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Sample records for ac conductivity dielectric

  1. AC Conductivity and Dielectric Properties of Borotellurite Glass

    NASA Astrophysics Data System (ADS)

    Taha, T. A.; Azab, A. A.

    2016-10-01

    Borotellurite glasses with formula 60B2O3-10ZnO-(30 - x)NaF- xTeO2 ( x = 0 mol.%, 5 mol.%, 10 mol.%, and 15 mol.%) have been synthesized by thermal melting. X-ray diffraction (XRD) analysis confirmed that the glasses were amorphous. The glass density ( ρ) was determined by the Archimedes method at room temperature. The density ( ρ) and molar volume ( V m) were found to increase with increasing TeO2 content. The direct-current (DC) conductivity was measured in the temperature range from 473 K to 623 K, in which the electrical activation energy of ionic conduction increased from 0.27 eV to 0.48 eV with increasing TeO2 content from 0 mol.% to 15 mol.%. The dielectric parameters and alternating-current (AC) conductivity ( σ ac) were investigated in the frequency range from 1 kHz to 1 MHz and temperature range from 300 K to 633 K. The AC conductivity and dielectric constant decreased with increasing TeO2 content from 0 mol.% to 15 mol.%.

  2. Impedance, AC conductivity and dielectric behavior Adeninium Trichloromercurate (II)

    NASA Astrophysics Data System (ADS)

    Fersi, M. Amine; Chaabane, I.; Gargouri, M.

    2016-09-01

    In this work, we report the measurements impedance spectroscopy technique for the organic-inorganic hybrid compound (C5H6N5) HgCl3, 11/2H2O measured in the 209 Hz-5 MHz frequency range from 378 to 428 K. Besides, the Cole-Cole (Z″ versus Z‧) plots were well fitted to an equivalent circuit built up by a parallel combination of resistance (R), fractal capacitance (CPE) and capacitance (C). Furthermore, the AC conductivity was investigated as a function of temperature and frequency in the same range. The experiment results indicated that AC conductivityac) was proportional to σdc + A ωS . The obtained results are discussed in terms of the correlated barrier hopping (CBH) model. An agreement between the experimental and theoretical results suggests that the AC conductivity behavior of Adeninium Trichloromercurate (II) can be successfully explained by CBH model. The contribution of single polaron hopping to AC conductivity in a present alloy was also studied.

  3. Dielectric behavior and ac electrical conductivity in samarium substituted Mg-Ni ferrites

    NASA Astrophysics Data System (ADS)

    Melagiriyappa, E.; Veena, M.; Somashekarappa, A.; Shankaramurthy, G. J.; Jayanna, H. S.

    2014-08-01

    Samarium substituted MgNi ferrites with composition Mg1-xNixFe2-ySmyO4 ( x = 0, 0.2, 0.4, 0.6, 0.8, 1.0; y = 0.0, 0.05, 0.1) have been prepared by ceramic method. Dielectric measurements of the samples have been carried out at room temperature as a function of frequency and composition. X-ray diffraction patterns have confirmed the single-phase spinel cubic structure for all the samples. Dielectric constant ( ɛ') and dielectric loss (tan δ) decrease while ac electrical conductivity ( σ ac ) increases with increase in frequency. Dielectric properties have been explained on the basis of Maxwell-Wagner's two layer model. The conduction mechanism in these ferrites is due to electron hopping between Ni2+ and Ni3+ as well as Fe3+ and Fe2+ ions on octahedral sites. Dielectric constant and ac conductivity increases and decreases respectively with nickel content. A significant reduction in the values of dielectric constant and ac electrical conductivity has been observed in Sm3+ ions substituted samples.

  4. Structural, dielectric and AC conductivity properties of Co2+ doped mixed alkali zinc borate glasses

    NASA Astrophysics Data System (ADS)

    Madhu, B. J.; Banu, Syed Asma; Harshitha, G. A.; Shilpa, T. M.; Shruthi, B.

    2013-02-01

    The Co2+ doped 19.9ZnO+5Li2CO3+25Na2CO3+50B2O3 (ZLNB) mixed alkali zinc borate glasses have been prepared by a conventional melt quenching method. The structural (XRD & FT-IR), dielectric and a.c. conductivityac) properties have been investigated. Amorphous nature of these glasses has been confirmed from their XRD pattern. The dielectric properties and electrical conductivityac) of these glasses have been studied from 100Hz to 5MHz at the room temperature. Based on the observed trends in the a.c. conductivities, the present glass samples are found to exhibit a non-Debye behavior.

  5. Temperature characterization of dielectric permittivity and AC conductivity of nano copper oxide-doped polyaniline composite

    NASA Astrophysics Data System (ADS)

    Shubha, L. N.; Madhusudana Rao, P.

    2016-06-01

    The polyaniline/copper oxide (PANI/CuO) nanocomposite was prepared by mixing solutions of polyaniline and copper oxide nanoparticles in dimethyl sulfoxide (DMSO). The synthesized polymer nanocomposites were characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM) and UV-visible spectroscopy. The characteristic peaks in XRD and UV-visible spectra confirmed the presence of CuO in the polymer structure. SEM images indicated morphological changes in the composite matrix as compared to the pristine PANI. The DC conductivity measurements were performed using two-probe method for various temperatures. AC conductivity and dielectric response of the composites were investigated in the frequency range of 102-106Hz using LCR meter. Dielectric permittivity ɛ‧(w) and dielectric loss factor ɛ‧‧(w) were investigated. It was observed that ɛ‧(w) and ɛ‧‧(w) decrease with increase in frequency at all temperatures. At a particular frequency it is observed that both ɛ‧(w) and ɛ‧‧(w) increase with increase in temperature. It was also observed that AC conductivity increased with increase in frequency and temperature.

  6. Ac-conductivity and dielectric response of new zinc-phosphate glass/metal composites

    NASA Astrophysics Data System (ADS)

    Maaroufi, A.; Oabi, O.; Lucas, B.

    2016-07-01

    The ac-conductivity and dielectric response of new composites based on zinc-phosphate glass with composition 45 mol%ZnO-55 mol%P2O5, filled with metallic powder of nickel (ZP/Ni) were investigated by impedance spectroscopy in the frequency range from 100 Hz to 1 MHz at room temperature. A high percolating jump of seven times has been observed in the conductivity behavior from low volume fraction of filler to the higher fractions, indicating an insulator - semiconductor phase transition. The measured conductivity at higher filler volume fraction is about 10-1 S/cm and is frequency independent, while, the obtained conductivity for low filler volume fraction is around 10-8 S/cm and is frequency dependent. Moreover, the elaborated composites are characterized by high dielectric constants in the range of 105 for conductive composites at low frequencies (100 Hz). In addition, the distribution of the relaxation processes was also evaluated. The Debye, Cole-Cole, Davidson-Cole and Havriliak-Negami models in electric modulus formalism were used to model the observed relaxation phenomena in ZP/Ni composites. The observed relaxation phenomena are fairly simulated by Davidson-Cole model, and an account of the interpretation of results is given.

  7. The change in dielectric constant, AC conductivity and optical band gaps of polymer electrolyte film: Gamma irradiation

    SciTech Connect

    Raghu, S. Subramanya, K. Sharanappa, C. Mini, V. Archana, K. Sanjeev, Ganesh Devendrappa, H.

    2014-04-24

    The effects of gamma (γ) irradiation on dielectric and optical properties of polymer electrolyte film were investigated. The dielectric constant and ac conductivity increases with γ dose. Also optical band gap decreased from 4.23 to 3.78ev after irradiation. A large dependence of the polymer properties on the irradiation dose was noticed. This suggests that there is a possibility of improving polymer electrolyte properties on gamma irradiation.

  8. Dielectric and ac conductivity studies of ZnO/Eu3+: Titanosilicate matrix

    NASA Astrophysics Data System (ADS)

    Arun Kumar, K. V.; Sunil, Thomas; Ann Mary, K. A.; Cyriac, Joseph; Biju, P. R.; Unnikrishnan, N. V.

    2014-01-01

    ZnO nanoparticles /Eu3+ doped SiO2-TiO2 matrices were synthesized through sol-gel route. Structural and dielectric properties of ZnO nanocrystallites co-doped with Eu3+ in SiO2-TiO2 matrices were presented. The HRTEM and XRD measurements confirm the presence of ZnO nanocrystallites. The dielectric and electrical conductivity studies of the samples are completed for a frequency of 100 Hz to 2 MHz. The conductivity variation with the ZnO content in the Eu3+ doped SiO2-TiO2 system were explained by correlating the presence of ionic contribution to the electrical conductivity process. From the frequency dependence of dielectric constant and conductivity, the Cole-Cole parameters and power law parameters were evaluated. The dielectric relaxation phenomena were investigated using the dielectric moduli formulation.

  9. Anomalous dielectric and AC conductivity behavior of the nanocrystalline Ni-Cu ferrite synthesized via combustion method

    SciTech Connect

    Madhu, B. J.; Rashmi, B. N.; Banu, Arshiya; Seema, G. A.; Shruthi, B.; Jayanna, H. S.

    2013-02-05

    Nanocrystalline Ni-Cu ferrites (Ni{sub 0.5}Cu{sub 0.5}Fe{sub 2}O{sub 4}) were prepared using solution combustion method. The structure of the samples were studied with the X-ray diffraction (XRD) using Cu-K{sub {alpha}} radiation. Frequency and temperature dependence of dielectric and a.c. conductivity studies have been undertaken on the Ni-Cu nanoferrites in the frequency region 100Hz-5MHz. The dielectric constant ({epsilon} Prime ) is found to decrease initially with the frequency and finally reaching a constant value at higher frequencies. Observed trends in the dielectric constant are ascribed to the Maxwell-Wagner type interfacial polarization, which is in agreement with the Koop'fs phenomenological theory. The a.c. conductivity ({sigma}{sub ac}) is found to increase with an increase in the frequency from room temperature up to 300 Degree-Sign C. However, at a temperature of 400 Degree-Sign C, the a.c. conductivity is found to decrease with an increase in the frequency exhibiting an abnormal behavior. The electrical conduction mechanism in the present nano nickel-copper ferrite is found to be in accordance with the electron hopping model.

  10. Anomalous dielectric and AC conductivity behavior of the nanocrystalline Ni-Cu ferrite synthesized via combustion method

    NASA Astrophysics Data System (ADS)

    Madhu, B. J.; Rashmi, B. N.; Banu, Arshiya; Seema, G. A.; Shruthi, B.; Jayanna, H. S.

    2013-02-01

    Nanocrystalline Ni-Cu ferrites (Ni0.5Cu0.5Fe2O4) were prepared using solution combustion method. The structure of the samples were studied with the X-ray diffraction (XRD) using Cu-Kα radiation. Frequency and temperature dependence of dielectric and a.c. conductivity studies have been undertaken on the Ni-Cu nanoferrites in the frequency region 100Hz-5MHz. The dielectric constant (ɛ') is found to decrease initially with the frequency and finally reaching a constant value at higher frequencies. Observed trends in the dielectric constant are ascribed to the Maxwell-Wagner type interfacial polarization, which is in agreement with the Koop'fs phenomenological theory. The a.c. conductivityac) is found to increase with an increase in the frequency from room temperature up to 300 °C. However, at a temperature of 400 °C, the a.c. conductivity is found to decrease with an increase in the frequency exhibiting an abnormal behavior. The electrical conduction mechanism in the present nano nickel-copper ferrite is found to be in accordance with the electron hopping model.

  11. A.c. conductivity and dielectric properties of LiNi 3/5Cu 2/5VO 4 ceramics

    NASA Astrophysics Data System (ADS)

    Ram, Moti

    2010-03-01

    The LiNi 3/5Cu 2/5VO 4 was synthesized using solution-based chemical method whose dielectric and a.c. conductivity properties were investigated using complex impedance spectroscopy (CIS) technique. Variation of dielectric constant ( εr) as a function of frequency at different temperatures indicates low frequency dispersion. A.c conductivity analysis indicates that electrical conduction in the material is a thermally activated process. Frequency dependence of a.c. conductivity at different temperatures obeys Jonscher's universal law: σ ac= σ dc+ A( ω) n.

  12. Dielectric relaxation and ac conductivity behavior of carboxyl functionalized multiwalled carbon nanotubes/poly (vinyl alcohol) composites

    NASA Astrophysics Data System (ADS)

    Amrin, Sayed; Deshpande, V. D.

    2017-03-01

    We study the dielectric relaxation and ac conductivity behavior of MWCNT-COOH/Polyvinyl alcohol nanocomposite films in the temperature (T) range 303-423 K and in the frequency (f) range 0.1 Hz-1 MHz. The dielectric constant increases with an increase in temperature and also with an increase in MWCNT-COOH loading into the polymer matrix, as a result of interfacial polarization. The permittivity data were found to fit well with the modified Cole-Cole equation. Temperature dependent values of the relaxation times, free charge carrier conductivity and space charge carrier conductivity were extracted from the equation. An observed increment in the ac conductivity for the nanocomposites was analysed by a Jonscher power law which suggests that the correlated barrier hopping is the dominant charge transport mechanism for the nanocomposite films. The electric modulus study revealed deviations from ideal Debye-type behavior which are explained by considering a generalized susceptibility function. XRD and DSC results show an increase in the degree of crystallinity.

  13. 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*.

  14. AC conductivity and dielectric relaxation in Ba(Sm 1/2Nb 1/2)O 3 ceramic

    NASA Astrophysics Data System (ADS)

    Kumar, Pritam; Singh, B. P.; Sinha, T. P.; Singh, N. K.

    2011-01-01

    The complex perovskite oxide a barium samarium niobate (BSN) synthesized by solid-state reaction technique has single phase with cubic structure. The scanning electron micrograph of the sample shows the average grain size of BSN∼1.22 μm. The field dependence of dielectric response and loss tangent were measured in the temperature range from 323 to 463 K and in the frequency range from 50 Hz to 1 MHz. The complex plane impedance plots show the grain boundary contribution for higher value of dielectric constant in the low frequency region. An analysis of the dielectric constant ( ε‧) and loss tangent (tan δ) with frequency was performed assuming a distribution of relaxation times as confirmed by the scaling behaviour of electric modulus spectra. The low frequency dielectric dispersion corresponds to DC conductivity. The logarithmic angular frequency dependence of the loss peak is found to obey the Arrhenius law with an activation energy of 0.71 eV. The frequency dependence of electrical data is also analyzed in the framework of conductivity and electric modulus formalisms. Both these formalisms show qualitative similarities in relaxation times. The scaling behaviour of imaginary part of electric modulus M″ and dielectric loss spectra suggest that the relaxation describes the same mechanism at various temperatures in BSN. All the observations indicate the polydispersive relaxation in BSN.

  15. Influence of temperature on the electric, dielectric and AC conductivity properties of nano-crystalline zinc substituted cobalt ferrite synthesized by solution combustion technique

    NASA Astrophysics Data System (ADS)

    Rani, Ritu; Kumar, Gagan; Batoo, Khalid M.; Singh, M.

    2014-06-01

    Cobalt-zinc nanoferrites with formulae Co ZnFeO, where x = 0.0, 0.1, 0.2 and 0.3, have been synthesized by solution combustion technique. The variation of DC resistivity with temperature shows the semiconducting behavior of all nanoferrites. The dielectric properties such as dielectric constant (') and dielectric loss tangent (tan are investigated as a function of temperature and frequency. Dielectric constant and loss tangent are found to be increasing with an increase in temperature while with an increase in frequency both, ' and tan , are found to be decreasing. The dielectric properties have been explained on the basis of space charge polarization according to Maxwell-Wagner's two-layer model and the hopping of charge between Fe and Fe. Further, a very high value of dielectric constant and a low value of tan are the prime achievements of the present work. The AC electrical conductivity ( is studied as a function of temperature as well as frequency and is observed to be increasing with the increase in temperature and frequency.

  16. Dielectric and AC-conductivity studies of Dy2O3 doped (K0.5Na0.5)NbO3 ceramics

    NASA Astrophysics Data System (ADS)

    Peddigari, Mahesh; Thota, Subhash; Pamu, Dobbidi

    2014-08-01

    (K0.5Na0.5)NbO3 + x wt.% Dy2O3 (x = 0-1.5) ferroelectric ceramics were prepared by conventional solid state reaction method. XRD patterns revealed that orthorhombic symmetry has transformed into psuedocubic symmetry with increasing the substitution of Dy3+ in the Na+ site. Temperature and frequency dependences of relative dielectric permittivity maximum conforms the transformation from normal ferroelectric to relaxor ferroelectric behaviour. Frequency dependence of the relative dielectric permittivity maximum temperature observed for the samples with x ≥ 1.0 and satisfied the Vogel-Fulcher law. The diffuseness exponent γ (1.27-1.95) estimated from the high temperature slopes of the diffused dielectric permittivity data reveals that the degree of relaxor behavior increases with increasing the amount of Dy2O3. The temperature dependence of AC-conductivity σAC (T) analysis in the range 310 K < T < 470 K reveals the existence of variable range hopping of charge carriers with average hopping length RH and hopping energy EH are in the range 8.5-27 Å and 48-153 meV, respectively. Voltage dependent dielectric constant measurements confirm the ferroelectric nature of KNN+ x wt% Dy2O3 ceramics.

  17. Dielectric properties and study of AC electrical conduction mechanisms by non-overlapping small polaron tunneling model in Bis(4-acetylanilinium) tetrachlorocuprate(II) compound

    NASA Astrophysics Data System (ADS)

    Abkari, A.; Chaabane, I.; Guidara, K.

    2016-09-01

    In the present work, the synthesis and characterization of the Bis(4-acetylanilinium) tetrachlorocuprate(II) compound are presented. The structure of this compound is analyzed by X-ray diffraction which confirms the formation of single phase and is in good agreement the literature. Indeed, the Thermo gravimetric Analysis (TGA) shows that the decomposition of the compound is observed in the range of 420-520 K. However, the differential thermal analysis (DTA) indicates the presence of a phase transition at T=363 k. Furthermore, the dielectric properties and AC conductivity were studied over a temperature range (338-413 K) and frequency range (200 Hz-5 MHz) using complex impedance spectroscopy. Dielectric measurements confirmed such thermal analyses by exhibiting the presence of an anomaly in the temperature range of 358-373 K. The complex impedance plots are analyzed by an electrical equivalent circuit consisting of resistance, constant phase element (CPE) and capacitance. The activation energy values of two distinct regions are obtained from log σT vs 1000/T plot and are found to be E=1.27 eV (T<363 K) and E=1.09 eV (363 Kac conductivity, σac, has been analyzed by Jonscher's universal power law σ(ω)=σdc+Aωs. The value of s is to be temperature-dependent, which has a tendency to increase with temperature and the non-overlapping small polaron tunneling (NSPT) model is the most applicable conduction mechanism in the title compound. Complex impedance spectra of [C8H10NO]2CuCl4 at different temperatures.

  18. Frequency and voltage dependence dielectric properties, ac electrical conductivity and electric modulus profiles in Al/Co3O4-PVA/p-Si structures

    NASA Astrophysics Data System (ADS)

    Bilkan, Çiğdem; Azizian-Kalandaragh, Yashar; Altındal, Şemsettin; Shokrani-Havigh, Roya

    2016-11-01

    In this research a simple microwave-assisted method have been used for preparation of cobalt oxide nanostructures. The as-prepared sample has been investigated by UV-vis spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM). On the other hand, frequency and voltage dependence of both the real and imaginary parts of dielectric constants (ε‧, ε″) and electric modulus (M‧ and M″), loss tangent (tanδ), and ac electrical conductivityac) values of Al/Co3O4-PVA/p-Si structures were obtained in the wide range of frequency and voltage using capacitance (C) and conductance (G/ω) data at room temperature. The values of ε‧, ε″ and tanδ were found to decrease with increasing frequency almost for each applied bias voltage, but the changes in these parameters become more effective in the depletion region at low frequencies due to the charges at surface states and their relaxation time and polarization effect. While the value of σ is almost constant at low frequency, increases almost as exponentially at high frequency which are corresponding to σdc and σac, respectively. The M‧ and M″ have low values at low frequencies region and then an increase with frequency due to short-range mobility of charge carriers. While the value of M‧ increase with increasing frequency, the value of M″ shows two peak and the peaks positions shifts to higher frequency with increasing applied voltage due to the decrease of the polarization and Nss effects with increasing frequency.

  19. Crystal structure, NMR study, dielectric relaxation and AC conductivity of a new compound [Cd3(SCN)2Br6(C2H9N2)2]n

    NASA Astrophysics Data System (ADS)

    Saidi, K.; Kamoun, S.; Ayedi, H. Ferid; Arous, M.

    2013-11-01

    The crystal structure, the 13C NMR spectroscopy and the complex impedance have been carried out on [Cd3(SCN)2Br6(C2H9N2)2]n. Crystal structure shows a 2D polymeric network built up of two crystallographically independent cadmium atoms with two different octahedral coordinations. This compound exhibits a phase transition at (T=355±2 K) which has been characterized by differential scanning calorimetry (DSC), X-rays powder diffraction, AC conductivity and dielectric measurements. Examination of 13C CP/MAS line shapes shows indirect spin-spin coupling (14N and 13C) with a dipolar coupling constant of 1339 Hz. The AC conductivity of this compound has been carried out in the temperature range 325-376 K and the frequency range from 10-2 Hz to 10 MHz. The impedance data were well fitted to two equivalent electrical circuits. The results of the modulus study reveal the presence of two distinct relaxation processes. One, at low frequency side, is thermally activated due to the ionic conduction of the crystal and the other, at higher frequency side, gradually disappears when temperature reaches 355 K which is attributed to the localized dipoles in the crystal. Moreover, the temperature dependence of DC-conductivity in both phases follows the Arrhenius law and the frequency dependence of σ(ω,T) follows Jonscher's universal law. The near values of activation energies obtained from the conductivity data and impedance confirm that the transport is through the ion hopping mechanism.

  20. AC conductivity and dielectric properties of 2-(2,3-dihydro-1,5-dimethyl-3-oxo-2-phenyl-1 H-pyrazol-4-ylimino)-2-(4-nitrophenyl)acetonitrile thin films

    NASA Astrophysics Data System (ADS)

    El-Menyawy, E. M.; Zeyada, H. M.; El-Nahass, M. M.

    2010-12-01

    The dark AC conductivity and dielectric properties of thermally evaporated 2-(2,3-dihydro-1,5-dimethyl-3-oxo-2-phenyl-1 H-pyrazol-4-ylimino)-2-(4-nitrophenyl)acetonitrile (DOPNA) thin films in sandwich structure employing symmetrical gold ohmic contacts have been investigated as function of temperature (303-443 K) and frequency (100 Hz-5 MHz). The AC conductivity, σAC( ω), is found to obey Jonscher's universal power law, σAC( ω)= Aω s ( ω is the angular frequency). The AC conductivity of DOPNA thin films has been analyzed with reference to various theoretical models. The correlated barrier hopping is found to be the dominant conduction mechanism for charge carrier transport; the maximum barrier height, hopping length and the density of localized states are estimated. The temperature dependence of the AC conductivity shows Arrhenius type with two thermal activation energies. The activation energies are determined as a function of frequency. The behavior of the real and imaginary parts of the dielectric constant as a function of both temperature and frequency is discussed.

  1. Dielectric Relaxation Behavior and AC Electrical Conductivity Study of 2-(1,2-Dihydro-7-Methyl-2-Oxoquinoline-5-yl) Malononitrile (DMOQMN)

    NASA Astrophysics Data System (ADS)

    El-Nahass, M. M.; El-Zaidia, E. F. M.; Darwish, A. A. A.; Salem, G. F.

    2017-02-01

    Dielectric relaxation and alternative current conductivity of a new organic compound 2-(1,2-dihydro-7-methyl-2-oxoquinoline-5-yl) malononitrile (DMOQMN) have been investigated. X-ray diffraction (XRD) at room temperature reveals that DMOQMN samples have a polycrystalline structure of the triclinic system. The analysis of the dielectric constant and dielectric loss index suggested the dominant polarization is performed and the Maxwell-Wagner-Sillar type polarization is dominating at low frequency and high temperature. These results have been confirmed by the XRD and dielectric modulus. The estimated relaxation time and the activation energy are 9 × 10-13 s and 0.43 eV, respectively. Our results indicated that the conduction mechanism of DMOQMN is controlled by the correlation barrier hopping (CBH) model.

  2. Electrical conduction in polymer dielectrics

    NASA Technical Reports Server (NTRS)

    Cotts, D. B.

    1985-01-01

    The use of polymer dielectrics with moderate resistivities could reduce or eliminate problems associated with spacecraft charging. The processes responsible for conduction and the properties of electroactive polymers are reviewed, and correlations drawn between molecular structure and electrical conductivity. These structure-property relationships led to the development of several new electroactive polymer compositions and the identification of several systems that have the requisite thermal, mechanical, environmental and electrical properties for use in spacecraft.

  3. Dielectric properties of conductive ionomers

    NASA Astrophysics Data System (ADS)

    Klein, Robert James

    Ion and polymer dynamics of ion-containing polymers were investigated, with the majority of results obtained from application of a physical model of electrode polarization (EP) to dielectric spectroscopy data. The physical model of MacDonald, further developed by Coelho, was extended for application to tan delta (the ratio of dielectric loss to dielectric constant) as a function of frequency. The validity of this approach was confirmed by plotting the characteristic EP time as a function of thickness and comparing the actual and predicted unrelaxed dielectric constant for a poly(ethylene oxide) (PEO)-based ionomer neutralized by lithium, sodium, and cesium. Results were obtained for ion mobility and mobile ion concentration for a neat PEO-based ionomer, two (methoxyethoxy-ethoxy phosphazene) (MEEP) -based ionomers, two MEEP-based salt-doped polymers, sulfonated polystyrene (SPS) neutralized by sodium with a high sulfonation fraction, and SPS neutralized by zinc with a low sulfonation fraction. Additionally, the conductivity parameters of six plasticized forms of a neat PEO-based ionomer were characterized, but the method apparently failed to correctly evaluate bulk ionic behavior. In all cases except the SPS ionomers ion mobility follows a Vogel-Fulcher-Tammann (VFT) temperature dependence. In all cases, mobile ion concentration follows an Arrhenius temperature dependence. Fitting parameters from these two relationships yielded direct information about the state of ionic diffusion and ion pairing in each system. Combination of these two functionalities predicts a relationship for conductivity that is significantly different than the VFT relation typically used in the literature to fit conductivity. The most outstanding result was the extremely small fraction of ions found to be mobile. For ionomers it can be concluded that the primary reason for low conductivities arises from the low fraction of mobile ions. The local and segmental dynamics of the neat and

  4. Dielectric relaxation in AC powder electroluminescent devices

    NASA Astrophysics Data System (ADS)

    Zhang, Shuai; Su, Haibin; Tan, Chuan Seng; Wong, Terence Kin Shun; Teo, Ronnie Jin Wah

    2017-01-01

    The dielectric properties of AC powder electroluminescent devices were measured and analyzed using complex impedance spectroscopy to determine the relaxation processes occurring within the devices. The relaxation processes identified were ascribed to the electrode polarization caused by ion accumulation at the electrode/resin interfaces, the Maxwell-Wagner-Sillars effects at the (ZnS or BaTiO3) particle/resin interfaces, and the dipolar reorientation of polymer chains in the resin matrix. Each relaxation process was represented by its corresponding equivalent circuit component. Space charge polarization at the electrodes were represented by a Warburg element, a resistor, and a constant phase element. The resin matrix, ZnS/resin and BaTiO3/resin interfaces could each be modeled by a resistor and a capacitor in parallel. The simulated equivalent circuits for three different printed structures showed good fitting with their experimental impedance results.

  5. Structural characterization, thermal, ac conductivity and dielectric properties of (C7H12N2)2[SnCl6]Cl2.1.5H2O

    NASA Astrophysics Data System (ADS)

    Hajji, Rachid; Oueslati, Abderrazek; Hajlaoui, Fadhel; Bulou, Alain; Hlel, Faouzi

    2016-05-01

    (C7H12N2)2[SnCl6]Cl2.1.5H2O is crystallized at room temperature in the monoclinic system (space group P21/n). The isolated molecules form organic and inorganic layers parallel to the (a, b) plane and alternate along the c-axis. The inorganic layer is built up by isolated SnCl6 octahedrons. Besides, the organic layer is formed by 2,4-diammonium toluene cations, between which the spaces are filled with free Cl- ions and water molecules. The crystal packing is governed by means of the ionic N-H...Cl and Ow-H...Cl hydrogen bonds, forming a three-dimensional network. The thermal study of this compound is reported, revealing two phase transitions around 360(±3) and 412(±3) K. The electrical and dielectric measurements were reported, confirming the transition temperatures detected in the differential scanning calorimetry (DSC). The frequency dependence of ac conductivity at different temperatures indicates that the correlated barrier hopping (CBH) model is the probable mechanism for the ac conduction behavior.

  6. Polaron conductivity mechanism in potassium acid phthalate crystal: AC-conductivity investigation

    NASA Astrophysics Data System (ADS)

    Filipič, Cene; Levstik, Iva; Levstik, Adrijan; Hadži, Dušan

    2016-08-01

    The complex dielectric constant, \\varepsilon *(ν ,T), of potassium acid phthalate monocrystal (KAP) was investigated over the broad frequency and temperature range. While the imaginary part of dielectric constant ε‧‧(ν) increases rapidly with increasing temperature in the studied temperature range, the real part of dielectric constant ε‧(ν) increases only at high temperatures; there is almost no change of ε‧(ν) below 200 K. Both values of ε‧ and ε‧‧ are frequency dependent; the values increase with decreasing frequencies. At temperatures below 450 K the ac electrical conductivity and dielectric constant follow simultaneously the universal dielectric response (UDR). The analysis of the temperature dependence of the UDR parameter s in terms of the theoretical model for small polarons revealed that this mechanism governs the charge transport in KAP crystal in the studied temperature range.

  7. AC field induced-charge electroosmosis over leaky dielectric blocks embedded in a microchannel.

    PubMed

    Zhao, Cunlu; Yang, Chun

    2011-02-01

    An effective electrical boundary condition is formulated to describe AC field-driven induced-charge electrokinetic (ICEK) phenomena at the interface between a liquid and a leaky dielectric solid. Since most materials in reality possess finite dielectric and conductive properties, i.e. leaky dielectric, the present boundary condition can be used to describe the induced zeta potential on a leaky dielectric surface with consideration of both bond charges (due to polarization) and free charges (due to conduction). Two well-known limiting cases, i.e. the perfectly dielectric and the perfectly conducting wall boundary conditions can be recovered from the present formulation. Utilizing the derived boundary condition, we obtain analytical solutions in closed form for the AC field-driven induced-charge electroosmosis (ICEO) over two symmetric leaky dielectric blocks embedded in the walls of an infinitely long microchannel. Two important factors for the induced zeta potential are identified to respectively account for the polarization charges and the free charges, and their effects on AC field-driven ICEO oscillating flow patterns are analyzed. It is found that the flow patterns exhibit two counter-rotating vortices, which can be deformed, relocated, eliminated and even reverse their rotating directions. It is very promising that such temporary evolution of flow patterns can possibly induce chaotic advection which can enhance microfluidic mixing.

  8. Electrical Conductivity and Dielectrical Properties of Bulk Methylene Green

    NASA Astrophysics Data System (ADS)

    El-Menyawy, E. M.; Zedan, I. T.; Mansour, A. M.

    2017-03-01

    Thermal stability, direct current electrical conductivity (σ DC), alternating current electrical conductivityAC) and dielectric properties of bulk methylene green (MG) have been investigated. The thermal stability of MG was studied by differential scanning calorimetry and thermogravimetry techniques. Temperature dependence of σ DC showed that the MG has semiconductor behavior with two activation energies determined as 0.12 eV and 0.31 eV in the temperature range 303-343 K and 363-463 K, respectively. The σ AC of bulk MG was performed in the frequency range 150 Hz-5 MHz and temperature range 303-463 K. The dependence of AC conductivity on frequency for MG is found to satisfy Jonscher's universal power law, especially at high frequencies. The correlated barrier hopping model is found to be applicable in which the density of localized states is determined. The σ AC is thermally activated and the activation energy decreases with the increases in frequency. The variation of the real and imaginary parts of the dielectric constant with the frequency and temperature is explained.

  9. Novel dielectric reduces corona breakdown in ac capacitors

    NASA Technical Reports Server (NTRS)

    Loehner, J. L.

    1972-01-01

    Dielectric system was developed which consists of two layers of 25-gage paper separated by one layer of 50-gage polypropylene to reduce corona breakdown in ac capacitors. System can be used in any alternating current application where constant voltage does not exceed 400 V rms. With a little research it could probably be increased to 700 to 800 V rms.

  10. High thermal conductivity lossy dielectric using a multi layer configuration

    DOEpatents

    Tiegs, Terry N.; Kiggans, Jr., James O.

    2003-01-01

    Systems and methods are described for loss dielectrics. A loss dielectric includes at least one high dielectric loss layer and at least one high thermal conductivity-electrically insulating layer adjacent the at least one high dielectric loss layer. A method of manufacturing a loss dielectric includes providing at least one high dielectric loss layer and providing at least one high thermal conductivity-electrically insulating layer adjacent the at least one high dielectric loss layer. The systems and methods provide advantages because the loss dielectrics are less costly and more environmentally friendly than the available alternatives.

  11. Ion transport study in polymer-nanocomposite films by dielectric spectroscopy and conductivity scaling

    NASA Astrophysics Data System (ADS)

    Tripathi, Namrata; Thakur, Awalendra K.; Shukla, Archana; Marx, David T.

    2015-07-01

    The dielectric and conductivity response of polymer nanocomposite electrolytes (films of PMMA4LiClO4 dispersed with nano-CeO2 powder) have been investigated. The dielectric behavior was analyzed via the dielectric permittivity (ε‧) and dissipation factor (tan δ) of the samples. The analysis has shown the presence of space charge polarization at lower frequencies. The real part of ac conductivity spectra of materials obeys the Jonscher power law. Parameters such as dc conductivity, hopping rate, activation energies and the concentration of charge carriers were determined from conductivity data using the Almond West formalism. It is observed that the higher ionic conductivity at higher temperature is due to increased thermally-activated hopping rates accompanied by a significant increase in carrier concentration. The contribution of carrier concentration to the total conductivity is also confirmed from activation energy of migration conduction and from Summerfield scaling. The ac conductivity results are also well correlated with TEM results.

  12. Dielectric constants and electrical conductivities of sodium dodecyl sulfate in aqueous solutions

    SciTech Connect

    Abe, M.; Ogino, K.

    1981-03-01

    Dielectric properties of sodium dodecyl sulfate in aqueous solution have been studied. The dielectric constant and ac electrical conductivity were measured in the frequency range 30 Hz to 6 MHz. At lower frequencies, with increasing concentrations of sodium dodecyl sulfate, dielectric properties were greatly affected by polarization on the surfaces of the electrode, the so-called space charge polarization. ac electrical conductivities were dependent on the concentration of sodium dodecyl sulfate at all frequencies. The activation energies of dc electrical conduction were much larger in the molecular state than in the aggregation state. The radius of a spherical particle with an electric double layer could be calculated through the measurement of dielectric constant and dc electrical conductivity. 18 references.

  13. Electrical conductivity and dielectric studies of MnO2 doped V2O5

    NASA Astrophysics Data System (ADS)

    Tan, Foo Khoon; Hassan, Jumiah; Wahab, Zaidan Abd.; Azis, Raba'ah Syahidah

    The investigation on electrical conductivity and dielectric properties of mixed oxide of manganese (Mn) and vanadium (V) was carried out to study the mixed oxides response to different frequencies and different measuring temperatures. The frequency and temperature dependence of AC conductivity, dielectric constant and dielectric loss factor of mixed oxides were studied in the frequency range of 40 Hz-1 MHz and a temperature range of 30-250 °C. Since the mixed oxides are multi phase materials, hence the properties of the pure oxides are also presented in this study to discuss the multi phase behaviour of the mixed oxides. The XRD pattern shows the Mn-V oxide is multiphase and quantitative phase analysis was performed to determine the relative phases. The overall results indicate that with increasing temperature, the AC conductivity, dielectric constant, dielectric loss factor and loss tangent of the Mn-V mixed oxide increases. However, it shows an overlap in the dielectric constant at 225 °C and 250 °C due to the V2O5 phase in the mixed oxide. From the AC activation energy, the mixed oxides underwent conduction mechanism transition from band to hopping in the investigated frequency range. The MnV2O6 has relatively good resistivity, therefore the mixed oxide sintered at 550 °C with the highest composition of MnV2O6 gives the highest dielectric constant of 9845 at 1 kHz, and at 250 °C.

  14. Dielectric and conduction behaviour of H2SO4 doped conducting Polyaniline

    NASA Astrophysics Data System (ADS)

    Mohanty, J.; Behera, P.; Mishra, S. R.; Badapanda, T.; Anwar, S.

    2017-02-01

    We report the effect of H2SO4 doping on the dielectric and conduction behaviour of Polyaniline (PANI) samples. The PANI salt prepared by oxidising aniline hydrochloride in distilled water with the oxidant ammonium persulphate with continuous stirring at room temperature and PANI base is produced by subjecting PANI salt to a reaction with 0.5M NaOH. H2SO4 doped PANI is prepared by subjecting PANI base to reaction with 1M H2SO4 at room temperature under constant stirring for 1h. The synthesied PANI along with the doped samples were further washed with acetone to study the effect of acetone washing on the electrical behaviour. It is observed that the dielectric constant as well as the dielectric loss decreases with frequency in the entire studied sample. The frequency dependent AC conductivity at room temperature obeys the power law and the DC conductivity was obtained from the fitting parameter. It is found that the non acetone washed PANI doped in 1M H2SO4 shows highest dielectric constant and conductivity.

  15. The investigation of dielectric properties and ac conductivity of new ceramic diphosphate Ag0.6Na0.4FeP2O7 using impedance spectroscopy method

    NASA Astrophysics Data System (ADS)

    Nasri, S.; Megdiche, M.; Gargouri, M.

    2016-10-01

    In this paper, Ag0.6Na0.4FeP2O7 has been synthesized by solid state reaction method. The ceramic compound was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), vibrational spectroscopy and impedance measurements. In fact, the investigated sample has shown single phase type monoclinic structure with P21/C space group. The frequency-dependent electrical data are analyzed in the frame-work of conductivity and electric modulus formalisms. The real and imaginary parts of complex impedance are well fitted to equivalent circuit model based on the Z-View-software. Besides, the observed frequency dependence of conductivity is found to obey Jonscher's universal law. The temperature dependence of both ac conductivity and the parameter s is reasonably well interpreted by the correlated barrier hopping (CBH). The theoretical fitting between the proposed model and the experimental data showed good agreement. The contribution of single polaron and bipolaron hopping to a.c. conductivity in present compound is also studied. The ionic conductivity is discussed on the basis of the structural characteristics of the sample.

  16. ac conductance in granular insulating Co-ZrO{sub 2} thin films: A universal response

    SciTech Connect

    Konstantinovic, Zorica; Garcia del Muro, Montserrat; Kovylina, Miroslavna; Batlle, Xavier; Labarta, Amilcar

    2009-03-01

    The ac conductance in granular insulating Co-ZrO{sub 2} thin films prepared by pulsed laser deposition is systematically studied as a function of the Co volume content x. An absorption phenomenon at low frequencies that mimics the universal response of disordered dielectric materials is observed in the range of metal content below the Co percolation threshold x{sub p}{approx_equal}0.35 in the so-called dielectric regime. The temperature and frequency dependences of this absorption phenomenon are successfully analyzed in terms of random competing conduction channels between Co particles through thermally assisted tunneling and capacitive conductance. The ac conductance is well correlated with the nanostructure of the samples obtained by the transmission electron microscopy and perfectly matches the calculated ac response for a random resistor-capacitor network. We also show the occurrence of fractional power-law dependences on the frequency of the ac conductance taking place at very low frequencies as compared to the typical ranges at which dispersive behavior is observed in classical-disordered dielectric materials.

  17. Dielectric and AC conductivity studies of Nd substituted 0.8BaTiO3-0.2(Bi0.5(1-x)Nd0.5xK0.5)TiO3 lead free ceramics

    NASA Astrophysics Data System (ADS)

    Ramesh, M. N. V.; Ramesh, K. V.

    2016-05-01

    0.8BaTiO3 - 0.2(Bi0.5(1-x)Nd0.5xK0.5)TiO3 (0.01 ≤ x ≤ 0.06) lead free ceramic materials have been prepared by solid state reaction method and followed by high energy ball milling process. X-ray diffraction studies confirm the tetragonal structure of the materials at room temperature. Lattice parameters and density are decreasing with increase of Nd substitution. Microstructure studies were done by using Scanning electron microscope and it found that grain size is decreasing with increase of Nd substitution. Temperature and frequency dependent dielectric studies reveal relaxor behaviour of the materials. Dielectric constant, dielectric loss and Curie temperature are decreasing with Nd substitution. Maximum Curie temperature of 195°C was observed at 1MHz for x=0.01 Nd substituted sample. Degree of diffuseness was calculated from the modified Curie-Weiss law and it is increasing with Nd substitution. AC conductivity is increasing with increase of Nd substitution and observed maximum activation energy of 0.52 eV for x=0.02 Nd substituted sample.

