ether-ketone-ketone), was studied by means of dielectric spectroscopy. The dynamics of the α relaxation of ether-ketone model compounds as compared with that of poly(arylether-ketone-ketone) (PEKK) (50/50), shows up differences which can be attributed to the variation of inter- and intramolecular correlations with the chain length. Model compounds exhibit a nearly similar degree of cooperativity regardless the differences in Tg values. The PEKK (50/50) polymer exhibits stronger cooperativity than the oligomers suggesting that in poly(ether-ketone-ketone)s molecular motions above Tg extend to more than one monomeric unit.

  10. Dielectric relaxation studies in Se90Cd8Sb2 glassy alloy

    NASA Astrophysics Data System (ADS)

    Shukla, Nitesh; Rao, Vandita; Dwivedi, D. K.

    2016-05-01

    Se90Cd8Sb2 chalcogenide semiconducting alloy was prepared by melt quench technique. The prepared glassy alloy has been characterized by techniques such as scanning electron microscopy (SEM) and energy dispersive X-ray (EDAX).Dielectric properties of Se90Cd8Sb2 chalcogenide semiconductor have been studied using impedance spectroscopic technique in the frequency range 5×102Hz - 1×105Hz and in temperature range 303-318K. It is found that dielectric constant ɛ' and dielectric loss factor ɛ″ are dependent on frequency and temperature.

  11. Double dielectric relaxations in SnO2 nanoparticles dispersed in conducting polymer

    NASA Astrophysics Data System (ADS)

    Dutta, Kousik; De, S. K.

    2007-10-01

    The tetragonal phase of SnO2 and the conducting form of polyaniline are characterized by x-ray diffraction and Fourier transform infrared spectroscopy. The electrical conductivity and the dielectric properties of tin dioxide (SnO2)-polyaniline hybrid nanocomposites have been investigated as a function of temperature and frequency for different concentrations of polyaniline. Electrical conductivity has been derived from the simple equivalent circuit pertaining to inhomogeneous polycrystalline materials. Grain and grain boundary conductivities follow an Arrhenius type of electrical conduction. The nanocomposites possess an extraordinarily high dielectric constant of about 103. Different conductivities of the grain and grain boundary give rise to a large dielectric constant in nanocomposites. The dielectric loss spectra reveal two peaks in the measured frequency interval for the maximum concentration of the SnO2 nanoparticles. The peaks are ascribed to interfacial polarization and the intrinsic oxygen defects in nanosized SnO2.

  12. A Study of Concrete Hydration and Dielectric Relaxation Mechanism Using Ground Penetrating Radar and Short-Time Fourier Transform

    NASA Astrophysics Data System (ADS)

    Lai, W. L.; Kind, T.; Wiggenhauser, H.

    2010-12-01

    Ground penetrating radar (GPR) was used to characterize the frequency-dependent dielectric relaxation phenomena in ordinary Portland cement (OPC) hydration in concrete changing from fresh to hardened state. The study was experimented by measuring the changes of GPR A-scan waveforms over a period of 90 days, and processed the waveforms with short-time Fourier transform (STFT) in joint time-frequency analysis (JTFA) domain rather than a conventional time or frequency domain alone. The signals of the direct wave traveled at the concrete surface and the reflected wave from an embedded steel bar were transformed with STFT, in which the changes of peak frequency over ages were tracked. The peak frequencies were found to increase with ages and the patterns were found to match closely with primarily the well-known OPC hydration process and secondarily, the evaporation effect. The close match is contributed to the simultaneous effects converting free to bound water over time, on both conventional OPC hydration and dielectric relaxation mechanisms.

  13. Ionic conductivity and dielectric relaxation in Y doped La2Mo2O9 oxide-ion conductors

    NASA Astrophysics Data System (ADS)

    Paul, T.; Ghosh, A.

    2014-10-01

    In this work, we have studied electrical conductivity and dielectric properties of polycrystalline La2-xYxMo2O9 (0.05 ≤ x ≤ 0.3) compounds in the temperature range from 358 K to 1088 K and the frequency range from 10 Hz to 3 GHz. The bulk and grain boundary contributions to the overall conductivity of these compounds show Arrhenius type behavior at low temperatures. The random free-energy barrier model has been used to analyze the frequency dependence of the conductivity. The charge carrier relaxation time and its activation energy have been determined from the analysis of the conductivity spectra using this model. The results obtained from the random free-energy barrier model satisfy Barton-Nakajima-Namikawa relation. The conduction mechanism has been also predicted using random free-energy barrier model and the scaling formalism. We have observed that the dielectric relaxation peaks arise from the diffusion of oxygen ions via vacancies.

  14. Relative permittivity measurement during the thrombus formation process using the dielectric relaxation method for various hematocrit values.

    PubMed

    Asakura, Yuta; Sapkota, Achyut; Maruyama, Osamu; Kosaka, Ryo; Yamane, Takashi; Takei, Masahiro

    2015-12-01

    The relative permittivity ε' and the dielectric loss ε″ for various hematocrit values H for static bovine blood condition have been measured using the dielectric relaxation method to detect thrombosis in real time. The suitable measurement frequency f m ranged within 60 kHz to 1 MHz, and the relaxation frequency of red blood cells (RBCs) f rc was observed to be 2 MHz. In the f m, the temporal change of normalized ε' exhibited a minimum (called as bottom point). The bottom point was observed to be exponentially shortened as H increased. This characteristic of the ε'* minimum is discussed from three viewpoints: during fibrin formation, direct thrombus formation, and rouleaux formation processes. ε'* during the fibrin formation process decreased over time, irrespective of f. However, ε'* in f m during the direct thrombus formation process and during the aggregation formation process increased immediately and rapidly over time. Therefore, the ε'* bottom point in f m might be the indication of micrometer-scale thrombus formation by RBC aggregation due to fibrin formation. PMID:26058831

  15. Dielectric relaxations and conduction mechanisms in polyether-clay composite polymer electrolytes under high carbon dioxide pressure.

    PubMed

    Kitajima, Shunsuke; Bertasi, Federico; Vezzù, Keti; Negro, Enrico; Tominaga, Yoichi; Di Noto, Vito

    2013-10-21

    The composite material P(EO/EM)-Sa consisting of synthetic saponite (Sa) dispersed in poly[ethylene oxide-co-2-(2-methoxyethoxy)ethyl glycidyl ether] (P(EO/EM)) is studied by "in situ" measurements using broadband electrical spectroscopy (BES) under pressurized CO2 to characterize the dynamic behavior of conductivity and the dielectric relaxations of the ion host polymer matrix. It is revealed that there are three dielectric relaxation processes associated with: (I) the dipolar motions in the short oxyethylene side chains of P(EO/EM) (β); and (II) the segmental motion of the main chains comprising the polyether components (αfast, αslow). αslow is attributed to the slow α-relaxation of P(EO/EM) macromolecules, which is hindered by the strong coordination interactions with the ions. Two conduction processes are observed, σDC and σID, which are attributed, respectively, to the bulk conductivity and the interdomain conductivity. The temperature dependence of conductivity and relaxation processes reveals that αfast and αslow are strongly correlated with σDC and σID. The "in situ" BES measurements under pressurized CO2 indicate a fast decrease in σDC at the initial CO2 treatment time resulting from the decrease in the concentration of polyether-M(n+) complexes, which is driven by the CO2 permeation. The relaxation frequency (fR) of αslow at the initial CO2 treatment time increases and shows a steep rise with time with the same behavior of the αfast mode. It is demonstrated that the interactions between polyether chains of P(EO/EM) and cations in the polymer electrolyte layers embedded in Sa are probably weakened by the low permittivity of CO2 (ε = 1.08). Thus, the formation of ion pairs in the polymer electrolyte domains of P(EO/EM)-Sa occurs, with a corresponding reduction in the concentration of ion carriers. PMID:23963202

  16. Low-temperature dipolar echoes in amorphous dielectrics: Significance of relaxation and decoherence free two-level systems

    NASA Astrophysics Data System (ADS)

    Burin, A. L.; Leveritt, J. M., III; Ruyters, G.; Schötz, C.; Bazrafshan, M.; Fassl, P.; von Schickfus, M.; Fleischmann, A.; Enss, C.

    2013-12-01

    The theoretical model for dielectric echoes in amorphous solids at low temperatures has been developed and applied to the recent two- and three-pulse echo experimental data in borosilicate glass BK7 where the amplitude of dipolar echoes has been observed for unprecedentedly long delay times extending the experimental window for studying the decay by several orders of magnitude. We show that at long delay times the echo amplitude is determined by a small subset of two-level systems (TLSs) with negligible relaxation and decoherence because of their weak coupling to phonons. The universal statistics of coupling is obtained by assuming that different TLS elastic tensor components are almost independent. Under this assumption the echo decay can be described approximately by the power law time dependences with different powers at times shorter and longer than the typical TLS relaxation time. These predictions are in a very good agreement with the experimental data and can be used to extract TLS relaxation and decoherence rates from the echo experiments.

  17. Dielectric relaxation of cytochrome c oxidase: Comparison of the microscopic and continuum models

    NASA Astrophysics Data System (ADS)

    Leontyev, I. V.; Stuchebrukhov, A. A.

    2009-02-01

    We have studied a charge-insertion process that models the deprotonation of a histidine side chain in the active site of cytochrome c oxidase (CcO) using both the continuum electrostatic calculations and the microscopic simulations. The group of interest is a ligand to CuB center of CcO, which has been previously suggested to play the role of the proton pumping element in the enzyme; the group is located near a large internal water cavity in the protein. Using the nonpolarizable Amber-99 force field in molecular dynamics (MD) simulations, we have calculated the nuclear part of the reaction-field energy of charging of the His group and combined it with the electronic part, which we estimated in terms of the electronic continuum (EC) model, to obtain the total reaction-field energy of charging. The total free energy obtained in this MDEC approach was then compared with that calculated using pure continuum electrostatic model with variable dielectric parameters. The dielectric constant for the "dry" protein and that of the internal water cavity of CcO were determined as those parameters that provide best agreement between the continuum and microscopic MDEC model. The nuclear (MD) polarization alone (without electronic part) of a dry protein was found to correspond to an unphysically low dielectric constant of only about 1.3, whereas the inclusion of electronic polarizability increases the protein dielectric constant to 2.6-2.8. A detailed analysis is presented as to how the protein structure should be selected for the continuum calculations, as well as which probe and atomic radii should be used for cavity definition. The dielectric constant of the internal water cavity was found to be 80 or even higher using "standard" parameters of water probe radius, 1.4Å, and protein atomic radii from the MD force field for cavity description; such high values are ascribed to the fact that the standard procedure produces unphysically small cavities. Using x-ray data for internal

  18. Dielectric relaxation of cytochrome c oxidase: Comparison of the microscopic and continuum models.

    PubMed

    Leontyev, I V; Stuchebrukhov, A A

    2009-02-28

    We have studied a charge-insertion process that models the deprotonation of a histidine side chain in the active site of cytochrome c oxidase (CcO) using both the continuum electrostatic calculations and the microscopic simulations. The group of interest is a ligand to Cu(B) center of CcO, which has been previously suggested to play the role of the proton pumping element in the enzyme; the group is located near a large internal water cavity in the protein. Using the nonpolarizable Amber-99 force field in molecular dynamics (MD) simulations, we have calculated the nuclear part of the reaction-field energy of charging of the His group and combined it with the electronic part, which we estimated in terms of the electronic continuum (EC) model, to obtain the total reaction-field energy of charging. The total free energy obtained in this MDEC approach was then compared with that calculated using pure continuum electrostatic model with variable dielectric parameters. The dielectric constant for the "dry" protein and that of the internal water cavity of CcO were determined as those parameters that provide best agreement between the continuum and microscopic MDEC model. The nuclear (MD) polarization alone (without electronic part) of a dry protein was found to correspond to an unphysically low dielectric constant of only about 1.3, whereas the inclusion of electronic polarizability increases the protein dielectric constant to 2.6-2.8. A detailed analysis is presented as to how the protein structure should be selected for the continuum calculations, as well as which probe and atomic radii should be used for cavity definition. The dielectric constant of the internal water cavity was found to be 80 or even higher using "standard" parameters of water probe radius, 1.4 A, and protein atomic radii from the MD force field for cavity description; such high values are ascribed to the fact that the standard procedure produces unphysically small cavities. Using x-ray data for

  19. Dielectric relaxation of hydration water in the Dickerson-Drew duplex solution probed by THz spectroscopy

    NASA Astrophysics Data System (ADS)

    Son, Heyjin; Choi, Da-Hye; Jung, Seonghoon; Park, Jaehun; Park, Gun-Sik

    2015-05-01

    The contribution of water to DNA conformational change, DNA-protein interactions, and DNA-ligand recognition has been underlined. Here, we investigate the relaxation process of water around the Dickerson-Drew B-DNA duplex using terahertz spectroscopy. By controlling the DNA concentration, the relaxation time for water reorientation and the width of the DNA hydration layer are determined. We found that a layer of weakly bound hydration water, with a relaxation time of 11.6 ps, extends 7.6 Å from the tight-binding water layer. This result demonstrates that a shell of hydration water, with reorientation time on the order of tens of picoseconds, exists beyond the structurally integrated water usually observed around DNA.