  18. Study of AC electrical conduction mechanisms in an epoxy polymer

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

    The AC conductivity of an epoxy resin was investigated in the frequency range 10^{-1} - 106 Hz at temperatures ranging from -100 to 120 °C. The frequency dependence of σ_{ac} was described by the law: σ_{ac}=ω \\varepsilon0\\varepsilon^''_{HN}+Aωs. The study of temperature variation of the exponent (s) reveals two conduction models: the AC conduction dependence upon temperature is governed by the small polaron tunneling mechanism (SPTM) at low temperature (-100 -60 °C) and the correlated barrier hopping (CHB) model at high temperature (80-120 °C).

  19. Thermal conductivity and dielectric constant of silicate materials

    NASA Technical Reports Server (NTRS)

    Simon, I.; Wechsler, A. E.

    1968-01-01

    Report on the thermal conductivity and dielectric constant of nonmetallic materials evaluates the mechanisms of heat transfer in evacuated silicate powders and establishes the complex dielectric constant of these materials. Experimental measurements and results are related to postulated lunar surface materials.

  20. Role of dielectric constant in electrohydrodynamics of conducting fluids

    NASA Technical Reports Server (NTRS)

    Rhodes, Percy H.; Snyder, Robert S.; Roberts, Glyn O.

    1992-01-01

    Electrohydrodynamic (EHD) flows are driven by the interaction of an electric field with variations in electric conductivity or dielectric constant. In reported EHD experiments on the deformation of drops of immiscible dielectric fluids, the role of conductivity has tended to overshadow the role of dielectric constant. Often, large conductivity contrasts were convenient because the conductivities of the dielectric fluid were relatively uncertain. As a result, the observed effects were always qualitatively the same as if there had been no contrast in dielectric constant. Our early experiments studying the EHC deformations of cylindrical streams readily showed the conductivity effect but the dielectric constant effect was not discernible. We have modified our flow chamber and improved our method of observation and can now see an unequivocal dielectric constant effect which is in agreement with the prior theory. In this paper we first give a brief description of the physics of charge buildup at the interface of an immersed spherical drop or flowing cylindrical sample stream and then show how these charge distributions lead to interface distortions and accompanying viscous flows which constitute EHD. We next review theory and experiment describing the deformation of spherical drops. We show that in the reported drop deformation experiments, the contrast in dielectric constant was never sufficient to reverse the deformation due to the conductivity contrast. We review our work describing the deformation of a cylindrical stream of one fluid flowing in a parallel flow of another, and we compare the deformation equations with those for spherical drops. Finally, we show a definite experimental dielectric constant effect for cylindrical stream of aqueous polystyrene latex suspension. The dielectric constant varies with the frequency of the imposed electric field, and the associated EHD flow change is very apparent.

  1. Effects of airflow on the distribution of filaments in atmospheric AC dielectric barrier discharge

    NASA Astrophysics Data System (ADS)

    Fan, Zhihui; Qi, Haicheng; Liu, Yidi; Yan, Huijie; Ren, Chunsheng

    2016-12-01

    Atmospheric-pressure dielectric barrier discharge (DBD) accompanied by airflow has attracted a significant attention for its extensive applications. In this paper, the effects of airflow on the characteristics of the atmospheric air DBD plasma are experimentally investigated using the DBD reactor excited by a 15 kHz AC power source. In order to study the discharge filaments distribution at different flow rates, transparent conductive indium tin oxide film is used as the upper electrode, and quartz glasses are used as insulated dielectrics. Experiment results prove that the breakdown voltage is decreased and more current pulses with declined amplitudes are produced when the airflow is introduced into the discharge gap. It is confirmed that although the discharge seems to be diffuse in the presence of airflow to the naked eyes, the discharge mode remains filamentary in the intensified charge-coupled device images within a single AC cycle. By acquiring the images with a different exposure time, it can be recognized that the discharge filaments move along the flow field direction with a velocity less than the corresponding flow rate. The movement of discharge filaments is attributed to the motion of the charge induced by the airflow.

  2. AC Conductivity and Diffuse Reflectance Studies of Ag-TiO2 Nanoparticles

    NASA Astrophysics Data System (ADS)

    Abdul Gafoor, A. K.; Musthafa, M. M.; Pradyumnan, P. P.

    2012-09-01

    Silver (Ag)-TiO2 nanoparticles synthesized by a low-temperature hydrothermal method in the anatase phase have been investigated by x-ray diffraction. Transmission electron microscopy has been used for morphological studies. Surface areas were studied by the Brunauer-Emmett-Teller method. Alternating-current (AC) conductivity and dielectric properties were studied for various dopant levels of 0.25 wt.%, 0.5 wt.%, and 1.0 wt.% at 300 K in the frequency range from 42 Hz to 5 MHz. AC conductivity and dielectric properties of TiO2 nanoparticles were greatly affected by loading with Ag. At high frequencies, the materials showed high AC conductivity and low dielectric constant. Diffuse reflectance studies were carried out for various dopant levels at 300 K by ultraviolet-visible (UV-Vis) spectroscopy. Considerable absorption of visible light by 0.5 wt.% and 1.0 wt.% Ag-TiO2 nanoparticles was observed due to the decrease of the energy band gap on Ag loading.

  3. Ionic conductivity and dielectric studies of LiClO4 doped poly(vinylalcohol)(PVA)/chitosan(CS) composites

    NASA Astrophysics Data System (ADS)

    Rathod, Sunil G.; Bhajantri, R. F.; Ravindrachary, V.; Pujari, P. K.; Sheela, T.

    2014-12-01

    This paper focuses on the dielectric constant (ɛ‧), dielectric loss factor (ɛ″) and frequency dependent conductivityac) properties of newly prepared poly(vinylalcohol) (PVA) chitosan (CS) composite films incorporated with different concentrations of LiClO4. The composite films were prepared using solution casting technique. The complexation between salt and polymer host is confirmed by FT Raman and UV-Vis studies. The sample containing 20 wt.% LiClO4 exhibits a highest ionic conductivity of 3 × 10-6 S/cm at room temperature. The dielectric properties of the composites follow non-Debye behavior.

  4. 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.

  5. Dielectric properties and charge transfer in (TlInSe2)0.1(TlGaTe2)0.9 for the DC and AC current

    NASA Astrophysics Data System (ADS)

    Mustafaeva, S. N.; Asadov, M. M.; Dzhabbarov, A. I.

    2014-06-01

    The experimental results of studying the temperature and frequency dependences of dc and ac conductivity as well as the dispersion of dielectric coefficients of the grown single crystals of the (TlInSe2)0.1(TlGaTe2)0.9 solid solution are presented. The nature of dielectric losses and the hopping charge transfer mechanism have been established, and parameters of localized states, such as the density of states near the Fermi level and their spread, the average time and the hopping length of charge carriers, and the concentration of deep traps responsible for dc and ac conductivity, have been evaluated.

  6. Scattering from thin dielectric straps surrounding a perfectly conducting structure

    NASA Technical Reports Server (NTRS)

    Al-Hekail, Zeyad O.; Gupta, Inder J.; Burnside, Walter D.

    1993-01-01

    Dielectric straps can support very heavy targets and have low backscattering levels, especially at low frequencies (below 8 GHz); thus, they can be used effectively to support targets during backscattered field measurements. In this paper, the scattered fields of nonmagnetic dielectric straps surrounding a perfectly conducting structure are presented, and the computed results are compared with experimental data. Empirical formulas for the strap scattered fields are also given. These formulas are good for general convex structures whose radii of curvature are large compared with the wavelength and are expected to give a reasonable estimate of the true backscattered fields from the dielectric straps when used as a target support structure.

  7. Evolution of AC conductivity of wet illitic clay during drying

    NASA Astrophysics Data System (ADS)

    Csáki, Š.; Štubňa, I.; Trnovcová, V.; Ondruška, J.; Vozár, L.; Dobroň, P.

    2017-02-01

    The evolution of the AC electrical conductivity during drying as well as the relationship between sample volume and moisture of green illite samples were investigated. The samples were prepared from illitic clay (80 mass % illite, 4 mass % montmorillonite, 12 mass % quartz and 4 mass % of orthoclase) and distilled water with initial moisture content 36 mass % and were freely dried in air. Conductivity was measured by the volt-ampere method with AC power supply of 5 V in the frequency range from 50 Hz to 10 kHz. The AC conductivity steeply increased with increasing moisture, up to 15 mass %. At higher values of the moisture, the AC conductivity was high and almost constant. The volume of samples increased with increasing moisture when the moisture was higher than 8 mass %. Below this value, the dimensions of samples do not significantly change. The dependence of the relative volume change on moisture is presented in a form of the Bigot’s curve.

  8. Dielectric function of media based on conductive particles

    SciTech Connect

    Kempa, K.

    2006-07-15

    The general formula for the dielectric function of a medium containing conductive particles of various sizes (e.g., nanoparticles) is derived, and shown that it is exact in spite of electron-electron interactions for a parabolic confinement of electrons in the particles. The derivation method explains the apparent universal applicability of this formula to other systems. It is also shown, how this formula can be used to design composites with desired dielectric properties.

  9. Role of dielectric constant in electrohydrodynamics of conducting fluids

    NASA Technical Reports Server (NTRS)

    Rhodes, Percy H.; Snyder, Robert S.; Roberts, Glyn O.

    1994-01-01

    Electrohydrodynamic sample distortion during continuous flow electrophoresis is an experiment to be conducted during the second International Microgravity Laboratory (IML-2) in July 1994. The specific objective of this experiment is the distortion caused by the difference in dielectric constant between the sample and surrounding buffer. Although the role of sample conductivity in electrohydrodynamic has been the subject of both flight and ground experiments, the separate role of dielectric constant, independent of sample conductivity, has not been measured. This paper describes some of the laboratory research and model development that will support the flight experiment on IML-2.

  10. AC Dielectric Properties and Positron Annihilation Study on Co and Ti Substitution Effect on Ca-Sr M-Hexaferrites

    NASA Astrophysics Data System (ADS)

    Mahmoud, K. R.; Eraky, M. R.

    2016-06-01

    The dependence of AC conductivity σ AC, dielectric constant έ, and dielectric loss tangent tan δ on frequency and composition have been investigated at room temperature for polycrystalline Ca0.5Sr0.5Co x Ti x Fe12 - 2 x O19 (where 0.0 ≤ x ≤ 0.8) hexaferrites. It was found that the parameters σ AC, ɛ ', and tan δ have maximum values at x = 0.4 of the Co and Ti substitution. The behavior of σ AC, ɛ ', and tan δ with frequency and composition was explained on the basis of the hopping conduction mechanism and the Koops model. Positron annihilation lifetime spectroscopy (PALS) was used to investigate the defects and changes in electron density for hexaferrite samples. The PAL parameters ( τ 1, I 1, τ 2, I 2, and mean lifetime) show that altering the doping percentage of the Co and Ti ions affects the size and concentration of defects. The results reveal that there are some large voids in the studied samples. The obtained results indicate the high sensitivity of the PALS technique to the enhanced structure changes with changing composition of the investigated samples and correlate the results with the measured electrical parameters.

  11. Dielectric and conducting behavior of gadolinium-terbium fumarate heptahydrate crystals

    NASA Astrophysics Data System (ADS)

    Shah, M. D.; Want, B.

    2015-07-01

    Gadolinium-terbium fumarate heptahydrate crystals were grown in silica gel by using single gel diffusion technique. The crystals were characterized by different physico-chemical techniques of characterization. Powder X-ray diffraction results showed that the grown material is purely crystalline in nature. Elemental analyses suggested the chemical formula of the compound to be Gd Tb (C4H2O4)3ṡ7H2O. Energy dispersive X-ray analysis confirmed the presence of Gd and Tb in the title compound. The dielectric and conductivity studies of the grown compound were carried as function of frequency of applied field and the temperature. The grown material showed a dielectric anomaly which was correlated with its thermal behavior. The ac conductivity of the material showed Jonscher's power law behavior: σ(ω)=σo+Aωs, with a temperature-dependent power exponent s(<1). The conductivity was found to be a function of temperature and frequency.

  12. Transient characterization of extreme field conduction in dielectrics

    NASA Astrophysics Data System (ADS)

    Li, Zongze; Xu, Chunchuan; Uehara, Hiroaki; Boggs, Steven; Cao, Yang

    2016-11-01

    High field degradation and electric breakdown of dielectrics are extremely complex phenomena as a result of the interplay among the electric field, temperature, material morphology, and extrinsic material properties. Fundamental understanding of carrier mobility related prebreakdown phenomena in dielectrics provides insights into high field transport phenomena as well as associated aging and onset of charge injection induced instability. Investigation of such extreme field conduction has been traditionally limited to the divergent field distribution generated using point-plane electrode configuration, as testing of parallel plate sample configuration under quasi steady-state conditions can only reach around two thirds of the breakdown field as a result of rapid high field aging. A circuit has been developed for transient characterization of conduction through a planar dielectric film during a linear ramp voltage to breakdown via the cancellation of displacement current to facilitate the measurement of small resistive currents down to 10ppm level. The dynamic cancellation of displacement current during an applied voltage waveform is realized through the use of a high frequency sinusoidal "bias" voltage to generate a capacitive current that can be cancelled using a feedback circuit based on a voltage-controlled amplifier with negligible phase shift and a dual-phase digital lock-in amplifier. Such capability of transient characterization of conduction in dielectrics will provide insights into dielectric aging and breakdown mechanism and form a quantitative basis for the extraction of critical transport parameters for conduction under extreme electric fields.

  13. AC Conductivity Studies of Lithium Based Phospho Vanadate Glasses

    NASA Astrophysics Data System (ADS)

    Nagendra, K.; Babu, G. Satish; Reddy, C. Narayana; Gowda, Veeranna

    2011-07-01

    Glasses in the system xLi2SO4-20Li2O-(80-x) [80P2O5-20V2O5] (5⩾x⩾20 mol%) has been prepared by melt quenching method. Dc and ac conductivity has been studied over a wide range of frequency (10 Hz to 10 MHz) and temperature (298 K-523 K). The dc conductivity found to increase with increase of Li2SO4 concentration. The ac conductivities have been fitted to the Almond-West type single power law equation σ(ω) = σ(0)+Aωs where `s' is the power law exponent. The ac conductivity found to increase with increase of Li2SO4 concentration. An attempt is made to elucidate the enhancement of lithium ion conduction in phosphor-vanadate glasses by considering the expansion of network structure.

  14. 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.

  15. 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.

  16. Dielectric Properties of Aligned Conducting Polymers

    DTIC Science & Technology

    1991-10-01

    It has been demonstrated that aligned polyacetylene and polyaniline possess remarkably enhanced conductivities. The increase in crystallinity and...and thermal stability compared to other CPs such as polyacetylenes, polythiophenes, and polyaniline . These favorable properties and the commercial...stretch-orientation of BF4- doped PPy films electrochemically deposited at -30,C, 7 pyrrole electropolymerization at a xylene/water interface, 8 and

  17. Radiation induced conductivity in space dielectric materials

    SciTech Connect

    Hanna, R.; Paulmier, T. Belhaj, M.; Dirassen, B.; Molinie, P.; Payan, D.; Balcon, N.

    2014-01-21

    The radiation-induced conductivity of some polymers was described mainly in literature by a competition between ionization, trapping/detrapping, and recombination processes or by radiation assisted ageing mechanisms. Our aim is to revise the effect of the aforementioned mechanisms on the complex evolution of Teflon{sup ®} FEP under space representative ionizing radiation. Through the definition of a new experimental protocol, revealing the effect of radiation dose and relaxation time, we have been able to demonstrate that the trapping/recombination model devised in this study agrees correctly with the observed experimental phenomenology at qualitative level and allows describing very well the evolution of radiation induced conductivity with irradiation time (or received radiation dose). According to this model, the complex behavior observed on Teflon{sup ®} FEP may be basically ascribed to the competition between electron/hole pairs generation and recombination: electrons are deeply trapped and act as recombination centers for free holes. Relaxation effects have been characterized through successive irradiations steps and have been again well described with the defined model at qualitative level: recombination centers created by the irradiation induce long term alteration on the electric properties, especially the effective bulk conductivity. One-month relaxation does not allow a complete recovery of the material initial charging behavior.

  18. Dielectric and conducting behaviors in quasi-amorphous hybrid poly(diallyldimethylammonium phosphomolybdate)

    NASA Astrophysics Data System (ADS)

    Gao, Xiao-Yan; Liu, Shao-Xian; Xue, Chen; Li, Li; Zou, Yang; Liu, Jian-Lan; Ren, Xiao-Ming

    2016-11-01

    A quasi-amorphous inorganic-organic hybrid solid, which is comprised of poly(diallyldimethylammonium) polyelectrolyte cations with phosphomolybdates and denoted as PDDA/PMA, was prepared and characterized using elemental analysis, powder x-ray diffraction, IR spectrum, thermal and energy dispersive X-ray analyses. The PDDA/PMA exhibits multistep dielectric anomalies and dielectric relaxations. The dielectric anomaly around 353 K arises partially from the water trapped in the PDDA/PMA network releasing. The PDDA/PMA was further dried under vacuum at 373 K to give water-free sample PDDA/PMA-1. With water being removed, the broad anomaly peak around 353 K in the ε‧-T plot of PDDA/PMA changes into a platform in that of PDDA/PMA-1, indicating that the dielectric anomalies result from not only losing water but also the network disorder in PDDA/PMA-1. In addition, the platform strongly depends on the AC frequency in PDDA/PMA-1; the electric modulus and ion conductance analyses demonstrated that the dielectric relaxations at elevated temperature are related to the PMA ions displacing motion.

  19. Effect of nanosilica on optical, electric modulus and AC conductivity of polyvinyl alcohol/polyaniline films

    NASA Astrophysics Data System (ADS)

    El-Sayed, Somyia; Abel-Baset, Tarob; Elfadl, Azza Abou; Hassen, Arafa

    2015-05-01

    Nanosilica (NS) was synthesized by a sol-gel method and mixed with 0.98 polyvinyl alcohol (PVA)/0.02 polyaniline (PANI) in different amounts to produce nanocomposite films. High-resolution transmission electron microscopy (HR-TEM) revealed the average particle size of the NS to be ca. 15 nm. Scanning electron microscopy (SEM) showed that the NS was well-dispersed on the surface of the PVA/PNAI films. The Fourier transform infrared (FTIR) spectra of the samples showed a significant change in the intensity of the characteristic peak of the functional groups in the composite films with the amount of NS added. The absorbance and refractive index (n) of the composites were studied in the UV-vis range, and the optical energy band gap, Eg, and different optical parameters were calculated. The dielectric loss modulus, M″ and ac conductivity, σac, of the samples were studied within 300-425 K and 0.1 kHz-5 MHz, respectively. Two relaxation peaks were observed in the frequency dependence of the dielectric loss modulus, M″. The behavior of σac(f) for the composite films indicated that the conduction mechanism was correlated barrier hopping (CBH). The results of this work are discussed and compared with those of previous studies of similar composites.

  20. 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

  1. Temperature dependent dielectric and conductivity studies of polyvinyl alcohol-ZnO nanocomposite films by impedance spectroscopy

    NASA Astrophysics Data System (ADS)

    Hemalatha, K. S.; Sriprakash, G.; Ambika Prasad, M. V. N.; Damle, R.; Rukmani, K.

    2015-10-01

    Dielectric and conductivity behaviors of nano ZnO doped polyvinyl alcohol (PVA) composites for various concentrations of dopant were investigated using impedance spectroscopy for a wide range of temperatures (303 K-423 K) and frequencies (5 Hz-30 MHZ). The dielectric properties of host polymer matrix have been improved by the addition of nano ZnO and are found to be highly temperature dependent. Anomalous dielectric behavior was observed in the frequency range of 2.5 MHz-5 MHz. Increase in dielectric permittivity and dielectric loss was observed with respect to temperature. The Cole-Cole plot could be modeled by low resistance regions in a high resistance matrix and the lowest resistance was observed for the 10 mol. % films. The imaginary part of the electric modulus showed asymmetric peaks with the relaxation following Debye nature below and non-Debye nature above the peaks. The ac conductivity is found to obey Jonscher's power law, whereas the variation of dc conductivity with temperature was found to follow Arrhenius behavior. Two different activation energy values were obtained from Arrhenius plot indicating that two conduction mechanisms are involved in the composite films. Fitting the ac conductivity data to Jonscher's law indicates that large polaron assisted tunneling is the most likely conduction mechanism in the composites. Maximum conductivity is observed at 423 K for all the samples and it is optimum for 10 mol. % ZnO doped PVA composite film. Significant increase in dc and ac conductivities in these composite films makes them a potential candidate for application in electronic devices.

  2. Temperature dependent dielectric and conductivity studies of polyvinyl alcohol-ZnO nanocomposite films by impedance spectroscopy

    SciTech Connect

    Hemalatha, K. S.; Damle, R.; Rukmani, K.; Sriprakash, G.; Ambika Prasad, M. V. N.

    2015-10-21

    Dielectric and conductivity behaviors of nano ZnO doped polyvinyl alcohol (PVA) composites for various concentrations of dopant were investigated using impedance spectroscopy for a wide range of temperatures (303 K–423 K) and frequencies (5 Hz–30 MHZ). The dielectric properties of host polymer matrix have been improved by the addition of nano ZnO and are found to be highly temperature dependent. Anomalous dielectric behavior was observed in the frequency range of 2.5 MHz–5 MHz. Increase in dielectric permittivity and dielectric loss was observed with respect to temperature. The Cole-Cole plot could be modeled by low resistance regions in a high resistance matrix and the lowest resistance was observed for the 10 mol. % films. The imaginary part of the electric modulus showed asymmetric peaks with the relaxation following Debye nature below and non-Debye nature above the peaks. The ac conductivity is found to obey Jonscher's power law, whereas the variation of dc conductivity with temperature was found to follow Arrhenius behavior. Two different activation energy values were obtained from Arrhenius plot indicating that two conduction mechanisms are involved in the composite films. Fitting the ac conductivity data to Jonscher's law indicates that large polaron assisted tunneling is the most likely conduction mechanism in the composites. Maximum conductivity is observed at 423 K for all the samples and it is optimum for 10 mol. % ZnO doped PVA composite film. Significant increase in dc and ac conductivities in these composite films makes them a potential candidate for application in electronic devices.

  3. ac and dc percolative conductivity of magnetite-cellulose acetate composites

    SciTech Connect

    Chiteme, C.; McLachlan, D. S.; Sauti, G.

    2007-03-01

    ac and dc conductivity results for a percolating system, which consists of a conducting powder (magnetite) combined with an 'insulating' powder (cellulose acetate), are presented. Impedance and modulus spectra are obtained in a percolation system. The temperature dependence of the resistivity of the cellulose acetate is such that at 170 deg. C, it is essentially a conductor at frequencies below 0.059{+-}0.002 Hz, and a dielectric above. The percolation parameters, from the dc conductivity measured at 25 and 170 deg. C, are determined and discussed in relation to the ac results. The experimental results scale as a function of composition, temperature, and frequency. An interesting result is the correlation observed between the scaling parameter (f{sub ce}), obtained from a scaling of the ac measurements, and the peak frequency (f{sub cp}) of the arcs, obtained from impedance spectra, above the critical volume fraction. Scaling at 170 deg. C is not as good as at 25 deg. C, probably indicating a breakdown in scaling at the higher temperature. The modulus plots show the presence of two materials: a conducting phase dominated by the cellulose acetate and the isolated conducting clusters below the critical volume fraction {phi}{sub c}, as well as the interconnected conducting clusters above {phi}{sub c}. These results are confirmed by computer simulations using the two exponent phenomenological percolation equation. These results emphasize the need to analyze ac conductivity results in terms of both impedance and modulus spectra in order to get more insight into the behavior of composite materials.

  4. AC and DC conductivity of ionic liquid containing polyvinylidene fluoride thin films

    NASA Astrophysics Data System (ADS)

    Frübing, Peter; Wang, Feipeng; Kühle, Till-Friedrich; Gerhard, Reimund

    2016-01-01

    Polarisation processes and charge transport in polyvinylidene fluoride (PVDF) with a small amount (0.01-10 wt%) of the ionic liquid (IL) 1-ethyl-3-methylimidazolium nitrate ({[EMIM]}^+[{NO}_3]^-) are investigated by means of dielectric spectroscopy. The response of PVDF that contains more than 0.01 wt% IL is dominated by a low-frequency relaxation which shows typical signatures of electrode polarisation. Furthermore, the α a relaxation, related to the glass transition, disappears for IL contents of more than 1 wt%, which indicates that the amorphous phase loses its glass-forming properties and undergoes structural changes. The DC conductivity is determined from the low-frequency limit of the AC conductivity and from the dielectric loss peak related to the electrode polarisation. DC conductivities of 10^{-10} to 10^{-2} {S}/{m} are obtained—increasing with IL content and temperature. The dependence of the DC conductivity on the IL content follows a power law with an exponent greater than one, indicating an increase in the ion mobility. The temperature dependence of the DC conductivity shows Vogel-Fulcher-Tammann behaviour, which implies that charge transport is coupled to polymer chain motion. Mobile ion densities and ion mobilities are calculated from the DC conductivity and the dielectric loss related to electrode polarisation, with the results that less than one per cent of the total ion concentration contributes to the conductivity and that the strong increase in conductivity with temperature is mainly caused by a strong increase in ion mobility. This leads to the conclusion that in particular the ion mobility must be reduced in order to decrease the DC conductivity.

  5. AC Conductivity Studies of Lithium Based Phospho Vanadate Glasses

    SciTech Connect

    Nagendra, K.; Babu, G. Satish; Gowda, Veeranna; Reddy, C. Narayana

    2011-07-15

    Glasses in the system xLi{sub 2}SO{sub 4}-20Li{sub 2}O-(80-x) [80P{sub 2}O{sub 5}-20V{sub 2}O{sub 5}](5{>=}x{>=}20 mol%) has been prepared by melt quenching method. Dc and ac conductivity has been studied over a wide range of frequency (10 Hz to 10 MHz) and temperature (298 K-523 K). The dc conductivity found to increase with increase of Li{sub 2}SO{sub 4} concentration. The ac conductivities have been fitted to the Almond-West type single power law equation {sigma}({omega}) = {sigma}(0)+A{omega}{sup s} where 's' is the power law exponent. The ac conductivity found to increase with increase of Li{sub 2}SO{sub 4} concentration. An attempt is made to elucidate the enhancement of lithium ion conduction in phosphor-vanadate glasses by considering the expansion of network structure.

  6. Experimental and theoretical study of AC electrical conduction mechanisms of semicrystalline parylene C thin films.

    PubMed

    Kahouli, Abdelkader; Sylvestre, Alain; Jomni, Fethi; Yangui, Béchir; Legrand, Julien

    2012-01-26

    The electrical conduction mechanisms of semicrystalline thermoplastic parylene C (-H(2)C-C(6)H(3)Cl-CH(2)-)(n) thin films were studied in large temperature and frequency regions. The alternative current (AC) electrical conduction in parylene C is governed by two processes which can be ascribed to a hopping transport mechanism: correlated barrier hopping (CBH) model at low [77-155 K] and high [473-533 K] temperature and the small polaron tunneling mechanism (SPTM) from 193 to 413 K within the framework of the universal law of dielectric response. The conduction mechanism is explained with the help of Elliot's theory, and the Elliot's parameters are determined. From frequency- and temperature-conductivity characteristics, the activation energy is found to be 1.27 eV for direct current (DC) conduction interpreted in terms of ionic conduction mechanism. The power law dependence of AC conductivity is interpreted in terms of electron hopping with a density N(E(F)) (~10(18) eV cm(-3)) over a 0.023-0.03 eV high barrier across a distance of 1.46-1.54 Å.

  7. Dielectric anomalies due to grain boundary conduction in chemically substituted BiFeO{sub 3}

    SciTech Connect

    Kumari, Shalini; Ortega, N.; Pavunny, S. P.; Katiyar, Ram S.; Kumar, A.; Hubbard, J. W.; Rinaldi, C.; Srinivasan, G.; Scott, J. F.

    2015-03-21

    We describe systematic studies on Nd and Mn co-doped BiFeO{sub 3}, i.e., (Bi{sub 0.95}Nd{sub 0.05})(Fe{sub 0.97}Mn{sub 0.03})O{sub 3} (BNFM) polycrystalline electroceramics. Raman spectra and X-ray diffraction patterns revealed the formation of rhombohedral crystal structure at room temperature, and ruled out structural changes in BiFeO{sub 3} (BFO) after low percentage chemical substitution. Strong dielectric dispersion and a sharp anomaly around 620 K observed near the Néel temperature (T{sub N} ∼ 643 K of BFO) support strong magneto-dielectric coupling, verified by the exothermic peak in differential thermal data. Impedance spectroscopy disclosed the appearance of grain boundary contributions in the dielectric data in the region, and their disappearance just near the Néel temperature suggests magnetically active grain boundaries. The resistive grain boundary components of the BNFM are mainly responsible for magneto-dielectric coupling. Capacitive grain boundaries are not observed in the modulus spectra and the dielectric behavior deviates from the ideal Debye-type. The ac conduction studies illustrate short-range order with ionic translations assisted by both large and small polaron hopping. Magnetic studies indicate that the weak antiferromagnetic phase of BNFM ceramics is dominated by a strong paramagnetic response (unsaturated magnetization even at applied magnetic field of 7 T). The bulk BNFM sample shows a good in-plane magnetoelectric coupling (ME) coefficient.

  8. High thermal conductivity lossy dielectric using co-densified multilayer configuration

    DOEpatents

    Tiegs, Terry N.; Kiggans, Jr., James O.

    2003-06-17

    Systems and methods are described for loss dielectrics. A method of manufacturing a lossy dielectric includes providing at least one high dielectric loss layer and providing at least one high thermal conductivity-electrically insulating layer adjacent the at least one high dielectric loss layer and then densifying together. The systems and methods provide advantages because the lossy dielectrics are less costly and more environmentally friendly than the available alternatives.

  9. Scattering from thin dielectric straps surrounding a perfectly conducting structure

    NASA Technical Reports Server (NTRS)

    Al-Hekail, Zeyad; Gupta, Inder J.

    1989-01-01

    A method to calculate the electromagnetic scattered fields from a dielectric strap wrapped around convex, conducting structure is presented. A moment method technique is used to find the current excited within the strap by the incident plane wave. Then, Uniform Geometrical Theory of Diffraction (UTD) is used to compute the fields scattered by the strap. Reasonable agreement was obtained between the computed and the measured results. The results found in this study are useful in evaluating straps as a target support structure for scattering measurements.

  10. Correlation of electrical conductivity, dielectric properties, microwave absorption, and matrix properties of composites filled with graphene nanoplatelets and carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Khurram, A. A.; Rakha, Sobia A.; Zhou, Peiheng; Shafi, M.; Munir, Arshad

    2015-07-01

    The DC electrical conductivity, percolation threshold, and dielectric properties of Graphene Nanoplatelets (GNPs) filled epoxy composites are studied and correlated with microwave absorption. The properties of GNPs filled composites are also compared with multiwalled carbon nanotubes (MWCNTs) composites, and GNPs are observed to have superior conductivity than MWCNTs. In all batches, the nanofillers have 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, and 3.5 wt. %. All composites irrespective of the type of nanofiller and viscosity of the matrix have shown electrical percolation threshold at 3.0 wt. %. The dielectric properties, i.e., complex permittivity, tan loss, and AC conductivity, are studied in 100 Hz-5.5 MHz. The DC and AC electrical conductivities (at and below the percolation) measured in 100 Hz-5.5 MHz are correlated to the GNPs and MWCNTs epoxy composites in the microwave frequency range (11-17 GHz). The maximum return loss of -12 dB and -6 dB was determined for MWCNTs and GNPs, respectively. The effects of nanofiller shape and the viscosity of the matrix on the dispersion and interparticle spacing of the conductive fillers within the polymer matrix have been discussed based on the results of conductivity, dielectric, and absorption properties.

  11. AC CONDUCTION PHENOMENON OF Li2O-WO3-B2O3 GLASSES DOPED WITH V2O5

    NASA Astrophysics Data System (ADS)

    Rao, Linganaboina Srinivasa; Veeraiah, Nalluri; Rao, Tumu Venkatappa

    2013-04-01

    The glass composition 40Li2O-5WO3-(55-x)B2O3: xV2O5 for x = 0.2, 0.4, 0.6 and 0.8 is chosen for the present study. The glass samples were synthesized by conventional melt-quenching technique. The dielectric properties such as constant (ɛ‧), loss (tan δ) and ac conductivityac) are carried out as a function of temperature (30-270°C) and frequency (102-105 Hz). The glass sample (at x = 0.6) exhibited highest ac conductivityac) and spreading factor (β) among all the samples. All glasses exhibited mixed conduction (both electronic and ionic) at high temperatures. The frequency exponent s denotes the ac conduction mechanism is associated with both QMT model (at low temperatures) and CBH model (at high temperatures).

  12. High Temperature Microwave Dielectric Properties of JSC-1AC Lunar Simulant

    NASA Technical Reports Server (NTRS)

    Allan, Shawn M.; Merritt, Brandon J.; Griffin, Brittany F.; Hintze, Paul E.; Shulman, Holly S.

    2011-01-01

    Microwave heating has many potential lunar applications including sintering regolith for lunar surface stabilization and heating regolith for various oxygen production reactors. The microwave properties of lunar simulants must be understood so this technology can be applied to lunar operations. Dielectric properties at microwave frequencies for a common lunar simulant, JSC-1AC, were measured up to 1100 C, which is approximately the melting point. The experimentally determined dielectric properties included real and imaginary permittivity (epsilon', epsilon"), loss tangent (tan delta), and half-power depth, the di stance at which a material absorbs 50% of incident microwave energy. Measurements at 2.45 GHz revealed tan delta of JSC-1A increases from 0.02 at 25 C to 0.31 at 110 C. The corresponding half-power depth decreases from a peak of 286 mm at 110 C, to 13 mm at 1100 C. These data indicate that JSC-1AC becomes more absorbing, and thus a better microwave heater as temperature increases. A half-power depth maximum at 100-200 C presents a barrier to direct microwave heating at low temperatures. Microwave heating experiments confirm the sluggish heating effect of weak absorption below 200 C, and increasingly strong absorption above 200 C, leading to rapid heating and melting of JSC-1AC.

  13. Electric field in an AC dielectric barrier discharge overlapped with a nanosecond pulse discharge

    NASA Astrophysics Data System (ADS)

    Goldberg, Benjamin M.; Shkurenkov, Ivan; Adamovich, Igor V.; Lempert, Walter R.

    2016-08-01

    The effect of ns discharge pulses on the AC barrier discharge in hydrogen in plane-to-plane geometry is studied using time-resolved measurements of the electric field in the plasma. The AC discharge was operated at a pressure of 300 Torr at frequencies of 500 and 1750 Hz, with ns pulses generated when the AC voltage was near zero. The electric field vector is measured by ps four-wave mixing technique, which generates coherent IR signal proportional to the square of electric field. Absolute calibration was done using an electrostatic (sub-breakdown) field applied to the discharge electrodes, when no plasma was generated. The results are compared with one-dimensional kinetic modeling of the AC discharge and the nanosecond pulse discharge, predicting behavior of both individual micro-discharges and their cumulative effect on the electric field distribution in the electrode gap, using stochastic averaging based on the experimental micro-discharge temporal probability distribution during the AC period. Time evolution of the electric field in the AC discharge without ns pulses, controlled by a superposition of random micro-discharges, exhibits a nearly ‘flat top’ distribution with the maximum near breakdown threshold, reproduced quite well by kinetic modeling. Adding ns pulse discharges on top of the AC voltage waveform changes the AC discharge behavior in a dramatic way, inducing transition from random micro-discharges to a more regular, near-1D discharge. In this case, reproducible volumetric AC breakdown is produced at a well-defined moment after each ns pulse discharge. During the reproducible AC breakdown, the electric field in the plasma exhibits a sudden drop, which coincides in time with a well-defined current pulse. This trend is also predicted by the kinetic model. Analysis of kinetic modeling predictions shows that this effect is caused by large-volume ionization and neutralization of surface charges on the dielectrics by ns discharge pulses. The present

  14. Dielectric dispersion and protonic conduction in hydrated purple membrane.

    PubMed

    Kovács, I; Váró, G

    1988-01-01

    Dielectric dispersion effects were studied in purple membranes of different hydration levels. The capacitance and conductivity were measured over the frequency range of 10(2) Hz to 10(5) Hz. With increase in the hydration level, the conductivity increases sharply above the critical hydration of hc = 0.06 g H2O/g protein. This critical hydration is close to the extent of the first continuous strongly bound water layer and is interpreted as the threshold for percolative proton transfer. The capacitance increases continuously with increasing hydration and a larger increase above the water content of 0.1 g H2O/g protein can be seen only at low frequencies. Maxwell-Wagner relaxation also appears above this hydration, showing the presence of a bulk water phase.

  15. Dielectric, Impedance and Conduction Behavior of Double Perovskite Pr2CuTiO6 Ceramics

    NASA Astrophysics Data System (ADS)

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

    2017-01-01

    Polycrystalline Pr2CuTiO6 (PCT) ceramics exhibits dielectric, impedance and modulus characteristics as a possible material for microelectronic devices. PCT was synthesized through the standard solid-state reaction method. The dielectric permittivity, impedance and electric modulus of PCT have been studied in a wide frequency (100 Hz-1 MHz) and temperature (303-593 K) range. Structural analysis of the compound revealed a monoclinic phase at room temperature. Complex impedance Cole-Cole plots are used to interpret the relaxation mechanism, and grain boundary contributions towards conductivity have been estimated. From electrical modulus formalism polarization and conductivity relaxation behavior in PCT have been discussed. Normalization of the imaginary part of impedance ( Z″) and the normalized imaginary part of modulus ( M″) indicates contributions from both long-range and localized relaxation effects. The grain boundary resistance along with their relaxation frequencies are plotted in the form of an Arrhenius plot with activation energy 0.45 eV and 0.46 eV, respectively. The ac conductivity mechanism has been discussed.

  16. A.C. Conductivity of Bi2Cu0.1V0.9O5.35 Films for Fuel Cell Application

    NASA Astrophysics Data System (ADS)

    Nimat, R. K.; Lokare, S. A.; Pawar, S. H.

    2011-07-01

    The A.C. conductivity and dielectric properties of Bi2Cu0.1V0.9O5.35 thin films were studied as a function of frequency and temperature. The A.C. conductivity of Bi2Cu0.1V0.9O5.35 film increases with frequency. The low frequency region corresponds to the D.C. conductivity where the inter-well hopping responsible for D.C. conduction completely dominates over the intra-well hopping associated with pure A.C. conduction. Higher values of A.C. conductivity for films formed on alumina substrates predict their suitability for fuel cell application

  17. Synthesis, Spectroscopic, ac Conductivity and Thermal Studies on Co(III) Acetylacetonate-Iodine Complex

    NASA Astrophysics Data System (ADS)

    Hashem, H. A.; Refat, M. S.

    A spectrophotometric study of 1:1 donor-acceptor complex, cobalt (III) acetylacetonate (donor) and iodine (σ-acceptor) has been preformed. The equilibrium constants, (K) and the absorpitivity (ɛ) for the formation of the iodine complex have been calculated. The predicted structure of the solid triiodide charge-transfer complex reported in this study is further supported by thermal, far and mid infrared spectroscopic measurements. Electron transfer from Co (acac = 2, 4-pentanedionate)3 to iodine leads to the formation of an organic semiconductor with the formula of [Co(acac)3]_2 I+. I3-. The kinetic parameters (nonisothermal method) for their decomposition have been evaluated by graphical methods using the equations of Freeman-Carroll (FC), Horowitz-Metzger (HM) and Coats-Redfern (CR). The ac conductivity and dielectric properties of [Co(acac)3]_2 I+. I3- have been measured over the frequency 50-106 Hz at temperature 298 K.

  18. Correction of the power law of ac conductivity in ion-conducting materials due to the electrode polarization effect.

    PubMed

    Khamzin, A A; Popov, I I; Nigmatullin, R R

    2014-03-01

    Based on the supposition related to fractal nature of transport processes in ion-conducting materials, an expression for the low-frequency ac conductivity dependence was derived. This expression for the ac conductivity generalizes the power-law dependence and gives a possibility to take into account the influence of the electrode polarization effect. The ac conductivity expression obtained is in excellent agreement with experimental data for a wide frequency range.

  19. Thermal, dielectric characteristics and conduction mechanism of azodyes derived from quinoline and their copper complexes.

    PubMed

    El-Ghamaz, N A; Diab, M A; El-Bindary, A A; El-Sonbati, A Z; Nozha, S G

    2015-05-15

    A novel series of (5-(4'-derivatives phenyl azo)-8-hydroxy-7-quinolinecarboxaldehyde) (AQLn) (n=1, p-OCH3; n=2, R=H; and n=3; p-NO2) and their complexes [Cu(AQLn)2]·5H2O are synthesized and investigated. The optimized bond lengths, bond angles and the calculated quantum chemical parameters for AQLn are investigated. HOMO-LUMO energy gap, absolute electronegativities, chemical potentials, and absolute hardness are also calculated. The thermal properties, dielectric properties, alternating current conductivityac) and conduction mechanism are investigated in the frequency range 0.1-100kHz and temperature range 293-568K for AQL1-3 and 318-693K for [Cu(AQL1-3)2]·5H2O complexes. The thermal properties are of ligands (AQLn) and their Cu(II) complexes investigated by thermogravimetric analysis (TGA). The temperature and frequency dependence of the real and the imaginary part of the dielectric constant are studied. The values of the thermal activation energy of conduction mechanism for AQLn and their complexes [Cu(AQLn)2]·5H2O under investigation are calculated at different test frequencies. The values of thermal activation energies ΔE1 and ΔE2 for AQLn and [Cu(AQLn)2]·5H2O decrease with increasing the values of frequency. The ac conductivity is found to be depending on the chemical structure of the compounds. Different conduction mechanisms have been proposed to explain the obtained experimental data. The small polaron tunneling (SPT) is the dominant conduction mechanism for AQL1 and its complex [Cu(AQL1)2]·5H2O. The quantum mechanical tunneling (QMT) is the dominant conduction mechanism for AQL2 and its complex [Cu(AQL2)2]·5H2O. The correlated barrier hopping (CBH) is the dominant conduction mechanism for AQL3 and its complex [Cu(AQL3)2]·5H2O, and the values of the maximum barrier height (Wm) are calculated.

  20. 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.

  1. Conduction mechanism and dielectric properties of a Se80Ge20- x Cd x ( x = 0, 6 and 12 at.wt%) films

    NASA Astrophysics Data System (ADS)

    Shakra, A. M.; Farid, A. S.; Hegab, N. A.; Afifi, M. A.; Alrebati, A. M.

    2016-09-01

    AC conductivity and dielectric properties of Se80Ge20- x Cd x (0 ≤ x ≤ 12 at.wt%) in thin film forms are reported in this paper. Thin films were deposited from the prepared compositions by thermal evaporation technique at 10-5 Torr. The films were well characterized by X-ray diffraction, differential thermal analysis and energy-dispersive X-ray spectroscopy. The AC conductivity and dielectric properties have been investigated for the studied films in the temperature range 293-393 K and over a frequency range of 102-105 Hz. The experimental results indicate that both AC conductivity σ AC( ω) and dielectric constants depend on temperature, frequency and Cd content. The frequency exponent s was calculated, and its value lies very close to unity and is temperature independent. This behavior can be explained in terms of the correlated barrier hopping between centers forming intimate valence alternation pairs. The density of localized states N( E F) at the Fermi level is estimated. The activation energy Δ E( ω) was found to decrease with increasing frequency. The maximum barrier height W m for the studied films was calculated from an analysis of the dielectric loss ɛ 2 according to the Guintini equation. Its values agree with that proposed by the theory of hopping of charge carriers over potential barrier as suggested by Elliott for chalcogenide glasses. The variation of the studied properties with Cd content was also investigated.

  2. Negative Dielectric Constant Material Based on Ion Conducting Materials

    NASA Technical Reports Server (NTRS)

    Gordon, Keith L. (Inventor); Kang, Jin Ho (Inventor); Park, Cheol (Inventor); Lillehei, Peter T. (Inventor); Harrison, Joycelyn S. (Inventor)

    2014-01-01

    Metamaterials or artificial negative index materials (NIMs) have generated great attention due to their unique and exotic electromagnetic properties. One exemplary negative dielectric constant material, which is an essential key for creating the NIMs, was developed by doping ions into a polymer, a protonated poly(benzimidazole) (PBI). The doped PBI showed a negative dielectric constant at megahertz (MHz) frequencies due to its reduced plasma frequency and an induction effect. The magnitude of the negative dielectric constant and the resonance frequency were tunable by doping concentration. The highly doped PBI showed larger absolute magnitude of negative dielectric constant at just above its resonance frequency than the less doped PBI.

  3. Studies on the activation energy from the ac conductivity measurements of rubber ferrite composites containing manganese zinc ferrite

    NASA Astrophysics Data System (ADS)

    Hashim, Mohd.; Alimuddin; Kumar, Shalendra; Shirsath, Sagar E.; Mohammed, E. M.; Chung, Hanshik; Kumar, Ravi

    2012-11-01

    Manganese zinc ferrites (MZF) have resistivities between 0.01 and 10 Ω m. Making composite materials of ferrites with either natural rubber or plastics will modify the electrical properties of ferrites. The moldability and flexibility of these composites find wide use in industrial and other scientific applications. Mixed ferrites belonging to the series Mn(1-x)ZnxFe2O4 were synthesized for different ‘x’ values in steps of 0.2, and incorporated in natural rubber matrix (RFC). From the dielectric measurements of the ceramic manganese zinc ferrite and rubber ferrite composites, ac conductivity and activation energy were evaluated. A program was developed with the aid of the LabVIEW package to automate the measurements. The ac conductivity of RFC was then correlated with that of the magnetic filler and matrix by a mixture equation which helps to tailor properties of these composites.

  4. AC conductivity and its scaling behavior in MgO-Li2O-B2O3-Bi2O3 glasses

    NASA Astrophysics Data System (ADS)

    Purnima, M.; Bale, Shashidhar; Samee, M. A.; Ahmmad, Shaik Kareem; Rahman, Syed

    2013-02-01

    In the present work, the compositional dependence of density, refractive index and glass transition temperature of xMgO-(25-x)Li2O-50B2O3-25Bi2O3 glasses is studied. Impedance spectroscopy technique is employed on these samples and the data are analyzed using Cole-Cole type impedance response function. The AC conductivity behavior of the present glasses has been investigated in the frequency range from 100 Hz to 1 MHz and as a function of temperature the measured AC data are analyzed using the Jonscher’s universal power law to explain the observed dispersive behavior of the electrical conductivity. The temperature and composition dependence scaling behavior in the AC conductivity are satisfactorily explained by scaling the AC conductivity σ‧(ω) by hopping frequency ωp. The frequency response of dielectric constant ɛ‧ and dielectric loss tanδ as a function of temperature were studied. The tanδ peak shifts to higher frequency with increasing temperature, indicating dipolar relaxation character of dielectric loss in the present glasses.

  5. Broadband AC Conductivity of XUV Excited Warm Dense Gold

    NASA Astrophysics Data System (ADS)

    Chen, Z.; Tsui, Y.; Toleikis, S.; Hering, P.; Brown, S.; Curry, C.; Tanikawa, T.; Hoeppner, H.; Levy, M.; Goede, S.; Ziaja-Motyka, B.; Rethfeld, B.; Recoules, Vanina; Ng, A.; Glenzer, S.

    2015-11-01

    The properties of ultrafast laser excited warm dense gold have been extensively studied in the past decade. In those studies, a 400nm ultrashort laser pulse was used to excite the 5 d electrons in gold to 6s/p state. Here we will present our recent study of warm dense gold with 245eV, 70fs pulses to selectively excite 4 f electrons using the XUV-FEL at FLASH. The AC conductivity of the warm dense gold was measured at different wavelengths (485nm, 520nm, 585nm, 640nm and 720nm) to cover the range from 5 d-6 s / p interband transitions to 6 s/ p intraband transitions. Preliminary result suggests that the onset of 5 d-6 s / p band transition shifts from 2.3eV to ~ 2eV, which is in agreement with the study of 400nm laser pulse excited warm dense gold. More detailed analysis of our data will also be presented.

  6. Effect of solution combusted TiO2 nanopowder within commercial BaTiO3 dielectric layer on the photoelectric properties for AC powder electroluminescence devices.

    PubMed

    Park, Sung; Choi, Gil Rak; Kim, Youn Cheol; Lee, Jae Chun; Lee, Ju Hyeon

    2013-05-01

    A unique synthesis method was developed, which is called solution combustion method (SCM). TiO2 nanopowder was synthesized by this method. This SCM TiO2 nanopowder (-35 nm) was added to the dielectric layer of AC powder electroluminescence (EL) device. The dielectric layer was made of commercial BaTiO3 powder (-1.2 microm) and binding polymer. 0, 5, 10 and 15 wt% of SCM TiO2 nanopowder was added to the dielectric layer during fabrication of AC powder EL device respectively. Dielectric constant of these four kinds of dielectric layers was measured. The brightness and current density of AC powder EL device were also measured. When 10 wt% of SCM TiO2 nanopowder was added, dielectric constant and brightness were increased by 30% and 101% respectively. Furthermore, the current density was decreased by 71%. This means that the brightness was double and the power consumption was one third.

  7. Electrical Conductivity and Dielectric Studies of Hydraulic Cements

    NASA Astrophysics Data System (ADS)

    Pena, Marianela Perez

    Electrical properties of portland cements and other non-portland cementitious materials have been studied at two different stages of hydration. The following relationships have been observed:. Higher water/cement (w/c) ratio (0.5 compared to 0.4) resulted in an increase of the relative permittivity and electrical conductivity of early stage hydrating materials. The relative permittivity values were close to 10('7). The phenomena giving rise to changes in electrical conductivity have been related to the heat of hydration. Higher alkali ion concentration resulted in higher electrical conductivity and relative permittivity values in cement pastes. Cations of inorganic admixtures were found to increase maximum peak of electrical conductivity and relative permittivity in the order: Ca('++) > Mg('++) > Sr('++) and K('+) (TURNEQ) Na('+) > Li('+). Dielectric properties of pressed hardened materials cured over water for 1 day with w/c = 0.20 and heat treated to 500(DEGREES)C prepared with type I, type III, and a microfine calcium silicate (MC500) cement have been compared as a function of temperature and frequency. The relative permittivity for type I hardened materials at 30(DEGREES)C was found to range from 12.5 to 9.4 at frequencies from 1 KHz to 2 MHz. The dissipation factor was found to range from 0.122 to 0.014. The relative permittivity and dissipation factors for type III hardened materials were found to range from 17.8 to 13.0 and from 0.035 to 0.071, respectively, and for MC500 hardened materials were determined to range from 7.6 to 6.9 and from 0.033 to 0.002, respectively. The activation energies determined from Arrhenius plots for the relaxation mechanism operating in these materials correspond to 0.33, 0.30, and 0.46 eV for type I, type III, and MC500 densified hardened materials, respectively. Cement/polymer composites have been prepared using 1.76 wt.% methyl cellulose polymer and a w/c ratio of 0.17. The relative permittivity and loss factor the samples

  8. 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.

  9. AC conductivity of a niobium thin film in a swept magnetic field.

    PubMed

    Tsindlekht, M I; Genkin, V M; Gazi, S; Chromik, S

    2013-02-27

    We report results of measurements of the ac conductivity of a Nb superconducting thin film in a swept dc magnetic field. In the mixed state the swept dc field creates vortices at the film surface which pass through the film and form the observed ac conductivity. Vortex rate generation does not depend on the value of the dc field and there is a large plateau-like region of dc magnetic fields where the dissipation is approximately constant. A proposed phenomenological model describes quite well the main features of the ac response in these fields, including its dependency on the sweep rate, ac amplitude, frequency, and value of the second and third harmonics.

  10. Ionic conductivity and dielectric permittivity of polymer electrolyte plasticized with polyethylene glycol

    NASA Astrophysics Data System (ADS)

    Das, S.; Ghosh, A.

    2016-05-01

    We have studied ionic conductivity and dielectric permittivity of PEO-LiClO4 solid polymer electrolyte plasticized with polyethylene glycol (PEG). The temperature dependence of the ionic conductivity has been well interpreted using Vogel-Tamman-Fulcher equation. The maximum dielectric constant is observed for 30 wt. % of PEG content. To get further insights into the ion dynamics, the complex dielectric permittivity has been studied with Havriliak-Negami function. The variation of relaxation time with inverse temperature obtained from HN formalism follows VTF nature.

  11. Scaling of the holographic AC conductivity for non-Fermi liquids at criticality

    NASA Astrophysics Data System (ADS)

    Kiritsis, Elias; Peña-Benitez, Francisco

    2015-11-01

    The frequency dependence of the AC conductivity is studied in a holographic model of a non-fermi liquid that is amenable to both analytical and numerical computation. In the regime that dissipation dominates the DC conductivity, the AC conductivity is described well in the IR by a Drude peak despite the absence of quasiparticles. In the regime where pair-production-like processes dominate the conductivity there is no Drude peak. A scaling tail is found for the AC conductivity that is independent of the charge density and momentum dissipation. Evidence is given that this scaling tail σ AC ˜ ω m appears generically in quantum critical holographic systems and the associated scaling exponent m is calculated in terms of the Lifshitz and conduction critical exponents.

  12. The conductivity and dielectric behavior of solutions of bitumen in toluene

    SciTech Connect

    Chow, R.S.; Tse, D.L.; Takamura, K.

    1988-06-01

    Previous work on the conductivity and dielectric behavior of residual oil (the fraction remaining in the distillation tower) has suggested that the asphaltene fraction (pentane insolubles) was responsible for the conductivity behavior of solutions of this oil in organic solvents. In this work it is shown that the asphaltenes in heavy crude oils determine the conductivity behavior of solutions of the bulk oil in toluene, while the dielectric behavior is influenced by each component of the oil. The strong dependence of the conductivity on the asphaltene fraction makes it possible to determine the asphaltene content of a heavy crude oil by a conductimetric technique. The conductivity and dielectric behavior of crude oils and fractions of the crude oils, as well as the technique for determining the asphaltene content by conductivity will be presented.

  13. Improving thrust by pulse-induced breakdown enhancement in AC surface dielectric barrier discharge actuators for airflow control

    NASA Astrophysics Data System (ADS)

    Yan, Huijie; Yang, Liang; Qi, Xiaohua; Ren, Chunsheng

    2016-07-01

    The characteristics of a plate-to-plate AC surface dielectric barrier discharge (SDBD) actuator using the pulse-induced breakdown enhancing method are experimentally investigated. The encapsulated electrode is supplied with a sine high AC voltage, while the exposed electrode is feed by a synchronized pulse voltage. Based on the thrust force and power consumption measurements, a parametric study was performed using a positive pulse applied at the trough phase of the AC cycles in which the thrust force was observed to increase by about 100% to 300% and the efficiency up to about 100% compared with the AC-only supply conditions for different AC voltages within the tested range. The pulse-induced breakdown effect was analyzed from the electrical and light emission waveforms to reveal the underlying mechanism. The surface potential due to the charge deposition effect was also measured using a specially designed corona-like discharge potential probe. It is shown that the pulse-induced breakdown was able to cause a temporarily intensified local electric field to enhance the glow-like discharge and meanwhile increase the time-average surface potential in the region further downstream. The improvement in the force by the enhancement in the pulse-induced breakdown was mainly due to enhancements in the glow-like discharge and the surface potential increment, with the latter being more important when the AC voltage is higher.

  14. AC motor controller with 180 degree conductive switches

    NASA Technical Reports Server (NTRS)

    Oximberg, Carol A. (Inventor)

    1995-01-01

    An ac motor controller is operated by a modified time-switching scheme where the switches of the inverter are on for electrical-phase-and-rotation intervals of 180.degree. as opposed to the conventional 120.degree.. The motor is provided with three-phase drive windings, a power inverter for power supplied from a dc power source consisting of six switches, and a motor controller which controls the current controlled switches in voltage-fed mode. During full power, each switch is gated continuously for three successive intervals of 60.degree. and modulated for only one of said intervals. Thus, during each 60.degree. interval, the two switches with like signs are on continuously and the switch with the opposite sign is modulated.

  15. General digital microfluidic platform manipulating dielectric and conductive droplets by dielectrophoresis and electrowetting.

    PubMed

    Fan, Shih-Kang; Hsieh, Tsung-Han; Lin, Di-Yu

    2009-05-07

    A general digital (droplet-based) microfluidic platform based on the study of dielectric droplet manipulation by dielectrophoresis (DEP) and the integration of DEP and electrowetting-on-dielectric (EWOD) is reported. Transporting, splitting, and merging dielectric droplets are achieved by DEP in a parallel-plate device, which expands the fluids of digital microfluidics from merely being conductive and aqueous to being non-conductive. In this work, decane, hexadecane, and silicone oil droplets were successfully transported in a 150 microm-high gap between two parallel plates by applying a DC voltage above threshold voltages. Non-volatile silicone oil droplets with viscosities of 20 and 50 cSt were studied in more detail in parallel-plate geometries with spacings of 75 microm, 150 microm, and 225 microm. The threshold voltages and the required driving voltages to achieve droplet velocities up to 4 mm/s in the different circumstances were measured. By adding a dielectric layer on the driving electrodes of the tested parallel-plate device, a general digital microfluidic platform capable of manipulating both dielectric and conductive droplets was demonstrated. DEP and EWOD, selectively generated by applying different signals on the same dielectric-covered electrodes, were used to drive silicone oil and water droplets, respectively. Concurrent transporting silicone oil and water droplets along an electrode loop, merging water and oil droplets, and transporting and separating the merged water-in-oil droplet were performed.

  16. 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.

  17. The ac-magnetic susceptibility and dielectric response of complex spin ordering processes in Mn₃O₄

    SciTech Connect

    Thota, Subhash E-mail: wilfrid.prellier@ensicaen.fr; Singh, Kiran; Simon, Ch.; Prellier, Wilfrid E-mail: wilfrid.prellier@ensicaen.fr; Nayak, Sanjib; Kumar, Jitendra

    2014-09-14

    We report a meticulous study of the ac-magnetization dynamics (χ{sub ac}(T)), relative dielectric permittivity ε{sub r}(T), and magneto-dielectric (Δε{sub r}/ε{sub r}(H)) response of various complex magnetic transitions that occur below the ferrimagnetic Néel temperature T{sub N} of Mn₃O₄. Besides the known sequence of transitions at T{sub N}~42.75 K, T₁~39 K, and T₂~34 K, the existence of a new anomaly reported recently at 38 K (T*) has been successfully probed by χ{sub ac}(T) and ε{sub r}(T) measurements. The effect of external dc-bias fields (H{sub DC}) and driving frequency (f) on the above mentioned transitions has been investigated in consonance with the ε{sub r}(T) and Δε{sub r}/ε{sub r}(T,H) results. For the first time, we observed a clear hysteresis of about 5.15 K in the zero-field ε{sub r}(T) across the incommensurate-to-commensurate transition T₂~34 K, which provides evidence to the first-order nature of this transition. The Arrott plot (H/M vs. M²}) criterion has been used to distinguish the nature of all the sequential transitions that take place below T{sub N}.

  18. Thermal interface conductance across metal alloy-dielectric interfaces

    NASA Astrophysics Data System (ADS)

    Freedman, Justin P.; Yu, Xiaoxiao; Davis, Robert F.; Gellman, Andrew J.; Malen, Jonathan A.

    2016-01-01

    We present measurements of thermal interface conductance as a function of metal alloy composition. Composition spread alloy films of A uxC u1 -x and A uxP d1 -x solid solutions were deposited on single crystal sapphire substrates via dual electron-beam evaporation. High throughput measurements of thermal interface conductance across the (metal alloy)-sapphire interfaces were made by positional scanning of frequency domain thermoreflectance measurements to sample a continuum of Au atomic fractions (x ˜0 →1 ) . At a temperature of 300 K, the thermal interface conductance at the A uxC u1 -x -sapphire interfaces monotonically decreased from 197 ±39 MW m-2K-1 to 74 ±11 MW m-2K-1 for x =0 →0.95 ±0.02 and at the A uxP d1 -x -sapphire interfaces from 167 ±35 MW m-2K-1 to 60 ±10 MW m-2K-1 for x =0.03 →0.97 ±0.02 . To shed light on the phonon physics at the interface, a Diffuse Mismatch Model for thermal interface conductance with alloys is presented and agrees reasonably with the thermal interface conductance data.

  19. The physics of gridded and conductive coated dielectrics for spacecraft

    NASA Technical Reports Server (NTRS)

    Okress, E. C.

    1977-01-01

    Theoretical aspects of electrostatic control and design of gridded and conductive film bonded polymers, for spacecraft Thermo-optical blankets are considered. Brief commentaries relative to the salient features of the primarily developed facility for and characterization of said polymers is also considered.

  20. Ocular vestibular evoked myogenic potentials to air conduction (AC oVEMP): useful in clinical practice?

    PubMed

    Walther, L E; Rogowski, M; Hörmann, K; Schaaf, H; Löhler, J

    2011-01-01

    Cervical vestibular-evoked myogenic potential (cVEMP) and ocular VEMP (oVEMP) stimuli can be used to measure otolith function using air (AC) and bone conducted (BC) stimuli. Cervical VEMPs reflect saccular function and can be recorded using air conduction (AC), whereas oVEMPs reflect probably predominantly utricular function. Air- and bone-conducted vibration can be used, because AC oVEMP methodology seems to be fast and simple in clinical practice to measure otolith function. In this study we discuss the advantages and problems of AC oVEMP stimulation. AC oVEMP can be easily and quickly obtained within a few seconds. N10 (first negative peak) and p15 (first positive peak) latencies may be used as parameters for clinical interpretation but amplitude fluctuations are relatively large. For daily clinical use of VEMP visualization in a normogram seems feasible. Especially the AC oVEMP methodology (100 dB nHL, tone burst 500 Hz) is fast and efficient in clinical practice to measure otolith function, predominantly utricular function.

  1. Dielectric properties and electrical conductivity of flat micronic graphite/polyurethane composites

    NASA Astrophysics Data System (ADS)

    Plyushch, Artyom; Macutkevic, Jan; Kuzhir, Polina P.; Banys, Juras; Fierro, Vanessa; Celzard, Alain

    2016-03-01

    Results of broadband dielectric spectroscopy of flat micronic graphite (FMG)/polyurethane (PU) resin composites are presented in a wide temperature range (25-450 K). The electrical percolation threshold was found to lie between 1 and 2 vol. % of FMG. Above the percolation threshold, the composites demonstrated a huge hysteresis of properties on heating and cooling from room temperature up to 450 K, along with extremely high values of dielectric permittivity and electrical conductivity. Annealing proved to be a very simple but powerful tool for significantly improving the electrical properties of FMG-based composites. In order to explain this effect, the distributions of relaxation times were calculated by the complex impedance formalism. Below room temperature, both dielectric permittivity and electrical conductivity exhibited a very low temperature dependence, mainly caused by the different thermal properties of FMG and pure PU matrix.

  2. Thermoluminescence and dielectric response of gamma irradiated muscovite mica

    SciTech Connect

    Kaur, Sukhnandan Singh, Surinder Singh, Lakhwant; Lochab, S. P.

    2014-04-24

    The effect of gamma radiation dose on the thermoluminescence (TL) and dielectric properties of muscovite mica was studied. TL glow curves exhibited a single peak around 141 {sup 0}C and its activation energy was estimated to be about 0.89 eV. Different dielectric parameters like dielectric constant, dielectric loss and ac conductivity have been calculated in both pristine and gamma irradiated samples. These dielectric parameters have been studied as a function of irradiation dose.

  3. Thermoluminescence and dielectric response of gamma irradiated muscovite mica

    NASA Astrophysics Data System (ADS)

    Kaur, Sukhnandan; Singh, Surinder; Singh, Lakhwant; Lochab, S. P.

    2014-04-01

    The effect of gamma radiation dose on the thermoluminescence (TL) and dielectric properties of muscovite mica was studied. TL glow curves exhibited a single peak around 141 0C and its activation energy was estimated to be about 0.89 eV. Different dielectric parameters like dielectric constant, dielectric loss and ac conductivity have been calculated in both pristine and gamma irradiated samples. These dielectric parameters have been studied as a function of irradiation dose.

  4. Advances in heat conduction models and approaches for the prediction of lattice thermal conductivity of dielectric materials

    NASA Astrophysics Data System (ADS)

    Saikia, Banashree

    2017-03-01

    An overview of predominant theoretical models used for predicting the thermal conductivities of dielectric materials is given. The criteria used for different theoretical models are explained. This overview highlights a unified theory based on temperature-dependent thermal-conductivity theories, and a drifting of the equilibrium phonon distribution function due to normal three-phonon scattering processes causes transfer of phonon momentum to (a) the same phonon modes (KK-S model) and (b) across the phonon modes (KK-H model). Estimates of the lattice thermal conductivities of LiF and Mg2Sn for the KK-H model are presented graphically.

  5. Dielectric behavior, conduction and EPR active centres in BiVO4 nanoparticles

    NASA Astrophysics Data System (ADS)

    Venkatesan, Rajalingam; Velumani, Subramaniam; Tabellout, Mohamed; Errien, Nicolas; Kassiba, Abdelhadi

    2013-12-01

    Bismuth vanadate (BiVO4) nanomaterials were synthesized by mechano-chemical ball milling method and complementary investigations were devoted to their structures, nanoparticle morphologies and electronic active centres. The dielectric and conductivity behaviour were analysed systematically in wide temperature and frequency ranges to correlate such physical responses with the peculiarities of the samples. Large interfacial polarisations favoured by high specific surfaces of nanoparticles account for a drastic enhancement of the dielectric function in the quasi-static regime. Exhaustive analyses of the dielectric experiments were achieved and account for the main features of dielectric functions and their related relaxation mechanisms. The electrical conductivity is thermally activated with energies in the range 0.1-0.6 eV depending on the sample features. DC conductivity up to 10-3 S/cm was obtained in well crystallized nanoparticles. Vanadium ions reduction was revealed by EPR spectroscopy with higher concentrations of the active centres (V4+) in more agglomerated and amorphous nanopowders. The EPR spectral parameters of V4+ were determined and correlated with the local environments of reduced vanadium ions and the characteristics of their electronic configurations. An insight is also made on the role of active electronic centres (V4+) on the conduction mechanism in nanostructured BiVO4.

  6. Inorganic backbone ionomers: Design and dielectric response of single-ion conducting polymers

    NASA Astrophysics Data System (ADS)

    Bartels, Joshua

    Ion-conducting polymers were studied primarily through the use of dielectric spectroscopy. The conclusions drawn from ion conduction models of the dielectric data are corroborated by additional independent experiments, including x-ray scattering, calorimetry, prism coupling, and DFT calculations. The broad concern of this dissertation is to understand and clarify a path forward in ion conducting polymer research. This is achieved by considering low-Tg ionomers and the advantages imparted by siloxane and phosphazene backbones. The most successful dielectric spectroscopy model for the materials studied is the electrode polarization model (EP), whereas other models, such as the Dyre random barrier model, fail to describe the experimental results. Seven nonionic ether oxygen (EO) containing polymers were studied in order to observe the effect that backbone chemistry has on dipole motion. Conventional carboncarbon backbone EO-containing polymers show no distinct advantage over similar EO-pendant polysiloxane or polyphosphazene systems. The mobility and effective backbone Tg imparted by the inorganic backbones are comparable. A short EO pendant results in a lower static dielectric constant due to restricted motion of dipoles close to the chain. The flexibility and chemical versatility of inorganic backbone polymers motivates further study of two ionomer systems. A polypohosphazene iodide conducting system was characterized by dielectric spectroscopy and x-ray scattering. Two end "tail" functionalization of the ammonium ion were used, a tail with two EOs and an alkyl tail of six carbons. This functional group plays an important role in ion dynamics and can wrap around the ion and self-solvate when EOs are present. The iodide-ammonium ionomers are observed to have unusually large high-frequency dielectric constants due to atomic polarization of ions. The strength of the atomic polarization scales with ion content. The aggregation state of ions is able to be determined from

  7. Conductance of a single electron transistor with a retarded dielectric layer in the gate capacitor

    NASA Astrophysics Data System (ADS)

    Udalov, O. G.; Chtchelkatchev, N. M.; Fedorov, S. A.; Beloborodov, I. S.

    2015-11-01

    We study the conductance of a single electron transistor (SET) with a ferroelectric (or dielectric) layer placed in the gate capacitor. We assume that the ferroelectric (FE) has a retarded response with arbitrary relaxation time. We show that in the case of "fast" but still retarded response of the FE (dielectric) layer an additional contribution to the Coulomb blockade effect appears leading to the suppression of the SET conductance. We take into account fluctuations of the FE (dielectric) polarization using Monte Carlo simulations. For "fast" FE, these fluctuations partially suppress the additional Coulomb blockade effect. Using Monte Carlo simulations, we study the transition from "fast" to "slow" FE. For high temperatures, the peak value of the SET conductance is almost independent of the FE relaxation time. For temperatures close to the FE Curie temperature, the conductance peak value nonmonotonically depends on the FE relaxation time. A maximum appears when the FE relaxation time is of the order of the SET discharging time. Below the Curie point the conductance peak value decreases with increasing the FE relaxation time. The conductance shows the hysteresis behavior for any FE relaxation time at temperatures below the FE transition point. We show that conductance hysteresis is robust against FE internal fluctuations.

  8. Impedance and AC conductivity study of nano crystalline, fine grained multiferroic bismuth ferrite (BiFeO3), synthesized by microwave sintering

    NASA Astrophysics Data System (ADS)

    Kolte, Jayant; Salame, Paresh H.; Daryapurkar, A. S.; Gopalan, P.

    2015-09-01

    In this paper, major reduction in sintering time,temperautre and significant improvement over final density of sitnered sample is reported for the microwave sintered nanocrystalline BiFeO3 (BFO) ceramic. Also, different sintering time and temperatures have been used to tailor the grain size and the final density of the resulting BFO ceramics synthesized from phase pure BFO nanoparticles ( d ¯ ≈ 10 n m ). Microwave sintering resulted in reducing the sintering time substantially (by 1h), and has resulted in submicron sized grains and high resistivity ˜1.8 GΩ-cm. The AC conductivity is seen to follow the Jonscher's power law behavior, suggesting correlated barrier hopping (CBH) mechanism in the sample. The role of oxygen vacancies at high temperature, due to volatility of bismuth, in dielectric and conductivity behavior is also discussed. Further, the sample displayed dielectric anomaly near magnetic transition temperature (˜180 °C) indicating bearing of magnetic moments on the dielectric properties. Using Impedance Spectroscopy (IS) we have established, the electrical heterogeneity of the ceramic BFO reavealing semiconducting nature of grains and insulating nature of grain boundary. This, formation of network of insulating grain boundaries and semiconducting grains could lead to formation of internal barrier layer capacitance (IBLC) leading to high dielectric constant in microwave sintered BFO.

  9. Low dielectric loss, dielectric response, and conduction behavior in Na-doped Y2/3Cu3Ti4O12 ceramics

    NASA Astrophysics Data System (ADS)

    Liang, Pengfei; Chao, Xiaolian; Yang, Zupei

    2014-07-01

    The Na-doped Y2/3Cu3Ti4O12 system has been prepared and investigated. Na doping facilitates the formation of oxygen vacancies, which is of great benefit to the growth of the grain size. Proper amount of Na substitution in NaxY(2-x)/3Cu3Ti4O12 ceramics makes the dielectric loss significantly decreased. As x = 0.050, Na0.050Y0.650Cu3Ti4O12 ceramics exhibit the lowest dielectric loss (about 0.022 at 1 kHz) and a relatively high dielectric constant (about 7500 at 1 kHz). The lowered dielectric loss is closely associated with the enhanced resistance of grain boundary. The conduction and dielectric processes of grain boundary become much more difficult after Na doping. Impedance analysis suggests that the same charge defects are responsible for the conduction and dielectric relaxation behaviors of grain boundary. Scaling behaviors indicate that the physical nature of their dielectric relaxation and conduction behavior are independent of the measurement temperature and the Na concentration.

  10. Effects of conductive particles on the actuating behavior of dielectric elastomer actuator

    NASA Astrophysics Data System (ADS)

    Zhang, Zhen; Liu, Yanju; Leng, Jinsong

    2010-04-01

    Dielectric elastomers (DEs) are one particular type of electroactive polymers. Dielectric elastomers work as a variable capacitor. The effects of conductive particles on the actuating behavior of silicone rubber-based dielectric elastomer are studied in this work. Two different materials, which are carbon nanotube and carbon black, respectively, are used to increase the overall permittivity of the composites. Although the addition of these conductive particles increases the permittivity of the composite, they also produce a highly inhomogeneous electric field and reduced breakdown strength of the composite. This reduction in breakdown strength could be a serious drawback of nanocomposite approach. The main challenge, therefore, becomes how to enhance the permittivity of the composite while maintaining its high breakdown strength. These composites are characterized by dielectric spectroscopy, tensile mechanical analysis, and electromechanical transduction tests. The effect of variation in filler loadings on the complex and real parts of permittivity are distinctly visible, which has been explained on the basis of interfacial polarization of fillers in a heterogeneous medium. The phenomenon of percolation was discussed based on the measured changes in permittivity and morphology of composites at different concentrations of these particles.

  11. Charging in the ac Conductance of a Double Barrier Resonant Tunneling Structure

    NASA Technical Reports Server (NTRS)

    Anantram, M. P.; Saini, Subhash (Technical Monitor)

    1998-01-01

    There have been many studies of the linear response ac conductance of a double barrier resonant tunneling structure (DBRTS), both at zero and finite dc biases. While these studies are important, they fail to self consistently include the effect of the time dependent charge density in the well. In this paper, we calculate the ac conductance at both zero and finite do biases by including the effect of the time dependent charge density in the well in a self consistent manner. The charge density in the well contributes to both the flow of displacement currents in the contacts and the time dependent potential in the well. We find that including these effects can make a significant difference to the ac conductance and the total ac current is not equal to the simple average of the non-selfconsistently calculated conduction currents in the two contacts. This is illustrated by comparing the results obtained with and without the effect of the time dependent charge density included correctly. Some possible experimental scenarios to observe these effects are suggested.

  12. AC Conductivity Studies in Lithium-Borate Glass Containing Gold Nanoparticles

    NASA Astrophysics Data System (ADS)

    Shivaprakash, Y.; Anavekar, R. V.

    2011-07-01

    Gold nanoparticles have been synthesized in a base glass with composition 30Li2O-70B2O3 using gold chloride (HAuCl4.3H2O) as a dopant. The samples are characterized using XRD, ESR, SEM and optical absorption in the visible range. AC conductivity studies have been performed at RT over a frequency range 100 to 10 MHz. The dc conductivity is calculated from the complex impedence plot. The dc conductivity is found to be increasing with the increase of dopant concentration. AC conductivity data is fitted with Almond-West law with power exponent `s'. The values of `s' is found to lie in the range of 0.70-0.73.

  13. Liquid Crystalline Epoxies with Lateral Substituents Showing a Low Dielectric Constant and High Thermal Conductivity

    NASA Astrophysics Data System (ADS)

    Guo, Huilong; Lu, Mangeng; Liang, Liyan; Wu, Kun; Ma, Dong; Xue, Wei

    2017-02-01

    In this work, liquid crystalline epoxies with lateral substituents were synthesized and cured with aromatic amines or anhydride. The liquid crystalline phase structure of liquid crystalline epoxies with lateral substituents was determined by polarized optical microscopy. The relationship between thermal conductivity and dielectric properties and liquid crystalline domain structure was discussed in the paper. The samples show high thermal conductivity up to 0.29 W/(m × K), due to the orientation of mesogenic units in epoxies. The sample's low dielectric constant of 2.29 is associated with the oriented mesogenic units and long nonpolar lateral substituents. This indicates a new way to obtain materials with high thermal conductivity and a low dielectric constant by introducing oriented mesogenic units into cross-linked epoxy systems. The water repellency is reflected in the contact angles of 92-98°, which are apparently higher than that of conventional epoxy systems. It was also found that the better toughness of liquid crystalline epoxies with lateral substituents was attributed to the existence of long flexible alkyl lateral substituents.

  14. Dependence of Ozone Generation on Gas Temperature Distribution in AC Atmospheric Pressure Dielectric Barrier Discharge in Oxygen

    NASA Astrophysics Data System (ADS)

    Takahashi, Go; Akashi, Haruaki

    AC atmospheric pressure multi-filament dielectric barrier discharge in oxygen has been simulated using two dimensional fluid model. In the discharge, three kinds of streamers have been obtained. They are primary streamers, small scale streamers and secondary streamers. The primary streamers are main streamers in the discharge and the small scale streamers are formed after the ceasing of the primary streamers. And the secondary streamers are formed on the trace of the primary streamers. In these streamers, the primary and the small scale streamers are very effective to generate O(3P) oxygen atoms which are precursor of ozone. And the ozone is generated mainly in the vicinity of the dielectrics. In high gas temperature region, ozone generation decreases in general. However, increase of the O(3P) oxygen atom density in high gas temperature region compensates decrease of ozone generation rate coefficient. As a result, amount of ozone generation has not changed. But if the effect of gas temperature was neglected, amount of ozone generation increases 10%.

  15. 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

    2015-09-03

    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

  16. On the Dielectric Study of Se80- x Te20Pb x ( x = 0, 1 and 2) Glasses

    NASA Astrophysics Data System (ADS)

    Thakur, Anjali; Patial, Balbir Singh; Thakur, Nagesh

    2017-03-01

    In the present paper, the dielectric parameters such as the dielectric constant ɛ'( ω), dielectric loss ɛ″( ω) and alternating current (ac) conductivity have been investigated for bulk amorphous chalcogenide Se80- x Te20Pb x ( x = 0, 1 and 2) glasses in the frequency range 10 Hz to 500 kHz and within the temperature range from 300 K to 320 K. Dielectric constant ɛ'( ω) and dielectric loss ɛ″( ω) are found to be highly frequency ( ω) and temperature dependent, and this behavior is interpreted on the basis of Guintini's theory of dielectric dispersion. The ac conductivity ( σ ac) is found to be temperature independent and obey the power law ω s , where s < 1 and decreases as temperature rises. The obtained results are discussed in terms of the correlation barrier hopping model proposed by Elliot. The composition dependence of the dielectric constant, dielectric loss and ac conductivity are also discussed and reported here.

  17. Electrical/dielectric properties and conductivity mechanism of epoxy/expanded graphite composites

    NASA Astrophysics Data System (ADS)

    Kanapitsas, Athanasios; Logakis, Emmanuel; Pandis, Christos; Pissis, Polycarpos; Jovic, Natasa; Djokovic, Vladimir

    2009-03-01

    In this work the electrical and dielectric properties, as well as the temperature dependence of the electrical conductivity of epoxy/expanded graphite (EG) composites, are studied by employing dielectric relaxation spectroscopy (DRS). For the preparation of the composites EG was sonicated in acetone for 10h and then the appropriate amount of epoxy resin added to the mixture. The sonication was prolonged for another 3 h. The mixture was dried at 60^oC for a few hours and then the appropriate amount of hardener (triethylenetetramine) was added followed by mechanical stirring for 15 min. Finally, the mixture was cast in a glass mould and outgassed overnight at room temperature. Before they were removed from the mould, all samples were post-cured at 127^oC for 10 min in air. Samples with EG weight fractions ranging from 0 to 8 wt.% were produced. Preliminary DRS results at room temperature indicate that electrical percolation threshold (pc) lies between 3-5 wt.% EG. The influence of the EG fillers (for concentrations below pc) on the dielectric relaxation mechanisms of the epoxy matrix, as well as the conductivity mechanism (for concentrations above pc) are investigated.

  18. Investigation on the AC loss characteristics of MgB 2 wires by using a conduction cooling device

    NASA Astrophysics Data System (ADS)

    Jin, H. B.; Li, Z.; Ryu, K.

    2011-11-01

    In this study, we have experimentally investigated the AC loss characteristics of MgB2 wires with matrix of Fe and Cu by using a conduction cooling device. We fabricated the conduction cooling device to cool MgB2 wires down to 4 K. We also developed our unique test method, which is called AC pulse technique, to evaluate their AC loss characteristics within few hundred milliseconds. The test results show that the AC loss of the Fe/MgB2 wire is mainly generated in the ferromagnetic Fe matrix. Its AC loss is ten times larger than that of the Cu/MgB2 wire. In this paper, the evaluation technique of AC loss by using the conduction cooling device is described and the test results are discussed.

  19. Noncontact conductivity and dielectric measurement for high throughput roll-to-roll nanomanufacturing

    NASA Astrophysics Data System (ADS)

    Orloff, Nathan D.; Long, Christian J.; Obrzut, Jan; Maillaud, Laurent; Mirri, Francesca; Kole, Thomas P.; McMichael, Robert D.; Pasquali, Matteo; Stranick, Stephan J.; Alexander Liddle, J.

    2015-11-01

    Advances in roll-to-roll processing of graphene and carbon nanotubes have at last led to the continuous production of high-quality coatings and filaments, ushering in a wave of applications for flexible and wearable electronics, woven fabrics, and wires. These applications often require specific electrical properties, and hence precise control over material micro- and nanostructure. While such control can be achieved, in principle, by closed-loop processing methods, there are relatively few noncontact and nondestructive options for quantifying the electrical properties of materials on a moving web at the speed required in modern nanomanufacturing. Here, we demonstrate a noncontact microwave method for measuring the dielectric constant and conductivity (or geometry for samples of known dielectric properties) of materials in a millisecond. Such measurement times are compatible with current and future industrial needs, enabling real-time materials characterization and in-line control of processing variables without disrupting production.

  20. Noncontact conductivity and dielectric measurement for high throughput roll-to-roll nanomanufacturing

    PubMed Central

    Orloff, Nathan D.; Long, Christian J.; Obrzut, Jan; Maillaud, Laurent; Mirri, Francesca; Kole, Thomas P.; McMichael, Robert D.; Pasquali, Matteo; Stranick, Stephan J.; Alexander Liddle, J.