  20. Induced tolerance expressed as relaxed behavioural threat response in millimetre-sized aquatic organisms

    PubMed Central

    Hylander, Samuel; Ekvall, Mikael T.; Bianco, Giuseppe; Yang, Xi; Hansson, Lars-Anders

    2014-01-01

    Natural selection shapes behaviour in all organisms, but this is difficult to study in small, millimetre-sized, organisms. With novel labelling and tracking techniques, based on nanotechnology, we here show how behaviour in zooplankton (Daphnia magna) is affected by size, morphology and previous exposure to detrimental ultraviolet radiation (UVR). All individuals responded with immediate downward swimming to UVR exposure, but when released from the threat they rapidly returned to the surface. Large individuals swam faster and generally travelled longer distances than small individuals. Interestingly, individuals previously exposed to UVR (during several generations) showed a more relaxed response to UVR and travelled shorter total distances than those that were naive to UVR, suggesting induced tolerance to the threat. In addition, animals previously exposed to UVR also had smaller eyes than the naive ones, whereas UVR-protective melanin pigmentation of the animals was similar between populations. Finally, we show that smaller individuals have lower capacity to avoid UVR which could explain patterns in natural systems of lower migration amplitudes in small individuals. The ability to change behavioural patterns in response to a threat, in this case UVR, adds to our understanding of how organisms navigate in the ‘landscape of fear’, and this has important implications for individual fitness and for interaction strengths in biotic interactions. PMID:24966309

  1. Recent developments in the experimental investigations of relaxations in pharmaceuticals by dielectric techniques at ambient and elevated pressure.

    PubMed

    Grzybowska, Katarzyna; Capaccioli, Simone; Paluch, Marian

    2016-05-01

    In recent years, there is a growing interest in improving the physicochemical stability of amorphous pharmaceutical solids due to their very promising applications to manufacture medicines characterized by a better water solubility, and consequently by a higher dissolution rate than those of their crystalline counterparts. In this review article, we show that the molecular mobility investigated both in the supercooled liquid and glassy states is the crucial factor required to understand molecular mechanisms that govern the physical stability of amorphous drugs. We demonstrate that pharmaceuticals can be thoroughly examined by means of the broadband dielectric spectroscopy, which is a very useful experimental technique to explore different relaxation processes and crystallization kinetics as well. Such studies conducted in the wide temperature and pressure ranges provide data needed in searching correlations between properties of molecular dynamics and crystallization process, which are aimed at developing effective and efficient methods for stabilizing amorphous drugs. PMID:26705851

  2. Structure refinement and dielectric relaxation of M-type Ba, Sr, Ba-Sr, and Ba-Pb hexaferrites

    NASA Astrophysics Data System (ADS)

    Ashima; Sanghi, Sujata; Agarwal, Ashish; Reetu; Ahlawat, Neetu; Monica

    2012-07-01

    M-type hexaferrites with compositions BaFe12O19 (BFO), SrFe12O19 (SFO), Ba0.5Sr0.5Fe12O19 (BSFO), and Ba0.5Pb0.5Fe12O19 (BPFO) were synthesized by commercial solid state reaction method. The Rietveld refinement of x-ray powder diffraction revealed a single hexagonal phase with space group P63/mmc for BFO, SFO, and BSFO samples, whereas BPFO sample contains hematite (α-Fe2O3) phase with space group R3c along with the M-type main phase. All the samples show dispersion in dielectric constant (ɛ') and dielectric loss (tan δ) values with frequency. The values of ɛ' and tan δ increase with increase in temperature due to increase in the number of charge carriers and their mobilities, which are thermally activated. The reciprocal temperature dependence of conductivity (σac) and the most probable relaxation time (τM″) satisfies the Arrhenius relation. A perfect overlapping of the normalized plots of modulus isotherms on a single "super curve" for all the studied temperatures reveals a temperature independence of dynamic processes involved in conduction and for relaxation. Further, the complex plots of M* (M″ vs M') indicate that dc conductivity dominates in the region below the M″max point. Above M″max, the variations follow Jonscher power law (σ = Aωs) implying that ac conductivity is dominating in this region. Among the prepared samples, SFO hexaferrite has lowest values of σac, ɛ', and tan δ making it suitable for use in microwave devices.

  3. Influence of moieties for the phase stability, spontaneous polarization and dielectric relaxations in an achiral ferroelectric bent liquid crystal, PBUOB

    NASA Astrophysics Data System (ADS)

    Chalapathi, P. V.; Srinivasulu, M.; Pisipati, V. G. K. M.; Satyanarayana, Ch.; Potukuchi, D. M.

    2011-05-01

    The occurrence of ferroelelectric phases and influence of chemical moieties in the area of supra-molecular achiral Bent core Liquid Crystals (BLCs) are reviewed. Synthesis of an intermediate/higher homolog of PBnOB series (for n=11), PBUOB, viz. 1,3-Phenyline-Bis(4-UndecylOxy Benzoate), is presented. Smectic LC phases exhibited by PBUOB are characterized by Polarized Optical Microscopy (POM), Differential Scanning Calorimetry (DSC) and Spontaneous Polarization ( PS) techniques. Observations infer a bi-variant FE LC smectic phase occurrence, viz., isotropic→B 2(FE)→B 5(FE)→solid phases in cooling and solid→B 5→isotropic phases in heating scans. Occurrence of B 2 phase is monotropic (in cooling), while B 5 phase is enantiotropic. I-B 2 and B 2-B 5 phase transitions are found to be of first order nature. The FE phases possess a moderate PS value of ∼40 nC cm -2. Transition temperatures from dielectric studies agree with those from TM and DSC. Two modes of relaxations are observed, viz., a slow scissor mode at ∼1 kHz and a fast mode at ∼1 MHz. Anisotropic Dipolar Model is proposed to explain the reorientation mechanism. Arrhenius shifts of Relaxation Frequency ( fR) show differing activation energies for two modes, i.e., 0.11 and 0.98 eV; 0.25 and 1.18 eV in B 2 and B 5 phases, respectively. Temperature variation of dielectric increment Δ ε and α-parameter LC phases reveals the relative fixture of dipole moment in polar smectic layers. An analytical study for the thermal stability, PS and fR in the FE phases is presented with respect to the constitution and configuration of moieties in BLCs.

  4. High temperature dielectric relaxation anomaly of Y³⁺ and Mn²⁺ doped barium strontium titanate ceramics

    SciTech Connect

    Yan, Shiguang; Mao, Chaoliang E-mail: xldong@mail.sic.ac.cn; Wang, Genshui; Yao, Chunhua; Cao, Fei; Dong, Xianlin E-mail: xldong@mail.sic.ac.cn

    2014-10-14

    Relaxation like dielectric anomaly is observed in Y³⁺ and Mn²⁺ doped barium strontium titanate ceramics when the temperature is over 450 K. Apart from the conventional dielectric relaxation analysis method with Debye or modified Debye equations, which is hard to give exact temperature dependence of the relaxation process, dielectric response in the form of complex impedance, assisted with Cole-Cole impedance model corrected equivalent circuits, is adopted to solve this problem and chase the polarization mechanism in this paper. Through this method, an excellent description to temperature dependence of the dielectric relaxation anomaly and its dominated factors are achieved. Further analysis reveals that the exponential decay of the Cole distribution parameter n with temperature is confirmed to be induced by the microscopic lattice distortion due to ions doping and the interaction between the defects. At last, a clear sight to polarization mechanism containing both the intrinsic dipolar polarization and extrinsic distributed oxygen vacancies hopping response under different temperature is obtained.

  5. Interconversion algorithm between mechanical and dielectric relaxation measurements for acetate of cis- and trans-2-phenyl-5-hydroxymethyl-1,3-dioxane

    NASA Astrophysics Data System (ADS)

    Garcia-Bernabé, A.; Lidón-Roger, J. V.; Sanchis, M. J.; Díaz-Calleja, R.; del Castillo, L. F.

    2015-10-01

    The dielectric and mechanical spectroscopies of acetate of cis- and trans-2-phenyl-5-hydroxymethyl-1,3-dioxane are reported in the frequency domain from 10-2 to 106Hz . This ester has been selected in this study for its predominant α relaxation with regard to the β relaxation, which can be neglected. This study consists of determining an interconversion algorithm between dielectric and mechanical measurements, given by using a relation between rotational and translational complex viscosities. These important viscosities were obtained from measures of the dielectric complex permittivity and by dynamic mechanical analysis, respectively. The definitions of rotational and translational viscosities were evaluated by means of fractional calculus, by using the fit parameters of the Havriliak-Negami empirical model obtained in the dielectric and mechanical characterization of the α relaxation. This interconversion algorithm is a generalization of the break of the Stokes-Einstein-Debye relationship. It uses a power law with an exponent defined as the shape factor, which modifies the translational viscosity. Two others factors are introduced for the interconversion, a shift factor, which displaces the translational viscosity in the frequency domain, and a scale factor, which makes equal values of the two viscosities. In this paper, the shape factor has been identified as the relation between the slopes of the moduli of the complex viscosities at higher frequency. This is interpreted as the degree of kinetic coupling between the molecular rotation and translational movements. Alternatively, another interconversion algorithm has been expressed by means of dielectric and mechanical moduli.

  6. Impedance response and dielectric relaxation in co-precipitation derived ferrite (Ni,Zn)Fe2O4 ceramics

    NASA Astrophysics Data System (ADS)

    Chen, D. G.; Tang, X. G.; Liu, Q. X.; Jiang, Y. P.; Ma, C. B.; Li, R.

    2013-06-01

    Dielectric spectra and magnetization hysteresis loops were used to investigate the grain size effect with temperature on the electrical and magnetic response of co-precipitation derived spinel (Ni0.5Zn0.5)Fe2O4 (NZFO) ceramics. Remarkable dielectric relaxation phenomena of non-Debye type have been observed in each NZFO ceramics as confirmed by two kinds of Cole-Cole plots of the 1100 °C sintered samples, mainly due to the electron-hopping mechanism between n-type and p-type carriers and interfacial ion effect when applied an increase of temperature. The high and low response of grain and grain-boundary regions were determined by modeling the impedance experimental results on two equivalent RC circuits taking into account grain deep trap states. By employing the modified Arrhenius equation, activation energy values of different sintering temperatures were calculated and analyzed in combination with oxygen vacancy. In addition, the magnetization of various sintering temperature samples is dominated by cation distribution and surface effect in different particle ranges.

  7. Dielectric relaxation in 0-3 PVDF-Ba(Fe1/2Nb1/2)O3 composites

    NASA Astrophysics Data System (ADS)

    Chandra, K. P.; Singh, Rajan; Kulkarni, A. R.; Prasad, K.

    2016-05-01

    (1-x)PVDF-xBa(Fe1/2Nb1/2)O3 ceramic-polymer composites with x = 0.025, 0.05, 0.10, 0.15 were prepared using melt-mixing technique. The crystal symmetry, space group and unit cell dimensions were determined from the XRD data of Ba(Fe1/2Nb1/2)O3 using FullProf software, whereas crystallite size and lattice strain were estimated using Williamson-Hall approach. The distribution of Ba(Fe1/2Nb1/2)O3 particles in the PVDF matrix were examined on the cryo-fractured surfaces using a scanning electron microscope. Cole-Cole and pseudo Cole-Cole analysis suggested the dielectric relaxation in this system to be of non-Debye type. Filler concentration dependent real and imaginary parts of dielectric constant as well as ac conductivity data followed definite trends of exponential growth types of variation.

  8. Dielectric relaxation and magnetodielectric response in DyMn0.5Cr0.5O3

    NASA Astrophysics Data System (ADS)

    Yuan, B.; Yang, J.; Zuo, X. Z.; Kan, X. C.; Zu, L.; Zhu, X. B.; Dai, J. M.; Song, W. H.; Sun, Y. P.

    2015-09-01

    We investigate the structural, magnetic, and magnetodielectric properties of DyMn0.5Cr0.5O3. The sample can be indexed with an orthorhombic phase with B site disordered space group Pbnm. The valence state of both Mn and Cr ions are suggested to be +3 based on the results of x-ray photoelectron spectroscopy. Two thermally excited dielectric relaxation at temperatures TN2 < T< 300 K and large magnetodielectric effect (MDC = 20%-30%) due to the disordered arrangement of Mn3+/Cr3+ ions associated with electron hopping between them are observed. The absence of any noticeable magnetoresistance effect (MR < 0.5%) demonstrates that the observed magnetodielectric effect is an intrinsic behavior. These results suggest that DyMn0.5Cr0.5O3 is a magnetodielectric compound, whose dielectric properties are dependence of the applied magnetic field, which exhibits such effects near room temperature and holds great promise for future device applications.

  9. Effects of Solvent Dielectric Constant and Viscosity on Two Rotational Relaxation Paths of Excited 9-(Dicyanovinyl) Julolidine.

    PubMed

    Yang, Songqiu; Han, Keli

    2016-07-14

    The understanding of the interplay between microenvironment and molecular rotors is helpful for designing and developing of molecular sensors of local physical properties. We present a study on the two rotational relaxation paths of excited 9-(dicyanovinyl) julolidine in several solvents. One rotational path (C-C single-bond rotation, τb) quickly leads to the formation of a twisted state. The other path (C═C double-bond rotation, τc) shows that the populations go back to the ground state directly via a conical intersection between the S1 and ground state. The increase in the solvent dielectric constant shows little effect on the τb lifetime for its small energy barrier (<0.01 eV), but τc lifetime is increased in larger dielectric constant solvents due to the larger energy gap at conical intersection. Both τb and τc are increased greatly with the increased solvent viscosity. τb is more sensitive to viscosity than τc may be due to its larger rotational moiety. PMID:26886050

  10. Dielectric relaxation and conduction mechanisms in sprayed TiO2 thin films as a function of the annealing temperature

    NASA Astrophysics Data System (ADS)

    Juma, Albert; Acik, Ilona Oja; Mere, Arvo; Krunks, Malle

    2016-04-01

    The electrical properties of TiO2 thin films deposited by chemical spray pyrolysis onto Si substrates were investigated in the metal-oxide-semiconductor (MOS) configuration using current-voltage characteristics and impedance spectroscopy. The electrical properties were analyzed in relation to the changes in microstructure induced during annealing in air up to a temperature of 950 °C. Anatase to rutile transformation started after annealing at 800 °C, and at 950 °C, only the rutile phase was present. The dielectric relaxation strongly depended upon the microstructure of TiO2 with the dielectric constant for the anatase phase between 45 and 50 and that for the rutile phase 123. Leakage current was reduced by three orders of magnitude after annealing at 700 °C due to the densification of the TiO2 film. A double-logarithmic plot of the current-voltage characteristics showed a linear relationship below 0.12 V consistent with Ohmic conduction, while space-charge-limited conduction mechanism as described by Child's law dominated for bias voltages above 0.12 V.

  11. A new paradigm of dielectric relaxation spectroscopy for non-invasive detection of breast abnormalities: a preliminary feasibility analysis

    NASA Astrophysics Data System (ADS)

    Dhurjaty, Sreeram; Qiu, Yuchen; Tan, Maxine; Qian, Wei; Zheng, Bin

    2016-03-01

    In order to improve efficacy of screening mammography, in recent years, we have been investigating the feasibility of applying a resonance-frequency based electrical impedance spectroscopy (REIS) technology to noninvasively detect breast abnormalities that may lead to the development of cancer in the near-term. Despite promising study-results, we found that REIS suffered from relatively poor reproducibility due to perturbations in electrode placement, contact pressure variation on the breast, as well as variation of the resonating inductor. To overcome this limitation, in this study, we propose and analyze a new paradigm of Dielectric Relaxation Spectroscopy (DRS) that measures polarization-lag of dielectric signals in breast-capacitance when excited by the pulses or sine waves. Unlike conventional DRS that operates using the signals at very high frequencies (GHz) to examine changes in polarization, our new method detects and characterizes the dielectric properties of tissue at low frequencies (<=10 MHz) due to the advent of inexpensive oscillators that are accurate to 1 pico-second (used in GPS receivers) as well as measurement of amplitudes of 1 ppm or better. From theoretical analysis, we have proved that the sensitivity of new DRS in detecting permittivity of water increased by >=80 times as compared to conventional DRS, which operates at frequencies around 4GHz. By analyzing and comparing the relationship between the new DRS and REIS, we found that this DRS has potential advantages in enhancing repeatability from various readings, including temperature-insensitive detection, and yielding higher resolution or sensitivity (up to 100 Femtofarads).

  12. Coupling behaviour of tapered highly multimodal dielectric waveguides as part of PCB-level optical interconnects

    NASA Astrophysics Data System (ADS)

    Soenmez, Yasin; Mrozynski, Gerd; Schrage, Juergen

    2010-05-01

    Optical interconnects replace electrical links increasingly at shorter distances. At printed circuit board (PCB) level highly multimodal polymer channel waveguides are the chosen approach to meet bandwidth-length and bandwidth-density requirements. One important challenge of board integrated waveguides is the coupling problem. The manufacturing process of PCBs leads to relatively high placement tolerances which cause poor optical coupling efficiency due to mechanical misalignment between separate components, e.g.: 1) Coupling between a VCSEL and the board integrated waveguides; 2) Coupling between waveguides in two separate boards. This paper deals with the deployment of tapered dielectric multimode waveguides for increasing the optical coupling robustness towards mechanical misalignments in these two coupling applications. A coupled mode approach for calculation of the mode coupling and power loss in a taper with decreasing width has been presented before [5]. In [6], the two above mentioned coupling applications for tapered dielectric waveguides have been dealt with, but only the coupling efficiency in case of longitudinal misalignment has been calculated. In this paper, results of advanced analysis of the two applications are presented. The coupling efficiency in case of transverse misalignment is simulated by a ray-optical approach. Furthermore the results of measurements of the coupling behaviour of board integrated tapered waveguides are presented. The results show that tapered multimodal dielectric waveguides have the capability to increase the coupling efficiency significantly if some conditions are fulfilled.

  13. Investigation of dielectric relaxation, Jahn-Teller distortion, and magnetic ordering in Y substituted Pr1-xYxMnO3 (0.1 ≤ x ≤ 0.4)

    NASA Astrophysics Data System (ADS)

    Yadav, Ruchika; Nair, Harikrishnan S.; Kumar, Amit; Adiga, Shilpa; Bhat, H. L.; Yusuf, S. M.; Elizabeth, Suja

    2015-03-01

    We report structural, magnetic, and dielectric properties of the perovskite compound Pr1-xYxMnO3 (0.1 ≤ x ≤ 0.4) studied using dc magnetization, ac susceptibility, neutron powder diffraction, and dielectric techniques. These compounds crystallize in orthorhombic space group (Pnma) in the temperature range 5-300 K. The Mn-O-Mn bond angle decreases with the Y substitution along with an increase in the Jahn-Teller distortion. The Jahn-Teller distortion for Pr0.9Y0.1MnO3 shows an anomalous change near 50 K, below which it falls sharply. Neutron powder diffraction patterns of all reported compositions at low temperature constitute additional magnetic Bragg peaks that suggest magnetic ordering. Magnetic reflections were indexed in the nuclear lattice with the propagation vector k = (0, 0, 0). Rietveld refinement of powder patterns conform to A type antiferromagnetic ordering where moments are aligned ferromagnetically in a-c plane and coupled nearly antiferromagnetically along b-axis resulting in a net ferromagnetic component along the b-direction. The antiferromagnetic transition temperature was deduced from dc magnetization and ac susceptibility data. The transition temperature decreases by nearly 22 K (from 81 K to 59 K) as yttrium content (x) increases from 0.1 to 0.4. Measurements reveal strong frequency dispersion in dielectric constant and dielectric loss. Activation energy and relaxation time are estimated from the Arrhenius plot. It is further shown that relaxation behaviour is altered with yttrium doping concentration.

  14. Respiratory Patterns in Students Enrolled in Schools for Disruptive Behaviour before, during, and after "Yoga Nidra" Relaxation

    ERIC Educational Resources Information Center

    Jensen, P. S.; Stevens, P. J.; Kenny, D. T.

    2012-01-01

    This study investigated the effects of one session of "Yoga Nidra" (relaxation technique) on the breathing patterns/respiratory effort in the thoracic and abdominal chest regions of boys with disruptive behaviour using a Respiratory Inductive Plethysmography (RIP). The participants (n = 7) were aged 10-15 years and attending NSW, Department of…

  15. Dielectric relaxation behavior in antiferroelectric metal organic framework [(CH3)2NH2][Fe(III)Fe(II)(HCOO)6] single crystals.

    PubMed

    Sieradzki, A; Pawlus, S; Tripathy, S N; Gągor, A; Ciupa, A; Mączka, M; Paluch, M

    2016-03-16

    The fundamental aspects of the relaxation dynamics in niccolite-type, mixed valence metal-organic framework, multiferroic [(CH3)2NH2][Fe(3+)Fe(2+)(HCOO)6] single crystals have been reported using dielectric relaxation spectroscopy covering eight decades in frequency (10(-2) ≤ f ≤ 10(6)) in the temperature range 120 K ≤ T ≤ 250 K. The compound shows antiferroelectric to paraelectric phase transition near T = 154 K with the relaxor nature of electric ordering. The temperature dependent dielectric response in modulus representation indicates three relaxation processes within the experimental window. The variable range hopping model of small polarons explains the bulk non-Debye type conductivity relaxation. The fastest relaxation with activation energy Ea = 0.17 eV is related to progressive freezing of the reorientation motions of DMA(+) cations. X-ray diffraction data revealed that complete freezing of orientational and translational motions of DMA(+) cations occurs well below phase transition temperature. These experimental observations are fundamentally important for the theoretical explanation of relaxation dynamics in niccolite-type metal-organic frameworks. PMID:26936014

  16. Dielectric Relaxation Study of Some Solutions Containing β-Cyclodextrin and Dimethylsulfoxide

    NASA Astrophysics Data System (ADS)

    Betting, H.; Stockhausen, M.

    1999-07-01

    Dielectric spectra have been measured up to 72 GHz at 20°C for solutions of β-cyclodextrin (CD) in the following solvents over the whole solubility range of CD: dimethylsulfoxide (DMSO), DMSO/ 1,4-dioxane mixture (2:1 molar ratio), DMSO/water mixtures (2:1 and 1:2). The spectra are analyzed into a sum of Debye type spectral components. These are likely to be caused by different physical pro-cesses. The discussion shows (i) that there is a preferential CD-DMSO interaction, by far exceeding the CD-water interaction, and (») that, concerning CD-DMSO, a loose interaction can be distinguished from the formation of an inclusion complex.

  17. Functionally distinct tendon fascicles exhibit different creep and stress relaxation behaviour

    PubMed Central

    Legerlotz, Kirsten; Demirci, Taylan; Klemt, Christian; Riley, Graham P; Screen, Hazel RC

    2014-01-01

    Most overuse tendinopathies are thought to be associated with repeated microstrain below the failure threshold, analogous to the fatigue failure that affects materials placed under repetitive loading. Investigating the progression of fatigue damage within tendons is therefore of critical importance. There are obvious challenges associated with the sourcing of human tendon samples for in vitro analysis so animal models are regularly adopted. However, data indicates that fatigue life varies significantly between tendons of different species and with different stresses in life. Positional tendons such as rat tail tendon or the bovine digital extensor are commonly applied in in vitro studies of tendon overuse, but there is no evidence to suggest their behaviour is indicative of the types of human tendon particularly prone to overuse injuries. In this study, the fatigue response of the largely positional digital extensor and the more energy storing deep digital flexor tendon of the bovine hoof were compared to the semitendinosus tendon of the human hamstring. Fascicles from each tendon type were subjected to either stress or strain controlled fatigue loading (cyclic creep or cyclic stress relaxation respectively). Gross fascicle mechanics were monitored after cyclic stress relaxation and the mean number of cycles to failure investigated with creep loading. Bovine extensor fascicles demonstrated the poorest fatigue response, while the energy storing human semitendinosus was the most fatigue resistant. Despite the superior fatigue response of the energy storing tendons, confocal imaging suggested a similar degree of damage in all three tendon types; it appears the more energy storing tendons are better able to withstand damage without detriment to mechanics. PMID:24285289

  18. Dynamics of plasma formation, relaxation, and topography modification induced by femtosecond laser pulses in crystalline and amorphous dielectrics

    SciTech Connect

    Puerto, D.; Siegel, J.; Gawelda, W.; Galvan-Sosa, M.; Solis, J.; Ehrentraut, L.; Bonse, J.

    2010-05-15

    We have studied plasma formation and relaxation dynamics along with the corresponding topography modifications in fused silica and sapphire induced by single femtosecond laser pulses (800 nm and 120 fs). These materials, representative of high bandgap amorphous and crystalline dielectrics, respectively, require nonlinear mechanisms to absorb the laser light. The study employed a femtosecond time-resolved microscopy technique that allows obtaining reflectivity and transmission images of the material surface at well-defined temporal delays after the arrival of the pump pulse which excites the dielectric material. The transient evolution of the free-electron plasma formed can be followed by combining the time-resolved optical data with a Drude model to estimate transient electron densities and skin depths. The temporal evolution of the optical properties is very similar in both materials within the first few hundred picoseconds, including the formation of a high reflectivity ring at about 7 ps. In contrast, at longer delays (100 ps-20 ns) the behavior of both materials differs significantly, revealing a longer lasting ablation process in sapphire. Moreover, transient images of sapphire show a concentric ring pattern surrounding the ablation crater, which is not observed in fused silica. We attribute this phenomenon to optical diffraction at a transient elevation of the ejected molten material at the crater border. On the other hand, the final topography of the ablation crater is radically different for each material. While in fused silica a relatively smooth crater with two distinct regimes is observed, sapphire shows much steeper crater walls, surrounded by a weak depression along with cracks in the material surface. These differences are explained in terms of the most relevant thermal and mechanical properties of the material. Despite these differences the maximum crater depth is comparable in both material at the highest fluences used (16 J/cm{sup 2}). The

  19. Associating behaviour of pure polar liquids: dielectric properties of lauric acid

    NASA Astrophysics Data System (ADS)

    Mognaschi, E. R.; Laboranti, L. M.

    1994-09-01

    In this paper measurements of the static dielectric permittivity of lauric acid at different temperatures from about 10 K above the MP to 352 K are reported. These data, together with the dependence of the refractive index and density on temperature, are used in order to investigate the associative behaviour of lauric acid. The Kirkwood correlation factor calculated both with the classical Kirkwood-Frddotohlich equation and with that corrected for eflipsoidal shaped molecules are reported and discussed. Both correlation factors obtained indicate the existence of a prevailing antiparallel order of dipole moments. The static permittivity and the correlation factors increase with increasing temperature and this suggests that the number of apolar dimers decreases on going from low to high temperature.