    2015-01-01

    Advances in roll-to-roll processing of graphene and carbon nanotubes have at last led to the continuous production of high-quality coatings and filaments, ushering in a wave of applications for flexible and wearable electronics, woven fabrics, and wires. These applications often require specific electrical properties, and hence precise control over material micro- and nanostructure. While such control can be achieved, in principle, by closed-loop processing methods, there are relatively few noncontact and nondestructive options for quantifying the electrical properties of materials on a moving web at the speed required in modern nanomanufacturing. Here, we demonstrate a noncontact microwave method for measuring the dielectric constant and conductivity (or geometry for samples of known dielectric properties) of materials in a millisecond. Such measurement times are compatible with current and future industrial needs, enabling real-time materials characterization and in-line control of processing variables without disrupting production. PMID:26592441

  1. Noncontact conductivity and dielectric measurement for high throughput roll-to-roll nanomanufacturing.

    PubMed

    Orloff, Nathan D; Long, Christian J; Obrzut, Jan; Maillaud, Laurent; Mirri, Francesca; Kole, Thomas P; McMichael, Robert D; Pasquali, Matteo; Stranick, Stephan J; Liddle, J Alexander

    2015-11-23

    Advances in roll-to-roll processing of graphene and carbon nanotubes have at last led to the continuous production of high-quality coatings and filaments, ushering in a wave of applications for flexible and wearable electronics, woven fabrics, and wires. These applications often require specific electrical properties, and hence precise control over material micro- and nanostructure. While such control can be achieved, in principle, by closed-loop processing methods, there are relatively few noncontact and nondestructive options for quantifying the electrical properties of materials on a moving web at the speed required in modern nanomanufacturing. Here, we demonstrate a noncontact microwave method for measuring the dielectric constant and conductivity (or geometry for samples of known dielectric properties) of materials in a millisecond. Such measurement times are compatible with current and future industrial needs, enabling real-time materials characterization and in-line control of processing variables without disrupting production.

  2. Influence of temperature on AC conductivity of nanocrystalline CuAlO2

    NASA Astrophysics Data System (ADS)

    Prakash, T.

    2012-07-01

    Nanocrystalline CuAlO2 was synthesized by mechanical alloying of Cu2O and α-Al2O3 powders in the molar ratio of 1:1 for 20 h in toluene medium with tungsten carbide balls and vials using planetary ball mill. The ball milling was carried out at 300 rpm with a ball to powder weight ratio of 10:1 and then annealed at 1373 K in a platinum crucible for 20 h to get CuAlO2 phase with average crystallite size 45 nm. Complex impedance spectroscopic measurement in the frequency region 1 Hz to 10 MHz between the temperatures 333 to 473 K was carried out for nanocrystalline CuAlO2 sample. The obtained complex impedance data was analyzed for AC conductivities, DC and AC conductivities correlations and crossover frequencies ( f co ). The BNN (Barton, Nakajima and Namikawa) relation was applied to understand the correlation between DC and AC conductivities. The observed experimental results were discussed in the paper.

  3. AC conductivity of (FeCoZr)x(PZT)(100-x) nanocomposites produced in vacuum chamber

    NASA Astrophysics Data System (ADS)

    Boiko, Oleksandr; Bondariev, Vitalii; Czarnacka, Karolina

    2015-09-01

    In this work, the temperature and frequency dependences of conductivity σ and Arrhenius plots of annealed nanocomposite films containing Fe45Co45Zr10 - based nanoparticles embedded in a doped PbZrTiO3 ferroelectric matrix were studied. The nanocomposites studied were deposited by sputtering with use of argon and oxygen ions in a vacuum chamber. Tested samples were followed by a 15-min annealing process in air in the temperature range of 398 K <= Ta <= 748 K with steps of 25 K. The σ(f,T) dependences of nanocomposite samples was measured in ambient temperature range of 77 K < Tp < 373 K at frequencies of 50 Hz < f < 1MHz. It was established that nanocomposite sample with metallic phase content x = 55.6 at.% demonstrates strong temperature and frequency dependences, which is typical for a percolation systems. Type of conduction in such nanostructure is defined as dielectric, which may be related with the additional oxidation of metallic nanoparticles during the annealing process. For the tested sample with x = 88.4 at.%. we observe metallic type of conduction, when metallic nanoparticles form a permanent conductive channels in dielectric matrix.

  4. Effect of CaO on the conductivity and dielectric properties of novel Fe 2O 3·CaO·Bi 2O 3 glasses

    NASA Astrophysics Data System (ADS)

    Sanghi, Sujata; Duhan, Sarita; Agarwal, Ashish; Aghamkar, Praveen

    2010-09-01

    Iron calcium bismuthate glasses having composition 0.05Fe 2O 3·0.95{ xCaO·(100- x)Bi 2O 3} ( x=30, 35 and 40 mol%) were prepared using normal melt quench technique. Complex impedance spectra of these glasses have been recorded in the temperature range 523-633 K and in the frequency range 20 Hz-1 MHz. The complex impedance data have been analyzed using the conductivity as well as electric modulus formalisms. The dc conductivity increases and activation energy decreases when CaO content increases. The modification of the glass network, due to the increase in CaO content, is responsible for the increase in conductivity. The frequency dependence of ac conductivity is found to obey the Jonscher power law. At low frequencies, dispersion was investigated in terms of dielectric loss. Significant changes in the values of the non exponential parameter ( β) and the power law exponent ( s) of the ac electrical properties have been observed as a function of CaO in the present glasses. A single ‘master curve’ for the normalized plots of all the modulus isotherms observed for a given composition indicates that the conductivity relaxation is temperature independent. The overlapping of the normalized peaks corresponding to impedance ( Z″) and electric modulus ( M″) suggests the same thermal activation energy for conduction and relaxation, which further suggests a single mechanism for the dynamic processes in the present glasses.

  5. Broad-band conductivity and dielectric spectroscopy of composites of multiwalled carbon nanotubes and poly(ethylene terephthalate) around their low percolation threshold.

    PubMed

    Nuzhnyy, D; Savinov, M; Bovtun, V; Kempa, M; Petzelt, J; Mayoral, B; McNally, T

    2013-02-08

    Composites of multiwalled carbon nanotubes with poly(ethylene terephthalate) (PET-MWCNT) with up to 3 vol% MWCNTs were prepared and characterized by broad-band AC conductivity and dielectric spectroscopy up to the infrared range using several techniques. A very low electrical percolation threshold of 0.07 vol% MWCNTs was revealed from the low-frequency conductivity plateau as well as from DC conductivity, whose values show the same critical power dependence on MWCNT concentration with the exponent t = 4.3. Above the plateau, the AC conductivity increases with frequency up to the THz range, where it becomes overlapped with the absorption of vibrational modes. The temperature dependence down to ~5 K has shown semiconductor behaviour with a concentration-independent but weakly temperature-dependent small activation energy of ~3 meV. The behaviour is compatible with the previously suggested fluctuation-induced tunnelling conductivity model through a thin (~1 nm) polymer contact layer among the adjacent MWCNTs within percolated clusters. At higher frequencies, deviations from the simple universal conductivity behaviour are observed, indicating some distribution of energy barriers for an electron hopping mechanism.

  6. A theory of electrical conductivity, dielectric constant, and electromagnetic interference shielding for lightweight graphene composite foams

    NASA Astrophysics Data System (ADS)

    Xia, Xiaodong; Wang, Yang; Zhong, Zheng; Weng, George J.

    2016-08-01

    This work was driven by the need to understand the electromagnetic interference (EMI) shielding effectiveness (SE) of light weight, flexible, and high performance graphene composite foams, but as EMI SE of a material depends on its electrical conductivity, dielectric permittivity, and magnetic permeability, the investigation of these three properties also became a priority. In this paper, we first present a continuum theory to determine these three electromagnetic properties, and then use the obtained properties to evaluate the EMI SE of the foam. A two-scale composite model is conceived to evaluate these three properties, with the large one being the skeleton-void composite and the small one being the graphene-polymer composite that serves as the skeleton of the foam. To evaluate the properties of the skeleton, the effective-medium approach is taken as the starting point. Subsequently, the effect of an imperfect interface and the contributions of electron tunneling to the interfacial conductivity and Maxwell-Wagner-Sillars polarization mechanism to the dielectric constant are also implemented. The derived skeleton properties are then utilized on the large scale to determine the three properties of the composite foam at a given porosity. Then a uniform plane electromagnetic wave is considered to evaluate the EMI SE of the foam. It is demonstrated that the electrical conductivity, dielectric constant, and EMI SE of the foam calculated from the developed theory are in general agreement with the reported experimental data of graphene/PDMS composite foams. The theory is further proven to be valid for the EMI SE of solid graphene/epoxy and solid carbon nanotube/epoxy nanocomposites. It is also shown that, among the three electromagnetic properties, electrical conductivity has the strongest influence on the EMI shielding effectiveness.

  7. Microwave a.c. conductivity of domain walls in ferroelectric thin films

    PubMed Central

    Tselev, Alexander; Yu, Pu; Cao, Ye; Dedon, Liv R.; Martin, Lane W.; Kalinin, Sergei V.; Maksymovych, Petro

    2016-01-01

    Ferroelectric domain walls are of great interest as elementary building blocks for future electronic devices due to their intrinsic few-nanometre width, multifunctional properties and field-controlled topology. To realize the electronic functions, domain walls are required to be electrically conducting and addressable non-destructively. However, these properties have been elusive because conducting walls have to be electrically charged, which makes them unstable and uncommon in ferroelectric materials. Here we reveal that spontaneous and recorded domain walls in thin films of lead zirconate and bismuth ferrite exhibit large conductance at microwave frequencies despite being insulating at d.c. We explain this effect by morphological roughening of the walls and local charges induced by disorder with the overall charge neutrality. a.c. conduction is immune to large contact resistance enabling completely non-destructive walls read-out. This demonstrates a technological potential for harnessing a.c. conduction for oxide electronics and other materials with poor d.c. conduction, particularly at the nanoscale. PMID:27240997

  8. Microwave a.c. conductivity of domain walls in ferroelectric thin films.

    PubMed

    Tselev, Alexander; Yu, Pu; Cao, Ye; Dedon, Liv R; Martin, Lane W; Kalinin, Sergei V; Maksymovych, Petro

    2016-05-31

    Ferroelectric domain walls are of great interest as elementary building blocks for future electronic devices due to their intrinsic few-nanometre width, multifunctional properties and field-controlled topology. To realize the electronic functions, domain walls are required to be electrically conducting and addressable non-destructively. However, these properties have been elusive because conducting walls have to be electrically charged, which makes them unstable and uncommon in ferroelectric materials. Here we reveal that spontaneous and recorded domain walls in thin films of lead zirconate and bismuth ferrite exhibit large conductance at microwave frequencies despite being insulating at d.c. We explain this effect by morphological roughening of the walls and local charges induced by disorder with the overall charge neutrality. a.c. conduction is immune to large contact resistance enabling completely non-destructive walls read-out. This demonstrates a technological potential for harnessing a.c. conduction for oxide electronics and other materials with poor d.c. conduction, particularly at the nanoscale.

  9. Microwave a.c. conductivity of domain walls in ferroelectric thin films

    SciTech Connect

    Tselev, Alexander; Yu, Pu; Cao, Ye; Dedon, Liv R.; Martin, Lane W.; Kalinin, Sergei V.; Maksymovych, Petro

    2016-05-31

    Ferroelectric domain walls are of great interest as elementary building blocks for future electronic devices due to their intrinsic few-nanometre width, multifunctional properties and field-controlled topology. To realize the electronic functions, domain walls are required to be electrically conducting and addressable non-destructively. However, these properties have been elusive because conducting walls have to be electrically charged, which makes them unstable and uncommon in ferroelectric materials. Here we reveal that spontaneous and recorded domain walls in thin films of lead zirconate and bismuth ferrite exhibit large conductance at microwave frequencies despite being insulating at d.c. We explain this effect by morphological roughening of the walls and local charges induced by disorder with the overall charge neutrality. a.c. conduction is immune to large contact resistance enabling completely non-destructive walls read-out. Finally, this demonstrates a technological potential for harnessing a.c. conduction for oxide electronics and other materials with poor d.c. conduction, particularly at the nanoscale.

  10. Microwave a.c. conductivity of domain walls in ferroelectric thin films

    DOE PAGES

    Tselev, Alexander; Yu, Pu; Cao, Ye; ...

    2016-05-31

    Ferroelectric domain walls are of great interest as elementary building blocks for future electronic devices due to their intrinsic few-nanometre width, multifunctional properties and field-controlled topology. To realize the electronic functions, domain walls are required to be electrically conducting and addressable non-destructively. However, these properties have been elusive because conducting walls have to be electrically charged, which makes them unstable and uncommon in ferroelectric materials. Here we reveal that spontaneous and recorded domain walls in thin films of lead zirconate and bismuth ferrite exhibit large conductance at microwave frequencies despite being insulating at d.c. We explain this effect by morphologicalmore » roughening of the walls and local charges induced by disorder with the overall charge neutrality. a.c. conduction is immune to large contact resistance enabling completely non-destructive walls read-out. Finally, this demonstrates a technological potential for harnessing a.c. conduction for oxide electronics and other materials with poor d.c. conduction, particularly at the nanoscale.« less

  11. Enhancement of Thermal Conductance at Metal-Dielectric Interfaces Using Subnanometer Metal Adhesion Layers

    NASA Astrophysics Data System (ADS)

    Jeong, Minyoung; Freedman, Justin P.; Liang, Hongliang Joe; Chow, Cheng-Ming; Sokalski, Vincent M.; Bain, James A.; Malen, Jonathan A.

    2016-01-01

    We show that the use of subnanometer adhesion layers significantly enhances the thermal interface conductance at metal-dielectric interfaces. A metal-dielectric interface between Au and sapphire (Al2O3) is considered using Cu (low optical loss) and Cr (high optical loss) as adhesion layers. To enable high throughput measurements, each adhesion layer is deposited as a wedge such that a continuous range of thicknesses could be sampled. Our measurements of thermal interface conductance at the metal-Al2O3 interface made using frequency-domain thermoreflectance show that a 1-nm-thick adhesion layer of Cu or Cr is sufficient to enhance the thermal interface conductance by more than a factor of 2 or 4, respectively, relative to the pure Au/Al2O3 interface. The enhancement agrees with the diffuse-mismatch-model-based predictions of accumulated thermal conductance versus adhesion-layer thickness assuming that it contributes phonons with wavelengths less than its thickness, while those with longer wavelengths transmit directly from the Au.

  12. Temperature and frequency dependence of AC conductivity of new quaternary Se-Te-Bi-Pb chalcogenide glasses

    NASA Astrophysics Data System (ADS)

    Yadav, Preeti; Sharma, Ambika

    2016-05-01

    The aim of the present work is to study the temperature and frequency dependence of ac conductivity of new quaternary Se84-xTe15Bi1.0Pbx chalcogenide glasses. The Se84-xTe15Bi1.0Pbx (x = 2, 6) glassy alloys are prepared by using melt quenching technique. The temperature and frequency dependent behavior of ac conductivity σac(ω) has been carried out in the frequency range 42 Hz to 5 MHz and in the temperature range of 298-323 K below glass transition temperature. The behavior of ac conductivity is described in terms of the power law ωs. The obtained temperature dependence behavior of ac conductivity and frequency component (s) are explained by means of correlated barrier hopping model recommended by Elliot.

  13. 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.

  14. Random free energy barrier hopping model for ac conduction in chalcogenide glasses

    NASA Astrophysics Data System (ADS)

    Murti, Ram; Tripathi, S. K.; Goyal, Navdeep; Prakash, Satya

    2016-03-01

    The random free energy barrier hopping model is proposed to explain the ac conductivityac) of chalcogenide glasses. The Coulomb correlation is consistently accounted for in the polarizability and defect distribution functions and the relaxation time is augmented to include the overlapping of hopping particle wave functions. It is observed that ac and dc conduction in chalcogenides are due to same mechanism and Meyer-Neldel (MN) rule is the consequence of temperature dependence of hopping barriers. The exponential parameter s is calculated and it is found that s is subjected to sample preparation and measurement conditions and its value can be less than or greater than one. The calculated results for a - Se, As2S3, As2Se3 and As2Te3 are found in close agreement with the experimental data. The bipolaron and single polaron hopping contributions dominates at lower and higher temperatures respectively and in addition to high energy optical phonons, low energy optical and high energy acoustic phonons also contribute to the hopping process. The variations of hopping distance with temperature is also studied. The estimated defect number density and static barrier heights are compared with other existing calculations.

  15. Dielectric relaxation and polaronic conduction in epitaxial BaFe12O19 hexaferrite thin film

    NASA Astrophysics Data System (ADS)

    Tang, Rujun; Zhou, Hao; Zhao, Run; Jian, Jie; Wang, Han; Huang, Jijie; Fan, Meng; Zhang, Wei; Wang, Haiyan; Yang, Hao

    2016-03-01

    The dielectric properties of epitaxial BaFe12O19 hexaferrite thin film have been investigated as a function of frequency (50 Hz  -  2 MHz) and temperature (100-375 K). The frequency dependent permittivity, impedance ({{Z}\\prime \\prime} ) and modulus ({{M}\\prime \\prime} ) spectra show that the dielectric responses of BaFe12O19 thin film are thermally activated. The activation energy of BaFe12O19 film (E a) is much smaller than that of the polycrystalline bulk BaFe12O19. In addition, E a increases with increasing temperature and there is a distribution of relaxation time in the sample. The scaling behavior of {{Z}\\prime \\prime} and {{M}\\prime \\prime} spectra of the sample further suggest that the distribution of relaxation time is temperature independent at low temperatures (<250 K) and temperature dependent at high temperatures. The temperature dependent dc conductivity shows that small polaron hopping is the most probable conduction mechanism for BaFe12O19 film.

  16. AC impedance spectroscopy and conductivity studies of Dy doped Bi4V2O11 ceramics

    NASA Astrophysics Data System (ADS)

    Bag, Sasmitarani; Das, Parthasarathi; Behera, Banarji

    2017-03-01

    The ac impedance and conductivity properties of Dy doped Bi4V2 - x Dy x O11 (x = 0.05, 0.10, 0.15 and 0.20) ceramics prepared by solid-state reaction technique, in a wide frequency range at different temperatures have been studied. All the samples exhibited β-type phase orthorhombic structure at room temperature. The Nyquist plot confirmed the presence of both grain and grain boundary effects for all Dy doped samples. Double relaxation behavior was also observed. The grain and grain boundary resistance decreases with rise in temperature for all the concentration and exhibits a typical negative temperature co-efficient of resistance (NTCR) behavior. An analysis of the electric modulus suggests the possible hopping mechanism for electrical transport processes of all the materials. The ac conductivity spectrum obeys Jonscher's universal power law. DC conductivity of the materials were also studied and values of the activation energy found to be 0.40, 0.49, 0.73 and 0.78 eV for the compositions x = 0.05, 0.10, 0.15 and 0.20, respectively, at different temperatures (150-375 °C).

  17. AC conductivity studies of Fe doped TiO2 nanotubes

    NASA Astrophysics Data System (ADS)

    Vijayan, P. P.; Thomas, M.; George, K. C.

    2015-02-01

    Fe-doped TiO2 nanotubes are prepared by the combination of sol-gel process with hydrothermal treatment. The morphology and crystalline structure of TiO2 nanotubes are characterized by transmission electron microscopy (TEM), X-ray diffraction respectively (XRD). Fe doping induces a structural transformation from anatase to rutile. The temperature dependence of the ac electrical conductivity is investigated in the temperature range 303-413 K. Positive temperature coefficient of resistance is observed in the Fe doped TiO2 nanotubes. PL spectrum shows the presence of oxygen vacancies and self trapped excitons in Fe doped TiO2 nanotubes and undoped samples.

  18. Sensing performance of electrically conductive fabrics and dielectric electro active polymers for parachutes

    NASA Astrophysics Data System (ADS)

    Favini, Eric; Niezrecki, Christopher; Manohar, Sanjeev K.; Willis, David; Chen, Julie; Niemi, Eugene; Desabrais, Kenneth; Charette, Christine

    2011-04-01

    This paper quantifies the sensing capabilities of novel smart materials in an effort to improve the performance, better understand the physics, and enhance the safety of parachutes. Based upon a recent review of actuation technologies for parachute applications, it was surmised that the actuators reviewed could not be used to effectively alter the drag or lift (i.e. geometry, porosity, or air vent openings) of a parachute during flight. However, several materials showed potential for sensing applications within a parachute, specifically electrically conductive fabrics and dielectric electro-active polymers. This paper introduces several new conductive fabrics and provides an evaluation of the sensing performance of these smart materials based upon test results using mechanical testing and digital image correlation for comparison.

  19. Dielectric relaxation and electrical conduction mechanism in A2HoSbO6 (A=Ba, Sr, Ca) Double Perovskite Ceramics: An impedance spectroscopic analysis

    NASA Astrophysics Data System (ADS)

    Halder, Saswata; Dutta, Alo; Sinha, T. P.

    2017-03-01

    The AC electrical properties of polycrystalline double perovskite oxides A2HoSbO6 (A=Ba, Sr, Ca; AHS) synthesized by solid state reaction technique has been explored by using impedance spectroscopic studies. The Rietveld refinement of the room temperature X-ray diffraction data show that Ba2HoSbO6 (BHS) has cubic phase and Sr2HoSbO6 (SHS) and Ca2HoSbO6 (CHS) crystallize in monoclinic phase. The samples show significant frequency dispersion in their dielectric properties. The polydispersive nature of the relaxation mechanism is explained by the modified Cole-Cole model. The scaling behavior of dielectric loss indicate the temperature independence of the relaxation mechanism. The magnitude of the activation energy indicates that the hopping mechanism is responsible for carrier transport in AHS. The frequency dependent conductivity spectra follow the double power law. Impedance spectroscopic data presented in the Nyquist plot (Z" versus Z‧) are used to identify an equivalent circuit along with to know the grain, grain boundary and interface contributions. The constant phase element (CPE) is used to analyze the experimental response of BHS, SHS and CHS comprehending the contribution of different microstructural features to the conduction process. The temperature dependent electrical conductivity shows a semiconducting behavior.

  20. AC conductivity scaling behavior in grain and grain boundary response regime of fast lithium ionic conductors

    NASA Astrophysics Data System (ADS)

    Mariappan, C. R.

    2014-05-01

    AC conductivity spectra of Li-analogues NASICON-type Li1.5Al0.5Ge1.5P3O12 (LAGP), Li-Al-Ti-P-O (LATP) glass-ceramics and garnet-type Li7La2Ta2O13 (LLTO) ceramic are analyzed by universal power law and Summerfield scaling approaches. The activation energies and pre-exponential factors of total and grain conductivities are following the Meyer-Neldel (M-N) rule for NASICON-type materials. However, the garnet-type LLTO material deviates from the M-N rule line of NASICON-type materials. The frequency- and temperature-dependent conductivity spectra of LAGP and LLTO are superimposed by Summerfield scaling. The scaled conductivity curves of LATP are not superimposed at the grain boundary response region. The superimposed conductivity curves are observed at cross-over frequencies of grain boundary response region for LATP by incorporating the exp ( {{{ - (EAt - EAg )} {{{ - (EAt - EAg )} {kT}}} ) factor along with Summerfield scaling factors on the frequency axis, where EAt and EAg are the activation energies of total and grain conductivities, respectively.

  1. AC conductivity and relaxation mechanism in (Nd1/2Li1/2)(Fe1/2V1/2)O3 ceramics

    NASA Astrophysics Data System (ADS)

    Nath, Susmita; Barik, Subrat Kumar; Choudhary, R. N. P.

    2016-05-01

    In the present study we have synthesized polycrystalline sample of (Nd1/2Li1/2)(Fe1/2V1/2)O3 ceramic by a standard high-temperature solid-state reaction technique. Studies of dielectric and electrical properties of the compound have been carried out in a wide range of temperature (RT - 400 °C) and frequency (1kHz - 1MHz) using complex impedance spectroscopic technique. The imaginary vs. real component of the complex impedance plot (Nyquist plot) of the prepared sample exhibits the existence of grain, grain boundary contributions in the complex electrical parameters and negative temperature coefficient of resistance (NTCR) type behavior like semiconductor. Details study of ac conductivity plot reveals that the material obeys universal Jonscher's power law.

  2. ac conduction in disordered solids: Comparison of effective-medium and distributed-transition-rate-response models

    NASA Astrophysics Data System (ADS)

    MacDonald, J. Ross

    1994-04-01

    Dyre has proposed that in the low-temperature limit an effective medium approximation, termed the Bryksin equation here (the BEM), predicts a universal frequency dependence for the normalized small-signal ac frequency relaxation response of nonmetallic disordered solids. This response has been claimed to be practically identical to that found for an exponential distribution of transition rates (EDTR) in the particular limiting uniform-energy-barrier-distribution case, but comparison of the two responses has been inadequate so far. Although it is shown here that they can be well differentiated, the question of which or either is universal still requires further comparisons with experiment for its answer. A generalization of the limiting low-temperature BEM equation applicable for nonzero temperatures, the GBEM, is developed and used to evaluate the temperature and frequency ranges for which the BEM is still adequate. It is found that GBEM response can be well approximated by the important EDTR solution and leads to a frequency exponent with the same temperature dependence as the latter. An expression derived herein for the dc conductivity predicted by the GBEM involves 1/3 of the maximum thermal activation energy (i.e., the effective percolation energy), however, rather than the energy itself. Further, unlike the BEM, the GBEM predicts the presence of an intrinsic temperature-independent high-frequency-limiting conductivity whose magnitude is evaluated. The combination of conductive- and dielectric-system response, always experimentally present for a conductive system, is evaluated for the GBEM, and in the frequency range where the GBEM and BEM are indistinguishable it leads to frequency and temperature response remarkably similar to that observed for most disordered materials. Finally, it is suggested that Dyre's macroscopic simulations of the relaxation problem do not seem fully relevant to physical situations of interest and thus should not be taken to confirm

  3. Waveguide Characterization of S-Band Microwave Mantle Cloaks for Dielectric and Conducting Objects

    PubMed Central

    Vitiello, Antonino; Moccia, Massimo; Papari, Gian Paolo; D’Alterio, Giuliana; Vitiello, Roberto; Galdi, Vincenzo; Andreone, Antonello

    2016-01-01

    We present the experimental characterization of mantle cloaks designed so as to minimize the electromagnetic scattering of moderately-sized dielectric and conducting cylinders at S-band microwave frequencies. Our experimental setup is based on a parallel-plate waveguide system, which emulates a two-dimensional plane-wave scattering scenario, and allows the collection of near-field maps as well as more quantitative assessments in terms of global scattering observables (e.g., total scattering width). Our results, in fairly good agreement with full-wave numerical simulations, provide a further illustration of the mantle- cloak mechanism, including its frequency-sensitivity, and confirm its effectiveness both in restoring the near-field impinging wavefront around the scatterer, and in significantly reducing the overall scattering. PMID:26803985

  4. Waveguide Characterization of S-Band Microwave Mantle Cloaks for Dielectric and Conducting Objects.

    PubMed

    Vitiello, Antonino; Moccia, Massimo; Papari, Gian Paolo; D'Alterio, Giuliana; Vitiello, Roberto; Galdi, Vincenzo; Andreone, Antonello

    2016-01-25

    We present the experimental characterization of mantle cloaks designed so as to minimize the electromagnetic scattering of moderately-sized dielectric and conducting cylinders at S-band microwave frequencies. Our experimental setup is based on a parallel-plate waveguide system, which emulates a two-dimensional plane-wave scattering scenario, and allows the collection of near-field maps as well as more quantitative assessments in terms of global scattering observables (e.g., total scattering width). Our results, in fairly good agreement with full-wave numerical simulations, provide a further illustration of the mantle- cloak mechanism, including its frequency-sensitivity, and confirm its effectiveness both in restoring the near-field impinging wavefront around the scatterer, and in significantly reducing the overall scattering.

  5. Electric properties of carbon nano-onion/polyaniline composites: a combined electric modulus and ac conductivity study

    NASA Astrophysics Data System (ADS)

    Papathanassiou, Anthony N.; Mykhailiv, Olena; Echegoyen, Luis; Sakellis, Ilias; Plonska-Brzezinska, Marta E.

    2016-07-01

    The complex electric modulus and the ac conductivity of carbon nano-onion/polyaniline composites were studied from 1 mHz to 1 MHz at isothermal conditions ranging from 15 K to room temperature. The temperature dependence of the electric modulus and the dc conductivity analyses indicate a couple of hopping mechanisms. The distinction between thermally activated processes and the determination of cross-over temperature were achieved by exploring the temperature dependence of the fractional exponent of the dispersive ac conductivity and the bifurcation of the scaled ac conductivity isotherms. The results are analyzed by combining the granular metal model (inter-grain charge tunneling of extended electron states located within mesoscopic highly conducting polyaniline grains) and a 3D Mott variable range hopping model (phonon assisted tunneling within the carbon nano-onions and clusters).

  6. Dielectric Properties of Lead Monoxide Filled Unsaturated Polyester Based Polymer Composites

    NASA Astrophysics Data System (ADS)

    Harish, V.; Kumar, H. G. Harish; Nagaiah, N.

    2011-07-01

    Lead monoxide filled isophthalate resin particulate polymer composites were prepared with different filler concentrations and investigated for physical, thermal, mechanical and gamma radiation shielding characteristics. This paper discusses about the dielectric properties of the composites. The present study showed that the dielectric constant (ɛ'), dielectric loss (ɛ″) and ac conductivityac) of isopthalate based unsaturated polyester resin increases with the increase in wt% PbO filler in polymer matrix.

  7. Influence of the electron-phonon interfacial conductance on the thermal transport at metal/dielectric interfaces.

    PubMed

    Lombard, J; Detcheverry, F; Merabia, S

    2015-01-14

    Thermal boundary conductance at a metal-dielectric interface is a quantity of prime importance for heat management at the nanoscale. While the boundary conductance is usually ascribed to the coupling between metal phonons and dielectric phonons, in this work we examine the influence of a direct coupling between the metal electrons and the dielectric phonons. The effect of electron-phonon processes is generally believed to be resistive and tends to decrease the overall thermal boundary conductance as compared to the phonon-phonon conductance σ(p). Here, we find that the effect of a direct electron-phonon interfacial coupling σ(e) is to enhance the effective thermal conductance between the metal and the dielectric. Resistive effects turn out to be important only for thin films of metals that have a low electron-phonon coupling strength. Two approaches are explored to reach these conclusions. First, we present an analytical solution of the two-temperature model to compute the effective conductance which accounts for all the relevant energy channels, as a function of σ(e), σ(p) and the electron-phonon coupling factor G. Second, we use numerical resolution to examine the influence of σ(e) on two realistic cases: a gold film on silicon or silica substrates. We point out the implications for the interpretation of time-resolved thermoreflectance experiments.

  8. AC conductivity and structural properties of Mg-doped ZnO ceramic

    NASA Astrophysics Data System (ADS)

    Othman, Zayani Jaafar; Hafef, Olfa; Matoussi, Adel; Rossi, Francesca; Salviati, Giancarlo

    2015-11-01

    Undoped ZnO and Zn1- x Mg x O ceramic pellets were synthesized by the standard sintering method at the temperature of 1200 °C. The influence of Mg doping on the morphological, structural and electrical properties was studied. The scanning electron microscopy images revealed rough surface textured by grain boundaries and compacted grains having different shapes and sizes. Indeed, the X-ray diffraction reveals the alloying of hexagonal ZnMgO phase and the segregation of cubic MgO phase. The crystallite size, strain and stress were studied using Williamson-Hall (W-H) method. The results of mean particle size of Zn1- x Mg x O composites showed an inter-correlation with W-H analysis and Sherrer method. The electrical conductivity of the films was measured from 173 to 373 K in the frequency range of 0.1 Hz-1 MHz to identify the dominant conductivity mechanism. The DC conductivity is thermally activated by electron traps having activation energy of about 0.09 to 0.8 eV. The mechanisms of AC conductivity are controlled by the correlated barrier hopping model for the ZnO sample and the small polaron tunneling (SPT) model for Zn0.64Mg0.36O and Zn0.60Mg0.40O composites.

  9. Phonon effects on the current noise spectra and the ac conductance of a single molecular junction.

    PubMed

    Ding, Guo-Hui; Dong, Bing

    2014-07-30

    By using nonequilibrium Green's functions and the equation of motion method, we formulate a self-consistent field theory for the electron transport through a single-molecule junction (SMJ) coupled with a vibrational mode. We show that the nonequilibrium dynamics of the phonons in a strong electron-phonon coupling regime can be taken into account appropriately in this self-consistent perturbation theory, and the self-energy of the phonons is connected with the current fluctuations in the molecular junction. We calculate the finite-frequency nonsymmetrized noise spectra and the ac conductance, which reveal a wealth of inelastic electron tunneling characteristics on the absorption and emission properties of this SMJ. In the presence of a finite bias voltage and the electron tunneling current, the vibration mode of the molecular junction is heated and driven to an unequilibrated state. The influences of unequilibrated phonons on the current and the noise spectra are investigated.

  10. Phonon effects on the current noise spectra and the ac conductance of a single molecular junction

    NASA Astrophysics Data System (ADS)

    Ding, Guo-Hui; Dong, Bing

    2014-07-01

    By using nonequilibrium Green’s functions and the equation of motion method, we formulate a self-consistent field theory for the electron transport through a single-molecule junction (SMJ) coupled with a vibrational mode. We show that the nonequilibrium dynamics of the phonons in a strong electron-phonon coupling regime can be taken into account appropriately in this self-consistent perturbation theory, and the self-energy of the phonons is connected with the current fluctuations in the molecular junction. We calculate the finite-frequency nonsymmetrized noise spectra and the ac conductance, which reveal a wealth of inelastic electron tunneling characteristics on the absorption and emission properties of this SMJ. In the presence of a finite bias voltage and the electron tunneling current, the vibration mode of the molecular junction is heated and driven to an unequilibrated state. The influences of unequilibrated phonons on the current and the noise spectra are investigated.

  11. Radio frequency and capacitive sensors for dielectric characterization of low-conductivity media

    NASA Astrophysics Data System (ADS)

    Sheldon, Robert T.

    Low-conductivity media are found in a vast number of applications, for example as electrical insulation or as the matrix polymer in high strength-to-weight ratio structural composites. In some applications, these materials are subjected to extreme environmental, thermal, and mechanical conditions that can affect the material's desired performance. In a more general sense, a medium may be comprised of one or more layers with unknown material properties that may affect the desired performance of the entire structure. It is often, therefore, of great import to be able to characterize the material properties of these media for the purpose of estimating their future performance in a certain application. Low-conductivity media, or dielectrics, are poor electrical conductors and permit electromagnetic waves and static electric fields to pass through with minimal attenuation. The amount of electrical energy that may be stored (and lost) in these fields depends directly upon the material property, permittivity, which is generally complex, frequency-dependent and has a measurable effect on sensors designed to characterize dielectric media. In this work, two different types of dielectric sensors: radio frequency resonant antennas and lower-frequency (<1 MHz) capacitive sensors, are designed for permittivity characterization in their respective frequency regimes. In the first part of this work, the capability of characterizing multilayer dielectric structures is studied using a patch antenna, a type of antenna that is primarily designed for data communications in the microwave bands but has application in the field of nondestructive evaluation as well. Each configuration of a patch antenna has a single lowest resonant (dominant mode) frequency that is dependent upon the antenna's substrate material and geometry as well as the permittivity and geometry of exterior materials. Here, an extant forward model is validated using well-characterized microwave samples and a new method

  12. Study of dielectric properties of Ca doped barium titanate ceramics

    NASA Astrophysics Data System (ADS)

    Pradhan, S. K.; Kumar, Amit; Sinha, A. N.; Kour, P.

    2016-05-01

    Ba1-xCax Zr0.52Ti0.48 O3 ceramics was prepared by sol gel method. The crystallite size was in nano scale range. The dielectric constant was increased with increase in Ca2+ concentration in the sample. The dielectric loss was decreased with increase in ca concentration in the sample. The ac conductivity of the sample was increased with increase in Ca2+ concentration in the sample. The ac conductivity of the sample follows Johnscher power law. AC conductivity analysis shows that the interactions between neighbouring dipoles were decreased with the increase in Ca2+ concentration in the sample.

  13. The study of electrical conduction mechanisms. [dielectric response of lunar fines

    NASA Technical Reports Server (NTRS)

    Morrison, H. F.

    1974-01-01

    The dielectric response of lunar fines 74241,2 is presented in the audio-frequency range and under lunarlike conditions. Results suggest that volatiles are released during storage and transport of the lunar sample. Apparently, subsequent absorption of volatiles on the sample surface alter its dielectric response. The assumed volatile influence disappear after evacuation. A comparison of the dielectric properties of lunar and terrestrial materials as a function of density, temperature, and frequency indicates that if the lunar simulator analyzed were completely devoid of atmospheric moisture it would present dielectric losses smaller than those of the lunar sample. It is concluded that density prevails over temperature as the controlling factor of dielectric permittivity in the lunar regolith and that dielectric losses vary slowly with depth.

  14. Conductivity percolation in loosely compacted microcrystalline cellulose: An in situ study by dielectric spectroscopy during densification.

    PubMed

    Nilsson, Martin; Frenning, Göran; Gråsjö, Johan; Alderborn, Göran; Strømme, Maria

    2006-10-19

    The present study aims at contributing to a complete understanding of the water-induced ionic charge transport in cellulose. The behavior of this transport in loosely compacted microcrystalline cellulose (MCC) powder was investigated as a function of density utilizing a new type of measurement setup, allowing for dielectric spectroscopy measurement in situ during compaction. The ionic conductivity in MCC was found to increase with increasing density until a leveling-out was observed for densities above approximately 0.7 g/cm3. Further, it was shown that the ionic conductivity vs density followed a percolation type behavior signifying the percolation of conductive paths in a 3D conducting network. The density percolation threshold was found to be between approximately 0.2 and 0.4 g/cm3, depending strongly on the cellulose moisture content. The observed percolation behavior was attributed to the forming of interparticulate bonds in the MCC and the percolation threshold dependence on moisture was linked to the moisture dependence of particle rearrangement and plastic deformation in MCC during compaction. The obtained results add to the understanding of the density-dependent water-induced ionic transport in cellulose showing that, at given moisture content, the two major parameters determining the magnitude of the conductivity are the connectedness of the interparticluate bonds and the connectedness of pores with a diameter in the 5-20 nm size range. At densities between approximately 0.7 and 1.2 g/cm3 both the bond and the pore networks have percolated, facilitating charge transport through the MCC compact.

  15. Theory of electrical conductivity and dielectric permittivity of highly aligned graphene-based nanocomposites.

    PubMed

    Xia, Xiaodong; Hao, Jia; Wang, Yang; Zhong, Zheng; Weng, George J

    2017-03-24

    Highly aligned graphene-based nanocomposites are of great interest due to their excellent electrical properties along the aligned direction. Graphene fillers in these composites are not necessarily perfectly aligned, but their orientations are highly confined to a certain angle, with 90-degree giving rise to the randomly oriented state and 0-degree to the perfectly aligned one. Recent experiments have shown that electrical conductivity and dielectric permittivity of highly aligned graphene-polymer nanocomposites are strongly dependent on this distribution angle, but at present no theory seems to exist to address this issue. In this work we present a new effective-medium theory that is derived from the underlying physical process including the effects of graphene orientation, filler loading, aspect ratio, percolation threshold, interfacial tunneling, and Maxwell-Wagner-Sillars polarization, to determine these two properties. The theory is formulated in the context of preferred orientational average. We highlight this new theory with an application to rGO/epoxy nanocomposites, and demonstrate that the calculated in-plane and out-of-plane conductivity and permittivity are in agreement with the experimental data as the range of graphene orientations changes from the randomly oriented to the highly aligned state. We also show that the percolation thresholds of highly aligned graphene nanocomposites are in general different along the planar and the normal directions, but they converge into a single one when the statistical distribution of graphene fillers is spherically symmetric.

  16. Quasiparticle energies, excitonic effects, and dielectric screening in transparent conducting oxides

    NASA Astrophysics Data System (ADS)

    Schleife, André

    Using the power of high-performance super computers, computational materials scientists nowadays employ highly accurate quantum-mechanical approaches to reliably predict materials properties. In particular, many-body perturbation theory is an excellent framework for performing theoretical spectroscopy on novel materials including transparent conducting oxides, since this framework accurately describes quasiparticle and excitonic effects.We recently used hybrid exchange-correlation functionals and an efficient implementation of the Bethe-Salpeter approach to investigate several important transparent conducting oxides. Despite their exceptional potential for applications in photovoltaics and optoelectronics their optical properties oftentimes remain poorly understood: Our calculations explain the optical spectrum of bixbyite indium oxide over a very large photon energy range, which allows us to discuss the importance of quasiparticle and excitonic effects at low photon energies around the absorption onset, but also for excitations up to 40 eV. We show that in this regime the energy dependence of the electronic self energy cannot be neglected. Furthermore, we investigated the influence of excitonic effects on optical absorption for lanthanum-aluminum oxide and hafnium oxide. Their complicated conduction band structures require an accurate description of quasiparticle energies and we find that for these strongly polar materials, a contribution of the lattice polarizability to dielectric screening needs to be taken into account. We discuss how this affects the electron-hole interaction and find a strong influence on excitonic effects.The deep understanding of electronic excitations that can be obtained using these modern first-principles techniques, eventually will allow for computational materials design, e.g. of band gaps, densities of states, and optical properties of transparent conducting oxides and other materials with societally important applications.

  17. The impact of the thermal conductivity of a dielectric layer on the self-heating effect of a graphene transistor.

    PubMed

    Pan, T S; Gao, M; Huang, Z L; Zhang, Y; Feng, Xue; Lin, Y

    2015-08-28

    The self-heating effect of a graphene transistor on the transport properties was studied. Different dielectric layers, SiO2 and AlN, which have different thermal conductivities, were used to tune the thermal dissipation of the graphene transistor. An obvious change in channel resistance and a shift of charge neutrality point were observed during the operation of the transistor with SiO2, while the change is slight when AlN is the dielectric layer. This observation is considered to be related to the temperature determined desorption rate of p-type dopants in graphene.