  20. Relaxor Behavior and Dielectric Relaxation in Lead-Free Solid Solutions of (1 - x)(Bi0.5Na0.5TiO3)- x(SrNb2O6)

    NASA Astrophysics Data System (ADS)

    Bajpai, P. K.; Singh, K. N.; Tamrakar, Preeti

    2016-02-01

    Lead-free compositions (1 - x) (Bi0.5Na0.5TiO3)- x(SrNb2O6) (BNT-SN) are synthesized by a simple solid state reaction route. SN diffuse in distorted perovskite BNT for low concentrations of SN ( x ≤ 0.03) and are stabilized in rhombohedral perovskite phase with experimentally observed relative density of the ceramics >92%. A temperature-dependent dielectric response exhibits a broad dielectric peak that shows frequency-dependent shifts towards higher temperatures reflecting typical relaxor behavior. Modified Curie-Weiss law and Lorentz-type empirical relationships are used to fit the dielectric data that exhibit almost complete diffuse phase transition characteristics. In addition, significant dielectric dispersion is observed in a low-frequency regime in both components of the dielectric response and a small dielectric relaxation peak is observed. Cole-Cole plots indicate the poly-dispersive nature of the dielectric relaxation.

  1. Electron energy-loss spectroscopy analysis of HfO2 dielectric films on strained and relaxed SiGe /Si substrates

    NASA Astrophysics Data System (ADS)

    Jang, Jiyoung; Park, Tae Joo; Kwon, Ji-Hwan; Jang, Jae Hyuck; Hwang, Cheol Seong; Kim, Miyoung

    2008-06-01

    In this investigation, HfO2 thin films were deposited on strained and strain-relaxed epitaxial-SiGe /Si substrates, and subsequently subjected to annealing. Electron energy-loss spectroscopy analysis was used to investigate the electronic structure and composition of the film as well as the interfacial layer (IL). While the energy-loss function of the dielectric films revealed predominant Si diffusion in the strained substrates, post deposition annealing (PDA) significantly influenced the diffusion and altered the local composition of the IL in strain-relaxed substrates. Analysis of electronic structures revealed the origin of significant loss of Ge atoms at the IL during PDA.

  2. Dielectric relaxation behavior in co-precipitation derived ferrite (Zn1-xNix)Fe2O4 (0.2 ≤ x ≤ 0.5) ceramics

    NASA Astrophysics Data System (ADS)

    Jiang, Y. P.; Li, R.; Tang, X. G.; Liu, Q. X.; Chen, D. G.

    2016-01-01

    The influence of nickel doping on the electrical properties and dielectric relaxation in Zn1-xNixFe2O4 (ZNFO, 0.2 ≤ x ≤ 0.5) ceramics has been investigated via the dielectric and complex impedance spectra measurements. According to the modified Curie-Weiss law, the diffusivity factor of the ZNFO ceramics from 1.69 to 2.02 with x increasing from 0.2 to 0.5, respectively. Two relaxation peaks are observed in the nickel doped samples, by employing the modified Arrhenius equation, two activation energy values of different sintering temperatures were calculated and analyzed in combination with oxygen vacancy. The Cole-Cole plots showed that the semicircular arcs which are nonideal Debye type, and the grain boundaries resistance increases with increasing Ni concentration.

  3. Diffuse phase transition and high-temperature dielectric relaxation study on (Bi0.5Na0.5)1-xBaxTiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Chen, Feng; Liu, Qiu-Xiang; Tang, Xin-Gui; Jiang, Yan-Ping; Yue, Jing-Long; Li, Jin-Kai

    2016-09-01

    Lead free (Bi0.5Na0.5)1-xBaxTiO3 (x=0.6, 0.7, 0.8, 0.9) ferroelectric ceramics were synthesized by the traditional solid state reaction method. Sintering was carried out at 1200 °C for 2 h in air atmosphere. The structural, microstructure and Ferroelectric of ceramics were investigated. In dielectric studies, a diffuse phase transition was exhibited and a dielectric relaxation behavious was observed at high temperature range. Impedance analysis characterized grain and grain boundaries resistivities of the ceramics and calculated activation energy and the activation energy for conduction. Polaron theory indicates that the relaxation of the samples at high temperatures was associated with the hopping ions caused by oxygen vacancies.

  4. Cole-Cole Plots for Linear and Nonlinear Dielectric Relaxation in Solutions of Rigid, Highly Dipolar, Symmetric-Top Molecules in Spherical Solvents

    NASA Astrophysics Data System (ADS)

    Alexiewicz, W.; Grygiel, K.

    2008-10-01

    The graphical analysis of the influence of the rotational diffusion tensor anisotropy and the orientation of the permanent dipole moment on the linear and nonlinear dielectric relaxation is shown. The solution of Smoluchowski-Debye rotational diffusion equation for rigid, and noninteracting polar, symmetric-top molecules, in the "weak molecular reorientation approximation", was used. In order to highlight the influence of the symmetric shape of molecule, in comparison with classical, spherical-top Smoluchowski rotational diffusion, we present sets of Argand-type plots and three-dimensional Cole-Cole diagrams for linear and nonlinear electric susceptibilities. The results indicate that, in describing the nonlinear dielectric relaxation, the simplest spherical-top rotational diffusion model may be a sufficient approximation in some special cases only.

  5. Consideration of fractal and ion-water cooperative interactions in aqueous Na2SO4 and K2SO4 solutions by dielectric relaxation spectroscopy

    NASA Astrophysics Data System (ADS)

    Liu, Shuang; Jia, Guo-zhu; Zhang, Shu

    2016-01-01

    This paper presents the analysis of the fractal and the ion-water cooperative interactions in aqueous Na2SO4 and K2SO4 solutions underlying the Cole-Cole symmetrical broadening and depicts the Cole-Cole relaxation process. Fractal analysis with α(ln(τ)) diagram from dielectric relaxation spectroscopy (DRS) draws a consistent microscopic picture of ion-water cooperative interactions in aqueous Na2SO4 and K2SO4 solutions. The density of the water molecules perturbed by ions in the hydration shell almost linearly increases with salt concentrations. The water molecules network perturbed by ions contributing to dielectric constant beyond the first hydration shell is obtained.

  6. Interconversion algorithm between mechanical and dielectric relaxation measurements for acetate of cis- and trans-2-phenyl-5-hydroxymethyl-1,3-dioxane.

    PubMed

    Garcia-Bernabé, A; Lidón-Roger, J V; Sanchis, M J; Díaz-Calleja, R; del Castillo, L F

    2015-10-01

    The dielectric and mechanical spectroscopies of acetate of cis- and trans-2-phenyl-5-hydroxymethyl-1,3-dioxane are reported in the frequency domain from 10(-2) to 10(6)Hz. This ester has been selected in this study for its predominant α relaxation with regard to the β relaxation, which can be neglected. This study consists of determining an interconversion algorithm between dielectric and mechanical measurements, given by using a relation between rotational and translational complex viscosities. These important viscosities were obtained from measures of the dielectric complex permittivity and by dynamic mechanical analysis, respectively. The definitions of rotational and translational viscosities were evaluated by means of fractional calculus, by using the fit parameters of the Havriliak-Negami empirical model obtained in the dielectric and mechanical characterization of the α relaxation. This interconversion algorithm is a generalization of the break of the Stokes-Einstein-Debye relationship. It uses a power law with an exponent defined as the shape factor, which modifies the translational viscosity. Two others factors are introduced for the interconversion, a shift factor, which displaces the translational viscosity in the frequency domain, and a scale factor, which makes equal values of the two viscosities. In this paper, the shape factor has been identified as the relation between the slopes of the moduli of the complex viscosities at higher frequency. This is interpreted as the degree of kinetic coupling between the molecular rotation and translational movements. Alternatively, another interconversion algorithm has been expressed by means of dielectric and mechanical moduli. PMID:26565240

  7. Variable-temperature measurements of the dielectric relaxation in carbon black loaded epoxy composites

    NASA Astrophysics Data System (ADS)

    Brosseau, C.; Achour, M. E.

    2009-06-01

    Technologically, an understanding of the temperature influence on the transport properties is essential to the study of many random conductor-insulator composites, while fundamentally it is related to a variety of questions in statistical physics, dielectrics, and materials science, to name a few. Variable-temperature measurements of the frequency dependent complex effective permittivity were performed on amine-cured epoxy resins loaded with carbon black (CB). Two series of prepercolative samples differing from the kind of CB particles (Raven 2000 and Raven 5000) mixed in an amine-cured epoxy matrix (diglycidylic ether of bisphenol F) were studied. In this effort to contribute to our understanding of the role of frequency (100 Hz-15 MHz) and temperature (from ambient temperature up to 90 °C) on the complex effective permittivity which describes the linear response of the system to an electromagnetic wave, we investigate these composites with CB loadings below the percolation threshold. Two features are observed. First, our observations cannot be understood in the typical framework of a simple Debye-like dipolar process. In this analysis, we argue that the appearance of the broad temperature and frequency dependent maximum loss can be understood within the heuristic framework proposed by Jonscher which applies to disordered heterogeneous systems. This theoretical framework is consistent with several aspects of the experiments, notably the power-law decays of the real and imaginary parts of the effective permittivity characterized by two fractional exponents m and n. These exponents are both positive and smaller than unity. We further quantified their different temperature variations: while m is strongly decreasing with increasing temperature, n takes a value close to 1. Second, the observed maximum loss frequency found for each CB volume fraction shifts to higher frequencies with increasing temperature and exhibits a non-Arrhenius temperature dependence well

  8. Oxygen-vacancy-related dielectric relaxation in SrBi2Ta1.8V0.2O9 ferroelectrics

    NASA Astrophysics Data System (ADS)

    Wu, Yun; Forbess, Mike J.; Seraji, Seana; Limmer, Steven J.; Chou, Tammy P.; Cao, Guozhong

    2001-05-01

    The strontium bismuth tantalate vanadate, SrBi2Ta1.8V0.2O9, (SBTV) layered perovskite ferroelectrics were made by solid state powder sintering. It was found that the SBTV ferroelectrics had the same crystal structure as that of strontium bismuth tantalate, SrBi2Ta2O9 (SBT), but an increased paraferroelectric transition temperature at ˜360 °C as compared to 305 °C for SBT. In addition, SBTV ferroelectrics showed a frequency dispersion at low frequencies and broadened dielectric peaks at the paraferroelectric transition temperature that shifted to a higher temperature with a reduced frequency. However, after a postsintering annealing at 850 °C in air for 60 h, SBTV ferroelectrics showed reduced dielectric constants and tangent loss, particularly at high temperatures. In addition, no frequency dependence of paraferroelectric transition was found in the annealed SBTV ferroelectrics. Furthermore, there was a significant reduction in dc conductivity with annealing. The prior results implied that the dielectric relaxation in the as-sintered SBTV ferroelectrics was most likely due to the oxygen-vacancy-related dielectric relaxation instead of relaxor ferroelectric behavior.

  9. Electrical conduction and dielectric relaxation properties of AlN thin films grown by hollow-cathode plasma-assisted atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Altuntas, Halit; Bayrak, Turkan; Kizir, Seda; Haider, Ali; Biyikli, Necmi

    2016-07-01

    In this study, aluminum nitride (AlN) thin films were deposited at 200 °C, on p-type silicon substrates utilizing a capacitively coupled hollow-cathode plasma source integrated atomic layer deposition (ALD) reactor. The structural properties of AlN were characterized by grazing incidence x-ray diffraction, by which we confirmed the hexagonal wurtzite single-phase crystalline structure. The films exhibited an optical band edge around ∼5.7 eV. The refractive index and extinction coefficient of the AlN films were measured via a spectroscopic ellipsometer. In addition, to investigate the electrical conduction mechanisms and dielectric properties, Al/AlN/p-Si metal-insulator-semiconductor capacitor structures were fabricated, and current density–voltage and frequency dependent (7 kHz–5 MHz) dielectric constant measurements (within the strong accumulation region) were performed. A peak of dielectric loss was observed at a frequency of 3 MHz and the Cole–Davidson empirical formula was used to determine the relaxation time. It was concluded that the native point defects such as nitrogen vacancies and DX centers formed with the involvement of Si atoms into the AlN layers might have influenced the electrical conduction and dielectric relaxation properties of the plasma-assisted ALD grown AlN films.

  10. Electrical study and dielectric relaxation behavior in nanocrystalline Ce0.85Gd0.15O2- δ material at intermediate temperatures

    NASA Astrophysics Data System (ADS)

    Kumar Baral, Ashok; Sankaranarayanan, V.

    2010-02-01

    The nanocrystalline material of 15 mol% Gd-doped ceria (Ce0.85Gd0.15O2- δ ) was prepared by citrate auto ignition method. The electrical study and dielectric relaxation technique were applied to investigate the ionic transport process in this nanocrystalline material with an average grain size of 13 nm and the dynamic relaxation parameters are deduced in the temperature range of 300-600°C. The ionic transference number in the material is found to be 0.85 at 500°C at ambient conditions. The oxygen ionic conduction in the nanocrystalline Ce0.85Gd0.15O2- δ material follows the hopping mechanism. The grain boundary relaxation is found to be associated with migration of charge carriers. The frequency spectra of modulus M″ exhibited a dielectric relaxation peak corresponding to defect associates (Gd-Vo^{_{_{{blacksquare blacksquare}}}})^{_{_{{blacksquare}}}}. The material exhibits very low values of migration energy and association energy of the oxygen vacancies in the long-range motion, i.e., 0.84 and 0.07 eV, respectively.

  11. Anomalous dielectric behaviour of poly(vinyl alcohol)-silicon dioxide (PVA-SiO2) nanocomposites

    NASA Astrophysics Data System (ADS)

    Choudhary, Shobhna; Sengwa, R. J.

    2016-05-01

    Complex dielectric function, electric modulus, ac conductivity and impedance spectra of PVA-SiO2 nanocomposite films have been investigated in the frequency range of 20 Hz to 1 MHz and temperature range from 30 °C to 60 °C. Real part of dielectric function of the nanocomposites slowly decreases with increase of frequency and it shows a non-linear increase with the increase of temperature. An anomalous variation is observed in dielectric and electrical functions with increase of SiO2 concentrations in the PVA matrix. The ac conductivity of these materials increases whereas impedance values decrease linearly by five orders of magnitude with increase of frequency from 20 Hz to 1 MHz. Dielectric loss values of these films are found minimum at intermediate frequency region, and it increases at low and high frequency regions confirming the presence of multiple relaxation processes. The contributions of interfacial polarization effect and dipolar ordering in dielectric properties of these materials have been explored, and their technological applications as nanodielectrics have been discussed. The XRD patterns reveal that the interactions between PVA and SiO2 disturb the dipolar ordering resulting decrease of crystallinity of the PVA in the nanocomposites.

  12. A Journey of Self-Discovery: An Intervention Involving Massage, Yoga and Relaxation for Children with Emotional and Behavioural Difficulties Attending Primary Schools

    ERIC Educational Resources Information Center

    Powell, Lesley; Gilchrist, Mollie; Stapley, Jacqueline

    2008-01-01

    This study reports on an intervention involving massage, yoga and relaxation delivered to young children with identified emotional and behavioural difficulties, and at risk of exclusion. Children (n = 126) were invited by the head teacher to participate in the Self-discovery Programme (involving massage, yoga, breath work and relaxation) with…

  13. Experimental and computational assessment of F-actin influence in regulating cellular stiffness and relaxation behaviour of fibroblasts.

    PubMed

    Fallqvist, Björn; Fielden, Matthew L; Pettersson, Torbjörn; Nordgren, Niklas; Kroon, Martin; Gad, Annica K B

    2016-06-01

    In biomechanics, a complete understanding of the structures and mechanisms that regulate cellular stiffness at a molecular level remain elusive. In this paper, we have elucidated the role of filamentous actin (F-actin) in regulating elastic and viscous properties of the cytoplasm and the nucleus. Specifically, we performed colloidal-probe atomic force microscopy (AFM) on BjhTERT fibroblast cells incubated with Latrunculin B (LatB), which results in depolymerisation of F-actin, or DMSO control. We found that the treatment with LatB not only reduced cellular stiffness, but also greatly increased the relaxation rate for the cytoplasm in the peripheral region and in the vicinity of the nucleus. We thus conclude that F-actin is a major determinant in not only providing elastic stiffness to the cell, but also in regulating its viscous behaviour. To further investigate the interdependence of different cytoskeletal networks and cell shape, we provided a computational model in a finite element framework. The computational model is based on a split strain energy function of separate cellular constituents, here assumed to be cytoskeletal components, for which a composite strain energy function was defined. We found a significant influence of cell geometry on the predicted mechanical response. Importantly, the relaxation behaviour of the cell can be characterised by a material model with two time constants that have previously been found to predict mechanical behaviour of actin and intermediate filament networks. By merely tuning two effective stiffness parameters, the model predicts experimental results in cells with a partly depolymerised actin cytoskeleton as well as in untreated control. This indicates that actin and intermediate filament networks are instrumental in providing elastic stiffness in response to applied forces, as well as governing the relaxation behaviour over shorter and longer time-scales, respectively. PMID:26766328

  14. Superparamagnetic behaviour and T 1, T 2 relaxivity of ZnFe2O4 nanoparticles for magnetic resonance imaging

    NASA Astrophysics Data System (ADS)

    Manjura Hoque, S.; Srivastava, C.; Venkatesha, N.; Kumar, P. S. Anil; Chattopadhyay, K.

    2013-05-01

    In the present study, ZnFe2O4 nanoparticles were synthesized by the chemical co-precipitation followed by calcinations at 473 and 673 K for 4 h. Particle sizes obtained were 4 and 6 nm for the calcination temperatures of 473 and 673 K, respectively. To study the origin of system's low temperature spin dynamic behaviour, temperature dependence of susceptibility ? was investigated as a function of particle size and frequency. Slight increase in the grain size from 4 nm at 473 K to 6 nm at 673 K has led to a peak shift of temperature dependence of susceptibility measured at a constant frequency of 400 Hz. Temperature dependence of ? at different frequencies also resulted in peak shift. Relaxation time dependence of peak temperature obeys a power law, which provides the fitting parameters within the range of superparamagnetic nature of the particles. Further, dependence of relaxation time and peak temperature obeys Vogel-Fulcher law rather than Néel-Brown equation demonstrating that the particles follow the behaviour of superparamagnetism of slightly interacting system. Spin-lattice, T 1 and spin-spin, T 2 relaxivity of proton of the water molecule in the presence of chitosan-coated superparamagnetic ZnFe2O4 nanoparticle yields the values of 0.002 and 0.360 s-1 per ppm.

  15. Effect of high hydrostatic pressure on the dielectric relaxation in a non-crystallizable monohydroxy alcohol in its supercooled liquid and glassy states

    NASA Astrophysics Data System (ADS)

    Pawlus, S.; Paluch, M.; Nagaraj, M.; Vij, J. K.

    2011-08-01

    The complex relative permittivity of a non-crystallizable secondary alcohol, 5-methyl-2-hexanol, is measured over a wide range of temperatures and pressures up to 1750 MPa (17.5 kbar). The data at atmospheric pressure (P = 0.101 MPa) are analyzed in terms of three processes, and the results are in complete agreement with that of O. E. Kalinovskaya and J. K. Vij [J. Chem. Phys. 112, 3262 (2000)]. Process I is of the Debye type and process II is of the Davidson-Cole type, whereas process III is identified as the Johari-Goldstein relaxation process. For pressures of ˜500 MPa and higher, processes I and II are seen to merge into each other to form a single dominant process which unambiguously cannot be resolved into more than one process. The dielectric relaxation strength of process I decreases slightly initially with pressure and when the two processes have merged at elevated pressures, the total relaxation strength increases with increase in pressure. Process III is better resolvable at higher pressures especially above Tg in the supercooled liquid state for the reason that the separation in the time scales between the dominant and the JG relaxation process increases at elevated pressures. Surprisingly we find a change in the slope in the plot of log τJG vs. 1/T for P = 1750 MPa. The results for the relaxation time of alcohols are compared with the Kirkwood correlation factor, g, and it is found that higher is the g, lower is the relaxation time for process I, and it is more of the Debye type. On a reduction in g brought about by an increase in pressure at lower temperatures, the dominant process becomes non-Debye though extensive hydrogen bonding is still present. The dielectric strength of the merged processes increases with increase in pressure. The values of the steepness index, m = |d log τ/d(Tg/T)|T = Tg for processes I and II are different for P = 0.1 MPa. However the value of m, for the composite process, which is a merger of processes I and II, for P

  16. AC conductivity and dielectric relaxation of tris(N,N-dimethylanilinium) hexabromidostannate(IV) bromide: (C8H12N)3SnBr6.Br

    NASA Astrophysics Data System (ADS)

    Chouaib, H.; Kamoun, S.

    2015-10-01

    The X-ray powder analysis, thermogravimetric analysis, differential scanning calorimetry analysis and complex impedance spectroscopic data have been carried out on (C8H12N)3SnBr6.Br compound. The results show that this compound exhibits a phase transition at (T=365±2 K) which has been characterized by differential scanning calorimetry (DSC), AC conductivity and dielectric measurements. The AC conductivity, the modulus analysis, the dielectric constants and the polarizability have been studied using impedance in the temperature range from 334 K to 383 K and in the frequency range between 20 Hz and 2 MHz. The temperature dependence of DC conductivity follows the Arrhenius law. Moreover, the frequency dependence of conductivity follows Jonscher's dynamical law with the relation: σ(ω , T) =σDC + B(T)ω s(T) . Relaxation peaks can be observed in the complex modulus analysis and after a transformation of the complex permittivity ε* to the complex polarizability α*.

  17. Dielectric Relaxations of (Acetamide + Electrolyte) Deep Eutectic Solvents in the Frequency Window, 0.2 ≤ ν/GHz ≤ 50: Anion and Cation Dependence.

    PubMed

    Mukherjee, Kallol; Das, Anuradha; Choudhury, Samiran; Barman, Anjan; Biswas, Ranjit

    2015-06-25

    Dielectric relaxation (DR) measurements in the frequency range 0.2 ≤ ν/GHz ≤ 50 have been carried out for neat molten acetamide and six different (acetamide + electrolyte) deep eutectic solvents (DESs) for investigating ion effects on DR dynamics in these ionic DESs. Electrolytes used are lithium salts of bromide (LiBr), nitrate (LiNO3), and perchlorate (LiClO4); sodium salts of perchlorate (NaClO4) and thiocyante (NaSCN); and potassium thiocyanate (KSCN). With these electrolytes acetamide forms DESs approximately at an 80:20 mol ratio. Simultaneous fits to the measured permittivity (ε′) and loss (ε″) spectra of these DESs at ∼293 K require a sum of four Debye (4-D) processes with relaxation times spread over picosecond to nanosecond regime. In contrast, DR spectra for neat molten acetamide (∼354 K) depict 2-D relaxation with time constants ∼50 ps and ∼5 ps. For both the neat and ionic systems, the undetected dispersion, ε∞ – n(D)2, remains to be ∼3–4. Upon comparison, measured DR dynamics reveal pronounced anion and cation effects. Estimated static dielectric constants (ε0) from fits for these DESs cover the range 12 < ε0 < 30 and are remarkably lower than that (ε0 ∼ 64) measured for molten acetamide at ∼354 K. Hydrodynamic effective rotation volumes (Veff) estimated from the slowest DR relaxation time constants vary with ion identity and are much smaller than the molecular volume of acetamide. This decrease of ε0 and Veff is attributed respectively to the pinning of acetamide molecules by ions and orientation jumps and undetected portion to the limited frequency coverage employed in these measurements PMID:26012789

  18. Observation of a new cryogenic temperature dielectric relaxation in multiferroic Bi7Fe3Ti3O21

    NASA Astrophysics Data System (ADS)

    Patwe, S. J.; Achary, S. N.; Manjanna, J.; Tyagi, A. K.; Deshpande, S. K.; Mishra, S. K.; Krishna, P. S. R.; Shinde, A. B.

    2013-09-01

    In this communication, we report details of structural, magnetic, and dielectric properties of multiferroic Bi7Fe3Ti3O21 at cryogenic temperatures. The low temperature impedance spectroscopic studies showed a relaxor-like dielectric anomaly which follows Vogel-Fulcher relation with freezing temperature (TVF) of 33 K. Temperature and field dependent magnetization indicate the onset of a possible antiferromagnetic ordering below 150 K. Variable temperature powder neutron diffraction studies indicate no structural change down to 22 K. The appearance of the low temperature dielectric anomaly along with evidence of magnetic ordering at low temperatures suggests the presence of magnetic domains of mesoscopic scale within the bulk matrix.

  19. Role of (Bi1/2K1/2)TiO3 in the dielectric relaxations of BiFeO3-(Bi1/2K1/2)TiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Cheon, Chae Il; Choi, Jin Hong; Kim, Jeong Seog; Zang, Jiadong; Frömling, Till; Rödel, Jürgen; Jo, Wook

    2016-04-01

    Temperature-dependent dielectric relaxations of (1 - x)BiFeO3-x(Bi1/2K1/2)TiO3 (BF-BKT) lead-free piezoceramics (0.4 ≤ x ≤ 0.8) were investigated via impedance spectroscopic techniques. Regardless of the compositions, the dielectric maximum temperatures exhibit a frequency-dependent dispersion, originating from a Debye relaxation due to the presence of oxygen vacancies. It was also observed that there exist local dielectric maxima due to the relaxation of polar nanoregions as a shoulder on the lower temperature side. The onset temperature for the Debye-type relaxation decreased with decreasing BKT content, gradually overlapping with the low-temperature dielectric dispersion from the relaxation of polar nanoregions. It is proposed that the role of BKT in the BF-BKT system is to enhance the random fields that favor a relaxor state and to suppress the Debye-type relaxation of oxygen vacancy related dipoles.

  20. Dielectric relaxation and underlying dynamics of electrolyte solutions and solvent-molten salt mixtures using terahertz time-domain transmission spectroscopy

    NASA Astrophysics Data System (ADS)

    Asaki, Melanie Lynette Thongs

    Terahertz (THz) transmission spectroscopy is used to obtain the frequency dependent complex dielectric constants of water, methanol, and propylene carbonate, and solutions of lithium salts in these solvents, as well as mixtures of acetonitrile and a room-temperature molten salt. The behavior of the pure solvents is modeled with either two (water and acetonitrile) or three (methanol and propylene carbonate) Debye relaxations. For solutions of lithium salts, the effects of ionic solvation on the relaxation behavior of the solvents is discussed in terms of modifications to the values of the Debye parameters of the pure solvents. In this way we obtain estimates for numbers of irrotationally bound solvent molecules, the numbers of bonds broken or formed, and the effects of ions on the higher frequency relaxations. The same information was obtained for molten salt-acetonitrile systems. In addition, it was determined that at low molten salt concentrations, the mixtures behave like electrolyte solutions of a crystalline salt dissolved in a solvent. At higher molten salt concentrations, the behavior is that of a mixture of two liquids.