  18. Ionic ac and dc conductivities of NaCrP2O7 compound

    NASA Astrophysics Data System (ADS)

    Sassi, M.; Oueslati, A.; Gargouri, M.

    2015-05-01

    The NaCrP2O7 compound was prepared by the solid-state reaction method. The formation of a single-phase material was confirmed by the X-ray diffraction studies and found to be a monoclinic system. The electrical properties of this compound have been measured in the temperature range from 523 to 673 K and the frequency range from 209 Hz to 5 MHz. The Nyquist plots are well fitted to an equivalent circuit consisting of a series of combination of grains and grain boundary elements. The ac conductivity of NaCrP2O7 has been analyzed as a function of temperature and frequency. The scaling behavior of the imaginary part of the complex modulus suggests that the relaxation describes the same mechanism at various temperatures. The conductivity and modulus formalisms provide nearly the same activation energies for electrical relaxation of mobile ions suggesting that the ion transport is probably due to a hopping mechanism dominated by the motion of the monovalent ions Na+ along tunnels presented in the structure of the investigated material.

  19. Electrical conductivity, dielectric response and space charge dynamics of an electroactive polymer with and without nanofiller reinforcement

    NASA Astrophysics Data System (ADS)

    Kochetov, R.; Tsekmes, I. A.; Morshuis, P. H. F.

    2015-07-01

    Electroactive polymers have gained considerable attention over the last 20 years for exhibiting a large displacement in response to electrical stimulation. The promising fields of application include wave energy converters, muscle-like actuators, sensors, robotics, and biomimetics. For an electrical engineer, electroactive polymers can be seen as a dielectric elastomer film or a compliant capacitor with a highly deformable elastomeric medium. If the elastomer is pre-stretched and pre-charged, a reduction of the tensile force lets the elastomer revert to its original form and increases the electrical potential. The light weight of electroactive polymers, low cost, high intrinsic breakdown strength, cyclical way of operation, reliable performance, and high efficiency can be exploited to utilize the elastomeric material as a transducer. The energy storage for a linear dielectric polymer is determined by its relative permittivity and the applied electric field. The latter is limited by the dielectric breakdown strength of the material. Therefore, to generate a high energy density of a flexible capacitor, the film must be used at the voltage level close to the material’s breakdown or inorganic particles with high dielectric permittivity which can be introduced into the polymer matrix. In the present study, silicone-titania elastomer nanocomposites were produced and the influence of nanoparticles on the macroscopic dielectric properties of the neat elastomer including space charge dynamics, complex permittivity, and electrical conductivity, were investigated.

  20. Broad-frequency dielectric behaviors in multiwalled carbon nanotube/rubber nanocomposites

    NASA Astrophysics Data System (ADS)

    Jiang, Mei-Juan; Dang, Zhi-Min; Bozlar, Michael; Miomandre, Fabien; Bai, Jinbo

    2009-10-01

    Broad-frequency dielectric behaviors of multiwalled carbon nanotubes (MWCNTs) embedded in room temperature vulcanization silicone rubber (RT-SR) matrix were studied by analyzing alternating current (ac) impedance spectra, which would make a remarkable contribution for understanding some fundamental electrical properties in the MWCNT/RT-SR nanocomposites. Equivalent circuits of the MWCNT/RT-SR nanocomposites were built, and the law of polarization and mechanism of electric conductance under the ac field were acquired. Two parallel RC circuits in series are the equivalent circuits of the MWCNT/RT-SR composites. At different frequency ranges, dielectric parameters including conductivity, dielectric permittivity, dielectric loss, impedance phase, and magnitude present different behaviors.

  1. Temperature and frequency dependent dielectric properties of electrically conducting oxidatively synthesized polyazomethines and their structural, optical, and thermal characterizations

    NASA Astrophysics Data System (ADS)

    Dineshkumar, Sengottuvelu; Muthusamy, Athianna; Chandrasekaran, J.

    2017-01-01

    Three azomethine diol monomers were synthesized by condensing with methanolic solution of aromatic aldehydes with ethylenediamine. These monomers were oxidatively polymerized using NaOCl as an oxidant. The structures of the monomers and polymers were confirmed by various spectroscopic techniques. Spectral results showed that the repeating units are linked by Csbnd C and Csbnd Osbnd C couplings. The polyazomethines have fluorescent property with high stokes shift. Solid state electrical conductivity of polymers both in I2 doped and undoped states, temperature and frequency dependent dielectric measurements were made by two probe method. The electrical conductivities of polyazomethines were compared based on the charge densities on imine nitrogens obtained from Huckel calculation. The conductivity of polymers increases with increase in iodine vapour contact time. Among the synthesized polymers PHNAE has shown high dielectric constant at low applied frequency of 50 Hz at 393 K due the presence of bulky naphthalene unit in polymer chain.

  2. Influence of mashed potato dielectric properties and circulating water electric conductivity on radio frequency heating at 27 MHz.

    PubMed

    Wang, Jian; Olsen, Robert G; Tang, Juming; Tang, Zhongwei

    2008-01-01

    Experiments and computer simulations were conducted to systematically investigate the influence of mashed potato dielectric properties and circulating water electric conductivity on electromagnetic field distribution, heating rate, and heating pattern in packaged food during radio frequency (RF) heating processes in a 6 kW, 27 MHz laboratory scale RF heating system. Both experimental and simulation results indicated that for the selected food (mashed potato) in this study, the heating rate decreased with an increase of electric conductivity of circulating water and food salt content. Simplified analytical calculations were carried out to verify the simulation results, which further indicated that the electric field distribution in the mashed potato samples was also influenced by their dielectric properties and the electric conductivity of the surrounding circulating water. Knowing the influence of water electric conductivity and mashed potato dielectric properties on the heating rate and heating pattern is helpful in optimizing the radio frequency heating process by properly adjusting these factors. The results demonstrate that computer simulation has the ability to demonstrate influence on RF heat pattern caused by the variation of material physical properties and the potential to aid the improvement on construction and modification of RF heating systems.

  3. Interaction of atomized colloid with an ac electric field in a dielectric barrier discharge reactor used for deposition of nanocomposite coatings

    NASA Astrophysics Data System (ADS)

    Profili, Jacopo; Dap, Simon; Levasseur, Olivier; Naude, Nicolas; Belinger, Antoine; Stafford, Luc; Gherardi, Nicolas

    2017-02-01

    Nanocomposite thin films can be obtained by polymerization of a colloidal solution in a dielectric barrier discharge (DBD) at atmospheric pressure. In such a process, the dispersion of nanoparticles into the matrix is driven by the charging, transport, and deposition dynamics of the atomized colloid. This work examines the interaction of atomized TiO2 nanoparticles with ac electric fields in a plane-to-plane dielectric barrier discharge reactor. Experiments are performed with the discharge off to examine transport and deposition phenomena over a wide range of experimental conditions with a fixed particle charge distribution. Scanning electron microscopy reveals that the size distribution of TiO2 nanoparticles collected at different locations along the substrate surface placed on the bottom electrode of the DBD reactor can judiciously be controlled by varying the amplitude and frequency of the ac electric field. These results are also compared to the predictions of a simple particle motion model accounting for the electrostatic force, the gravitational force, and the neutral drag force in the laminar flow. It is found that while the initial charge distribution of atomized particles strongly influences the total deposition yield, its maximal position on the substrate, and the width of the deposited area, the initial size distribution of the particles at the entrance of the reactor mostly changes the size distribution at each position along the substrate surface.

  4. Influence of Dopants on Electrical Properties of ZnO-V2O5 Varistors Deduced from AC Impedance and Variable-Temperature Dielectric Spectroscopy

    NASA Astrophysics Data System (ADS)

    Wu, Jun; Li, Taotao; Qi, Ting; Qin, Qingwei; Li, Guangqiang; Zhu, Bailin; Wu, Run; Xie, Changsheng

    2012-07-01

    The influence of MnO2, PbO, and a mixture of MnO2, PbO, and B2O3 on the electrical and dielectric properties of ZnO-V2O5 ceramics was studied by alternating-current (AC) impedance and variable-temperature dielectric spectroscopy. The results show that, compared with the resistivity of the intervening layer at the grain boundary, the Schottky barrier present at the grain boundary is much more important for varistor performance, which can be significantly improved by using a mixture of MnO2, PbO, and B2O3. Consequently, better varistor performance is achieved for 94.5 mol.% ZnO + 0.5 mol.% V2O5 + 1.0 mol.% MnO2 + 2.0 mol.% PbO + 2.0 mol.% B2O3 (ZVMPB), i.e., nonlinear coefficient α = 35.3 and leakage current density I l = 2.72 μA/cm2. The activation energy for the characteristic dielectric relaxation process is in the range of 0.339 eV to 0.365 eV, indicating that it is only associated with oxygen vacancy V{O/·}.

  5. Influence of Al2O3 nano-filler on dielectric properties and conductivity of two different PVA-PEO blend systems

    NASA Astrophysics Data System (ADS)

    Joge, Prajakta; Kanchan, D. K.; Dave, Gargi

    2015-06-01

    System-1: PVA-PEO-PEG-AgNO3 and System-2: PVA-PEO-EC-LiCF3SO3, are two blend systems prepared for different concentrations of Al2O3 nano-filler ranging from 2 to 10 wt%. The effect of Al2O3 nano filler on the conductivity (σdc) and dielectric properties such as dielectric constant (ɛ') and dielectric loss (ɛ") of the systems is thoroughly investigated using impedance spectroscopic analysis technique.

  6. Temperature-dependent dielectric properties of a thermoplastic gelatin

    NASA Astrophysics Data System (ADS)

    Landi, Giovanni; Neitzert, Heinz C.; Sorrentino, Andrea

    2016-05-01

    The frequency and the temperature dependence of the dielectric properties of a thermoplastic gelatin based bio-material have been investigated. At lower frequencies the dielectric response is strongly affected by charge carrier accumulation at the electrodes which modifies the dominating hopping conduction mechanism. The variation of the ac conductivity with frequency obeys a Jonscher type power law except for a small deviation in the low frequency range due to the electrode polarization effect. The master curve of the ac conductivity data shows that the conductivity relaxation of the gelatin is temperature independent.

  7. Noninvasive quantitative mapping of conductivity and dielectric distributions using RF wave propagation effects in high-field MRI

    NASA Astrophysics Data System (ADS)

    Wen, Han

    2003-06-01

    In this paper I show with phantom and animal experiments a non-invasive and quantitative method for measuring the conductivity and dielectric distributions based on high field magnetic resonance imaging. High field MRI is accompanied by significant RF wave propagation effects. They are observed as phase and magnitude variations of the image that cannot be removed by optimizing the static field homogeneity, or by improving the RF coils. These variations reflect the RF field distribution in the sample, and in fact obey a modified Helmholtz equation. By mapping both the phase and magnitude of the field with MRI techniques, both the conductivity and the dielectric constant are determined non-invasively. In phantom experiments at 1.5 tesla, conductivity values were measured at 4 mm resolution to 0.5 S/m accuracy. At 4.7 tesla, the accuracy was improved to 0.2 S/m, and the dielectric constant was measured to an accuracy of 5 (relative to vacuum) for 2cm regions.

  8. Ionic conductivity and dielectric permittivity of PEO-LiClO{sub 4} solid polymer electrolyte plasticized with propylene carbonate

    SciTech Connect

    Das, S.; Ghosh, A.

    2015-02-15

    We have studied ionic conductivity and dielectric permittivity of PEO-LiClO{sub 4} solid polymer electrolyte plasticized with propylene carbonate. Differential scanning calorimetry and X-ray diffraction studies confirm minimum volume fraction of crystalline phase for the polymer electrolyte with 40 wt. % propylene carbonate. The ionic conductivity exhibits a maximum for the same composition. The temperature dependence of the ionic conductivity has been well interpreted using Vogel-Tamman-Fulcher equation. Ion-ion interactions in the polymer electrolytes have been studied using Raman spectra and the concentrations of free ions, ion-pairs and ion-aggregates have been determined. The ionic conductivity increases due to the increase of free ions with the increase of propylene carbonate content. But for higher content of propylene carbonate, the ionic conductivity decreases due to the increase of concentrations of ion-pairs and ion-aggregates. To get further insights into the ion dynamics, the experimental data for the complex dielectric permittivity have been studied using Havriliak–Negami function. The variation of relaxation time with temperature obtained from this formalism follows Vogel-Tamman-Fulcher equation similar to the ionic conductivity.

  9. Experimental Investigation of Electrical Conductivity and Permittivity of SC-TiO 2 -EG Nanofluids.

    PubMed

    Fal, Jacek; Barylyak, Adriana; Besaha, Khrystyna; Bobitski, Yaroslav V; Cholewa, Marian; Zawlik, Izabela; Szmuc, Kamil; Cebulski, Józef; Żyła, Gaweł

    2016-12-01

    The paper presents experimental studies of dielectric properties of nanofluids based on ethylene glycol and SC-TiO2 nanoparticles with average size of 15-40 nm with various mass concentrations. The dielectric permittivity both real part and imaginary part as a function of temperature and frequency were measured. Also, dependence ac conductivity on frequency, temperature, and mass concentration were investigated. Based on the curves of ac conductivity, dc conductivity was calculated, and 400 % enhancement in dc conductivity was exposed.

  10. Experimental Investigation of Electrical Conductivity and Permittivity of SC-TiO 2 -EG Nanofluids

    NASA Astrophysics Data System (ADS)

    Fal, Jacek; Barylyak, Adriana; Besaha, Khrystyna; Bobitski, Yaroslav V.; Cholewa, Marian; Zawlik, Izabela; Szmuc, Kamil; Cebulski, Józef; żyła, Gaweł

    2016-08-01

    The paper presents experimental studies of dielectric properties of nanofluids based on ethylene glycol and SC-TiO2 nanoparticles with average size of 15-40 nm with various mass concentrations. The dielectric permittivity both real part and imaginary part as a function of temperature and frequency were measured. Also, dependence ac conductivity on frequency, temperature, and mass concentration were investigated. Based on the curves of ac conductivity, dc conductivity was calculated, and 400 % enhancement in dc conductivity was exposed.

  11. A layered microchip conductance detector with through-layer access to detection fields and high sensitivity to dielectric constant

    NASA Astrophysics Data System (ADS)

    Suganuma, Y.; Dhirani, A.-A.

    2011-04-01

    The present study explores a novel apertured microchip conductance detector (AMCD) that is sensitive to dielectric constant. Fashioned on silicon oxide/silicon using optical microlithography, the detector has novel parallel-plate geometry with a top mesh electrode, a middle apertured insulator, and a bottom conducting electrode. This monolithic apertured architecture is planar and may be provided with a thin insulator layer enabling large capacitances, while the top mesh electrode and middle apertured-insulator enable access to regions of the capacitor where electric fields are strong. Hence, the detector is sensitive yet mechanically robust. To test its response, the AMCD was immersed in various solvents, namely water, methanol, acetonitrile, and hexanes. Its response was found to vary in proportion to the solvents' respective dielectric constants. The AMCD was also able to distinguish quantitatively the presence of various molecules in solution, including molecules with chromophores [such as acetylsalicylic acid (ASA)] in methanol and those without chrompohores [such as polyethylene glycol 200 Daltons (PEG200)] in methanol or water. The universal nature of dielectric constant and the microchip detector's sensitivity point to a wide range of potential applications.

  12. Study on electromagnetic scattering from the time-varying lossy dielectric ocean and a moving conducting plate above it.

    PubMed

    Wang, R; Guo, L-X

    2009-03-01

    The problem of electromagnetic (EM) scattering between the time-varying lossy dielectric ocean and a moving target is always solved by using some numerical algorithm. However, the elements of the impedance matrix and the surface electric and magnetic currents of the lossy dielectric ocean must be determined and evaluated again at different moments due to the varying of the ocean with time, and the numerical algorithm will produce an enormous amount of calculation. To overcome this shortcoming, the reciprocity theorem is used to solve the coupling field between a time-varying lossy dielectric ocean and a moving conducting plate above it. Due to the advantage of the reciprocity theorem, the difficulty in computing the secondary scattered fields is reduced. The polarization currents of the ocean and the first scattered field from the conducting plate are both evaluated by using the physical optics (PO) method. The backscattered field from the ocean is evaluated by using the Kirchhoff approximation (KA) method. The characteristics of the coupling backscattered field and the Doppler spectrum are analyzed in detail for different incident conditions.

  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. Development of a new medium frequency EM device: Mapping soil water content variations using electrical conductivity and dielectric permittivity

    NASA Astrophysics Data System (ADS)

    Kessouri, P.; Buvat, S.; Tabbagh, A.

    2012-12-01

    Both electrical conductivity and dielectric permittivity of soil are influenced by its water content. Dielectric permittivity is usually measured in the high frequency range, using GPR or TDR, where the sensitivity to water content is high. However, its evaluation is limited by a low investigation depth, especially for clay rich soils. Electrical conductivity is closely related not only to soil water content, but also to clay content and soil structure. A simultaneous estimation of these electrical parameters can allow the mapping of soil water content variations for an investigation depth close to 1m. In order to estimate simultaneously both soil electrical conductivity and dielectric permittivity, an electromagnetic device working in the medium frequency range (between 100 kHz and 10 MHz) has been designed. We adopted Slingram geometry for the EM prototype: its PERP configuration (vertical transmission loop Tx and horizontal measuring loop Rx) was defined using 1D ground models. As the required investigation depth is around 1m, the coil spacing was fixed to 1.2m. This prototype works in a frequency range between 1 and 5 MHz. After calibration, we tested the response of prototype to objects with known properties. The first in situ measurements were led on experimental sites with different types of soils and different water content variations (artificially created or natural): sandy alluvium on a plot of INRA (French National Institute for Agricultural Research) in Orléans (Centre, France), a clay-loam soil on an experimental site in Estrée-Mons (Picardie, France) and fractured limestone at the vicinity of Grand (Vosges, France). In the case of the sandy alluvium, the values of dielectric permittivity measured are close to those of HF permittivity and allow the use of existing theoretical models to determine the soil water content. For soils containing higher amount of clay, the coupled information brought by the electrical conductivity and the dielectric

  15. Gas sensing properties of magnesium doped SnO{sub 2} thin films in relation to AC conduction

    SciTech Connect

    Deepa, S.; Skariah, Benoy Thomas, Boben; Joseph, Anisha

    2014-01-28

    Conducting magnesium doped (0 to 1.5 wt %) tin oxide thin films prepared by Spray Pyrolysis technique achieved detection of 1000 ppm of LPG. The films deposited at 304 °C exhibit an enhanced response at an operating temperature of 350 °C. The microstructural properties are studied by means of X-ray diffraction. AC conductivity measurements are carried out using precision LCR meter to analyze the parameters that affect the variation in sensing. The results are correlated with compositional parameters and the subsequent modification in the charge transport mechanism facilitating an enhanced LPG sensing action.

  16. Gas sensing properties of magnesium doped SnO2 thin films in relation to AC conduction

    NASA Astrophysics Data System (ADS)

    Deepa, S.; Joseph, Anisha; Skariah, Benoy; Thomas, Boben

    2014-01-01

    Conducting magnesium doped (0 to 1.5 wt %) tin oxide thin films prepared by Spray Pyrolysis technique achieved detection of 1000 ppm of LPG. The films deposited at 304 °C exhibit an enhanced response at an operating temperature of 350 °C. The microstructural properties are studied by means of X-ray diffraction. AC conductivity measurements are carried out using precision LCR meter to analyze the parameters that affect the variation in sensing. The results are correlated with compositional parameters and the subsequent modification in the charge transport mechanism facilitating an enhanced LPG sensing action.

  17. Dielectric Properties of Rare Earth Substituted Cu-Zn Ferrites

    NASA Astrophysics Data System (ADS)

    Sattar, A. A.; Rahman, Samy A.

    2003-12-01

    Samples with the chemical formula Cu0.5Zn0.5Fe2-xRxO4 (R = La, Nd, Sm and Gd; x = 0 and 0.1) were prepared by the standard ceramic method. The real part of the dielectric constant and the ac electrical conductivity ac are measured and the dielectric loss tangent tan δ is calculated in the frequency range 50-105 Hz and from room temperature up to 800 K. and tan δ are found to decrease with increasing the frequency while ac is generally increased. On the contrary , ac and tan δ are increased with temperature. No relaxation was detected in tan δ(f) in the investigated frequency range while tan δ(T) showed two maxima. The composition dependence of the dielectric parameters is discussed and the results are explained using Koops's model. (

  18. The effect of surface conductivity and adhesivity on the electrostatic manipulation condition for dielectric microparticles using a single probe

    NASA Astrophysics Data System (ADS)

    Fujiwara, Ryo; Hemthavy, Pasomphone; Takahashi, Kunio; Saito, Shigeki

    2016-05-01

    By clarifying the effect of surface conductivity and adhesivity on the electrostatic manipulation condition, a dielectric particle made of any material can be manipulated with surface conductivity. The manipulation system consists of three elements: a conductive probe as a manipulator, a conductive plate as a substrate, and a dielectric particle as the target object for manipulation. The particle can be successfully picked up/placed if a rectangular pulse voltage is applied between the probe and the plate. Four kinds of particle materials are used in the experiment: silica, soda-lime glass, polymethyl methacrylate coated by conductive polymer, and polystyrene coated by surfactant. The radius of each particle is 15 μm. A first-order resistor-capacitor (RC) circuit model is adopted to describe the effect of surface conductivity and adhesivity on the manipulation condition. The manipulation system is modeled as a series circuit consisting of a resistor and a capacitor by considering the surface conductivity. A detachment voltage is defined as the capacitance voltage to detach the particle adhered to the plate or probe. Parameters of the RC model, surface resistance, surface capacitance and detachment voltage are identified by a simulation and measurements. To verify the RC model, the particle’s behavior is observed by a high-speed camera, and the electrical current is measured by an electrometer. A manipulation experiment is demonstrated to show the effectiveness of the model. The particle reaction is observed for each duration and magnitude of the pulse voltage for the manipulation. The optimum pulse voltage for successful manipulation is determined by the parameters of the RC model as the standard. This knowledge is expected to expand the possibility of micro-fabrication technology.

  19. Calculation of the ac to dc resistance ratio of conductive nonmagnetic straight conductors by applying FEM simulations

    NASA Astrophysics Data System (ADS)

    Riba, Jordi-Roger

    2015-09-01

    This paper analyzes the skin and proximity effects in different conductive nonmagnetic straight conductor configurations subjected to applied alternating currents and voltages. These effects have important consequences, including a rise of the ac resistance, which in turn increases power loss, thus limiting the rating for the conductor. Alternating current (ac) resistance is important in power conductors and bus bars for line frequency applications, as well as in smaller conductors for high frequency applications. Despite the importance of this topic, it is not usually analyzed in detail in undergraduate and even in graduate studies. To address this, this paper compares the results provided by available exact formulas for simple geometries with those obtained by means of two-dimensional finite element method (FEM) simulations and experimental results. The paper also shows that FEM results are very accurate and more general than those provided by the formulas, since FEM models can be applied in a wide range of electrical frequencies and configurations.

  20. Combined DC Resistivity Survey and Electric Conductivity- Dielectric Permittivity Measurement at Sag Pond near Lembang Fault, West Java, Indonesia

    NASA Astrophysics Data System (ADS)

    Iryanti, Mimin; Srigutomo, Wahyu; Bijaksana, Satria; Setiawan, Tedy

    2016-08-01

    Lembang Fault is a normal fault situated at the southern flank of Tangkuban Parahu Volcano in West Java Indonesia. The fault's movement may have caused the formation of sag pond in the vicinity of its which is characterized by the soil layers of the sag pond. The characteristics of the soil can be examined based on its electrical properties such as conductivity (the inverse of resistivity) and dielectric permittivity. Direct field measurement was conducted using DC-resistivity Wenner-Schlumberger method on the sag pond as well as laboratory resistivity measurement of cores taken from the sag pond. Two resistivity crosssections were obtained after performing 2D inversion of the data which reveal that the resistivity distribution consist of a resistive layer (40-60 ohm.m) overlying a medium resistive layer (30-35 ohm.m). The third layer has relatively low resistivity of 16-25 ohm.m. At the intersection of these two lines we took coring samples down to depth of 5 m below surface and measured the electrical conductivity and dielectric permittivity for each 1 cm of sample using EM-50 data logger. Results from both field and laboratory measurement were analysed to get a better understanding of the sag pond.

  1. AC impedance spectroscopy studies on solid-state sintered zinc aluminum oxide (ZnAl2O4) ceramics

    NASA Astrophysics Data System (ADS)

    Kumar, B. Rajesh; Rao, T. Subba

    2012-07-01

    In the present investigation Zinc Aluminum Oxide (ZnAl2O4) is prepared by solid-state reaction technique. Dielectric constant (ɛ'), dielectric loss(tan δ), ac conductivityac) as a function of temperature are studied by varying frequencies from 100 Hz to 1MHz using an impedance analyzer. The dielectric constant and dielectric loss increases gradually with an increase of temperature, but it decreases with increase of frequency. The ac conductivityac) also increases with increases of frequency. The transition peaks for ZnAl2O4 are observed at 490°C, 510°C, 520°C for the frequencies 1 KHz, 10 KHz and 100 KHz. No transition peaks are found for the frequency 100 Hz and 1 MHz because of high conductive loss.

  2. AC magnetic field-assisted method to develop porous carbon nanotube/conducting polymer composites for application in thermoelectric materials

    NASA Astrophysics Data System (ADS)

    Chuang, Chun-Yu; Yang, Shu-Chian; Chang, Su-Hua; Yang, Ta-I.

    2015-04-01

    Thermoelectric materials are very effective in converting waste heat sources into useful electricity. Researchers are continuing to develop new polymeric thermoelectric materials. The segregated-network carbon nanotube (CNT)- polymer composites are most promising. Thus, the goal of this study is to develop novel porous CNT -polymer composites with improved thermoelectric properties. The research efforts focused on modifying the surface of the CNT with magnetic nanoparticles so that heat was released when subjecting to an AC magnetic field. Subsequently, polymers covered on the surface of the CNT were crosslinked. The porous CNT -polymer composites can be obtained by removing the un-crosslinked polymers. Polydimethylsiloxane polymer was utilized to investigate the effect of porosity and electrical conductivity on the thermoelectric properties of the composites. This AC magnetic field-assisted method to develop porous carbon nanotube/polymer composites for application in thermoelectric materials is introduced for the first time. The advantage of this method is that the electrical conductivity of the composites was high since we can easily to manipulate the CNT to form a conducting path. Another advantage is that the high porosity significantly reduced the thermal conductivity of the composites. These two advantages enable us to realize the polymer composites for thermoelectric applications. We are confident that this research will open a new avenue for developing polymer thermoelectric materials.

  3. Development of the Exams Data Analysis Spreadsheet as a Tool to Help Instructors Conduct Customizable Analyses of Student ACS Exam Data

    ERIC Educational Resources Information Center

    Brandriet, Alexandra; Holme, Thomas

    2015-01-01

    The American Chemical Society Examinations Institute (ACS-EI) has recently developed the Exams Data Analysis Spread (EDAS) as a tool to help instructors conduct customizable analyses of their student data from ACS exams. The EDAS calculations allow instructors to analyze their students' performances both at the total score and individual item…

  4. Percolation phenomenon of calcium bis(2-ethylhexyl) sulfosuccinate water-in-oil microemulsions by conductivity and dielectric spectroscopy measurements.

    PubMed

    Capuzzi, G; Baglioni, P; Gambi, C M; Sheu, E Y

    1999-07-01

    The sodium counterion (Na+) of the sodium bis(2-ethylhexyl) sulfosuccinate (AOT) surfactant was exchanged with calcium Ca2+ to investigate the counterion charge effect on the structure of water in normal decane microemulsions. Ohmic conductivity and dielectric permittivity measurements were performed on samples at constant water to surfactant mole ratio [water]/[Ca(AOT)(2)]=26.6. Increasing the volume fraction of the dispersed phase phi, a percolation phenomenon was observed at the constant temperature of 25 degrees C. The percolation threshold was found at phi approximately 15% by Ohmic conductivity and static dielectric permittivity studied as a function of phi, and by the frequency dependence of the complex permittivity. Critical exponents typical of the static percolation mechanism (formation of bicontinuous microemulsions) were found below and above threshold. The comparison of these results obtained for the two different counterions, Ca2+ and Na+, in AOT surfactant water in normal decane microemulsions allows detection of an important difference. The percolation below threshold is dynamic for the sodium-based microemulsions, accounting for the formation of clusters of droplets, whereas calcium-based microemulsions show a static percolation. For this system, the coalescence of droplets begins to occur below threshold at phi approximately 12%.

  5. Leakage current conduction behaviors of 0.65 nm equivalent-oxide-thickness HfZrLaO gate dielectrics

    NASA Astrophysics Data System (ADS)

    Lin, K. C.; Chen, J. Y.; Hsu, H. W.; Chen, H. W.; Liu, C. H.

    2012-11-01

    The high κ gate dielectrics of MOS capacitors with LaO/HfZrO stacked (denoted as HfZrLaO) have been fabricated by atomic-layer-deposited (ALD). In this study, the data show that the gate leakage current density (Jg) is about 1.9 A/cm2, and the equivalent oxide thickness (EOT) is about 0.65 nm with quantum effects taken into account. The analysis of the leakage current conduction characteristics is based on the temperature dependence of the leakage current from 300 to 475 K. The dominant current conduction behaviors are Schottky emission in the region of low electric fields (<1 MV/cm) and high temperatures (450-475 K), Poole-Frankel (P-F) emission in the region of medium electric fields (2.3-3.83 MV/cm) and low temperatures (300-350 K), and Fowler-Nordheim (F-N) tunneling in the region of high electric fields (>4 MV/cm) and low temperatures (<300 K). The electron barrier height (ΦB) at gate interface and the trap energy level (Φt) in the dielectric are extracted to be 1.07 and 1.38 eV, respectively.

  6. 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.

  7. Optical, electrical and ac conductivity measurements of nonlinear optical Dimethylaminomethylphthalimide doped with cadmium chloride single crystal for nano applications

    NASA Astrophysics Data System (ADS)

    Subramani, K.; Joseph, P. S.; Shankar, G.

    2013-07-01

    Single crystals of Dimethylaminomethylphthalimide cadmium chloride (DAMPCC) were grown by a slow evaporation technique. The unit cell parameters and crystal structure were measured by the powder X-ray diffraction analysis. The modes of vibrations of different molecular groups present in the DAMPCC crystal have been identified by FTIR spectral analysis. The UV-vis-NIR spectral analysis is used to study the optical behaviors like absorption and transmission properties of the crystal. The diffuse reflectance spectrum in absorption studies is calculated. The optical band gap of the DAMPCC crystal is calculated to be cut off wavelength 360 nm at photon energy 4.772 eV. The optical conductivity, electrical conductivity and ac conductivity are also calculated. Finally the nonlinear optics (NLO) property of DAMPCC crystal was confirmed by second harmonic generation (SHG) test using the Nd:YAG laser of fundamental wavelength 1064 nm.

  8. Complex impedance, dielectric relaxation and electrical conductivity studies of Ba1-xSrxTiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Elbasset, A.; Sayouri S, S.; Abdi, F.; Lamcharfi, T.; Mrharrab, L.

    2017-03-01

    In this work, we prepared series of Ba1-xSrxTiO3 (BSxT) powders, with different strontium concentrations (x = 0, 0.025, 0.75, 0.10, 0.125 and 0.15), by the sol-gel method. The variation of structure in the Ba1-xSrxTiO3 system was analyzed using XRD and Raman techniques. The field dependence of dielectric relaxation and conductivity was measured over a wide frequency range from room temperature to 400 °C. The activation energy, calculated from the thermal variation of the conductivity for different frequencies, showed that the Sr has significant effects on the properties of BaTiO3. Relaxation times extracted using the imaginary part of the complex impedance (Z’’(ω)) and the modulus (M’’(ω)) were also found to follow the Arrhenius law and showed an anomaly around the phase transition temperature.

  9. Conductivity and Dielectric Characteristics of Planetary Surfaces Measured with Mutual Impedance Probes: From Huygens and Rosetta Lander to Netlanders and Future Missions

    NASA Astrophysics Data System (ADS)

    Hamelin, M.; Grard, R.; Laakso, H.; Ney, R.; Schmidt, W.; Simoes, F.; Trautner, R.

    2004-04-01

    probes should be able to detect also the vertical inhomogeneity of the medium (match with a two layer model). After presenting the actual instruments and projects (on HUYGENS, ROSETTA Lander and NETLANDER), we show the particular interest to use a flat system of electrodes laying on the surface at some distance from the spacecraft body that is particularly well suited for the case of a rover. We will show the design of a prototype actually prepared in CETP to be used in common calibrations with the other instruments in selected well-known terrains. 1. PRINCIPLE AND HERITAGE The measurement of the planetary surface complex permittivity (electrical conductivity and dielectric constant) vs. frequency has a twofold interest: i) to contribute with other parameters to the identification of the close sub-surface materials without penetrating the surface; ii) to characterize the electrical properties of the planetary surface which control the boundary conditions for electromagnetic waves and fields, including possible DC atmospheric electric currents. The mutual impedance (MI) probes of today's planetary missions are the heritage of the quadrupolar probes developed in the first half of the XXth century for oil prospecting [1]. The principle is to inject an AC current I in the planar homogeneous ground of relative permittivity eg through a first dipole and to measure the induced potential by this dipole or by a second dipole to obtain respectively the self and mutual impedances.

  10. Anomalous three-dimensional bulk ac conduction within the Kondo gap of SmB6 single crystals

    NASA Astrophysics Data System (ADS)

    Laurita, N. J.; Morris, C. M.; Koohpayeh, S. M.; Rosa, P. F. S.; Phelan, W. A.; Fisk, Z.; McQueen, T. M.; Armitage, N. P.

    2016-10-01

    The Kondo insulator SmB6 has long been known to display anomalous transport behavior at low temperatures, T <5 K. In this temperatures range, a plateau is observed in the dc resistivity, contrary to the exponential divergence expected for a gapped system. Recent theoretical calculations suggest that SmB6 may be the first topological Kondo insulator (TKI) and propose that the residual conductivity is due to topological surface states which reside within the Kondo gap. Since the TKI prediction many experiments have claimed to observe high mobility surface states within a perfectly insulating hybridization gap. Here, we investigate the low energy optical conductivity within the hybridization gap of single crystals of SmB6 via time domain terahertz spectroscopy. Samples grown by both optical floating zone and aluminum flux methods are investigated to probe for differences originating from sample growth techniques. We find that both samples display significant three-dimensional bulk conduction originating within the Kondo gap. Although SmB6 may be a bulk dc insulator, it shows significant bulk ac conduction that is many orders of magnitude larger than any known impurity band conduction. The nature of these in-gap states and their coupling with the low energy spin excitons of SmB6 is discussed. Additionally, the well-defined conduction path geometry of our optical experiments allows us to show that any surface states, which lie below our detection threshold if present, must have a sheet resistance of R /square≥ 1000 Ω .

  11. Dielectric studies on struvite urinary crystals, a gateway to the new treatment modality for urolithiasis

    NASA Astrophysics Data System (ADS)

    Rajan, Reshma; Raj, N. Arunai Nambi; Madeswaran, S.; Babu, D. Rajan

    2015-09-01

    Struvite or magnesium ammonium phosphate hexahydrate (MAPH) are biological crystals, found in the kidney, which are formed due to the infection caused by urea splitting bacteria in the urinary tract. The struvite crystals observe different morphologies and were developed using single diffusion gel growth technique. The crystalline nature and its composition were studied from different characterization techniques like X-ray Diffraction (XRD) and FTIR. The dielectric behavior of the developed crystal was studied by varying temperature and at different frequencies. The parameters like dielectric constant, dielectric loss, ac conductivity, ac resistivity, impedance and admittance of the struvite crystals were calculated. The studies proved that the dielectric loss or dissipation heat is high in lower frequencies at normal body temperature, which develops a plasma state in the stones and in turn leads to the disintegration of urinary stones. The dielectric nature of the stones leads to the dielectric therapy, which will be a gateway for future treatment modality for urolithiasis.

  12. Dielectric studies on struvite urinary crystals, a gateway to the new treatment modality for urolithiasis.

    PubMed

    Rajan, Reshma; Raj, N Arunai Nambi; Madeswaran, S; Babu, D Rajan

    2015-09-05

    Struvite or magnesium ammonium phosphate hexahydrate (MAPH) are biological crystals, found in the kidney, which are formed due to the infection caused by urea splitting bacteria in the urinary tract. The struvite crystals observe different morphologies and were developed using single diffusion gel growth technique. The crystalline nature and its composition were studied from different characterization techniques like X-ray Diffraction (XRD) and FTIR. The dielectric behavior of the developed crystal was studied by varying temperature and at different frequencies. The parameters like dielectric constant, dielectric loss, ac conductivity, ac resistivity, impedance and admittance of the struvite crystals were calculated. The studies proved that the dielectric loss or dissipation heat is high in lower frequencies at normal body temperature, which develops a plasma state in the stones and in turn leads to the disintegration of urinary stones. The dielectric nature of the stones leads to the dielectric therapy, which will be a gateway for future treatment modality for urolithiasis.

  13. Thermally conductive, dielectric PCM-boron nitride nanosheet composites for efficient electronic system thermal management.

    PubMed

    Yang, Zhi; Zhou, Lihui; Luo, Wei; Wan, Jiayu; Dai, Jiaqi; Han, Xiaogang; Fu, Kun; Henderson, Doug; Yang, Bao; Hu, Liangbing

    2016-11-24

    Phase change materials (PCMs) possessing ideal properties, such as superior mass specific heat of fusion, low cost, light weight, excellent thermal stability as well as isothermal phase change behavior, have drawn considerable attention for thermal management systems. Currently, the low thermal conductivity of PCMs (usually less than 1 W mK(-1)) greatly limits their heat dissipation performance in thermal management applications. Hexagonal boron nitride (h-BN) is a two-dimensional material known for its excellent thermally conductive and electrically insulating properties, which make it a promising candidate to be used in electronic systems for thermal management. In this work, a composite, consisting of h-BN nanosheets (BNNSs) and commercialized paraffin wax was developed, which inherits high thermally conductive and electrically insulating properties from BNNSs and substantial heat of fusion from paraffin wax. With the help of BNNSs, the thermal conductivity of wax-BNNS composites reaches 3.47 W mK(-1), which exhibits a 12-time enhancement compared to that of pristine wax (0.29 W mK(-1)). Moreover, an 11.3-13.3 MV m(-1) breakdown voltage of wax-BNNS composites was achieved, which shows further improved electrical insulating properties. Simultaneously enhanced thermally conductive and electrically insulating properties of wax-BNNS composites demonstrate their promising application for thermal management in electronic systems.

  14. Chemical bonding-induced low dielectric loss and low conductivity in high-K poly(vinylidenefluoride-trifluorethylene)/graphene nanosheets nanocomposites.

    PubMed

    Wen, Fei; Xu, Zhuo; Tan, Shaobo; Xia, Weimin; Wei, Xiaoyong; Zhang, Zhicheng

    2013-10-09

    Blending high-permittivity (εr) ceramic powders or conductive fillers into polymers to form 0-3-type composites has been regarded as one of the most promising processes to achieve high-dielectric-permittivity materials with excellent processing performance. The high dielectric loss and conductivity induced by the interface between the matrix and fillers as well as the leakage current have long been a great challenge of dielectric composites, and the resolution of these challenges is still an open question. In this work, poly(vinylidenefluoride-trifluorethylene with double bonds)/graphene nanosheets (P(VDF-TrFE-DB)/GNS) terpolymer nanocomposites were fabricated via a solution-cast process. GNSs were functionalized with KH550 to improve the dispersion in the terpolymer matrix solution and crosslinked with P(VDF-TrFE-DB) by a free-radical addition reaction in the nanocomposites. Compared with neat terpolymer, significantly increased dielectric permittivity and a low loss were observed for the composites. For instance, at 1 kHz the P(VDF-TrFE-DB)/GNS composites with 4 vol % GNS possessed a dielectric permittivity of 74, which is over seven times larger than that of neat terpolymer. However, a rather low dielectric loss (0.08 at 1 kHz) and conductivity (3.47 × 10(-7) S/m at 1 kHz) are observed in the P(VDF-TrFE-DB)/GNS composites containing up to 12 vol % GNS. The covalent bonding constructed between P(VDF-TrFE-DB) and GNS is responsible for the reduced aspect ratio of the GNS and the crystalline properties of P(VDF-TrFE-DB) as well as the improved compatibility between them. As a result, the high-dielectric-loss conductivity of polymer composites, mainly induced by conduction loss and the interface polarization between the matrix and filler, were effectively restricted. Meanwhile, the 3D network established between P(VDF-TrFE-DB) and GNS endows the P(VDF-TrFE-DB)/GNS composites at high temperature with excellent mechanical and dielectric properties. Besides preparing

  15. Structural, electrical conductivity and dielectric behavior of Na2SO4–LDT composite solid electrolyte

    PubMed Central

    Iqbal, Mohd Z.; Rafiuddin

    2015-01-01

    A series of composite materials of general molecular formula (1 − x) Na2SO4 − (x) LDT was prepared by solid state reaction method. The phase structure and functionalization of these materials were defined by X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FT-IR) respectively. Differential thermal analysis (DTA) revealed that the hump of phase transition at 250 °C has decreased while its thermal stability was enhanced. Scanning electron microscopy signifies the presence of improved rigid surfaces and interphases that are accountable for the high ionic conduction due to dispersion of LDT particles in the composite systems. Arrhenius plots of the conductance show the maximum conductivity, σ = 4.56 × 10−4 S cm−1 at 500 °C for the x = 0.4 composition with the lowest activation energy 0.34 eV in the temperature range of 573–773 K. The value of dielectric constant was decreased with increasing frequency and follows the usual trend. PMID:26843979

  16. Uncorrelated multiple conductive filament nucleation and rupture in ultra-thin high-κ dielectric based resistive random access memory

    NASA Astrophysics Data System (ADS)

    Wu, Xing; Li, Kun; Raghavan, Nagarajan; Bosman, Michel; Wang, Qing-Xiao; Cha, Dongkyu; Zhang, Xi-Xiang; Pey, Kin-Leong

    2011-08-01

    Resistive switching in transition metal oxides could form the basis for next-generation non-volatile memory (NVM). It has been reported that the current in the high-conductivity state of several technologically relevant oxide materials flows through localized filaments, but these filaments have been characterized only individually, limiting our understanding of the possibility of multiple conductive filaments nucleation and rupture and the correlation kinetics of their evolution. In this study, direct visualization of uncorrelated multiple conductive filaments in ultra-thin HfO2-based high-κ dielectric resistive random access memory (RRAM) device has been achieved by high-resolution transmission electron microscopy (HRTEM), along with electron energy loss spectroscopy (EELS), for nanoscale chemical analysis. The locations of these multiple filaments are found to be spatially uncorrelated. The evolution of these microstructural changes and chemical properties of these filaments will provide a fundamental understanding of the switching mechanism for RRAM in thin oxide films and pave way for the investigation into improving the stability and scalability of switching memory devices.