  1. Automated, low-temperature dielectric relaxation apparatus for measurement of air-sensitive, corrosive, hygroscopic, powdered samples

    NASA Astrophysics Data System (ADS)

    Bessonette, Paul W. R.; White, Mary Anne

    1999-07-01

    An automated apparatus for dielectric determinations on solid samples was designed to allow cryogenic measurements on air-sensitive, corrosive, hygroscopic, powdered samples, without determination of sample thickness, provided that it is uniform. A three-terminal design enabled measurements that were not affected by errors due to dimensional changes of the sample or the electrodes with changes in temperature. Meaningful dielectric data could be taken over the frequency range from 20 Hz to 1 MHz and the temperature range from 12 to 360 K. Tests with Teflon and with powdered NH4Cl gave results that were accurate within a few percent when compared with literature values.

  2. Dielectric relaxation in complex systems: quality sensing and dielectric properties of honeydew melons from 10 MHz to 1.8 GHz

    NASA Astrophysics Data System (ADS)

    Nigmatullin, R. R.; Arbuzov, A. A.; Nelson, S. O.; Trabelsi, S.

    2006-10-01

    Based on new data treatment methods, it is possible to identify the fitting function for the complex permittivity ɛ(jω) measured for a complex system representing plant tissues of honeydew melons in the frequency range (107 to 1.8×109 Hz) at 25°C. The identified fitting function contains 9 fitting parameters and well describes the plant tissue permittivity. These parameters vary for different tissues; their correlation behavior with respect to soluble solids content (SSC), tissue density (TD) and moisture content (MC) are found by a new approach based on the statistics of the fractional moments (SFM). These correlation dependencies expressed in the form of correlation functions can be used for quality sensing of different complex systems, in particular, for ripe fruits and vegetables, where direct relationships between molecular and fitting parameters are not easy to find. These correlation functions can be used for practical purposes to construct a desired calibration curve with respect to quality factors, as for example, moisture content or degree of maturity, expressed in terms of SSC value. The discovered common ``universality'' in dielectric behavior of such complex materials as plant tissues opens a possibility to use dielectric spectroscopy as a nondestructive method of control in analysis of electrical behavior (measured in the form of complex permittivity or impedance) for other complex materials.

  3. Possible mechanism of charge transport and dielectric relaxation in SrO-Bi2O3-B2O3 glasses

    NASA Astrophysics Data System (ADS)

    Majhi, Koushik; Varma, K. B. R.; Rao, K. J.

    2009-10-01

    Transparent SrBi2B2O7 glasses were prepared via melt-quenching technique and characterized using differential scanning calorimetry and x-ray powder diffraction. The ac conductivities of the glasses were studied as a function of frequency (100 Hz-10 MHz) at different temperatures. The frequency dependence of conductivity has been analyzed using Almond-West expression. The exponent n was nearly unaffected by temperature. Impedance and modulus spectroscopies were employed to further examine the electrical data. Dielectric relaxation exhibited a stretched exponential behavior with a stretching exponent β independent of temperature. From conductivity analysis we have proposed that the charge transport occurs through the participation of nonbridging oxygen (NBO), which switches positions in a facile manner. The stretched exponential behavior appears to be a direct consequence of the NBO switching mechanism of charge transport.

  4. Possible mechanism of charge transport and dielectric relaxation in SrO-Bi{sub 2}O{sub 3}-B{sub 2}O{sub 3} glasses

    SciTech Connect

    Majhi, Koushik; Varma, K. B. R.; Rao, K. J.

    2009-10-15

    Transparent SrBi{sub 2}B{sub 2}O{sub 7} glasses were prepared via melt-quenching technique and characterized using differential scanning calorimetry and x-ray powder diffraction. The ac conductivities of the glasses were studied as a function of frequency (100 Hz-10 MHz) at different temperatures. The frequency dependence of conductivity has been analyzed using Almond-West expression. The exponent n was nearly unaffected by temperature. Impedance and modulus spectroscopies were employed to further examine the electrical data. Dielectric relaxation exhibited a stretched exponential behavior with a stretching exponent beta independent of temperature. From conductivity analysis we have proposed that the charge transport occurs through the participation of nonbridging oxygen (NBO), which switches positions in a facile manner. The stretched exponential behavior appears to be a direct consequence of the NBO switching mechanism of charge transport.

  5. Growth, strain relaxation properties and high-κ dielectric integration of mixed-anion GaAs{sub 1-y}Sb{sub y} metamorphic materials

    SciTech Connect

    Zhu, Y.; Clavel, M.; Goley, P.; Hudait, M. K.

    2014-10-07

    Mixed-anion, GaAs{sub 1-y}Sb{sub y} metamorphic materials with a wide range of antimony (Sb) compositions extending from 15% to 62%, were grown by solid source molecular beam epitaxy (MBE) on GaAs substrates. The impact of different growth parameters on the Sb composition in GaAs{sub 1-y}Sb{sub y} materials was systemically investigated. The Sb composition was well-controlled by carefully optimizing the As/Ga ratio, the Sb/Ga ratio, and the substrate temperature during the MBE growth process. High-resolution x-ray diffraction demonstrated a quasi-complete strain relaxation within each composition of GaAs{sub 1-y}Sb{sub y}. Atomic force microscopy exhibited smooth surface morphologies across the wide range of Sb compositions in the GaAs{sub 1-y}Sb{sub y} structures. Selected high-κ dielectric materials, Al{sub 2}O{sub 3}, HfO{sub 2}, and Ta{sub 2}O{sub 5} were deposited using atomic layer deposition on the GaAs{sub 0.38}Sb{sub 0.62} material, and their respective band alignment properties were investigated by x-ray photoelectron spectroscopy (XPS). Detailed XPS analysis revealed a valence band offset of >2 eV for all three dielectric materials on GaAs{sub 0.38}Sb{sub 0.62}, indicating the potential of utilizing these dielectrics on GaAs{sub 0.38}Sb{sub 0.62} for p-type metal-oxide-semiconductor (MOS) applications. Moreover, both Al{sub 2}O{sub 3} and HfO{sub 2} showed a conduction band offset of >2 eV on GaAs{sub 0.38}Sb{sub 0.62}, suggesting these two dielectrics can also be used for n-type MOS applications. The well-controlled Sb composition in several GaAs{sub 1-y}Sb{sub y} material systems and the detailed band alignment analysis of multiple high-κ dielectric materials on a fixed Sb composition, GaAs{sub 0.38}Sb{sub 0.62}, provides a pathway to utilize GaAs{sub 1-y}Sb{sub y} materials in future microelectronic and optoelectronic applications.

  6. Impedance response and dielectric relaxation in co-precipitation derived ferrite (Ni,Zn)Fe{sub 2}O{sub 4} ceramics

    SciTech Connect

    Chen, D. G.; Tang, X. G.; Liu, Q. X.; Jiang, Y. P.; Ma, C. B.; Li, R.

    2013-06-07

    Dielectric spectra and magnetization hysteresis loops were used to investigate the grain size effect with temperature on the electrical and magnetic response of co-precipitation derived spinel (Ni{sub 0.5}Zn{sub 0.5})Fe{sub 2}O{sub 4} (NZFO) ceramics. Remarkable dielectric relaxation phenomena of non-Debye type have been observed in each NZFO ceramics as confirmed by two kinds of Cole-Cole plots of the 1100 Degree-Sign C sintered samples, mainly due to the electron-hopping mechanism between n-type and p-type carriers and interfacial ion effect when applied an increase of temperature. The high and low response of grain and grain-boundary regions were determined by modeling the impedance experimental results on two equivalent RC circuits taking into account grain deep trap states. By employing the modified Arrhenius equation, activation energy values of different sintering temperatures were calculated and analyzed in combination with oxygen vacancy. In addition, the magnetization of various sintering temperature samples is dominated by cation distribution and surface effect in different particle ranges.

  7. Vertical Interface Induced Dielectric Relaxation in Nanocomposite (BaTiO3)1-x:(Sm2O3)x Thin Films

    NASA Astrophysics Data System (ADS)

    Li, Weiwei; Zhang, Wei; Wang, Le; Gu, Junxing; Chen, Aiping; Zhao, Run; Liang, Yan; Guo, Haizhong; Tang, Rujun; Wang, Chunchang; Jin, Kuijuan; Wang, Haiyan; Yang, Hao

    2015-06-01

    Vertical interfaces in vertically aligned nanocomposite thin films have been approved to be an effective method to manipulate functionalities. However, several challenges with regard to the understanding on the physical process underlying the manipulation still remain. In this work, because of the ordered interfaces and large interfacial area, heteroepitaxial (BaTiO3)1-x:(Sm2O3)x thin films have been fabricated and used as a model system to investigate the relationship between vertical interfaces and dielectric properties. Due to a relatively large strain generated at the interfaces, vertical interfaces between BaTiO3 and Sm2O3 are revealed to become the sinks to attract oxygen vacancies. The movement of oxygen vacancies is confined at the interfaces and hampered by the misfit dislocations, which contributed to a relaxation behavior in (BaTiO3)1-x:(Sm2O3)x thin films. This work represents an approach to further understand that how interfaces influence on dielectric properties in oxide thin films.

  8. Vertical Interface Induced Dielectric Relaxation in Nanocomposite (BaTiO3)1-x:(Sm2O3)x Thin Films

    PubMed Central

    Li, Weiwei; Zhang, Wei; Wang, Le; Gu, Junxing; Chen, Aiping; Zhao, Run; Liang, Yan; Guo, Haizhong; Tang, Rujun; Wang, Chunchang; Jin, Kuijuan; Wang, Haiyan; Yang, Hao

    2015-01-01

    Vertical interfaces in vertically aligned nanocomposite thin films have been approved to be an effective method to manipulate functionalities. However, several challenges with regard to the understanding on the physical process underlying the manipulation still remain. In this work, because of the ordered interfaces and large interfacial area, heteroepitaxial (BaTiO3)1-x:(Sm2O3)x thin films have been fabricated and used as a model system to investigate the relationship between vertical interfaces and dielectric properties. Due to a relatively large strain generated at the interfaces, vertical interfaces between BaTiO3 and Sm2O3 are revealed to become the sinks to attract oxygen vacancies. The movement of oxygen vacancies is confined at the interfaces and hampered by the misfit dislocations, which contributed to a relaxation behavior in (BaTiO3)1-x:(Sm2O3)x thin films. This work represents an approach to further understand that how interfaces influence on dielectric properties in oxide thin films. PMID:26061829

  9. Nonstoichiometric control of tunnel-filling order, thermal expansion, and dielectric relaxation in tetragonal tungsten Bronzes Ba0.5-xTaO3-x.

    PubMed

    Pan, Fengjuan; Li, Xiaohui; Lu, Fengqi; Wang, Xiaoming; Cao, Jiang; Kuang, Xiaojun; Véron, Emmanuel; Porcher, Florence; Suchomel, Matthew R; Wang, Jing; Allix, Mathieu

    2015-09-21

    Ordering of interpolated Ba(2+) chains and alternate Ta-O rows (TaO)(3+) in the pentagonal tunnels of tetragonal tungsten bronzes (TTB) is controlled by the nonstoichiometry in the highly nonstoichiometric Ba0.5-xTaO3-x system. In Ba0.22TaO2.72, the filling of Ba(2+) and (TaO)(3+) groups is partially ordered along the ab-plane of the simple TTB structure, resulting in a √2-type TTB superstructure (Pbmm), while in Ba0.175TaO2.675, the pentagonal tunnel filling is completely ordered along the b-axis of the simple TTB structure, leading to a triple TTB superstructure (P21212). Both superstructures show completely empty square tunnels favoring Ba(2+) conduction and feature unusual accommodation of Ta(5+) cations in the small triangular tunnels. In contrast with stoichiometric Ba6GaTa9O30, which shows linear thermal expansion of the cell parameters and monotonic decrease of permittivity with temperature within 100-800 K, these TTB superstructures and slightly nonstoichiometric simple TTB Ba0.4TaO2.9 display abnormally broad and frequency-dependent extrinsic dielectric relaxations in 10(3)-10(5) Hz above room temperature, a linear deviation of the c-axis thermal expansion around 600 K, and high dielectric permittivity ∼60-95 at 1 MHz at room temperature. PMID:26347025

  10. Vertical Interface Induced Dielectric Relaxation in Nanocomposite (BaTiO3)1-x:(Sm2O3)x Thin Films.

    PubMed

    Li, Weiwei; Zhang, Wei; Wang, Le; Gu, Junxing; Chen, Aiping; Zhao, Run; Liang, Yan; Guo, Haizhong; Tang, Rujun; Wang, Chunchang; Jin, Kuijuan; Wang, Haiyan; Yang, Hao

    2015-01-01

    Vertical interfaces in vertically aligned nanocomposite thin films have been approved to be an effective method to manipulate functionalities. However, several challenges with regard to the understanding on the physical process underlying the manipulation still remain. In this work, because of the ordered interfaces and large interfacial area, heteroepitaxial (BaTiO3)1-x:(Sm2O3)x thin films have been fabricated and used as a model system to investigate the relationship between vertical interfaces and dielectric properties. Due to a relatively large strain generated at the interfaces, vertical interfaces between BaTiO3 and Sm2O3 are revealed to become the sinks to attract oxygen vacancies. The movement of oxygen vacancies is confined at the interfaces and hampered by the misfit dislocations, which contributed to a relaxation behavior in (BaTiO3)1-x:(Sm2O3)x thin films. This work represents an approach to further understand that how interfaces influence on dielectric properties in oxide thin films. PMID:26061829

  11. Dielectric relaxation, lattice dynamics and polarization mechanisms in Bi0.5Na0.5TiO3-based lead-free ceramics

    NASA Astrophysics Data System (ADS)

    Viola, Giuseppe; Ning, Huanpo; Wei, Xiaojong; Deluca, Marco; Adomkevicius, Arturas; Khaliq, Jibran; John Reece, Michael; Yan, Haixue

    2013-07-01

    In 0.95[0.94Bi0.5Na0.5TiO3-0.06BaTiO3]-0.05CaTiO3 ceramics, the temperature TS (dielectric permittivity shoulder at about 125 °C) represents a transition between two different thermally activated dielectric relaxation processes. Below TS, the approximately linear decrease of the permittivity with the logarithm of frequency was attributed to the presence of a dominant ferroelectric phase. Above TS, the permittivity shows a more complicated dependence of the frequency and Raman modes indicate a sudden increase in the spatial disorder of the material, which is ascribed to the presence of a nonpolar phase and to a loss of interaction between polar regions. From 30 to 150 °C, an increase in the maximum polarization with increasing temperature was related to three possible mechanisms: polarization extension favoured by the simultaneous presence of polar and non-polar phases; the occurrence of electric field-induced transitions from weakly polar relaxor to ferroelectric polar phase; and the enhanced polarizability of the crystal structure induced by the weakening of the Bi-O bond with increasing temperature. The occurrence of different electric field induced polarization processes with increasing temperature is supported by the presence of additional current peaks in the current-electric field loops.