  17. AC conductivity and electrochemical studies of PVA/PEG based polymer blend electrolyte films

    NASA Astrophysics Data System (ADS)

    Polu, Anji Reddy; Kumar, Ranveer; Dehariya, Harsha

    2012-06-01

    Polymer blend electrolyte films based on Polyvinyl alcohol(PVA)/Poly(ethylene glycol)(PEG) and magnesium nitrate (Mg(NO3)2) were prepared by solution casting technique. Conductivity in the temperature range 303-373 K and transference number measurements have been employed to investigate the charge transport in this polymer blend electrolyte system. The highest conductivity is found to be 9.63 × 10-5 S/cm at 30°C for sample with 30 weight percent of Mg(NO3)2 in PVA/PEG blend matrix. Transport number data shows that the charge transport in this polymer electrolyte system is predominantly due to ions. Using this electrolyte, an electrochemical cell with configuration Mg/(PVA+PEG+Mg(NO3)2)/(I2+C+electrolyte) was fabricated and its discharge characteristics profile has been studied.

  18. Effects of Luttinger leads on the AC conductance of a quantum dot

    NASA Astrophysics Data System (ADS)

    Yang, Kai-Hua; Qin, Chang-Dong; Wang, Huai-Yu; Liu, Kai-Di

    2017-04-01

    We investigate the joint effects of the intralead electron interaction and an external alternating gate voltage on the transport of a quantum dot coupled to two Luttinger liquid leads in the Kondo regime. We find the transferring between two Kondo physics mechanics by investigation of differential conductance. For very weak intralead interaction, the satellite and main Kondo resonant peaks appear in the differential conductance. For moderately strong intralead interaction, all the peaks disappear and evolve into dips, which signifies that a photon-assisted single-channel Kondo (1CK) physics turns into two-channel Kondo (2CK) physics. The 1CK and 2CK mechanisms can coexist within a region of the intralead interaction parameter. The 1CK physics transits to the 2CK one gradually, not suddenly. In the limit of strong interaction, all dips disappear. When the bias voltage is small, there is no photon exchange between the quantum dot and alternative field, and the differential conductance scales as a power law both in bias voltage and in temperature. As the field becomes stronger, the quantum dot will emit and absorb photons.

  19. Estimation of Density of Localized States in Amorphous Se80Te20 and Se80Te10M10 (M = Cd, In, Sb) Alloys Using AC Conductivity Measurements

    NASA Astrophysics Data System (ADS)

    Chandel, N.; Mehta, N.; Kumar, A.

    2015-08-01

    The ac conductivity of amorphous Se80Te20 (a-Se80Te20) and amorphous Se80Te10M10 (a-Se80Te10M10) alloys has been measured as a function of temperature and frequency in a low-temperature regime. An analysis of the experimental data confirms that ac conductivity is reasonably well interpreted by the Austin-Mott model. The density of localized states was determined in the low-temperature region from 201 K to 280 K. Possible explanations of "metal-induced effects" on the conduction mechanism of a-Se80Te20 alloy are discussed.

  20. Insight into Understanding Dielectric Behavior of a Zn-MOF Using Variable-Temperature Crystal Structures, Electrical Conductance, and Solid-State (13)C NMR Spectra.

    PubMed

    Tong, Yuan-Bo; Liu, Shao-Xian; Zou, Yang; Xue, Chen; Duan, Hai-Bao; Liu, Jian-Lan; Ren, Xiao-Ming

    2016-11-21

    A Zn-based metal-organic framework (MOF)/porous coordination polymer (PCP), (EMIM)[Zn(SIP)] (1) (SIP(3-) = 5-sulfoisophthalate, EMIM(+) = 1-ethyl-3-methylimidazolium), was synthesized using the ionothermal reaction. The Zn(2+) ion adopts distorted square pyramid coordination geometry with five oxygen atoms from three carboxylates and one sulfo group. One of two carboxylates in SIP(3-) serves as a μ2-bridge ligand to link two Zn(2+) ions and form the dinuclear SBU, and such SBUs are connected by SIP(3-) ligands to build the three-dimensional framework with rutile (rtl) topology. The cations from the ion-liquid fill the channels. This MOF/PCP shows two-step dielectric anomalies together with two-step dielectric relaxations; the variable-temperature single-crystal structure analyses disclosed the dielectric anomaly occurring at ca. 280 K is caused by an isostructural phase transition. Another dielectric anomaly is related to the dynamic disorder of the cations in the channels. Electric modulus, conductance, and variable-temperature solid-state (13)C CP/MAS NMR spectra analyses revealed that two-step dielectric relaxations result from the dynamic motion of the cations as well as the direct-current conduction and electrode effect, respectively.

  1. Changes in Properties of Dielectric Barrier Discharge Plasma Jets for Different Gases and for Insulating and Conducting Transfer Plates

    NASA Astrophysics Data System (ADS)

    do Nascimento, Fellype; Moshkalev, Stanislav; Machida, Munemasa

    2017-03-01

    Dielectric barrier discharge (DBD) plasma jets have been studied extensively in recent years because of its wide range of applications. DBD plasmas can be produced using many different gases and can be applied to a broad variety of surfaces and substrates. This work provides comparisons of DBD plasmas generated using argon (Ar), helium (He), and nitrogen (N2), as well as their mixtures with water vapor in order to know how some plasma properties are affected by the use of different gases. All plasmas were studied in two different conditions: using a transfer plate made of a conductive material and using a transfer plate made of an insulating one. It was observed that the process of Penning ionization of nitrogen molecules by direct collisions with metastable atoms and molecules is evident and significant only in plasmas that use He as the working gas, which means that He atoms in metastable states have greater ability to transfer energy to molecules of nitrogen in the plasma. The collisions of metastable He with N2 molecules determine the vibrational temperature (T vib) values in He plasmas, while in Ar and N2 plasmas, the T vib values are determined mainly by collisions of electrons with N2 molecules. It was noticed that the use of an insulating or a conducting transfer plate as the sample holder affects the results of adhesion between poly(dimethylsiloxane) samples, and it is mainly due to the differences in the plasma power, with a higher plasma power leading to better adhesion.

  2. Proton Conducting Graphene Oxide/Chitosan Composite Electrolytes as Gate Dielectrics for New-Concept Devices

    PubMed Central

    Feng, Ping; Du, Peifu; Wan, Changjin; Shi, Yi; Wan, Qing

    2016-01-01

    New-concept devices featuring the characteristics of ultralow operation voltages and low fabrication cost have received increasing attention recently because they can supplement traditional Si-based electronics. Also, organic/inorganic composite systems can offer an attractive strategy to combine the merits of organic and inorganic materials into promising electronic devices. In this report, solution-processed graphene oxide/chitosan composite film was found to be an excellent proton conducting electrolyte with a high specific capacitance of ~3.2 μF/cm2 at 1.0 Hz, and it was used to fabricate multi-gate electric double layer transistors. Dual-gate AND logic operation and two-terminal diode operation were realized in a single device. A two-terminal synaptic device was proposed, and some important synaptic behaviors were emulated, which is interesting for neuromorphic systems. PMID:27688042

  3. Proton Conducting Graphene Oxide/Chitosan Composite Electrolytes as Gate Dielectrics for New-Concept Devices

    NASA Astrophysics Data System (ADS)

    Feng, Ping; Du, Peifu; Wan, Changjin; Shi, Yi; Wan, Qing

    2016-09-01

    New-concept devices featuring the characteristics of ultralow operation voltages and low fabrication cost have received increasing attention recently because they can supplement traditional Si-based electronics. Also, organic/inorganic composite systems can offer an attractive strategy to combine the merits of organic and inorganic materials into promising electronic devices. In this report, solution-processed graphene oxide/chitosan composite film was found to be an excellent proton conducting electrolyte with a high specific capacitance of ~3.2 μF/cm2 at 1.0 Hz, and it was used to fabricate multi-gate electric double layer transistors. Dual-gate AND logic operation and two-terminal diode operation were realized in a single device. A two-terminal synaptic device was proposed, and some important synaptic behaviors were emulated, which is interesting for neuromorphic systems.

  4. Effect of surface moisture on dielectric behavior of ultrafine BaTiO3 particulates.

    NASA Technical Reports Server (NTRS)

    Mountvala, A. J.

    1971-01-01

    The effects of adsorbed H2O on the dielectric properties of ultrafine BaTiO3 particulates of varying particle size and environmental history were determined. The dielectric behavior depends strongly on surface hydration. No particle size dependence of dielectric constant was found for dehydroxylated surfaces in ultrafine particulate (unsintered) BaTiO3 materials. For equivalent particle sizes, the ac conductivity is sensitive to surface morphology. Reactions with H2O vapor appear to account for the variations in dielectric properties. Surface dehydration was effectively accomplished by washing as-received powders in isopropanol.

  5. Radiative heat conductances between dielectric and metallic parallel plates with nanoscale gaps

    NASA Astrophysics Data System (ADS)

    Song, Bai; Thompson, Dakotah; Fiorino, Anthony; Ganjeh, Yashar; Reddy, Pramod; Meyhofer, Edgar

    2016-06-01

    Recent experiments have demonstrated that radiative heat transfer between objects separated by nanometre-scale gaps considerably exceeds the predictions of far-field radiation theories. Exploiting this near-field enhancement is of great interest for emerging technologies such as near-field thermophotovoltaics and nano-lithography because of the expected increases in efficiency, power conversion or resolution in these applications. Past measurements, however, were performed using tip-plate or sphere-plate configurations and failed to realize the orders of magnitude increases in radiative heat currents predicted from near-field radiative heat transfer theory. Here, we report 100- to 1,000-fold enhancements (at room temperature) in the radiative conductance between parallel-planar surfaces at gap sizes below 100 nm, in agreement with the predictions of near-field theories. Our measurements were performed in vacuum gaps between prototypical materials (SiO2-SiO2, Au-Au, SiO2-Au and Au-Si) using two microdevices and a custom-built nanopositioning platform, which allows precise control over a broad range of gap sizes (from <100 nm to 10 μm). Our experimental set-up will enable systematic studies of a variety of near-field-based thermal phenomena, with important implications for thermophotovoltaic applications, that have been predicted but have defied experimental verification.

  6. AC Hopping Conductance in Nanocomposite Films with Ferromagnetic Alloy Nanoparticles in a PbZrTiO3 Matrix

    NASA Astrophysics Data System (ADS)

    Koltunowicz, T. N.; Zukowski, P.; Boiko, O.; Saad, A.; Fedotova, J. A.; Fedotov, A. K.; Larkin, A. V.; Kasiuk, J.

    2015-07-01

    In this work, the temperature and frequency dependences of the real part of the admittance [ σ( f, T)] of annealed nanocomposite films containing Co45 Fe45Zr10-based nanoparticles covered with native oxides and embedded in a doped PbZrTiO3 ferroelectric matrix were studied. The nanocomposites studied were deposited by ion sputtering a complex target in a mixed Ar/O2 atmosphere followed by a 15-min annealing process (with steps of 25 K) in air in the temperature range of 398 K ≤ T a ≤ 573 K. The σ( f, T) of the annealed samples was measured in the temperature range of 77 K < T p < 373 K at frequencies of 50 Hz < f < 1 MHz. The observed σ( f, T) dependences confirmed that the annealed samples displayed the effects of negative capacitance over the whole frequency and temperature ranges studied because of the pronounced oxidation of the nanoparticles. The σ( f, T) dependences obtained are described using an earlier-developed AC hopping conductance model. Comparisons between experimental and simulation results allow the model parameters to be estimated, such as the activation energies of the hopping conductance and the lifetimes of the electrons in the nanoparticles.

  7. Electromagnetic fields and currents excited by dipoles normal to the conducting surface of dielectric loaded bodies of revolution

    NASA Astrophysics Data System (ADS)

    Ozzaim, Cengiz

    1999-12-01

    A modulated laser beam incident upon a conducting surface can cause electrons to be emitted in such a way that the resulting electromagnetic radiation is closely approximated by that from a distribution of electric dipoles normal to the surface. A major goal of this research has been to develop an understanding of the coupling of electromagnetic energy from the modulated laser light to objects and to the medium surrounding the object. Specific attention is focused upon coupling of the laser-induced electromagnetic field to structures which exhibit some of the characteristics of symmetric antennas. A method is presented for computing the signal caused by a modulated laser beam at a load impedance terminating a coaxial waveguide whose center conductor protrudes into a thin-wall cylindrical tube. The tube is open at one end and, on the other, it has a planar bottom through which the coax center conductor protrudes. Two case are treated: one in which the cavity is empty (free space) and a second in which it is partially filled with a dielectric insert. The excitation is the signal radiated by electrons emitted from the conducting surface by an impinging laser beam, modulated in such a way that the electrons at the surface oscillate harmonically in time. The computations are based on a procedure involving the formulation and numerical solution of integral equations plus utilization of the reciprocity theorem. A model was fabricated and experimental data were obtained to corroborate the results obtained from theory and numerical analysis. A similar analysis was conducted to determine the axial electric field at the focal point of the common parabolic reflector antenna illuminated by the laser-induced dipoles, but no experiments were performed in this case. It has been found that for the dipole excitation, penetration and coupling results are markedly different from those expected for more traditional excitations.

  8. A single-shot spatial chirp method for measuring initial AC conductivity evolution of femtosecond laser pulse excited warm dense matter

    SciTech Connect

    Chen, Z.; Hering, P.; Brown, S. B.; Curry, C.; Tsui, Y. Y.; Glenzer, S. H.

    2016-09-19

    To study the rapid evolution of AC conductivity from ultrafast laser excited warm dense matter (WDM), a spatial chirp single-shot method is developed utilizing a crossing angle pump-probe configuration. The pump beam is shaped individually in two spatial dimensions so that it can provide both sufficient laser intensity to excite the material to warm dense matter state and a uniform time window of up to 1 ps with sub-100 fs FWHM temporal resolution. Here, temporal evolution of AC conductivity in laser excited warm dense gold was also measured.

  9. A single-shot spatial chirp method for measuring initial AC conductivity evolution of femtosecond laser pulse excited warm dense matter.

    PubMed

    Chen, Z; Hering, P; Brown, S B; Curry, C; Tsui, Y Y; Glenzer, S H

    2016-11-01

    To study the rapid evolution of AC conductivity from ultrafast laser excited warm dense matter (WDM), a spatial chirp single-shot method is developed utilizing a crossing angle pump-probe configuration. The pump beam is shaped individually in two spatial dimensions so that it can provide both sufficient laser intensity to excite the material to warm dense matter state and a uniform time window of up to 1 ps with sub-100 fs FWHM temporal resolution. Temporal evolution of AC conductivity in laser excited warm dense gold was also measured.

  10. 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.

  11. Dielectric α-relaxation and ionic conductivity in propylene glycol and its oligomers measured at elevated pressure

    NASA Astrophysics Data System (ADS)

    Casalini, Riccardo; Roland, C. Michael

    2003-12-01

    Structural dynamics and volume were measured as a function of both temperature and pressure for a propylene glycol and its oligomers (PPG), and the results compared with previous data on higher molecular weight polypropylene glycols. PPG is of special interest because the terminal groups form hydrogen bonds; thus, by studying different molecular weights, the manner in which hydrogen bonding influences the dynamics in the supercooled regime can be systematically investigated. The fragility (Tg-normalized temperature dependence) of the dimer and trimer of PPG increases with pressure, similar to results for other H-bonded liquids, but different from van der Waals glass formers. This behavior is believed to be due to the effect of pressure in decreasing the extent of hydrogen bonding. From the combined temperature and volume dependences of the relaxation times, the relative degree to which thermal energy and volume govern the dynamics was quantified. With decreasing molecular weight, the relative contribution of thermal energy to the dynamics was found to strongly increase, reflecting the role of hydrogen bonding. By comparing the ionic conductivity and the dielectric relaxation times, a decoupling between rotational and translational motions was observed. Interestingly, this decoupling was independent of both pressure and molecular weight, indicating that hydrogen bonds have a negligible effect on the phenomenon.

  12. Electrical, optical and dielectric properties of HCl doped polyaniline nanorods

    NASA Astrophysics Data System (ADS)

    Chutia, P.; Kumar, A.

    2014-03-01

    In this report we have investigated the optical, electrical and dielectric properties of HCl doped polyaniline nanorods synthesized by the interfacial polymerization technique. High resolution transmission electron microscope (HRTEM) micrographs confirm the formation of nanorods. X-ray diffraction pattern shows the semicrystalline nature of polyaniline nanorods with a diameter distribution in the range of 10-22 nm. The chemical and electronic structures of the polyaniline nanorods are investigated by micro-Raman and UV-vis spectroscopy. Dielectric relaxation spectroscopy has been applied to study the dielectric permittivity, modulus formalism and ac conductivity as a function of frequency and temperature. The ac conductivity follows a power law with frequency. The variation of frequency exponent with temperature suggests that the correlated barrier hopping is the dominant charge transport mechanism. The existence of both polaron and bipolaron in the transport mechanism has been confirmed from the binding energy calculations.

  13. Thickness dependence of the dielectric properties of thermally evaporated Sb2Te3 thin films

    NASA Astrophysics Data System (ADS)

    Ulutas, K.; Deger, D.; Yakut, S.

    2013-03-01

    Sb2Te3 thin films of different thickness (23 - 350 nm) were prepared by thermal evaporation technique. The thickness dependence of the ac conductivity and dielectric properties of the Sb2Te3 films have been investigated in the frequency range 10 Hz- 100 kHz and within the temperature range 293-373K. Both the dielectric constant epsilon1 and dielectric loss factor epsilon2 were found to depend on frequency, temperature and film thickness. The frequency and temperature dependence of ac conductivityac(ω)) has also been determined. The ac conductivity of our samples satisfies the well known ac power law; i.e., σac(ω) propto ωs where s<1 and independent of the film thickness. The temperature dependence of ac conductivity and parameter s is reasonably well interpreted by the correlated barrier hopping (CBH) model. The activation energies were evaluated for various thicknesses. The temperature coefficient of the capacitance (TCC) and permitivity (TCP) were determined as a function of the film thickness. The microstructure of the samples were analyzed using X-ray diffraction (XRD). This results are discussed on the base of the differences in their morphologies and thicknesses. The tendency for amorphization of the crystalline phases becomes evident as the film thickness increases.

  14. Influence of n-type nickel ferrite in enhancing the AC conductivity of optimized polyaniline-nickel ferrite nanocomposite

    NASA Astrophysics Data System (ADS)

    Megha, R.; Ravikiran, Y. T.; Vijaya Kumari, S. C.; Thomas, S.

    2017-04-01

    In the present work, n-type nickel ferrite (NF) particles prepared by sol gel autocombustion method were used to synthesize optimized polyaniline-nickel ferrite (PANI-NF) nanocomposite by in situ polymerization method. Then, NF, PANI and the composite were structurally characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. Improved π-electron delocalization in PANI-NF composite as compared to that in PANI was confirmed from FTIR analysis. Interfacial interaction between PANI and NF was confirmed from XRD studies. Highly agglomerated, more densely packed particles of the composite facilitating easier charge transport were confirmed from SEM image. Transmission electron microscopy (TEM) image was analysed to calculate accurate average particle size of the composite by fitting the data to log-normal distribution function. Crystalline nature of the composite was confirmed from selected area electron diffraction (SAED) analysis. Remarkable increase in AC conductivity of the PANI-NF composite as compared to that of PANI due mainly to the formation of interfacial heterojunction barrier between p-type PANI and n-type NF was confirmed experimentally and well supported theoretically by calculating binding energy, hopping distance and density of states at Fermi level as per correlated barrier hopping (CBH) model.

  15. 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.

  16. Studies on frequency and gate voltage effects on the dielectric properties of Au/n-Si (110) structure with PVA-nickel acetate composite film interfacial layer

    NASA Astrophysics Data System (ADS)

    Tunç, T.; Gökçen, M.; Uslu, İ.

    2012-11-01

    The admittance technique was used in order to investigate the frequency dependence of dielectric constant ( ɛ'), dielectric loss ( ɛ″), dielectric loss tangent (tan δ), the ac electrical conductivity ( σ ac), and the electric modulus of PVA (Ni-doped) structure. Experimental results revealed that the values of ɛ' , ɛ″, (tan δ), σ ac and the electric modulus show fairly large frequency and gate bias dispersion due to the interface charges and polarization. The σ ac is found to increase with both increasing frequency and voltage. It can be concluded that the interface charges and interfacial polarization have strong influence on the dielectric properties of metal-polymer-semiconductor (MIS) structures especially at low frequencies and in depletion and accumulation regions. The results of this study indicate that the ɛ' values of Au/PVA/n-Si with Nickel-doped PVA interfacial layer are quite higher compared to those with pure and other dopant/mixture's of PVA.

  17. Effects of Ni{sup 3+} substitution on structural and temperature dependent dielectrical properties of NdFeO{sub 3}

    SciTech Connect

    Kaur, Pawanpreet Pandit, Rabia Sharma, K. K.; Kumar, Ravi

    2014-04-24

    The polycrystalline samples of NdFe{sub 1−x}Ni{sub x}O{sub 3} (x=0.0, 0.2) were prepared by solid state reaction route, the single phase of powdered samples were ensured by Rietveld refinement of their X-ray diffraction (XRD) data. We have also studied the variation of dielectric constant (ε′), tangent loss (tan δ) and AC conductivity (σ{sub ac}) as a function of frequency and temperature for both the compositions. It is noticed that both the increase in temperature and Ni{sup 3+} ion substitution results in enhancement of dielectric constant, tangent loss and AC conductivity.

  18. Mutation Glu82Lys in lamin A/C gene is associated with cardiomyopathy and conduction defect

    SciTech Connect

    Wang Hu; Wang Jizheng; Zheng Weiyue; Wang Xiaojian; Wang Shuxia; Song Lei; Zou Yubao; Yao Yan; Hui Rutai . E-mail: huirutai@sglab.org

    2006-05-26

    Dilated cardiomyopathy is a form of heart muscle disease characterized by impaired systolic function and ventricular dilation. The mutations in lamin A/C gene have been linked to dilated cardiomyopathy. We screened genetic mutations in a large Chinese family of 50 members including members with dilated cardiomyopathy and found a Glu82Lys substitution mutation in the rod domain of the lamin A/C protein in eight family members, three of them have been diagnosed as dilated cardiomyopathy, one presented with heart dilation. The pathogenic mechanism of lamin A/C gene defect is poorly understood. Glu82Lys mutated lamin A/C and wild type protein was transfected into HEK293 cells. The mutated protein was not properly localized at the inner nuclear membrane and the emerin protein, which interacts with lamin A/C, was also aberrantly distributed. The nuclear membrane structure was disrupted and heterochromatin was aggregated aberrantly in the nucleus of the HEK293 cells stably transfected with mutated lamin A/C gene as determined by transmission electron microscopy.

  19. Dielectric relaxation and anhydrous proton conduction in [C2H5NH3][Na0.5Fe0.5(HCOO)3] metal-organic frameworks.

    PubMed

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

    2017-03-14

    Metal-organic frameworks (MOFs), in which metal clusters are coupled by organic moieties, exhibit inherent porosity and crystallinity. Although these systems have been examined for vast potential applications, the elementary proton conduction in anhydrous MOFs still remains elusive. One of the approaches to deal with this problem is the utilization of protic organic molecules, to be accommodated in the porous framework. In this work we report the temperature-dependent crystal structure and proton conduction in [C2H5NH3][Na0.5Fe0.5(HCOO)3] metal-organic frameworks using X-ray diffraction and broadband dielectric spectroscopic techniques. The detailed analysis of the crystal structure reveals disorder of the terminal ethylene groups in the polar phase (space group Pn). The structural phase transition from Pn to P21/n at T ≈ 363 K involves the distortion of the metal formate framework and ordering of EtA(+) cations due to the reduction of the cell volume. The dielectric data have been presented in the dynamic window of permittivity formalism to understand the ferroelectric phase transition. The relaxation times have been estimated from the Kramers-Kronig transformation of the dielectric permittivity. A Grotthuss type mechanism of the proton conduction is possible at low temperatures with the activation energy of 0.23 eV. This type of experimental observation is expected to provide new prospective on the fundamental aspect of elementary proton transfer in anhydrous MOFs.

  20. Synthesis, characterization, and anomalous dielectric and conductivity performance of one-dimensional (bdaH)InSe{sub 2} (bda = 1,4-butanediamine)

    SciTech Connect

    Du, Ke-Zhao; Hu, Wan-Biao; Hu, Bing; Guan, Xiang-Feng; Huang, Xiao-Ying

    2011-11-15

    Graphical abstract: Anomalous dielectric and conductivity performance have been observed in the organic-containing indium selenide (bdaH)InSe{sub 2}, which are attributed to the water molecules existing in the crystal boundary rather than phase transition. Highlights: {yields} The title compound is the first example of organic-containing one-dimensional indium selenide. {yields} The anomalous dielectric peak is attributed to water molecules in crystal boundary. {yields} The inorganic and organic components of the title compound are connected via hydrogen bonding to form a supramolecular three-dimensional network. -- Abstract: A new indium selenide, namely (bdaH)InSe{sub 2} (1) (bda = 1,4-butanediamine) has been solvothermally synthesized and structurally characterized. It belongs to the non-centrosymmetric space group Fdd2. Its structure features an infinite one-dimensional anionic chain of [InSe{sub 2}]{sub n}{sup n-} with monoprotonated [bdaH]{sup +} as charge compensating cation. The organic [bdaH]{sup +} cations are joined into a supramolecular one-dimensional chain via N-H...N hydrogen bonding, which further interacts with the inorganic chain via N-H...Se and C-H...Se hydrogen bonding, forming a supramolecular three-dimensional network. Based on such a well-defined structure, the thermal stability, optical, conductivity, and dielectric properties were systematically investigated, showing that dielectric constant, as well as conductivity, had a hump at about 95 {sup o}C, which could be attributed to water molecules in the crystal boundary.

  1. Doping of a dielectric layer as a new alternative for increasing sensitivity of the contactless conductivity detection in microchips.

    PubMed

    Lima, Renato Sousa; Segato, Thiago Pinotti; Gobbi, Angelo Luiz; Coltro, Wendell Karlos Tomazelli; Carrilho, Emanuel

    2011-12-21

    This communication describes a new procedure to increase the sensitivity of C(4)D in PDMS/glass microchips. The method consists in doping the insulating layer (PDMS) over the electrodes with nanoparticles of TiO(2), increasing thus its dielectric constant. The experimental protocol is simple, inexpensive, and fast.

  2. Modification of the dielectric properties of copper-doped CdIn2S4 single crystal

    NASA Astrophysics Data System (ADS)

    Mustafaeva, S. N.; Asadov, M. M.; Guseynov, D. T.

    2014-02-01

    The study of the dielectric properties of a CdIn2S4<3 mol % Cu> single crystal in alternating-current (ac) electric fields with frequencies f = 5 × 104-3.5 × 107 Hz has revealed the origin of dielectric loss (relaxation loss that is changed by the through current loss at high frequencies). It has been found that CdIn2S4 has permittivity increment Δɛ' = 123, relaxation frequency f r = 2.3 × 104 Hz, and relaxation time τ = 43 μs. The doping of CdIn2S4 single crystal with copper (3 mol %) is established to substantially increase the permittivity (ɛ'), dielectric loss tangent (tanδ), and ac conductivityac). In this case, the frequency dispersion of ɛ' and tanδ increases and that of σac decreases.

  3. Ferromagnetic resonance and ac conductivity of a polymer composite of Fe3O4 and Fe3C nanoparticles dispersed in a graphite matrix

    NASA Astrophysics Data System (ADS)

    Guskos, N.; Anagnostakis, E. A.; Likodimos, V.; Bodziony, T.; Typek, J.; Maryniak, M.; Narkiewicz, U.; Kucharewicz, I.; Waplak, S.

    2005-01-01

    Ferromagnetic resonance (FMR) and ac conductivity have been applied to study a polymer composite containing as filler a binary mixture of magnetite (Fe3O4) and cementite (Fe3C) nanoparticles (30-50nm) dispersed in a diamagnetic carbon matrix, which was synthesized by the carburization of nanocrystalline iron. Ac conductivity measurements showed thermally activated behavior involving a range of activation energies and power law frequency dependence at high frequencies similar to conducting polymer composites randomly filled with metal particles. Ferromagnetic resonance measurements revealed a relatively narrow FMR line at high temperatures indicating the presence of ferromagnetic nanoparticles, where thermal fluctuations and interparticle interactions determine the FMR temperature variation. An abrupt change of the FMR spectra was observed at T <81K (ΔT⩽1K) coinciding with a sharp anomaly resolved in the temperature derivative of the ac conductivity. This behavior is attributed to the Verwey transition of Fe3O4 nanoparticles, where the concurrent skin depth variation unveils the FMR of large magnetite conglomerates and thus allows discriminating their contribution from relatively isolated nanoparticles.

  4. HfO{sub 2} dielectric thickness dependence of electrical properties in graphene field effect transistors with double conductance minima

    SciTech Connect

    Zhang, Cheng; Xie, Dan Xu, Jian-Long; Sun, Yi-Lin; Dai, Rui-Xuan; Li, Xian; Li, Xin-Ming; Zhu, Hong-Wei

    2015-10-14

    We investigate the electrical properties in back-gated graphene field effect transistors (GFETs) with SiO{sub 2} dielectric and different thickness of high-k HfO{sub 2} dielectric. The results show that transform characteristic (I{sub ds}–V{sub gs}) curves of GFETs are uniquely W-shaped with two charge neutrality point (left and right) in both SiO{sub 2} and HfO{sub 2} dielectric (SiO{sub 2}-GFETs and HfO{sub 2}-GFETs). The gate voltage reduces drastically in HfO{sub 2}-GFETs compared with that in SiO{sub 2}-GFETs, and it becomes much smaller with the decline of HfO{sub 2} thickness. The left charge neutrality point in I{sub d}–V{sub g} curves of all HfO{sub 2}-GFETs is negative, compared to the positive ones in SiO{sub 2}-GFETs, which means that there exists n-doping in graphene with HfO{sub 2} as bottom dielectric. We speculate that this n-doping comes from the HfO{sub 2} layer, which brings fixed charged impurities in close proximity to graphene. The carrier mobility is also researched, demonstrating a decreasing trend of hole mobility in HfO{sub 2}-GFETs contrast to that in SiO{sub 2}-GFETs. In a series of HfO{sub 2}-GFETs with different HfO{sub 2} dielectric thickness, the hole mobility shows a tendency of rise when the thickness decreases to 7 nm. The possible reason might be due to the introduced impurities into HfO{sub 2} film from atomic layer deposition process, the concentration of which varies from the thickness of HfO{sub 2} layer.

  5. Semicrystalline Structure-Dielectric Property Relationship and Electrical Conduction in a Biaxially Oriented Poly(vinylidene fluoride) Film under High Electric Fields and High Temperatures.

    PubMed

    Yang, Lianyun; Ho, Janet; Allahyarov, Elshad; Mu, Richard; Zhu, Lei

    2015-09-16

    Poly(vinylidene fluoride) (PVDF)-based homopolymers and copolymers are attractive for a broad range of electroactive applications because of their high dielectric constants. Especially, biaxially oriented PVDF (BOPVDF) films exhibit a DC breakdown strength as high as that for biaxially oriented polypropylene films. In this work, we revealed the molecular origin of the high dielectric constant via study of a commercial BOPVDF film. By determination of the dielectric constant for the amorphous phase in BOPVDF, a high value of ca. 21-22 at 25 °C was obtained, and a three-phase (i.e., lamellar crystal/oriented interphase/amorphous region) semicrystalline model was proposed to explain this result. Meanwhile, electronic conduction mechanisms in BOPVDF under high electric fields and elevated temperatures were investigated by thermally stimulated depolarization current (TSDC) spectroscopy and leakage current studies. Space charge injection from metal electrodes was identified as a major factor for electronic conduction when BOPVDF was poled above 75 °C and 20 MV/m. In addition, when silver or aluminum were used as electrodes, new ions were generated from electrochemical reactions under high fields. Due to the electrochemical reactions between PVDF and the metal electrode, a question is raised for practical electrical applications using PVDF and its copolymers under high-field and high-temperature conditions. A potential method to prevent electrochemical degradation of PVDF is proposed in this study.

  6. Dielectric spectroscopy of high aspect ratio graphene-polyurethane nanocomposites

    NASA Astrophysics Data System (ADS)

    Jan, Rahim; Habib, Amir; Abbassi, Hina; Amir, Shahid

    2015-03-01

    High aspect ratio graphene nanosheets (GNS), prepared via liquid exfoliation, are homogeneously dispersed in thermoplastic polyurethane (TPU). Dielectric spectroscopy results are reported for these nanocomposites (up to 0.55 vol. % GNS) in the frequency range of 100 Hz to 5 MHz. The as-prepared GNS increased the AC conductivity 10-1000 times across the given frequency range. The dielectric constant is increased 5-6 times at 100 Hz for the maximum loading of GNS when compared with the pristine TPU, with subsequently high dielectric loss making them a suitable candidate for high energy dissipation applications such as EMI shielding. The temperature effects on the dielectric characteristics of 0.55 vol. % GNS/TPU nanocomposites beyond 400 K are more pronounced due to the interfacial and orientation polarization. Mechanical characteristics evaluation of GNS/TPU composites shows a marked increase in the ultimate tensile strength without compromising their ductility and stiffness. [Figure not available: see fulltext.

  7. Cole-cole analysis and electrical conduction mechanism of N{sup +} implanted polycarbonate

    SciTech Connect

    Chawla, Mahak; Shekhawat, Nidhi; Aggarwal, Sanjeev Sharma, Annu; Nair, K. G. M.

    2014-05-14

    In this paper, we present the analysis of the dielectric (dielectric constant, dielectric loss, a.c. conductivity) and electrical properties (I–V characteristics) of pristine and nitrogen ion implanted polycarbonate. The samples of polycarbonate were implanted with 100 keV N{sup +} ions with fluence ranging from 1 × 10{sup 15} to 1 × 10{sup 17} ions cm{sup −2}. The dielectric measurements of these samples were performed in the frequency range of 100 kHz to 100 MHz. It has been observed that dielectric constant decreases whereas dielectric loss and a.c. conductivity increases with increasing ion fluence. An analysis of real and imaginary parts of dielectric permittivity has been elucidated using Cole-Cole plot of the complex permittivity. With the help of Cole-Cole plot, we determined the values of static dielectric constant (ε{sub s}), optical dielectric constant (ε{sub ∞}), spreading factor (α), average relaxation time (τ{sub 0}), and molecular relaxation time (τ). The I–V characteristics were studied using Keithley (6517) electrometer. The electrical conduction behaviour of pristine and implanted polycarbonate specimens has been explained using various models of conduction.

  8. Dielectric properties of nickel doped bismuth lithium borate glasses

    NASA Astrophysics Data System (ADS)

    Dalal, Seema; Dahiya, Sunita; Ashima, Khasa, S.

    2016-05-01

    Glasses with composition xBi2O3•(30-x)Li2O•70B2O3 (x = 0, 2, 5, 7 and 10 mol% with codes BLBN1-5 respectively) containing 2 mol% of NiO were prepared via melt-quenching technique and dielectric properties are discussed. The dielectric properties have been studied using impedance spectroscopy. The frequency dependent conductivity investigations for prepared compositions have been carried out using impedance spectroscopy over a frequency range of 1 KHz to 5 MHz and in the temperature range of 300K-523K. The complex impedance data have been analyzed by using both the conductivity and the electric modulus formalisms. Standard dielectric behavior is observed in prepared samples. The ac conductivity variations satisfy the Arrhenius relation. The study of the equivalent circuit analysis up to a temperature of 473K shows a significant change in the equivalent circuit with change in temperature and composition.

  9. Investigation on dielectric properties of atomic layer deposited Al{sub 2}O{sub 3} dielectric films

    SciTech Connect

    Yıldız, Dilber Esra; Yıldırım, Mert; Gökçen, Muharrem

    2014-05-15

    Al/Al{sub 2}O{sub 3}/p-Si Schottky barrier diodes (SBDs) were fabricated using atomic layer deposition technique in order to investigate dielectric properties of SBDs. For this purpose, admittance measurements were conducted at room temperature between −1 V and 3 V in the frequency range of 10 kHz and 1 MHz. In addition to the investigation of Al{sub 2}O{sub 3} morphology using atomic force microscope, dielectric parameters; such as dielectric constant (ε′), dielectric loss (ε″), dielectric loss tangent (tan δ), and real and imaginary parts of dielectric modulus (M′ and M″, respectively), were calculated and effect of frequency on these parameters of Al/Al{sub 2}O{sub 3}/p-Si SBDs was discussed. Variations in these parameters at low frequencies were associated with the effect of interface states in low frequency region. Besides dielectric parameters, ac electrical conductivity of these SBDs was also investigated.

  10. Electrical modulus and dielectric behavior of Cr3+ substituted Mg-Zn nanoferrites

    NASA Astrophysics Data System (ADS)

    Mansour, S. F.; Abdo, M. A.

    2017-04-01

    The dielectric parameters and ac electrical conductivity of Mg0.8Zn0.2CrxFe2-xO4; (0≤x≤0.025) nanoferrites synthesized citrate-nitrate auto-combustion method were studied using the complex impedance technique in the frequency and temperature ranges 4 Hz-5 MHz and 303-873 K respectively. Hopping of charge carriers plus interfacial polarization could interpret the behaviors of dielectric constant (ε‧), dielectric loss tangent (tanδ) and ac electrical conductivityac) with frequency, temperatures and composition. The up-normal behavior observed in tanδ trend with temperatures confirms the presence of relaxation loss (dipoles losses). Correlated barrier hopping (CBH) of electron is the conduction mechanism of the investigated nanoferrites. Cole-Cole plots at different temperatures emphasize the main role of grain and grain boundaries in the properties of the investigated nanoferrites. Cr3+ substitution can control the dielectric parameters and ac electrical conductivity of Mg-Zn nanoferrites making it candidates for versatile applications.

  11. Antenna with Dielectric Having Geometric Patterns

    NASA Technical Reports Server (NTRS)

    Dudley, Kenneth L. (Inventor); Elliott, Holly A. (Inventor); Cravey, Robin L. (Inventor); Connell, John W. (Inventor); Ghose, Sayata (Inventor); Watson, Kent A. (Inventor); Smith, Jr., Joseph G. (Inventor)

    2013-01-01

    An antenna includes a ground plane, a dielectric disposed on the ground plane, and an electrically-conductive radiator disposed on the dielectric. The dielectric includes at least one layer of a first dielectric material and a second dielectric material that collectively define a dielectric geometric pattern, which may comprise a fractal geometry. The radiator defines a radiator geometric pattern, and the dielectric geometric pattern is geometrically identical, or substantially geometrically identical, to the radiator geometric pattern.

  12. Investigations on spectral and dielectric properties of semi-organic single crystal – morpholinium nitrate

    SciTech Connect

    Arul, H.; Babu, D. Rajan Vizhi, R. Ezhil

    2015-06-24

    Semi organic nonlinear optical crystal Morpholinium nitrate (MN) was synthesized and subsequently grown from the solution by slow evaporation method. The sample has been subjected to powder X-ray diffraction to identify the crystalline nature and the prominent peaks were indexed. The crystal belongs to the monoclinic system with a space group P2{sub 1}/C. Carbon NMR analysis confirms the presence of carbon in the structure of the title compound. Dielectric studies have been carried out on the grown crystal as a function of frequencies at different temperatures. Dielectric constant, dielectric loss and AC conductivity were also calculated.

  13. TM surface wave diffraction by a truncated dielectric slab recessed in a perfectly conducting surface. [considering flush mounted space shuttle antenna

    NASA Technical Reports Server (NTRS)

    Pathak, P. H.; Kouyoumjian, R. G.

    1974-01-01

    The diffraction of a TM sub o surface wave by a terminated dielectric slab which is flush mounted in a perfectly conducting surface is studied. The incident surface wave gives rise to waves reflected and diffracted by the termination; these reflected and diffracted fields may be expressed in terms of the geometrical theory of diffraction by introducing surface wave reflection and diffraction coefficients which are associated with the termination. In this investigation, the surface wave reflection and diffraction coefficients have been deduced from a formally exact solution to this canonical problem. The solution is obtained by a combination of the generalized scattering matrix technique and function theoretic methods.

  14. Effect of conducting polymer poly (3,4-ethylenedioxythiophene) (PEDOT) nanotubes on electro-optical and dielectric properties of a ferroelectric liquid crystal.

    PubMed

    Ghosh, S; Nayek, P; Roy, S K; Gangopadhyay, R; Rahaman Molla, M; Majumder, T P

    2011-04-01

    A detailed comparative study of the dielectric and electro-optical properties of a ferroelectric liquid crystal (FLC) and FLC after having doped with conducting polymer Poly (3,4-ethylenedioxythiophene) (PEDOT) nanotubes is done. The electro-optic study reveals a lower electrical response time, rotational viscosity and spontaneous polarization in the FLC/PEDOT nanocomposite system. By fitting the capacitance with voltage in a Preisach model, four dipolar species in both FLC and composites system have been obtained. The orientation of the four dipolar species in the composites system is such that the effective dipole moment in the transverse direction of the FLC molecule is less than that in FLC compound.

  15. Dielectric properties and alternating current conductivity of sol-gel made La0.8Ca0.2FeO3 compound

    NASA Astrophysics Data System (ADS)

    Benali, A.; Souissi, A.; Bejar, M.; Dhahri, E.; Graça, M. F. P.; Valente, M. A.

    2015-09-01

    In this work, single phase La0.8Ca0.2FeO3 nanomaterial has been synthesized by the sol-gel method using the citric acid route. By employing impedance spectroscopy, ac electrical properties have been measured over a temperature range from 300 to 673 K at various frequencies. With the analysis based on Debye's theory and a series of Arrhenius relations, the relaxation was argued to be associated with the hopping motions of charge carriers between Fe ions. The relaxation in the La0.8Ca0.2FeO3 compound was ascribed to be a polaronic relaxation. The ac electrical conduction was studied and associated to the non-overlapping small polaron tunneling (NSPT) model.

  16. 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.

  17. Dielectric Performance of a High Purity HTCC Alumina at High Temperatures - a Comparison Study with Other Polycrystalline Alumina

    NASA Technical Reports Server (NTRS)

    Chen, Liangyu

    2014-01-01

    A very high purity (99.99+%) high temperature co-fired ceramic (HTCC) alumina has recently become commercially available. The raw material of this HTCC alumina is very different from conventional HTCC alumina, and more importantly there is no glass additive in this alumina material for co-firing processing. Previously, selected HTCC and LTCC (low temperature co-fired ceramic) alumina materials were evaluated at high temperatures as dielectric and compared to a regularly sintered 96% polycrystalline alumina (96% Al2O3), where 96% alumina was used as the benchmark. A prototype packaging system based on regular 96% alumina with Au thickfilm metallization successfully facilitated long term testing of high temperature silicon carbide (SiC) electronic devices for over 10,000 hours at 500 C. In order to evaluate this new high purity HTCC alumina for possible high temperature packaging applications, the dielectric properties of this HTCC alumina substrate were measured and compared with those of 96% alumina and a previously tested LTCC alumina from room temperature to 550 C at frequencies of 120 Hz, 1 KHz, 10 KHz, 100 KHz, and 1 MHz. A parallel-plate capacitive device with dielectric of the HTCC alumina and precious metal electrodes were used for measurements of the dielectric constant and dielectric loss of the co-fired alumina material in the temperature and frequency ranges. The capacitance and AC parallel conductance of the capacitive device were directly measured by an AC impedance meter, and the dielectric constant and parallel AC conductivity of the dielectric were calculated from the capacitance and conductance measurement results. The temperature and frequency dependent dielectric constant, AC conductivity, and dissipation factor of the HTCC alumina substrate are presented and compared to those of 96% alumina and a selected LTCC alumina. Other technical advantages of this new co-fired material for possible high packaging applications are also discussed.

  18. Dielectric Performance of High Purity HTCC Alumina at High Temperatures - A Comparison Study with Other Polycrystalline Alumina

    NASA Technical Reports Server (NTRS)

    Chen, Liang-Yu

    2012-01-01

    A very high purity (99.99+) high temperature co-fired ceramic (HTCC) alumina has recently become commercially available. The raw material of this HTCC alumina is very different from conventional HTCC alumina, and more importantly there is no glass additive in this co-fired material. Previously, selected HTCC and LTCC (low temperature co-fired ceramic) alumina materials were evaluated at high temperatures as dielectric and compared to a regularly sintered 96 polycrystalline alumina (96 Al2O3), where 96 alumina was used as the benchmark. A prototype packaging system based on regular 96 alumina with Au thick-film metallization successfully facilitated long term testing of high temperature silicon carbide (SiC) electronic devices for over 10,000 hours at 500C. In order to evaluate this new HTCC alumina for possible high temperature packaging applications, the dielectric properties of this HTCC alumina substrate were measured and compared with those of 96 alumina and a LTCC alumina from room temperature to 550C at frequencies of 120 Hz, 1 KHz, 10 KHz, 100 KHz, and 1 MHz. A parallel-plate capacitive device with dielectric of the HTCC alumina and precious metal electrodes were used for measurements of the dielectric constant and dielectric loss of the co-fired alumina material in the temperature and frequency ranges. The capacitance and AC parallel conductance of the capacitive device were directly measured by an AC impedance meter, and the dielectric constant and parallel AC conductivity of the dielectric were calculated from the capacitance and conductance measurement results. The temperature and frequency dependent dielectric constant, AC conductivity, and dissipation factor of the HTCC alumina substrate are presented and compared to those of 96 alumina. Other technical advantages of this new co-fired material for possible high packaging applications are also discussed.

  19. Polyaniline coated cellulose fiber / polyvinyl alcohol composites with high dielectric permittivity and low percolation threshold

    NASA Astrophysics Data System (ADS)

    Anju, V. P.; Narayanankutty, Sunil K.

    2016-01-01

    Cost effective, high performance dielectric composites based on polyvinyl alcohol, cellulose fibers and polyaniline were prepared and the dielectric properties were studied as a function of fiber content, fiber dimensions and polyaniline content over a frequency range of 40 Hz to 30 MHz. The short cellulose fibers were size-reduced to micro and nano levels prior to coating with polyaniline. Fiber surface was coated with Polyaniline (PANI) by an in situ polymerization technique in aqueous medium. The composites were then prepared by solution casting method. Short cellulose fiber composites showed a dielectric constant (DEC) of 2.3 x 105 at 40 Hz. For the micro- and nano- cellulose fiber composites the DEC was increased to 4.5 x 105 and 1.3 x 108, respectively. To gain insight into the inflection point of the dielectric data polynomial regression analysis was carried out. The loss tangent of all the composites remained at less than 1.5. Further, AC conductivity, real and imaginary electric moduli of all the composites were evaluated. PVA nanocomposite attained an AC conductivity of 3 S/m. These showed that by controlling the size of the fiber used, it was possible to tune the permittivity and dielectric loss to desired values over a wide range. These novel nanocomposites, combining high dielectric constant and low dielectric loss, can be effectively used in applications such as high-charge storage capacitors.

  20. Synthesis, dielectric behavior and impedance measurement studies of Cr-substituted Zn-Mn ferrites

    SciTech Connect

    Hankare, P.P.; Patil, R.P.; Garadkar, K.M.; Sasikala, R.; Chougule, B.K.

    2011-03-15

    Graphical abstract: Variation of dielectric constant with frequency. Research highlights: {yields} Sol-gel route synthesized spherical crystalline nanoparticles of ZnMn{sub 1-x}Cr{sub x}FeO{sub 4}. {yields} XRD, DTA, FTIR, SEM, dielectric and impedance study. {yields} The ferrites show concentration dependence of ac electrical conductivity. {yields} Impedance response is dominated by grain boundary behavior. -- Abstract: Nanocrystalline ZnMn{sub 1-x}Cr{sub x}FeO{sub 4} (1.0 {>=} x {>=} 0) ferrites were synthesized by sol-gel technique. X-ray diffraction (XRD) confirmed the formation of single phasic cubic spinel lattice for all the compositions studied. Lattice parameter shows a decreasing trend with an increase in Cr content in the compositions. Formation of spherical nanoparticles was revealed by scanning electron microscopy (SEM) analysis. Infrared spectroscopic studies revealed two main absorption bands in the range 400-800 cm{sup -1} arising due to tetrahedral (A) and octahedral (B) site vibrations. Dielectric constant, dielectric loss tangent, ac conductivity and complex impedance were measured as a function of frequency in the range 20 Hz to 1 MHz. Frequency dependence of dielectric constant shows dielectric dispersion due to the Maxwell-Wagner type of interfacial polarization. The role of chromium in modifying structural and dielectric properties of these ferrites has been explained.

  1. Dielectric relaxation spectroscopy of phlogopite mica

    NASA Astrophysics Data System (ADS)

    Kaur, Navjeet; Singh, Mohan; Singh, Anupinder; Awasthi, A. M.; Singh, Lakhwant

    2012-11-01

    An in-depth investigation of the dielectric characteristics of annealed phlogopite mica has been conducted in the frequency range 0.1 Hz-10 MHz and over the temperature range 653-873 K through the framework of dielectric permittivity, electric modulus and conductivity formalisms. These formalisms show qualitative similarities in relaxation processes. The frequency dependence of the M″ and dc conductivity is found to obey an Arrhenius law and the activation energy of the phlogopite mica calculated both from dc conductivity and the modulus spectrum is similar, indicating that same type of charge carriers are involved in the relaxation phenomena. The electric modulus and conductivity data have been fitted with the Havriliak-Negami function. Scaling of M‧, M″, ac conductivity has also been performed in order to obtain insight into the relaxation mechanisms. The scaling behaviour indicates that the relaxation describes the same mechanism at different temperatures. The relaxation mechanism was also examined using the Cole-Cole approach. The study elaborates that the investigation regarding the temperature and frequency dependence of dielectric relaxation in the phlogopite mica will be helpful for various cutting edge applications of this material in electrical engineering.

  2. Study of low weight percentage filler on dielectric properties of MCWNT-epoxy nanocomposites

    NASA Astrophysics Data System (ADS)

    Trihotri, Manindra; Dwivedi, U. K.; Malik, M. M.; Khan, Fozia Haque; Qureshi, M. S.

    2016-09-01

    An attempt is made to study the effect of low weight percentage multiwall carbon nanotube (MWCNT) powder on dielectric properties of MWCNT reinforced epoxy composites. For that MWCNT (of different low weight percentage) reinforced epoxy composite was prepared by dispersing the MWCNT in resin. Samples were prepared by solution casting process and characterized for their dielectric properties such as dielectric constant (ɛ‧), dielectric dissipation factor (tan δ) and AC conductivityac). The main objective is the investigation of the dielectric properties of the prepared samples at the low weight percentage of the filler at different temperatures and frequencies. From the two mechanisms of electrical conduction, first the leakage current obtained by the formation of a percolation network in the matrix and the other by tunneling of electrons formed among conductors nearby (tunneling current); here we are getting conduction by the second mechanism. Generally, leakage current makes more contribution to conductivity than tunneling current. Dielectric dissipation factor at 250Hz frequency is greater than all other frequencies and starts increasing from 60∘C. The peak height of the transition temperature decreases with increasing frequency. This study shows that the addition of a low weight percentage of MWCNT can modify considerably the electrical behavior of epoxy nanocomposites without chemical functionalization of filler.

  3. AC Electrical Conduction of Cr-Doped SrTiO3 Thin Films with an Oxygen-Deficient Interface Layer

    NASA Astrophysics Data System (ADS)

    Phan, Bach Thang; Eom, Ki Tae; Lee, Jaichan

    2017-01-01

    The ac electrical conduction of Cr-doped SrTiO3 thin films with an oxygen-deficient interface layer was investigated as a function of temperature and frequency. The Cr-doped SrTiO3 (Cr-STO) thin films with an ultra-thin (˜2 nm) oxygen-deficient layer inserted between the top electrode and the Cr-STO layer exhibited two ac conduction mechanisms, i.e., variable-range hopping and small-polaron hopping conduction, accompanied by a relaxation process. Since high oxygen deficiency induces large lattice distortion in the depletion layer, the first relaxation process occurs at low frequencies in the thin oxygen depletion layer Cr-SrTiO3-δ , and the corresponding conduction behavior follows the small-polaron tunneling model. In the high frequency range, an additional relaxation process is involved and is associated with the variable-range hopping between the localized states in the band gap of the thick Cr-SrTiO3 layer.

  4. Electrical conductivity of polyazomethine/fullerene C60 nanocomposites

    NASA Astrophysics Data System (ADS)

    Bronnikov, Sergei; Podshivalov, Aleksandr; Kostromin, Sergei; Asandulesa, Mihai; Cozan, Vasile

    2017-02-01

    We prepared the polyazomethine/fullerene C60 nanocomposites varying in C60 loading. With a broadband dielectric relaxation spectrometer, we measured their electrical conductivity σm being a sum of dc conductivity σdc and ac conductivity σac. A small C60 content (0.25 and 0.5 wt.%) was shown to decrease σdc, whereas a larger amount of C60 (2.5 wt.%) was found to increase σdc of the nanocomposite. The temperature dependences of σac were described with the Arrhenius equation, while the frequency dependences of σac were characterized with a power function. The correlated barrier hopping was accepted as the most suitable mechanism to explain the σac behavior of the nanocomposites.

  5. Comparison effects and dielectric properties of different dose methylene-blue-doped hydrogels.

    PubMed

    Yalçın, O; Coşkun, R; Okutan, M; Öztürk, M

    2013-08-01

    The dielectric properties of methylene blue (MB)-doped hydrogels were investigated by impedance spectroscopy. The real part (ε') and the imaginary part (ε") of the complex dielectric constant and the energy loss tangent/dissipation factor (tan δ) were measured in the frequency range of 10 Hz to 100 MHz at room temperature for pH 5.5 value. Frequency variations of the resistance, the reactance, and the impedance of the samples have also been investigated. The dielectric permittivity of the MB-doped hydrogels is sensitive to ionic conduction and electrode polarization in low frequency. Furthermore, the dielectric behavior in high-frequency parts was attributed to the Brownian motion of the hydrogen bonds. The ionic conduction for MB-doped samples was prevented for Cole-Cole plots, while the Cole-Cole plots for pure sample show equivalent electrical circuit. The alternative current (ac) conductivity increases with the increasing MB concentration and the frequency.

  6. A study of thermal, dielectric and magnetic properties of strontium malonate crystals

    NASA Astrophysics Data System (ADS)

    Mathew, Varghese; Jacob, Sabu; Mahadevan, C. K.; Abraham, K. E.

    2012-01-01

    Crystals of strontium malonate (SrC 3H 2O 4) were grown in silica gel by the single diffusion technique. The thermo gravimetric (TG), differential thermal analysis (DTA) and differential scanning calorimetric (DSC) studies were carried out to investigate the thermal stability of the crystal. The dielectric behavior of the title compound crystal was investigated by measuring the dielectric parameters - dielectric constant, dielectric loss and AC conductivity as a function of four frequencies -1 kHz, 10 kHz, 100 kHz and 1 MHz at temperatures ranging from 50 to 170 °C. Results indicate that the title compound is thermally stable up to about 409 °C and is a promising low εr-value dielectric material. The magnetic behavior of the crystal was also explored using a vibrating sample magnetometer.

  7. Heat treatment effects on dielectric properties of SRFe{sub 12}O{sub 19} hexaferrite prepared by an SHS route

    SciTech Connect

    Panchal, Nital R.; Jotania, Rajshree B. E-mail: rbjotania@gmail.com

    2011-07-01

    The M-type Strontium Hexaferrite SRFe{sub 12}O{sub 19} particles were prepared by a Self propagating High temperature Synthesis (SHS) route. Precursors were heated under two different conditions: microwave heating for 30 minutes and sintered at 950 deg C for 4 hrs. The dielectric properties: dielectric constant ({epsilon}{sup '}), dielectric loss (tan {delta} ) and ac conductivity ({sigma}{sub ac}) were measured at room temperature in the frequency range from 100 Hz to 2 MHz. The samples present a non-linear behavior for the dielectric constant at 1 kHz, 100 kHz and 2 MHz. The dielectric properties of prepared Strontium Hexaferrite samples were discussed in view of applications as a material for microwave devices, permanent magnets and high density magnetic recording media. (author)

  8. Inductive dielectric analyzer

    NASA Astrophysics Data System (ADS)

    Agranovich, Daniel; Polygalov, Eugene; Popov, Ivan; Ben Ishai, Paul; Feldman, Yuri

    2017-03-01

    One of the approaches to bypass the problem of electrode polarization in dielectric measurements is the free electrode method. The advantage of this technique is that, the probing electric field in the material is not supplied by contact electrodes, but rather by electromagnetic induction. We have designed an inductive dielectric analyzer based on a sensor comprising two concentric toroidal coils. In this work, we present an analytic derivation of the relationship between the impedance measured by the sensor and the complex dielectric permittivity of the sample. The obtained relationship was successfully employed to measure the dielectric permittivity and conductivity of various alcohols and aqueous salt solutions.

  9. A METHOD OF OBTAINING AN ELECTRIC CONDUCTING LAYER ON THE SURFACE OF DIELECTRICS (SPOSOB POLUCHENIYA NA POVERKHNOSTI DIELEKTRIKOV ELEKTROPROVODYASHCHEGO SLOYA),

    DTIC Science & Technology

    oxide film on the copper surface thereby lowering the conductivity of the covering. In the method proposed here a layer of copper selenide is...the technology of the treatment and improves the quality of the covering. Electric conducting layers of copper selenide can be used to produce

  10. An atomically detailed description of metal-dielectric interfaces: The crossover from surface to bulk conducting properties of Ag-Xe

    NASA Astrophysics Data System (ADS)

    Shah, Vaishali; Bowen, H. F.; Space, Brian

    2000-06-01

    An atomically detailed simulation method designed to be efficacious for modeling conduction properties of closed shell atoms or molecules resident at interfaces that was developed earlier is applied to a metal-dielectric interface of Ag-Xe. The effective mass of conduction electrons resident at Ag-Xe interfaces as a function of the number of layers of xenon present has been measured experimentally by the Harris group [J. D. McNeill, R. L. Lingle, Jr., R. E. Jordan, D. F. Padowitz, and C. B. Harris, J. Chem. Phys. 105, 3883 (1996)]. Here a simple yet effective theoretical model of the interface is developed and the effective mass that results is in quantitative agreement with the empirical measurements. The effective mass of a conduction electron is calculated by solving the Schrödinger-Bloch equation using Lanczos grid methods to obtain the Bloch wave vector (k) dependent energies. The metal is treated as a continuum within the effective mass approximation for the purpose of calculating the eigenenergies. To model the explicit potential energy functions, the electron-atom interaction is taken as a local pseudopotential that is fit to simultaneously reproduce the experimentally measured gas phase s-, p-, and d-wave scattering phase shifts. In simulating the interfacial environment the potential energy interaction between the electron and xenon atoms is modified to account for many-body polarization effects. This approach shows promise in modeling the conduction properties of more complex interfacial environments, including those of technological interest.

  11. Synergetic effect of TiO2 nano filler additives on conductivity and dielectric properties of PEO/PVP nanocomposite electrolytes for electrochemical cell applications

    NASA Astrophysics Data System (ADS)

    Koduru, H. K.; Kondamareddy, K. K.; Iliev, M. T.; Marinov, Y. G.; Hadjichristov, G. B.; Karashanova, D.; Scaramuzza, N.

    2017-01-01

    Sodium-ion conducting PEO/PVP blend based solid polymer electrolyte films complexed with NaIO4 salt and nano-sized TiO2 fillers are fabricated by employing a solution casting technique for Na-ion battery applications. Measurements of X-ray diffraction (XRD) and thermogravimetric analysis (TGA) are carried out to investigate the crystallinity and thermal stability of the solid polymer electrolytes. Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) studies are performed to understand the modifications in surface morphological features and to evaluate the size and distribution of dispersed nano-sized TiO2 fillers. The room temperature ionic conductivities of polymer electrolyte films are investigated by impedance analysis in the frequency range 1 MHz - 1 Hz. The nano-sized TiO2 (3 wt%) filled composite electrolyte of ‘PEO/PVP/NaIO4 (10 wt%)’ demonstrates a maximum room temperature conductivity of 9.82 X 10-6 S/cm. The influence of TiO2 filler on conductivity and dielectric properties are presented in this report.

  12. Dielectric and impedance behavior of neodymium substituted strontium hexaferrite

    NASA Astrophysics Data System (ADS)

    Bhat, Bilal Hamid; Samad, Rubiya; Want, Basharat

    2016-09-01

    In this study, dielectric behavior and complex impedance of neodymium (Nd) substituted strontium hexaferrite system: Sr1- x Nd x Fe12O19 ( x = 0.0, 0.05, 0.1, 0.15, 0. 20), synthesized by citrate precursor technique, have been evaluated as a function of applied frequency and temperature. Variation of dielectric constant and dielectric loss with frequency shows the identical behavior for all the compositions. The value of dielectric constant increases with Nd doping. Relaxation process is observed in the composition x = 0.20, and the peaks in this composition shift toward the higher-frequency region as the temperature increases. The dielectric constants show temperature-independent behavior at low temperature, whereas at higher temperatures it increases for all the frequencies. The AC conductivity follows Jonscher's power law, showing that conduction mechanism is due to polaron hopping. Complex impedance as a function of composition and temperature is used to examine the role of grain and grain boundary in the prepared material. Cole-cole plot shows only one semicircle up to x = 0.15, while as for x = 0.20 two semicircles are observed. The conduction mechanism is explained on the basis of both grain and grain boundary.

  13. Structure and dielectric behavior of TlSbS2

    NASA Astrophysics Data System (ADS)

    Parto, M.; Deger, D.; Ulutas, K.; Yakut, Ş.

    2013-09-01

    A comparison of structure and dielectric properties of TlSbS2 thin films, deposited in different thicknesses (400-4100 Å) by thermal evaporation of TlSbS2 crystals that were grown by the Stockbarger-Bridgman technique and the bulk material properties of TlSbS2 are presented. Dielectric constant ɛ 1 and dielectric loss ɛ 2 have been calculated by measuring capacitance and dielectric loss factor in the frequency range 20 Hz-10 KHz and in the temperature range 273-433 K. It is observed that at 1 kHz frequency and 293 K temperature the dielectric constant of TlSbS2 thin films is ɛ 1=1.8-6 and the dielectric loss of TlSbS2 thin films is ɛ 2=0.5-3 depending on film thickness. In the given intervals, both of dielectric constant and dielectric loss decrease with frequency, but increase with temperature. The maximum barrier height W m is calculated from the dielectric measurements. The values of W m for TlSbS2 films and bulk are obtained as 0.56 eV and 0.62 eV at room temperature, respectively. The obtained values agree with those proposed by the theory of hopping over the potential barrier. The temperature variation of ac conductivity can be reasonably interpreted in terms of the correlated barrier hopping model since it obeys the ω s law with a temperature dependent s ( s<1) and going down as the temperature is increased. The temperature coefficient of capacitance (TCC) and permittivity (TCP) are evaluated for both thin films and bulk material of TlSbS2.

  14. Electrode effects in dielectric spectroscopy measurements on (Nb +In) co-doped TiO2

    NASA Astrophysics Data System (ADS)

    Crandles, David; Yee, Susan; Savinov, Maxim; Nuzhnyy, Dimitri; Petzelt, Jan; Kamba, Stanislav; Prokes, Jan

    Recently, several papers reported the discovery of giant permittivity and low dielectric loss in (Nb+In) co-doped TiO2. A series of tests was performed which included the measurement of the frequency dependence of the dielectric permittivity and ac conductivity of co-doped (Nb+In)TiO2 as a function of electrode type, sample thickness and temperature. The data suggest that the measurements are strongly affected by the electrodes. The consistency between four contact van der Pauw dc conductivity measurements and bulk conductivity values extracted from two contact ac conductivity measurements suggest that the values of colossal permittivity are, at least in part, a result of Schottky barrier depletion widths that depend on electrode type and temperature. Nserc, Czech Science Foundation (Project 15-08389S).

  15. Nearly constant dielectric loss behavior in poly(3-hydroxybutyrate-co-3-hydroxyvalerate) biodegradable polyester

    NASA Astrophysics Data System (ADS)

    Ke, Shanming; Huang, Haitao; Ren, Li; Wang, Yingjun

    2009-05-01

    The measurement of dielectric spectroscopy over a broad frequency range of 0.01-107 Hz has been conducted to examine the segmental motions in poly[3-hydroxybutyrate-co-3-hydroxyvalerate] (PHBV) biopolymers. The ac conductivity at either low temperatures or high frequencies is almost temperature independent, indicating clearly that the nearly constant loss (NCL) phenomenon also takes place in polymers. The respective data were analyzed by adding a NCL term to the Jonscher relation. NCL in PHBV is discussed to be originated from the vibrational motion model. PHBV may have potential application as a biodegradable dielectric material.

  16. Low-temperature AC conductivity of Bi 2Sr 2CaCu 2O 8+ δ

    NASA Astrophysics Data System (ADS)

    Corson, J.; Orenstein, J.; Eckstein, J. N.; Bozovic, I.

    2000-05-01

    We report measurements of anamolously large dissipative conductivities, σ1, in Bi 2Sr 2CaCu 2O 8+ δ at low temperatures. We have measured the complex conductivity of Bi 2Sr 2CaCu 2O 8+ δ thin films at 100-600 GHz as a function of doping from the underdoped to the overdoped state. At low temperatures there exists a residual σ1 which scales with the T=0 superfluid density as the doping is varied. This residual σ1 is larger than the possible contribution to σ1 from a thermal population of quasiparticles (QP) at the d-wave gap nodes.

  17. Powder XRD and dielectric studies of gel grown calcium pyrophosphate crystals

    NASA Astrophysics Data System (ADS)

    Parekh, Bharat; Parikh, Ketan; Joshi, Mihir

    2013-06-01

    Formation of calcium pyrophosphate dihydrate (CPPD) crystals in soft tissues such as cartilage, meniscus and synovial tissue leads to CPPD deposition diseases. The appearance of these crystals in the synovial fluid can give rise to an acute arthritic attack with pain and inflammation of the joints, a condition called pseudo-gout. The growth of CPP crystals has been carried out, in the present study, using the single diffusion gel growth technique, which can broadly mimic in vitro the condition in soft tissues. The crystals were characterized by different techniques. The FTIR study revealed the presence of various functional groups. Powder XRD study was also carried out to verify the crystal structure. The dielectric study was carried out at room temperature by applying field of different frequency from 500 Hz to 1 MHz. The dielectric constant, dielectric loss and a.c. resistivity decreased as frequency increased, whereas the a.c. conductivity increased as frequency increased.

  18. A comparative study of nano-SiO2 and nano-TiO2 fillers on proton conductivity and dielectric response of a silicotungstic acid-H3PO4-poly(vinyl alcohol) polymer electrolyte.

    PubMed

    Gao, Han; Lian, Keryn

    2014-01-08

    The effects of nano-SiO2 and nano-TiO2 fillers on a thin film silicotungstic acid (SiWA)-H3PO4-poly(vinyl alcohol) (PVA) proton conducting polymer electrolyte were studied and compared with respect to their proton conductivity, environmental stability, and dielectric properties, across a temperature range from 243 to 323 K. Three major effects of these fillers have been identified: (a) barrier effect; (b) intrinsic dielectric constant effect; and (c) water retention effect. Dielectric analyses were used to differentiate these effects on polymer electrolyte-enabled capacitors. Capacitor performance was correlated to electrolyte properties through dielectric constant and dielectric loss spectra. Using a single-ion approach, proton density and proton mobility of each polymer electrolyte were derived as a function of temperature. The results allow us to deconvolute the different contributions to proton conductivity in SiWA-H3PO4-PVA-based electrolytes, especially in terms of the effects of fillers on the dynamic equilibrium of free protons and protonated water in the electrolytes.

  19. Synthesis, crystal structure, NMR study and AC conductivity of [(C3H7)4N]2Cd2ClF5 compound

    NASA Astrophysics Data System (ADS)

    Hajji, Rachid; Oueslati, Abderrazak; Body, Monique; Hlel, Faouzi

    2015-08-01

    The [(C3H7)4N]2Cd2ClF5 compound was crystallized in the triclinic system with space group P1. The crystal structure consists of organic-inorganic layers, stacked along direction. The organic part consists of two cations types. The inorganic layer is made up of Cd2ClF5 dimmers composed of two in-equivalent irregular tetrahedra sharing one edge (Cl-F). The MAS NMR spectra showed two, three and five isotropic resonances relative to 111Cd, 13C and 19F nuclei, respectively. DSC measurement disclosed a phase transition at around 380 K. The impedance spectroscopy and AC electrical conductivity measurements of our compound were taken from 209 Hz to 5 MHz over the temperature range of 350-381 K. Nyquist plots ( Z″ vs Z') show semicircle arcs at different temperatures, and an electrical equivalent circuit has been proposed to explain the impedance results. The circuits consist of the parallel combination of bulk resistance ( R), capacitance ( C) and fractal capacitance (CPE). The conductivity σ p follows the Arrhenius relation. The near value of activation energies obtained from the conductivity data and circuit equivalent confirms that the transport is through hopping mechanism. The analysis of the experimental data shows that the reorientation motion of [N(C3H7)4]+ cations and/or [Cd2ClF5]2- anions is probably responsible for the observed conductivity.

  20. AC impedance analysis of ionic and electronic conductivities in electrode mixture layers for an all-solid-state lithium-ion battery

    NASA Astrophysics Data System (ADS)

    Siroma, Zyun; Sato, Tomohiro; Takeuchi, Tomonari; Nagai, Ryo; Ota, Akira; Ioroi, Tsutomu

    2016-06-01

    The ionic and electronic effective conductivities of an electrode mixture layers for all-solid-state lithium-ion batteries containing Li2Ssbnd P2S5 as a solid electrolyte were investigated by AC impedance measurements and analysis using a transmission-line model (TLM). Samples containing graphite (graphite electrodes) or LiNi0.5Co0.2Mn0.3O2 (NCM electrodes) as the active material were measured under a "substrate | sample | bulk electrolyte | sample | substrate" configuration (ion-electron connection) and a "substrate | sample | substrate" configuration (electron-electron connection). Theoretically, if the electronic resistance is negligibly small, which is the case with our graphite electrodes, measurement with the ion-electron connection should be effective for evaluating ionic conductivity. However, if the electronic resistance is comparable to the ionic resistance, which is the case with our NCM electrodes, the results with the ion-electron connection may contain some inherent inaccuracy. In this report, we theoretically and practically demonstrate the advantage of analyzing the results with the electron-electron connection, which gives both the ionic and electronic conductivities. The similarity of the behavior of ionic conductivity with the graphite and NCM electrodes confirms the reliability of this analysis.

  1. Electrical conductivity of highly concentrated electrolytes near the critical consolute point: A study of tetra-n-butylammonium picrate in alcohols of moderate dielectric constant

    NASA Astrophysics Data System (ADS)

    Oleinikova, A.; Bonetti, M.

    2001-12-01

    The electrical conductivity of highly concentrated solutions of tetra-n-butylammonium picrate (TBAP) in 1-dodecanol (dielectric constant ɛ=4.6) and 1,4-butanediol (ɛ=25.9), and in mixtures of both alcohols, is measured in an extended temperature range ≈10-5<τ<≈10-1, where τ=(T-Tc)/Tc is the reduced temperature with Tc, the critical temperature. The electrical conductivity Λ(T) obeys the Vogel-Fulcher-Tammann (VFT) law for the temperatures far from the critical one. In the temperature range τ<10-2 a systematic deviation of the electrical conductivity from the regular VFT behavior is observed. This deviation is attributed to a critical anomaly. At the critical point the amplitude of the critical anomaly is finite with a value which varies between ≈0.4 and ≈2.7% of Λ(Tc), depending on the solvent. The (1-α) critical exponent describes well the conductivity anomaly, α being the exponent of the specific heat anomaly at constant pressure. The value of the Walden product (Λeqvη), with Λeqv, the equivalent conductivity and η, the shear viscosity, allows the degree of dissociation αdiss of TBAP to be determined at the critical point. αdiss becomes larger for increasing values of ɛ: for TBAP in 1-dodecanol αdiss≈0.25 and in 1,4-butanediol αdiss≈0.73. When the degree of dissociation of the salt is accounted for the Debye screening length is found almost independent on ɛ.

  2. Experimental study on the dielectric properties of polyacrylate dielectric elastomer

    NASA Astrophysics Data System (ADS)

    Qiang, Junhua; Chen, Hualing; Li, Bo

    2012-02-01

    The dielectric constant of elastomeric dielectric material is an essential physical parameter, whose value may affect the electromechanical deformation of a dielectric elastomer actuator. Since the dielectric constant is influenced by several external factors as reported before, and no certain value has been confirmed to our knowledge, in the present paper, on the basis of systematical comparison of recent past literature, we conducted extensive works on the measurement of dielectric properties of VHB films, involving five influencing factors: prestretch (both equal and unequal biaxial), electrical frequency, electrode material, stress relaxation time and temperature. Experimental results directly show that the dielectric response changes according to these factors, based on which we investigate the significance of each factor, especially the interaction of two external conditions on the dielectric constant of deformable dielectric, by presenting a physical picture of the mechanism of polarization.

  3. Synthesis and characterization of cancrinite-type zeolite, and its ionic conductivity study by AC impedance analysis

    NASA Astrophysics Data System (ADS)

    Kriaa, A.; Ben Saad, K.; Hamzaoui, A. H.

    2012-12-01

    The synthesis of cancrinite in the system NaOH-SiO2-Al2O3-NaHCO3-H2O was performed, according to methods described in the literature, in an autoclave under hydrothermal conditions at T = 473 K. The electrical properties of cancrinite-type zeolite pellets were investigated by complex impedance spectroscopy in the temperature range 465-800°C. The effect of temperature on impedance parameters was studied using an impedance analyzer in a wide frequency range (1 Hz to 13 MHz). The real and imaginary parts of complex impedance trace semicircles in the complex plane are plotted. The bulk resistance of the material decreases with rise in temperature. This exhibits a typical negative temperature coefficient of resistance (NTCR) behavior of the material. The results of bulk electrical conductivity and its activation energy are presented. The modulus analysis suggests that the electrical transport processes in the material are very likely to be of electronic nature. Relaxation frequencies follow an Arrhenius behavior with activation energy values not comparable to those found for the electrical conductivity.

  4. First-principles study of dielectric properties and optical conductivity of Cd1-xMnxTe

    NASA Astrophysics Data System (ADS)

    Bouarissa, N.; Gueddim, A.; Siddiqui, S. A.; Boucenna, M.; Al-Hajry, A.

    2014-08-01

    The optical response functions and their derived reflectivity spectrum, the absorption coefficient and the optical conductivity are calculated for zinc-blende-structured Cd1-xMnxTe with Mn concentration in the range 0-1. The evolution of the optical spectra with increased Mn concentrations is examined and discussed. The calculations are performed within the generalized gradient approximation of Engel-Vosko to the density functional theory, and the one-electron equations are solved by means of the full potential linearized augmented plane wave method. Generally, our results are found to be in reasonable agreement with the available experimental and theoretical data reported in the literature.

  5. Electrical, dielectric and electrochemical measurements of bulk aluminum phthalocyanine chloride (AlPcCl)

    NASA Astrophysics Data System (ADS)

    Soliman, I. M.; El-Nahass, M. M.; Mansour, Y.

    2016-01-01

    AC conductivity and the related dielectric properties of bulk aluminum phthalocyanine chloride (AlPcCl) have been studied over a temperature range (303-403 K) and frequency range (42-106 Hz). The universal power law σac (ω)=Aωs has been used to investigate dependence of AC conductivity on frequency. The variation of the frequency exponent (s) with temperature was analyzed in terms of different conduction mechanisms; the predominant conduction mechanism was found to be the correlated barrier hopping (CBH) model. The barrier height was calculated by using (CBH) model, it was found to be 1.41 eV. Dependence of σac (ω) on temperature refers to a linear increase with increasing temperature at different frequencies. The density of states N (EF) was calculated to be equal 4.11×1019 cm-3 using Elliott model. It has been found that AC activation energy decreases with increasing frequency. Dielectric values were analyzed using complex permittivity and complex electric modulus for bulk AlPcCl at different temperatures. The obtained value of HOMO-LUMO energy gap was found to be 1.48 eV.

  6. The Dielectric Loss Characteristic of Ice by Dielectric Heating Method for The Thawing of Foods or Biomaterials

    NASA Astrophysics Data System (ADS)

    Bai, Xianglan; Shirakashi, Ryo; Nishio, Shigefumi

    The thawing of ice crystal is very important for thawing of frozen foods and cryopreserved biomaterials. It was found that an alternative current (AC) electric field may effect the thawing process of frozen foods and cryopreserved biomaterials. In the present study, the spectrum of dielectric loss of ice crystal (50Hz~1.8GHz) was measured at various temperatures(-60°C to -2°C). The experiments of heating ice crystal using electric field were done to investigate the absorption of AC electric energy, which changes with the frequency of electric field. In order to evaluate the rapidness and the uniformity of thawing quantitatively, a numerical simulation of one-dimensional heat transfer was also conducted based on the measured spectrum of the dielectric loss of ice. The results showed that AC electric field have the uniform heating effect, only when the value of the frequency multiplied by dielectric loss (fε") decreases as the temperature increases. One of the optimum frequencies for a rapid and uniform thawing was found to be at around 3MHz.

  7. Experimental and theoretical study of AC electrical conduction mechanisms of Organic-inorganic hybrid compound Bis (4-acetylanilinium) tetrachlorocadmiate (II)

    NASA Astrophysics Data System (ADS)

    Jellibi, A.; Chaabane, I.; Guidara, K.

    2016-06-01

    A new organic-inorganic bis (4-acetylaniline) tetrachlorocadmate [C8H10NO]2[CdCl4] can be obtained by slow evaporation at room temperature and characterized by X-ray powder diffraction. It crystallized in an orthorhombic system (Cmca space group). The material electrical properties were characterized by impedance spectroscopy technique in the frequency range from 209 Hz-5 MHz and temperature 413 to 460 K. Besides, the impedance plots show semicircle arcs at different temperatures and an electrical equivalent circuit has been proposed to interpret the impedance results. The circuits consist of the parallel combination of a resistance (R), capacitance (C) and fractal capacitance (CPE). The variation of the exponent s as a function of temperature suggested that the conduction mechanism in Bis (4-acetylanilinium) tetrachlorocadmiate compound is governed by two processes which can be ascribed to a hopping transport mechanism: correlated barrier hopping (CBH) model below 443 K and the small polaron tunneling (SPT) model above 443 K.

  8. Synthesis and dielectric studies of poly (vinyl pyrrolidone) / titanium dioxide nanocomposites

    NASA Astrophysics Data System (ADS)

    Vasudevan, Prathibha; Thomas, Sunil; V, Arunkumar K.; S, Karthika; V, Unnikrishnan N.

    2015-02-01

    In this paper, we present the synthesis of poly vinyl pyrrolidone (PVP) / titanium dioxide nanocomposites via sol- gel technique. The structural and dielectric properties of the samples were also analysed in this work. PVP doped with varying concentrations of TiO2 are prepared by the sol-gel route. The prepared composites were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and impedance spectroscopy. XRD and TEM confirm the presence of TiO2 nanoparticles in the composites. The dielectric response and the AC electrical conductivity of the samples are investigated for the frequency range 1 kHz-2MHz at room temperature. The dielectric studies show low values for dielectric constant and loss at high frequencies.

  9. Thermal kinetic and dielectric parameters of acenaphthene crystal grown by vertical Bridgman technique

    NASA Astrophysics Data System (ADS)

    Karuppusamy, S.; Dinesh Babu, K.; Nirmal Kumar, V.; Gopalakrishnan, R.

    2016-05-01

    The bulk acenaphthene crystal was grown in a single-wall ampoule by vertical Bridgman technique. X-ray diffraction analysis confirmed the orthorhombic crystal system of title compound with space group Pcm21. Thermal behavior of compound was studied using thermogravimetry—differential scanning calorimetry analysis. Thermal kinetic parameters like activation energy, frequency factor, Avrami exponent, reaction rate and degree of conversion were calculated using Kissingers and Ozawa methods under non-isothermal condition for acenaphthene crystal and reported for the first time. The calculated thermal kinetic parameters are presented. Dielectric studies were performed to calculate the dielectric parameters such as dielectric constant, dielectric loss, AC conductivity, and activation energy from Arrhenius plot.