  12. Dielectric relaxation and magnetodielectric response in DyMn{sub 0.5}Cr{sub 0.5}O{sub 3}

    SciTech Connect

    Yuan, B.; Yang, J. Zuo, X. Z.; Zhu, X. B.; Dai, J. M.; Song, W. H.; Kan, X. C.; Zu, L.; Sun, Y. P.

    2015-09-28

    We investigate the structural, magnetic, and magnetodielectric properties of DyMn{sub 0.5}Cr{sub 0.5}O{sub 3}. The sample can be indexed with an orthorhombic phase with B site disordered space group Pbnm. The valence state of both Mn and Cr ions are suggested to be +3 based on the results of x-ray photoelectron spectroscopy. Two thermally excited dielectric relaxation at temperatures T{sub N2} < T< 300 K and large magnetodielectric effect (MDC = 20%–30%) due to the disordered arrangement of Mn{sup 3+}/Cr{sup 3+} ions associated with electron hopping between them are observed. The absence of any noticeable magnetoresistance effect (MR < 0.5%) demonstrates that the observed magnetodielectric effect is an intrinsic behavior. These results suggest that DyMn{sub 0.5}Cr{sub 0.5}O{sub 3} is a magnetodielectric compound, whose dielectric properties are dependence of the applied magnetic field, which exhibits such effects near room temperature and holds great promise for future device applications.

  13. Dielectric relaxation and electrical conductivity in Bi 5NbO 10 oxygen ion conductors prepared by a modified sol-gel process

    NASA Astrophysics Data System (ADS)

    Hou, Jungang; Vaish, Rahul; Qu, Yuanfang; Krsmanovic, Dalibor; Varma, K. B. R.; Kumar, R. V.

    Crystalline Bi 5NbO 10 nanoparticles have been achieved through a modified sol-gel process using a mixture of ethylenediamine and ethanolamine as a solvent. The Bi 5NbO 10 nanoparticles were characterized by X-ray diffraction (XRD), differential scanning calorimetry/thermogravimetry (DSC/TG), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM) and Raman spectroscopy. The results showed that well-dispersed 5-60 nm Bi 5NbO 10 nanoparticles were prepared through heat-treating the precursor at 650 °C and the high density pellets were obtained at temperatures lower than those commonly employed. The frequency and temperature dependence of the dielectric constant and the electrical conductivity of the Bi 5NbO 10 solid solutions were investigated in the 0.1 Hz to 1 MHz frequency range. Two distinct relaxation mechanisms were observed in the plots of dielectric loss and the imaginary part of impedance (Z″) versus frequency in the temperature range of 200-350 °C. The dielectric constant and the loss in the low frequency regime were electrode dependent. The ionic conductivity of Bi 5NbO 10 solid solutions at 700 °C is 2.86 Ω -1 m -1 which is in same order of magnitude for Y 2O 3-stabilized ZrO 2 ceramics at same temperature. These results suggest that Bi 5NbO 10 is a promising material for an oxygen ion conductor.

  14. A Journey of Self-Discovery: An Intervention Involving Massage, Yoga and Relaxation for Children with Emotional and Behavioural Difficulties Attending Primary Schools

    ERIC Educational Resources Information Center

    Powell, Lesley; Gilchrist, Mollie; Stapley, Jacqueline

    2008-01-01

    This study reports on an intervention involving massage, yoga and relaxation delivered to young children with emotional and behavioural difficulties. Children (n = 126) were invited to participate in the Self-discovery Programme (SDP) with parental consent. A total of 107 children aged 8-11 years completed the SDP and all measures. Children were…

  15. Field and dilution effects on the magnetic relaxation behaviours of a 1D dysprosium(iii)-carboxylate chain built from chiral ligands.

    PubMed

    Han, Tian; Leng, Ji-Dong; Ding, You-Song; Wang, Yanyan; Zheng, Zhiping; Zheng, Yan-Zhen

    2015-08-14

    A one-dimensional dysprosium(iii)-carboxylate chain in which the Dy(III) ions sit in a pseudo D(2d)-symmetry environment is synthesized and shows different slow magnetic relaxation behaviours depending on the field and dilution effects. Besides, the chiral ligand introduces the additional functions of the Cotton effect and polarization for this compound. PMID:26159885

  16. Stress-relaxation and fatigue behaviour of synthetic brow-suspension materials.

    PubMed

    Kwon, Kyung-Ah; Shipley, Rebecca J; Edirisinghe, Mohan; Rayment, Andrew W; Best, Serena M; Cameron, Ruth E; Salam, Tahrina; Rose, Geoffrey E; Ezra, Daniel G

    2015-02-01

    Ptosis describes a low position of the upper eyelid. When this condition is due to poor function of the levator palpebrae superioris muscle, responsible for raising the lid, "brow-suspension" ptosis correction is usually performed, which involves internally attaching the malpositioned eyelid to the forehead musculature using brow-suspension materials. In service, such materials are exposed to both rapid tensile loading and unloading sequences during blinking, and a more sustained tensile strain during extended periods of closure. In this study, various mechanical tests were conducted to characterise and compare some of commonly-used synthetic brow-suspension materials (Prolene(®), Supramid Extra(®) II, Silicone rods (Visitec(®) Seiff frontalis suspension set) and Mersilene(®) mesh) for their time-dependent response. At a given constant tensile strain or load, all of the brow-suspension materials exhibited stress-relaxation or creep, with Prolene(®) having a statistically different relaxation or creep ratio as compared with those of others. Uniaxial tensile cyclic tests through preconditioning and fatigue tests demonstrated drastically different time-dependent response amongst the various materials. Although the tests generated hysteresis force-strain loops for all materials, the mechanical properties such as the number of cycles required to reach the steady-state, the reduction in the peak force, and the cyclic energy dissipation varied considerably. To reach the steady-state, Prolene(®) and the silicone rod required the greatest and the least number of cycles, respectively. Furthermore, the fatigue tests at physiologically relevant conditions (15% strain controlled at 6.5 Hz) demonstrated that the reduction in the peak force during 100,000 cycles ranged from 15% to 58%, with Prolene(®) and the silicone rod exhibiting the greatest and the least value, respectively. Many factors need to be considered to select the most suitable brow-suspension material for

  17. Investigation of dielectric relaxation, Jahn-Teller distortion, and magnetic ordering in Y substituted Pr{sub 1−x}Y{sub x}MnO{sub 3} (0.1 ≤ x ≤ 0.4)

    SciTech Connect

    Yadav, Ruchika Elizabeth, Suja; Nair, Harikrishnan S.; Kumar, Amit; Yusuf, S. M.; Adiga, Shilpa

    2015-03-07

    We report structural, magnetic, and dielectric properties of the perovskite compound Pr{sub 1−x}Y{sub x}MnO{sub 3} (0.1 ≤ x ≤ 0.4) studied using dc magnetization, ac susceptibility, neutron powder diffraction, and dielectric techniques. These compounds crystallize in orthorhombic space group (Pnma) in the temperature range 5–300 K. The Mn-O-Mn bond angle decreases with the Y substitution along with an increase in the Jahn-Teller distortion. The Jahn-Teller distortion for Pr{sub 0.9}Y{sub 0.1}MnO{sub 3} shows an anomalous change near 50 K, below which it falls sharply. Neutron powder diffraction patterns of all reported compositions at low temperature constitute additional magnetic Bragg peaks that suggest magnetic ordering. Magnetic reflections were indexed in the nuclear lattice with the propagation vector k = (0, 0, 0). Rietveld refinement of powder patterns conform to A type antiferromagnetic ordering where moments are aligned ferromagnetically in a–c plane and coupled nearly antiferromagnetically along b-axis resulting in a net ferromagnetic component along the b-direction. The antiferromagnetic transition temperature was deduced from dc magnetization and ac susceptibility data. The transition temperature decreases by nearly 22 K (from 81 K to 59 K) as yttrium content (x) increases from 0.1 to 0.4. Measurements reveal strong frequency dispersion in dielectric constant and dielectric loss. Activation energy and relaxation time are estimated from the Arrhenius plot. It is further shown that relaxation behaviour is altered with yttrium doping concentration.

  18. Glass Transition and Dynamics of the Polymer and Water in the Poly(vinylpyrrolidone)-Water Mixtures Studied by Dielectric Relaxation Spectroscopy.

    PubMed

    Sasaki, Kaito; Matsui, Yurika; Miyara, Masahiko; Kita, Rio; Shinyashiki, Naoki; Yagihara, Shin

    2016-07-14

    In this study, broadband dielectric spectroscopy and differential scanning calorimetry (DSC) measurements are performed to study the dynamics of water and polymers in an aqueous solution of poly(vinylpyrrolidone) (PVP) with concentrations of 60, 65, and 70 wt % PVP in a temperature range of 123-298 K. Two distinct relaxation processes, l- and h-processes, which originate from the segmental chain motion of PVP and the primary relaxation process of water, respectively, are observed simultaneously. The relationship between l- and h-processes and their temperature dependences mimic those of the α-process and Johari-Goldstein β-process, which are observed in ordinal glass formers. The relaxation time of the l-process, τl, obeys the Vogel-Fulcher (VF)-type temperature dependence, and the glass-transition temperature of the l-process, Tg,l, which is defined by the temperature that is reached in a τl of 100-1000 s, shows good agreement with the calorimetric Tg obtained by DSC. The temperature dependence of the relaxation time of the h-process, τh, exhibits a crossover from VF to Arrhenius behavior at the so-called fragile-to-strong transition (FST) of water at Tg,l. The temperature dependence of the relaxation strength of the h-process, Δεh, increases with a decrease in temperature from 298 K to Tg,l. Below Tg,l, Δεh is nearly constant or slightly decreases with decreasing temperature. According to previous studies on aqueous solutions of sugars and alcohols, the Δε of the ν-process, which originates from local motion of water, decreases with decreasing temperature above the Tg of the α-process, which originates from the cooperative motion of the solute and water. Therefore, the l-process in the PVP-water mixture is not a result of the cooperative motion of PVP and water but rather a result of the polymer-polymer cooperative motion of PVP. In addition, agreement among Tg,l, the temperature of the FST of water, and calorimetric Tg suggests that the FST of water

  19. Dielectric relaxation study of amorphous TiTaO thin films in a large operating temperature range

    SciTech Connect

    Rouahi, A.; Kahouli, A.; Challali, F.; Besland, M. P.; Salimy, S.; Goullet, A.; Vallee, C.; Pairis, S.; Yangui, B.; Sylvestre, A.

    2012-11-01

    Two relaxation processes have been identified in amorphous TiTaO thin films deposited by reactive magnetron sputtering. The parallel angle resolved x-ray photoelectron spectroscopy and field emission scanning electron microscopy analyses have shown that this material is composed of an agglomerates mixture of TiO{sub 2}, Ta{sub 2}O{sub 5}, and Ti-Ta bonds. The first relaxation process appears at low temperature with activation energy of about 0.26 eV and is related to the first ionisation of oxygen vacancies and/or the reduction of Ti{sup 4+} to Ti{sup 3+}. The second relaxation process occurs at high temperature with activation energy of 0.95 eV. This last peak is associated to the diffusion of the doubly ionized oxygen vacancies V{sub O}e. The dispersion phenomena observed at high temperature can be attributed to the development of complex defect such as (V{sub O}e - 2Ti{sup 3+}).

  20. Dielectric controlled excited state relaxation pathways of a representative push-pull stilbene: A mechanistic study using femtosecond fluorescence up-conversion technique

    NASA Astrophysics Data System (ADS)

    Rafiq, Shahnawaz; Sen, Pratik

    2013-02-01

    Femtosecond fluorescence up-conversion technique was employed to reinvestigate the intriguing dependence of fluorescence quantum yield of trans-4-dimethylamino-4'-nitrostilbene (DNS) on dielectric properties of the media. In polar solvents, such as methanol and acetonitrile, the two time components of the fluorescence transients were assigned to intramolecular charge transfer (ICT) dynamics and to the depletion of the ICT state to the ground state via internal conversion along the torsional coordinate of nitro moiety. The viscosity independence of the first time component indicates the absence of any torsional coordinate in the charge transfer process. In slightly polar solvent (carbon tetrachloride) the fluorescence transients show a triple exponential behavior. The first time component was assigned to the formation of the ICT state on a 2 ps time scale. Second time component was assigned to the relaxation of the ICT state via two torsion controlled channels. First channel involves the torsional motion about the central double bond leading to the trans-cis isomerization via a conical intersection or avoided crossing. The other channel contributing to the depopulation of ICT state involves the torsional coordinates of dimethylanilino and/or nitrophenyl moieties and leads to the formation of a conformationally relaxed state, which subsequently relaxes back to the ground state radiatively, and is responsible for the high fluorescence quantum yield of DNS in slightly polar solvents such as carbon tetrachloride, toluene, etc. The excited singlet state which is having a dominant π-π* character may also decay via intersystem crossing to the n-π* triplet manifold and thus accounts for the observed triplet yield of the molecule in slightly polar solvents.

  1. Dielectric spectra of supercooled halogenobenzene-decalin solutions: A single particle site model for relaxation and resonant behaviors

    NASA Astrophysics Data System (ADS)

    Reid, C. J.; Vij, J. K.

    1983-11-01

    Dielectric loss spectra for 10% V/V decalin solutions of PhBr, PhCl, and PhF have been measured using a precision, coaxial three-terminal cell at temperatures from 77 to 150 K and for a frequency range 200 Hz-5 MHz. These results which are in agreement and which extend previous measurements, are interpreted within the context of cosinal itinerant oscillation. Data for PhBr decalin are simulated using a model of a single Brownian particle rotating in the presence of a cosinal potential, which is a special case of the cosine itinerant oscillator model.

  2. Thermal behaviour of a periodic structure supported by dielectric rods in vacuum

    NASA Astrophysics Data System (ADS)

    Gahlaut, V.; Alvi, P. A.; Ghosh, S.

    2014-06-01

    In a traveling-wave tube (TWT) the helical periodic slow-wave structure (SWS) is supported by dielectric supports in a metal envelope in high vacuum. The heat generated in the helix during beam-wave interaction, restricts the average power handling capability of a TWT, dissipated by conduction through support rods. Thermal contact resistances, arises at different joints of different materials, affect heat dissipation from the helix which have been studied and presented here.

  3. Low temperature dielectric behaviour of yttria fully-stabilized zirconia single crystals

    NASA Astrophysics Data System (ADS)

    Cachadińa, I.; Gómez-García, D.; Solier, J. D.; Domínguez-Rodríguez, A.

    The dielectric contribution to the electric response of yttria fully-stabilized zirconia (YFSZ) single crystals was included by using the Kohlrausch-Williams-Watts step response function. The results obtained can be explained by assuming an elastic coupling between a hopping vacancy and the lattice approximated by a continuous elastic media. The wavelength for this elastic coupling was in all cases at least 190 times the unit-cell parameters.

  4. Dielectric measurement method for real-time monitoring of initial hardening of backfill materials used for underground construction

    NASA Astrophysics Data System (ADS)

    Karlovšek, Jurij; Schwing, Moritz; Chen, Zhen; Wagner, Norman; Williams, David J.; Scheuermann, Alexander

    2016-04-01

    The broadband dielectric measurement method based on the vector network analysis technique, in combination with an open-ended coaxial probe, was applied to the determination of the dielectric relaxation behaviour of one- and two-component backfilling grout materials in the frequency range from 40 MHz to 2 GHz. The cement hydration process and the gelling of commercial grouts was monitored in real-time to investigate the application of non-destructive testing methods in the tunnelling industry. It was found that the time-dependent dielectric relaxation behaviour can accurately reveal the different stages of the hydration process and delineate the start of gel hardening. These measurement results demonstrate the practicability of the real-time dielectric measurement method to determine the broadband dielectric parameters of conventional backfill materials used in underground construction to determine construction integrity using non-destructive testing methods.

  5. Dielectric relaxation in hafnium oxide: A study of transient currents and admittance spectroscopy in HfO2 metal-insulator-metal devices

    NASA Astrophysics Data System (ADS)

    Mannequin, C.; Gonon, P.; Vallée, C.; Bsiesy, A.; Grampeix, H.; Jousseaume, V.

    2011-11-01

    Dielectric relaxation is studied in 10 nm HfO2 thin films which are deposited by atomic layer deposition on TiN and Pt electrodes. Transient currents are recorded from 10-3 s to 10 s, as a function of bias (0.1 V to 1 V) and temperature (20 °C to 180 °C). A Curie-von Schweidler law is observed, I = Q0/tα. The power law exponent α is constant with bias and strongly depends on the temperature (varying in the 0.65-1.05 range, with a peak at 75 °C). The amplitude Q0 is described by a relation of the form Q0 = C0Vβ, where the factor C0 is weakly activated and the exponent β varies with temperature (in the 0.9-1.5 range as T varies). Transient currents are discussed along with tunneling based models from the literature. To complement transient current experiments, admittance spectroscopy (conductance G and capacitance C) is performed at low frequencies, from 0.01 Hz to 10 kHz. The dispersion law of the conductance is of the form G ˜ ωs. The capacitance is the sum of two terms, a non-dispersive term (C∞) and a low-frequency dispersive term, CLF ˜ ω-n. The critical exponents s and n verify s ≈ α and n ≈ 1-α. At room temperature, the dielectric constant is expressed as ɛ' = Δɛ' f-n+ ɛ'∞, where ɛ'∞ = 11.1, n ≈ 0.2/0.3 (Pt/TiN), and Δɛ' ≈ 1.5/0.7 (Pt/TiN).

  6. Rietveld refinement and dielectric relaxation of a new rare earth based double perovskite oxide: BaPrCoNbO{sub 6}

    SciTech Connect

    Bharti, Chandrahas; Das, Mrinmoy K.; Sen, A.; Chanda, Sadhan; Sinha, T.P.

    2014-02-15

    A new rare earth based double perovskite oxide barium praseodymium cobalt niobate, BaPrCoNbO{sub 6} (BPCN) is synthesized by solid-state reaction technique. Rietveld analysis of X-ray diffraction (XRD) data shows that the compound crystallizes in a perovskite like tetragonal structure which belongs to the I4/mmm space group with lattice parameters a=b=5.6828(9) Å, c=8.063(2) Å. Structural analysis reveals 1:1 ordered arrangement for the Co{sup 2+} and Nb{sup 5+} cations over the six-coordinate B-sites of BPCN. The superlattice line (1 0 1) at 2θ=19.10° arising from the alternate ordering of Co{sup 2+} and Nb{sup 5+} sites is observed in the XRD pattern which confirms the presence of cation ordering in BPCN. Fourier transform infrared spectrum shows two phonon modes of the sample due to the antisymmetric NbO{sub 6} stretching vibration. The relaxation dynamics of the conductive process in BPCN is investigated in the temperature range 303 to 503 K and in the frequency range 100 Hz to 1 MHz using impedance spectroscopy. The relaxation mechanism of the sample in the framework of electric modulus formalism is modeled by Davidson–Cole model (DCM). The values of α (distribution of relaxation time) for the DCM varies from 0.1 to 0.3 which suggests the asymmetric distribution of relaxation time for BPCN. The activation energy of the sample, calculated from both conductivity and modulus spectra, are found to be almost the same ∼0.4 eV, which indicates that the conduction mechanism for BPCN is polaron hopping. The scaling behaviour of the imaginary part of electric modulus suggests that the relaxation follows the same mechanism at various temperatures. - Graphical abstract: Rietveld refinement plot for BPCN. Inset shows the schematic presentation of the BPCN tetragonal unit cell. The Co{sup 2+} atoms are located at the centers of the CoO{sub 6} (blue) octahedra. The Nb{sup 5+} atoms are located at the centers of the NbO{sub 6} (green) octahedra. Display Omitted

  7. PREFACE: Dielectrics 2009: Measurement Analysis and Applications

    NASA Astrophysics Data System (ADS)

    Vaughan, Alun; Williams, Graham

    2009-07-01

    The conference Dielectrics 2009: Measurements, Analysis and Applications represents a significant milestone in the evolution of dielectrics research in the UK. It is reasonable to state that the academic study of dielectrics has led to many fundamental advances and that dielectric materials underpin the modern world in devices ranging from field effect transistors, which operate at extremely high fields, albeit low voltages, to the high voltage plants that provide the energy that powers our economy. The origins of the Dielectrics Group of the Institute of Physics (IOP), which organized this conference, can be traced directly back to the early 1960s, when Professor Mansel Davies was conducting research into the dielectric relaxation behaviour of polar liquids and solids at The Edward Davies Chemical Laboratories of the University College of Wales, Aberystwyth. He was already well-known internationally for his studies of molecular structure and bonding of small molecules, using infra-red-spectroscopy, and of the physical properties of hydrogen-bonded liquids and solids, using thermodynamic methods. Dielectric spectroscopy was a fairly new area for him and he realized that opportunities for scientists in the UK to gather together and discuss their research in this developing area of physical chemistry/chemical physics were very limited. He conceived the idea of forming a Dielectrics Discussion Group (DDG), which would act as a meeting point and provide a platform for dielectrics research in the UK and beyond and, as a result, a two-day Meeting was convened in the spring of 1968 at Gregynog Hall of the University of Wales, near Newtown, Montgomeryshire. It was organized by Mansel Davies, Alun Price and Graham Williams, all physical chemists from the UCW, Aberystwyth. Fifty scientists attended, being a mix of physical chemists, theoretical chemists, physicists, electrical engineers, polymer and materials scientists, all from the UK, except Dr Brendan Scaife of Trinity

  8. Dielectric properties of polyacrylate thick films used in sensors and actuators

    NASA Astrophysics Data System (ADS)

    Jean-Mistral, C.; Sylvestre, A.; Basrour, S.; Chaillout, J.-J.

    2010-07-01

    Dielectric polymers are emerging electro-active materials used in high performance applications such as micropumps, robots and artificial muscles. The development of such applications requires the use of models taking into account the electrical parameters of the material. However, there is still some controversy over the dielectric constant of the most widely used dielectric polymer (VHB 4910, 3M, USA). In this paper, we present an exhaustive study relating to changes in the dielectric constant of VHB 4910 over wide frequency and temperature ranges. We found that the permittivity was a function of: frequency, temperature, the nature of the electrodes and the pre-stress applied to material. Mechanisms of dielectric polarization (β-relaxation) explain the behaviour in temperature and frequency of this parameter. The use of silver grease-compliant electrodes induces an increase in the dielectric constant which moves to a value of 5.4 (against 4.7 with gold electrodes). A pre-strain applied to the material shows a reduction up to 15% in the value of the dielectric constant. Short-range dipolar relaxation, local mechanical constraints in the material and a possible crystallization of material induced by the stretching are suggested to explain these behaviours. Analytic equations of the dielectric constant according to the temperature and pre-strain are then proposed and used to validate the behaviour of these materials for actuator and scavenger devices.

  9. Intramolecular charge transfer reaction, polarity, and dielectric relaxation in AOT/water/heptane reverse micelles: pool size dependence.

    PubMed

    Biswas, Ranjit; Rohman, Nashiour; Pradhan, Tuhin; Buchner, Richard

    2008-08-01

    Intramolecular charge transfer (ICT) reaction in a newly synthesized molecule, of 4-(1-morpholenyl) benzonitrile (M6C), in AOT/water/heptane reverse micelles at different pool sizes has been studied by using steady-state and time-resolved fluorescence emission spectroscopy. The pool size dependences of the reaction equilibrium constant and reaction rate have been explained in terms of the average polarity of the confined solvent pools estimated from the fluorescence emission Stokes shift of a nonreactive probe, coumarin 153, dissolved in these microemulsions. The complex permittivity measurements in the frequency range 0.01relaxation time of approximately 600 ps has been observed at approximately 300 MHz and attributed to the average reorientation of water molecules residing in the close vicinity of the polar interface of the AOT headgroup and n-heptane. The reorientation of these interfacial water molecules is probably responsible for the nanosecond component observed in numerous polar solvation dynamics experiments in these reverse micelles. Subsequently, the estimated polarity and the measured reorientational time scale have been used to explain the dramatic slowing down of the ICT reaction rate and its dependence on pool size in these confined environments. PMID:18630864

  10. Characteristics and the nature of the low-frequency dielectric response in moderately concentrated KTaO3:Li

    NASA Astrophysics Data System (ADS)

    Prosandeev, S. A.; Trepakov, V. A.; Savinov, M. E.; Jastrabik, L.; Kapphan, S. E.

    2001-10-01

    The temperature-frequency behaviour of the complex dielectric permittivity of K0.957Li0.043TaO3 (KLT) was studied in detail. Below 250 K a pronounced relaxation-type dielectric dispersion occurs with two wide temperature maxima shifted to lower temperatures increasing in magnitude as the alternating-current monitoring frequency decreases. The results obtained are analysed by using a theory proposed considering the coupling of the TO1 soft mode (TO standing for transverse optical) to two Li relaxation modes known in moderately concentrated KLT as π- and (π/2)-relaxations.