  10. A study of frequency dependent electrical and dielectric properties of NiO nanoparticles

    NASA Astrophysics Data System (ADS)

    Usha, V.; Kalyanaraman, S.; Vettumperumal, R.; Thangavel, R.

    2017-01-01

    Nickel oxide nanoparticles were synthesized using low cost sol-gel method. The structure of as prepared NiO nanoparticles has been confirmed from X-ray diffraction (XRD), scanning electron microscope with energy dispersive X-ray (SEM and EDX) spectroscopic analysis. The electrical and dielectric properties were characterized by complex impedance spectroscopy as a function of frequency at different temperatures. To study the dielectric behavior of the nanoparticles different plots like Nyquist plot, modulus plot and Bode plot were used. Also the frequency dependent ac conductivity is analyzed and the activation energy is calculated. The dielectric constant and dielectric loss as a function of frequency at various temperatures are also studied.

  11. Synthesis and dielectric properties of Zn doped GdFeO3 ceramics

    NASA Astrophysics Data System (ADS)

    Sai Vandana, C.; Guravamma, J.; Hemalatha Rudramadevi, B.

    2016-09-01

    GdFeO3 and GdZn0.3Fe0.7O3 ceramics were prepared by standard Solid State Reaction method at 1200°C. The structural changes and crystallite sizes of the undoped and Zn doped ceramics were studied using the XRD data. Microstructural features and elemental composition of GdFeO3 and GdZn0.3Fe0.7O3 ceramics were determined from SEM and EDS analysis. Room temperature dielectric measurements such as dielectric constant (ɛ´), tangent loss (tan5) and AC conductivity (oac) were carried out in the frequency range (100Hz to 1MHz). Improved dielectric properties of GdZn0.3Fe0.7O3 over GdFeO3 ceramics with low values of dielectric loss render them as potential materials in the areas of microwave communication systems, information storage, spintronics, sensors, etc.

  12. Lithium ion conductivity and dielectric relaxation in dendritic nanostructured LiTaO3 glass-nanocrystal composites

    NASA Astrophysics Data System (ADS)

    Jaschin, P. W.; Varma, K. B. R.

    2017-03-01

    Lithium tantalate in single-crystalline and coarse-grained configurations is a poor ionic conductor and does not qualify as a solid electrolyte for lithium-based batteries. In this work, ionic conductivity was sought to be enhanced by the use of nanocrystals of LiTaO3 embedded in a borate-based glass matrix. Glasses of composition 3Li2O-4B2O3-Ta2O5 were formed by melt-quenching. The crystallization process was described by using isothermal crystallization kinetics, invoking the Johnson-Mehl-Avrami-Kolmogorov equation, which indicated a three-dimensional growth with an Avrami exponent of 3.5 and an effective activation energy for crystallization of 735 ± 65 kJ mol-1. Heat treatment of the as-quenched glasses was performed between 530 and 560 °C, and the evolution of LiTaO3 phase was studied by X-ray powder diffraction, scanning electron microscopy, and transmission electron microscopy. The heat treatment yielded coalesced LiTaO3 nanocrystals of 18-32 nm size, forming dendritic structures in the glass matrix. Impedance analyses of the as-quenched and heat-treated glasses showed a dramatic improvement in dc conductivity (σdc), with a maximum around 3 × 10-3 S m-1 at 200 °C (σdcT = 1.5 S m-1 K) and activation energy of 0.54 eV for 530 °C/3 h heat-treated glasses. The values of σdc of the as-quenched glasses and of the 530 °C/3 h and 540 °C/3 h heat-treated glasses were about seven orders of magnitude higher than those of the single crystalline LiTaO3. Furthermore, the effect of heat treatment on lithium ion dynamics in the 40-200 °C temperature range was investigated by modulus formalism invoking the stretched exponential Kohlrausch-Williams-Watts function. The 7Li magic angle spinning NMR was used to investigate lithium self-diffusion in the nanostructured glass nanocrystal composites as a function of temperature between -10 °C and 60 °C.

  13. Effect of substitution group on dielectric properties of 4H-pyrano [3, 2-c] quinoline derivatives thin films

    NASA Astrophysics Data System (ADS)

    H, M. Zeyada; F, M. El-Taweel; M, M. El-Nahass; M, M. El-Shabaan

    2016-07-01

    The AC electrical conductivity and dielectrical properties of 2-amino-6-ethyl-5-oxo-4-(3-phenoxyphenyl)-5,6-dihydro-4H-pyrano[3, 2-c]quinoline-3-carbonitrile (Ph-HPQ) and 2-amino-4-(2-chlorophenyl)-6-ethyl-5-oxo-5,6-dihydro-4H-pyrano [3, 2-c] quinoline-3-carbonitrile (Ch-HPQ) thin films were determined in the frequency range of 0.5 kHz-5 MHz and the temperature range of 290-443 K. The AC electrical conduction of both compounds in thin film form is governed by the correlated barrier hopping (CBH) mechanism. Some parameters such as the barrier height, the maximum barrier height, the density of charges, and the hopping distance were determined as functions of temperature and frequency. The phenoxyphenyl group has a greater influence on those parameters than the chlorophenyl group. The AC activation energies were determined at different frequencies and temperatures. The dielectric behaviors of Ph-HPQ and Ch-HPQ were investigated using the impedance spectroscopy technique. The impedance data are presented in Nyquist diagrams for different temperatures. The Ch-HPQ films have higher impedance than the Ph-HPQ films. The real dielectric constant and dielectric loss show a remarkable dependence on the frequency and temperature. The Ph-HPQ has higher dielectric constants than the Ch-HPQ.

  14. Synthesis of graphene-like transparent conductive films on dielectric substrates using a modified filtered vacuum arc system

    SciTech Connect

    Lux, Helge Schrader, Sigurd; Siemroth, Peter; Sgarlata, Anna; Prosposito, Paolo; Casalboni, Mauro; Schubert, Markus Andreas

    2015-05-21

    Here, we present a reliable process to deposit transparent conductive films on silicon oxide, quartz, and sapphire using a solid carbon source. This layer consists of partially ordered graphene flakes with a lateral dimension of about 5 nm. The process does not require any catalytic metal and exploits a high current arc evaporation (Φ-HCA) to homogeneously deposit a layer of carbon on heated substrates. A gas atmosphere consisting of Argon or Argon/Hydrogen blend acting as a buffer influences the morphology of the growing film. scanning tunneling microscopy, transmission electron microscopy, and Raman spectra were used for a thorough characterization of the samples in order to optimize the growth parameters. The best carbon layers have a surface resistance of 5.7 × 10{sup 3} Ω{sub ◻} whereas the optical transparency of the coatings is 88% with an excellent homogeneity over areas of several cm{sup 2}. Such results are compatible with most semiconductor fabrication processes and make this method very promising for various industrial applications.

  15. Flexible Dielectric Nanocomposites with Ultrawide Zero-Temperature Coefficient Windows for Electrical Energy Storage and Conversion under Extreme Conditions.

    PubMed

    Shehzad, Khurram; Xu, Yang; Gao, Chao; Li, Hanying; Dang, Zhi-Min; Hasan, Tawfique; Luo, Jack; Duan, Xiangfeng

    2017-03-01

    Polymer dielectrics offer key advantages over their ceramic counterparts such as flexibility, scalability, low cost, and high breakdown voltages. However, a major drawback that limits more widespread application of polymer dielectrics is their temperature-dependent dielectric properties. Achieving dielectric constants with low/zero-temperature coefficient (L/0TC) over a broad temperature range is essential for applications in diverse technologies. Here, we report a hybrid filler strategy to produce polymer composites with an ultrawide L/0TC window of dielectric constant, as well as a significantly enhanced dielectric value, maximum energy storage density, thermal conductivity, and stability. By creating a series of percolative polymer composites, we demonstrated hybrid carbon filler based composites can exhibit a zero-temperature coefficient window of 200 °C (from -50 to 150 °C), the widest 0TC window for all polymer composite dielectrics reported to date. We further show the electric and dielectric temperature coefficient of the composites is highly stable against stretching and bending, even under AC electric field with frequency up to 1 MHz. We envision that our method will push the functional limits of polymer dielectrics for flexible electronics in extreme conditions such as in hybrid vehicles, aerospace, power electronics, and oil/gas exploration.

  16. X-ray diffraction, dielectric, conduction and Raman studies in Na{sub 0.925}Bi{sub 0.075}Nb{sub 0.925}Mn{sub 0.075}O{sub 3} ceramic

    SciTech Connect

    Chaker, Chiheb; Gagou, Y.; Dellis, J.-L.; El Marssi, M.; Abdelmoula, N.; Khemakhem, H.; Masquelier, C.

    2012-02-15

    Ceramic with composition Na{sub 0.925}Bi{sub 0.075}Nb{sub 0.925}Mn{sub 0.075}O{sub 3} (NNBM0075) was synthesized by high temperature solid state reaction technique. It was studied using X-ray diffraction (XRD), dielectric measurements and Raman spectroscopy. The sample crystallizes in orthorhombic perovskite structure with space group Pbma at room temperature. Dielectric properties of the ceramic was investigated in a broad range of temperatures (-150 to 450 deg. C) and frequencies (0.1-10{sup 3} kHz), and show two different anomalies connected to the symmetry change and electrical conductivity. Dielectric frequency dispersion phenomena in the NNBM0075 ceramic was analyzed by impedance spectroscopy in the temperature range from 55 to 425 deg. C. The Cole-Cole analysis based on electrical circuit and least square method was used to characterize the conduction phenomenon. A separation of the grain and grain boundary properties was achieved using an equivalent circuit model. The different parameters of this circuit were determined using impedance studies. Four conduction ranges, with different activation energies, were determined using the Arrhenius model. Raman spectra were studied as a function of temperatures and confirmed the X-ray and dielectric results. This composition is of interest for applications due to his physical properties and environmentally friendly character.

  17. Comment on ``Electrical and dielectric propertiesof the Bi4Sr3Ca3Cu4Ox (4:3:3:4) glassy semiconductor''

    NASA Astrophysics Data System (ADS)

    Ghosh, A.

    1997-01-01

    A recent paper from Som and Chaudhuri [Phys. Rev. B 41, 1581 (1990)], regarding the electrical and dielectric properties of Bi4Sr3Ca3Cu4Ox glass is reanalyzed. It is shown that the theoretical analysis for the ac conductivity and its frequency exponent performed by the authors is incorrect.

  18. Dielectric relaxation of amides and tetrahydrofuran polar mixture in C6H6 from conductivity measurement under 9.90 GHz electric field

    NASA Astrophysics Data System (ADS)

    Sahoo, S.; Sit, S. K.

    2017-01-01

    Dielectric relaxation studies of binary ( jk) polar mixtures of tetrahydrofuran with N-methyl acetamide, N, N-dimethyl acetamide, N-methyl formamide and N, N-dimethyl formamide dissolved in benzene(i) for different weight fractions ( w j k 's) of the polar solutes and mole fractions ( x j 's) of tetrahydrofuran at 25 ∘C are attempted by measuring the conductivity of the solution under 9.90 GHz electric field using Debye theory. The estimated relaxation time ( τ j k 's) and dipole moment ( μ j k 's) agree well with the reported values signifying the validity of the proposed methods. Structural and associational aspects are predicted from the plot of τ j k and μ j k against x j of tetrahydrofuran to arrive at solute-solute (dimer) molecular association upto x j =0.3 of tetrahydrofuran and thereafter solute-solvent (monomer) molecular association upto x j =1.0 for all systems except tetrahydrofuran + N, N-dimethyl acetamide.

  19. Thermal and dielectric properties of gel-grown cobalt malonate dihydrate single crystals

    NASA Astrophysics Data System (ADS)

    Mathew, Varghese; Xavier, Lizymol; Mahadevan, C. K.; Abraham, K. E.

    2011-03-01

    Single crystals of cobalt malonate dihydrate were grown in a silica gel medium by the single diffusion method. The thermal behavior of the crystals was investigated by thermogravimetric and differential thermal analyses. The dielectric constant, dielectric loss and ac conductivity of the crystals were estimated as a function of temperature in the range 40-140 °C for four different frequencies. The results indicate that the grown crystals are thermally stable up to about 150 °C and exhibit a phase transition at 130 °C.

  20. Electrode effects in dielectric spectroscopy measurements on (Nb+In) co-doped TiO2

    NASA Astrophysics Data System (ADS)

    Crandles, D. A.; Yee, S. M. M.; Savinov, M.; Nuzhnyy, D.; Petzelt, J.; Kamba, S.; Prokeš, J.

    2016-04-01

    Recently, several papers reported the discovery of giant permittivity and low dielectric loss in (Nb+In) co-doped TiO2. A series of tests was performed which included the measurement of the frequency dependence of the dielectric permittivity and alternating current (ac) conductivity of co-doped (Nb+In)TiO2 as a function of electrode type, sample thickness, and temperature. The data suggest that the measurements are strongly affected by the electrodes. The consistency between four-contact van der Pauw direct current conductivity measurements and bulk conductivity values extracted from two-contact ac conductivity measurements suggest that the values of colossal permittivity are, at least in part, a result of Schottky barrier depletion widths that depend on electrode type and temperature.

  1. Investigation of structural, optical, electrical and dielectric properties of catalytic sprayed hausmannite thin film

    SciTech Connect

    Larbi, T.; Ouni, B.; Boukhachem, A.; Boubaker, K. Amlouk, M.

    2014-12-15

    Hausmannite Mn{sub 3}O{sub 4} thin film have been synthesized using spray pyrolysis method. These films are characterized using X-ray diffraction (XRD), atomic force microscope AFM, UV–vis–NIR spectroscopy and impedance spectroscopy. XRD study confirms the tetragonal structure of the as-deposited films with lattice parameters, a = 5.1822 Å and c = 9.4563 Å and a grain size of about 56 nm. UV–vis–NIR spectroscopy was further used to estimate optical constants such as extinction coefficient, refractive index, band gap and Urbach energy. Moreover, impedance spectroscopy analysis was employed to estimate electrical and dielectrical properties of the sprayed thin films. The activation energy values deduced from DC conductivity and relaxation frequency were almost the same, revealing that the transport phenomena is thermally activated by hopping between localized states. The AC conductivity is found to be proportional to ω{sup s}. The temperature dependence of the AC conductivity and the frequency exponent, s was reasonably well interpreted in terms of the correlated barrier-hopping CBH model. The dielectric properties were sensitive to temperature and frequency. The study of the electrical modulus indicated that the charge carrier was localized. Experimental results concerning optical constants as Urbach energy, dielectric constant, electric modulus and AC and DC conductivity were discussed in terms of the hopping model as suggested by Elliott.

  2. Synthesis modified structural and dielectric properties of semiconducting zinc ferrospinels

    NASA Astrophysics Data System (ADS)

    Kumari, N.; Kumar, V.; Singh, S. K.; Khasa, S.; Dahiya, M. S.

    2017-02-01

    The influence of preparation techniques on structural and dielectric properties of ZnCrxFe1-xO4 (x=0, 0.1 abbreviated as Z and ZC) ferrite nano-particles synthesized using chemical co-precipitation (CCP), sol-gel (SG) and solid state reaction (SS) techniques is discussed. XRD profiles are used to confirm the single phase spinel ferrite formation. TEM images indicate the change in size and shape of particles on changing either the composition or the synthesis methodology. The TEM micrograph of samples obtained through CCP shows uniform particle size formation compared to those obtained through SG and SS. Sample prepared through CCP possess porosity >70% making these materials suitable for sensing applications. The dielectric loss, dielectric constant and ac conductivity are analyzed as a function of frequency, temperature and composition using impedance spectroscopy. A universal dielectric behavior has been predicted through temperature and frequency variations of different parameters. Dielectric constant is found to possess highest value for sample synthesized through SG which marks the possibility of using the SG derived ferrospinels as microwave device components.

  3. Dielectric properties of flower-type ZnO nanorods and ZnO-SnO2 nanocomposites

    NASA Astrophysics Data System (ADS)

    Stella, C.; Mariammal, R. N.; Ramachandran, K.

    2012-06-01

    ZnO and ZnO: SnO2 nanocomposites were synthesized by simple co-precipitation method and the structural characterization was done by XRD. The surface morphology was studied by SEM analysis which showed the formation of flower-type nanorods in ZnO and spherical particles in ZnO: SnO2. The variation of dielectric constant and ac conductivity has been studied at 90°C by varying signal frequency from 100 Hz-5 MHz. The dielectric constant decreases with increasing frequency whereas the electrical conductivity increases with increasing frequency.

  4. Dielectrical properties of PANI/TiO2 nanocomposites

    NASA Astrophysics Data System (ADS)

    Chaturmukha, V. S.; Naveen, C. S.; Rajeeva, M. P.; Avinash, B. S.; Jayanna, H. S.; Lamani, Ashok R.

    2016-05-01

    Conducting polyaniline/titanium dioxide (PANI/TiO2) composites have been succesfully synthesized by insitu polymerization technique. The PANI/TiO2 nanocomposites of different compositions were prepared by varying weight percentage of TiO2 nanoparticles such as 10 wt%, 20 wt%, 30 wt%, 40 wt% and 50 wt% into the fixed amount of the aniline monomer. The prepared powder samples were characterized by X-ray diffractometer (XRD) and Scanning electron microscope (SEM). The intensity of diffraction peaks for PANI/TiO2 composites is lower than that for TiO2. SEM pictures show that the nanocomposite were prepared in the form of long PANi chains decorated with TiO2 nanoparticles. The dielectric properties and AC conductivity were studied in the frequency range1K Hz-10M Hz. At higher frequencies, the composites exhibit almost zero dielectric loss and maximum value of σac is found for a concentration of 20 wt% TiO2 in polyaniline. The interface between polyaniline and TiO2 plays an important role in yielding a large dielectric constant in nanocomposites.

  5. Memory effect in ac plasma displays

    NASA Astrophysics Data System (ADS)

    Szlenk, K.; Obuchowicz, E.

    1993-10-01

    The bistable or `memory' mode of operation of an ac plasma display panel is presented. The difference between dc and ac plasma panel operation from the point of view of memory function is discussed. The graphic ac plasma display with thin film Cr-Cu-Cr electrodes was developed in OBREP and its basic parameters are described. It consists of 36 X 59 picture elements, its outer dimensions are: 76 X 52 mm2 and the screen size is: 49 X 30 mm2. The different dielectric glass materials were applied as dielectric layers and the influence of the properties of these materials on display parameters and memory function was investigated.

  6. Reduction of Common-Mode Conducted Noise Emissions in PWM Inverter-fed AC Motor Drive Systems using Optimized Passive EMI Filter

    NASA Astrophysics Data System (ADS)

    Jettanasen, C.; Ngaopitakkul, A.

    2010-10-01

    Conducted electromagnetic interference (EMI) generated by PWM inverter-fed induction motor drive systems, which are currently widely used in many industrial and/or avionic applications, causes severe parasitic current problems, especially at high frequencies (HF). These restrict power electronic drive's evolution. In order to reduce or minimize these EMI problems, several techniques can be applied. In this paper, insertion of an optimized passive EMI filter is proposed. This filter is optimized by taking into account real impedances of each part of a considered AC motor drive system contrarily to commercial EMI filters designed by considering internal impedance of disturbance source and load, equal to 50Ω. Employing the latter EMI filter would make EMI minimization less effective. The proposed EMI filter optimization is mainly dedicated to minimize common mode (CM) currents due to its most dominant effects in this kind of system. The efficiency of the proposed optimization method using two-port network approach is deduced by comparing the minimized CM current spectra to an applied normative level (ex. DO-160D in aeronautics).

  7. Boron Nitride Nanotube Mat as a Low- k Dielectric Material with Relative Dielectric Constant Ranging from 1.0 to 1.1

    NASA Astrophysics Data System (ADS)

    Hong, Xinghua; Wang, Daojun; Chung, D. D. L.

    2016-01-01

    This paper reports that a boron nitride nanotube (BNNT) mat containing air and 1.4 vol.% BNNTs is a low- k dielectric material for microelectronic packaging, exhibiting relative dielectric constant of 1.0 to 1.1 (50 Hz to 2 MHz) and elastic modulus of 10 MPa. The mat is prepared by compacting BNNTs at 5.8 kPa. This paper also presents measurements of the dielectric properties of BNNTs (mostly multiwalled). The relative dielectric constant of the BNNT solid in the mat decreases with increasing frequency, with attractively low values ranging from 3.0 to 6.2; the alternating-current (AC) electrical conductivity increases with increasing frequency, with attractively low values ranging from 10-10 S/m to 10-6 S/m and an approximately linear relationship between log conductivity and log frequency. The specific contact capacitance of the interface between BNNTs and the electrical contact decreases with increasing frequency, with attractively high values ranging from 1.6 μF/m2 to 2.3 μF/m2. The AC electrical resistivity of the BNNT-contact interface decreases with increasing frequency, with high values ranging from 0.14 MΩ cm2 to 440 MΩ cm2.

  8. Dielectric properties of Ti4+ substituted BaFe12O19 nanoparticles

    NASA Astrophysics Data System (ADS)

    Ghoneim, A. I.; Amer, M. A.; Meaz, T. M.; Attalah, S. S.

    2017-02-01

    Series of nanocrystalline BaTixFe12-(4/3)xO19 hexagonal ferrites, 0≤x≤1, was prepared using the chemical co-precipitation method. As-prepared samples were heated at 1200 °C for 20 h and slowly cooled to room temperature (RT). XRD studies proved that the samples have single phase M-type hexagonal nanostructure, where their grain size lies in the range of 42.4 - 61.3 nm. Their dielectric properties were studied against temperature (T) and frequency (F). DC conductivity showed increase against T, whereas AC conductivity showed increase with increasing both T and F. This proved the semiconducting behavior of the samples. Activation energies were found to lie in the range of 0.054-0.169 eV for temperature range of RT 373 K and of 0.114-0.274 eV for higher temperatures up to 473 K. Variation of the dielectric constant and AC conductivity against F revealed dispersion in all these hexagonal nanostructures, which was assigned to Maxwell-Wagner type of interfacial polarization. Variation of the dielectric loss tangent against F showed a relaxation spectrum for all samples, whereas the dielectric constant and loss tangent showed an increasing trend against T. The relative magnetic permeability μr showed an increasing trend with temperature.

  9. Structural and dielectric properties of yttrium substituted nickel ferrites

    SciTech Connect

    Ognjanovic, Stevan M.; Tokic, Ivan; Cvejic, Zeljka; Rakic, Srdjan; Srdic, Vladimir V.

    2014-01-01

    Graphical abstract: - Highlights: • Dense NiFe{sub 2−x}Y{sub x}O{sub 4} ceramics (with 0 ≤ x ≤ 0.3) were prepared. • Pure spinels were obtained for x ≤ 0.07 while for x ≥ 0.15 samples had secondary phases. • With addition of yttrium, ac conductivity slightly increased. • We suggest several effects that can explain the observed changes in ac conduction. • With addition of yttrium, dielectric constant increased while the tg δ decreased. - Abstract: The influence of Y{sup 3+} ions on structural and dielectric properties of nickel ferrites (NiFe{sub 2−x}Y{sub x}O{sub 4}, where 0 ≤ x ≤ 0.3) has been studied. The as-synthesized samples, prepared by the co-precipitation method, were analyzed by XRD and FTIR which suggested that Y{sup 3+} ions were incorporated into the crystal lattice for all the samples. However, the XRD analysis of the sintered samples showed that secondary phases appear in the samples with x > 0.07. The samples have densities greater than 90% TD and the SEM images showed that the grain size decreases with the addition of yttrium. Dielectric properties measured from 150 to 25 °C in the frequency range of 100 Hz–1 MHz showed that the addition of yttrium slightly increases the ac conductivity and decreases the tg δ therefore making the materials better suited for the use in microwave devices.

  10. Thermal analysis and temperature dependent dielectric responses of Co doped anatase TiO{sub 2} nanoparticles

    SciTech Connect

    Alamgir; Khan, Wasi; Ahammed, Nashiruddin; Naqvi, A. H.; Ahmad, Shabbir

    2015-05-15

    Nanoparticles (NPs) of pure and 5 mol % cobalt doped TiO{sub 2} synthesized through acid modified sol-gel method were characterized to understand their thermal, structural, morphological, and temperature dependent dielectric properties. Thermogravimetric analysis (TGA) has been used for thermal studies and indicates the weight loss in two steps due to the removal of residual organics. X-ray diffraction study was employed to confirm the formation of single anatase phase with tetragonal symmetry for both pure and 5 mol % Co doped TiO{sub 2} NPs. The average crystallite size of both samples was calculated from the Scherrer’s formula and was found in the range from 9-11 nm. TEM micrographs of these NPs reflect their shape and distribution. The dielectric constant (ε′), dielectric loss (tanδ) and ac conductivity (σ{sub ac}) were also studied as a function of temperature at different frequencies. Electrical responses of the synthesized NPs have been analyzed carefully in the framework of relevant models. It is also noticed that the dielectric constant (ε′) of the samples found to decrease with increasing frequency but increases with increasing temperature up to a particular value and then sharply decreases. Temperature variation of dielectric constant exhibits step like escalation and shows relaxation behavior. Study of dielectric properties shows dominant dependence on the grain size as well as Co ion incorporation in TiO{sub 2}.

  11. Low-frequency dielectric properties of intrinsic and Al-doped rutile TiO2 thin films grown by the atomic layer deposition technique

    NASA Astrophysics Data System (ADS)

    Kassmi, M.; Pointet, J.; Gonon, P.; Bsiesy, A.; Vallée, C.; Jomni, F.

    2016-06-01

    Dielectric spectroscopy is carried out for intrinsic and aluminum-doped TiO2 rutile films which are deposited on RuO2 by the atomic layer deposition technique. Capacitance and conductance are measured in the 0.1 Hz-100 kHz range, for ac electric fields up to 1 MVrms/cm. Intrinsic films have a much lower dielectric constant than rutile crystals. This is ascribed to the presence of oxygen vacancies which depress polarizability. When Al is substituted for Ti, the dielectric constant further decreases. By considering Al-induced modification of polarizability, a theoretical relationship between the dielectric constant and the Al concentration is proposed. Al doping drastically decreases the loss in the very low frequency part of the spectrum. However, Al doping has almost no effect on the loss at high frequencies. The effect of Al doping on loss is discussed through models of hopping transport implying intrinsic oxygen vacancies and Al related centers. When increasing the ac electric field in the MVrms/cm range, strong voltage non-linearities are evidenced in undoped films. The conductance increases exponentially with the ac field and the capacitance displays negative values (inductive behavior). Hopping barrier lowering is proposed to explain high-field effects. Finally, it is shown that Al doping strongly improves the high-field dielectric behavior.

  12. 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.

  13. Dielectric, electrical transport and magnetic properties of Er3+substituted nanocrystalline cobalt ferrite

    NASA Astrophysics Data System (ADS)

    Kakade, S. G.; Kambale, R. C.; Kolekar, Y. D.; Ramana, C. V.

    2016-11-01

    Erbium substituted cobalt ferrite (CoFe2-xErxO4; x=0.0-0.2, referred to CFEO) materials were synthesized by sol-gel auto-combustion method. The effect of erbium (Er3+) substitution on the crystal structure, dielectric, electrical transport and magnetic properties of cobalt ferrite is evaluated. CoFe2-xErxO4 ceramics exhibit the spinel cubic structure without any impurity phase for x≤0.10 whereas formation of the ErFeO3 orthoferrite secondary phase was observed for x≥0.15. All the CFEO samples demonstrate the typical hysteresis (M-H) behavior with a decrease in magnetization as a function of Er content due to weak superexchange interaction. The frequency (f) dependent dielectric constant (ε‧) revealed the usual dielectric dispersion. The ε‧-f dispersion (f=20 Hz to 1 MHz) fits to the modified Debye's function with more than one ion contributing to the relaxation. The relaxation time and spread factor derived are ∼10-4 s and ∼0.61(±0.04), respectively. Electrical and dielectric studies indicate that ε‧ increases and the dc electrical resistivity decreases as a function of Er content (x≤0.15). Complex impedance analyses confirm only the grain interior contribution to the conduction process. Temperature dependent electrical transport and room temperature ac conductivityac) analyses indicate the semiconducting nature and small polaron hopping.

  14. Dielectric and Impedance Spectroscopy of Barium Bismuth Vanadate Ferroelectrics

    NASA Astrophysics Data System (ADS)

    Sutar, B. C.; Choudhary, R. N. P.; Das, Piyush R.

    2014-07-01

    Structural, micro-structural and electrical properties of barium bismuth vanadate Ba(Bi0.5V0.5)O3 ceramics were investigated. X-ray diffraction (XRD) analysis of the prepared material confirmed the formation of the compound with monoclinic crystal system. Scanning electron microscopy (SEM) of the compound exhibits well-defined grains that are uniformly distributed throughout the surface of the sample. Dielectric properties of the compound were studied as a function of temperature at different frequencies. An observation of dielectric anomaly at 295 °C is due to ferroelectric phase transition that was later confirmed by the appearance of hysteresis loop. Detailed studies of complex impedance spectroscopy have provided a better understanding of the relaxation process and correlations between the microstructure-electrical properties of the materials. The nature of frequency dependence of ac conductivity obeys the Debye power law. The dc conductivity, calculated from the ac conductivity spectrum, shows the negative temperature coefficient of resistance behavior similar to that of a semiconductor.

  15. Mechanical and dielectric properties of carbon nanotubes/poly (vinyl alcohol) nanocomposites

    NASA Astrophysics Data System (ADS)

    Amrin, Sayed; Deshpande, V. D.

    2016-05-01

    In this work, two series of nanocomposites of poly(vinyl alcohol) (PVA) incorporated with multiwalled carbon nanotubes (MWNT) and carboxyl functionalized multiwalled carbon nanotubes (MWNT-COOH) were fabricated using solution-cast method and their tensile and dielectric properties were studied. Tensile tests were carried out on composite films of MWNT/PVA and MWNT-COOH/PVA for different loading levels. Results show that overall mechanical properties of the MWNT-COOH/PVA composite was greatly improved as compared to the MWNT/PVA film. The dielectric properties of nanocomposites were investigated in a frequency range from 0.1Hz to 10MHz at room temperature respectively. Compared to MWNT/PVA composites, higher dielectric constant and ac conductivity was achieved in MWNT-COOH/PVA nanocomposite, which can be well explained by the interfacial polarization effect.

  16. Effect of gamma irradiation on dielectric properties of manganese zinc nanoferrites

    SciTech Connect

    Angadi, V. Jagadeesha Rudraswamy, B.; Melagiriyappa, E.; Somashekarappa, H. M.; Nagabhushana, H.

    2014-04-24

    Naocrystalline ferrites Mn{sub 1−x}Zn{sub x}Fe{sub 2}O{sub 4} (x = 0.00, 0.25, 0.50, 0.75 and 1.00) were prepared by combustion method. The samples were characterized by XRD technique. The dielectric measurements were carried out in the frequency range 40 Hz to 100 MHz at room temperature. All the measurements were performed before and after gamma {sup 60}Co irradiation. The X-ray diffraction patterns revealed the formation of nanocrystalline and single-phase spinel structure. The lattice parameter decrease with zinc ion concentration and increased after the irradiation due to ferric ions of smaller radius converted to ferrous ions of larger radius. The dielectric behavior is attributed to the Maxwell-Wagner type interfacial polarization. The dielctric contant, dielectric loss and AC conductivity enhanced after the irradiation.

  17. Leakage current conduction, hole injection, and time-dependent dielectric breakdown of n-4H-SiC MOS capacitors during positive bias temperature stress

    NASA Astrophysics Data System (ADS)

    Samanta, Piyas; Mandal, Krishna C.

    2017-01-01

    The conduction mechanism(s) of gate leakage current JG through thermally grown silicon dioxide (SiO2) films on the silicon (Si) face of n-type 4H-silicon carbide (4H-SiC) has been studied in detail under positive gate bias. It was observed that at an oxide field above 5 MV/cm, the leakage current measured up to 303 °C can be explained by Fowler-Nordheim (FN) tunneling of electrons from the accumulated n-4H-SiC and Poole-Frenkel (PF) emission of trapped electrons from the localized neutral traps located at ≈2.5 eV below the SiO2 conduction band. However, the PF emission current IPF dominates the FN electron tunneling current IFN at oxide electric fields Eox between 5 and 10 MV/cm and in the temperature ranging from 31 to 303 °C. In addition, we have presented a comprehensive analysis of injection of holes and their subsequent trapping into as-grown oxide traps eventually leading to time-dependent dielectric breakdown during electron injection under positive bias temperature stress (PBTS) in n-4H-SiC metal-oxide-silicon carbide structures. Holes were generated in the heavily doped n-type polycrystalline silicon (n+-polySi) gate (anode) as well as in the oxide bulk via band-to-band ionization by the hot-electrons depending on their energy and SiO2 film thickness at Eox between 6 and 10 MV/cm (prior to the intrinsic oxide breakdown field). Transport of hot electrons emitted via both FN and PF mechanisms was taken into account. On the premise of the hole-induced oxide breakdown model, the time- and charge-to-breakdown ( tBD and QBD ) of 8.5 to 47 nm-thick SiO2 films on n-4H-SiC were estimated at a wide range of temperatures. tBD follows the Arrhenius law with activation energies varying inversely with initial applied constant field Eox supporting the reciprocal field ( 1 /E ) model of breakdown irrespective of SiO2 film thicknesses. We obtained an excellent margin (6.66 to 6.33 MV/cm at 31 °C and 5.11 to 4.55 MV/cm at 303 °C) of normal operating field for a 10

  18. Frequency dependent dielectric properties of Cu0.5Tl0.5Ba2Ca2(Cu3-yMy)O10-δ superconductor

    NASA Astrophysics Data System (ADS)

    Mumtaz, M.; Khan, Nawazish A.; Khan, Sajid

    2012-01-01

    The frequency dependent dielectric properties such as dielectric constants (ɛ/r, ɛ//r), absolute dielectric loss |tanδ|, and ac-conductivityac) of Cu0.5Tl0.5Ba2Ca2(Cu3-yMy)O10-δ (M = Si, Ge, Sn, y = 0, 1) superconductor have been investigated by means of capacitance (C) and conductance (G) measurements with the test frequency (f) in the range of 10 KHz to 10 MHz at various temperatures from superconducting state to normal conducting state. The negative capacitance has been observed in all Cu0.5Tl0.5Ba2Ca2(Cu3-yMy)O10-δ samples. The large values of negative dielectric constant (ɛ/r) at lower frequencies and temperatures are linked with reduced thermal vibrations of the atoms due to which polarizability has been enhanced. The decreased value of dielectric constant observed in the Ge-doped samples may possibly be linked with its greater electronegativity (EN) and less polarization. The electronegativity of Si and Sn has approximately the same values as that of Cu, so almost all the dielectric properties do not vary significantly in Si-doped Cu0.5Tl0.5Ba2 Ca2(Cu2Si1)O10-δ and Sn-doped Cu0.5Tl0.5Ba2Ca2(Cu2Sn1)O10-δ samples. These experimental investigations on dielectric properties of Cu0.5Tl0.5Ba2Ca2(Cu3-yMy)O10-δ superconductor have shown lower dielectric loss and higher ac-conductivity at all frequencies and temperatures as compared to that of other high Tc superconductor families. The decreased dielectric loss in Cu0.5Tl0.5Ba2Ca2(Cu3-yMy)O10-δ samples suggests that the polarization is most likely arising from the charge carriers between Cu0.5Tl0.5Ba2O4-δ charge reservoir layer and conducting CuO2/MO2 planes; since the charge reservoir layer has localized charge carriers at Ba+2, Tl+3, and Cu+2 sites, whereas CuO2/MO2 planes contain mobile charge carriers, which are displaced from their equilibrium position by external applied ac-field.

  19. Investigation of high-k yttrium copper titanate thin films as alternative gate dielectrics

    NASA Astrophysics Data System (ADS)

    Grazia Monteduro, Anna; Ameer, Zoobia; Rizzato, Silvia; Martino, Maurizio; Caricato, Anna Paola; Tasco, Vittorianna; Chaitanya Lekshmi, Indira; Hazarika, Abhijit; Choudhury, Debraj; Sarma, D. D.; Maruccio, Giuseppe

    2016-10-01

    Nearly amorphous high-k yttrium copper titanate thin films deposited by laser ablation were investigated in both metal-oxide-semiconductor (MOS) and metal-insulator-metal (MIM) junctions in order to assess the potentialities of this material as a gate oxide. The trend of dielectric parameters with film deposition shows a wide tunability for the dielectric constant and AC conductivity, with a remarkably high dielectric constant value of up to 95 for the thick films and conductivity as low as 6  ×  10-10 S cm-1 for the thin films deposited at high oxygen pressure. The AC conductivity analysis points out a decrease in the conductivity, indicating the formation of a blocking interface layer, probably due to partial oxidation of the thin films during cool-down in an oxygen atmosphere. Topography and surface potential characterizations highlight differences in the thin film microstructure as a function of the deposition conditions; these differences seem to affect their electrical properties.

  20. Composites of hybrids BaTiO3/carbon nanotubes/polyvinylidene fluoride with high dielectric properties

    NASA Astrophysics Data System (ADS)

    Fan, Benhui; Bai, Jinbo

    2015-11-01

    High dielectric composites were prepared based on polyvinylidene fluoride (PVDF) and hybrids BaTiO3-carbon nanotubes (H-BT-CNTs) with a special structure. The hybrids that BT was a core and CNTs grew outside were fabricated by chemical vapor deposition. Due to the special structure, composite’s dielectric permittivity reached 1777 at 100 Hz and 80 at 1 MHz, while loss tangent maintained as 6 at 100 Hz and 0.56 at 1 MHz, respectively. Moreover, dielectric permittivity and ac conductivity of composite were further enhanced after annealing process at moderate temperature. These improved properties were originated from the reformation of conductive network and BT-CNTs structure inside PVDF matrix.

  1. Study of Dielectric Behavior and Charge Conduction Mechanism of Poly(Vinyl Alcohol) (PVA)-Copper (Cu) and Gold (Au) Nanocomposites as a Bio-resorbable Material for Organic Electronics

    NASA Astrophysics Data System (ADS)

    Mahendia, Suman; Goyal, Parveen Kumar; Tomar, Anil Kumar; Chahal, Rishi Pal; Kumar, Shyam

    2016-10-01

    Poly(vinyl alcohol) (PVA) embedded with varying concentrations of chemically synthesized copper (Cu) and gold (Au) nanoparticles (NPs) were prepared using ex situ sol-gel casting method. The addition of almost the same concentration of CuNPs in PVA improves the conducting properties, while that of AuNPs improves the dielectric nature of composite films. It has been found that addition of AuNPs up to ˜0.4 wt.% concentration enhaneces the capacitive nature due to the formation of small Coulomb tunneling knots as internal capacitors. The dielectric studies suggest the Maxwell-Wagner interfacial polarization as the dominant dielectric relaxation process, whereas the I- V characteristics indicate bulk limited Poole-Frenkel emission at high voltages as the dominant charge transport mechanism operating at room temperature in all specimens. These novel features lead to the conclusion that addition of a small quantity of metal nanoparticles can help tune the properties of PVA for desired applications in bio-compatible polymer-based organic electronic devices.

  2. Dielectric Constant of Suspensions

    NASA Astrophysics Data System (ADS)

    Mendelson, Kenneth S.; Ackmann, James J.

    1997-03-01

    We have used a finite element method to calculate the dielectric constant of a cubic array of spheres. Extensive calculations support preliminary conclusions reported previously (K. Mendelson and J. Ackmann, Bull. Am. Phys. Soc. 41), 657 (1996).. At frequencies below 100 kHz the real part of the dielectric constant (ɛ') shows oscillations as a function of the volume fraction of suspension. These oscillations disappear at low conductivities of the suspending fluid. Measurements of the dielectric constant (J. Ackmann, et al., Ann. Biomed. Eng. 24), 58 (1996). (H. Fricke and H. Curtis, J. Phys. Chem. 41), 729 (1937). are not sufficiently sensitive to show oscillations but appear to be consistent with the theoretical results.

  3. Dielectric assist accelerating structure

    NASA Astrophysics Data System (ADS)

    Satoh, D.; Yoshida, M.; Hayashizaki, N.

    2016-01-01

    A higher-order TM02 n mode accelerating structure is proposed based on a novel concept of dielectric loaded rf cavities. This accelerating structure consists of ultralow-loss dielectric cylinders and disks with irises which are periodically arranged in a metallic enclosure. Unlike conventional dielectric loaded accelerating structures, most of the rf power is stored in the vacuum space near the beam axis, leading to a significant reduction of the wall loss, much lower than that of conventional normal-conducting linac structures. This allows us to realize an extremely high quality factor and a very high shunt impedance at room temperature. A simulation of a 5 cell prototype design with an existing alumina ceramic indicates an unloaded quality factor of the accelerating mode over 120 000 and a shunt impedance exceeding 650 M Ω /m at room temperature.

  4. Study Of Structural And Dielectric Properties Of Ni-Mg Ferrite Nanoparticles

    SciTech Connect

    Nongjai, Razia; Batoo, Khalid Mujasam; Khan, Shakeel

    2010-12-01

    Ferrite nanoparticles of basic composition Ni{sub 0.7}Mg{sub 0.3}Fe{sub 2-x}Al{sub x}O{sub 4}(0.0{<=}x{<=}0.5) were prepared through citrate gel method and characterized using XRD, TEM and dielectric spectroscopy techniques. The dielectric properties were studied as a function of frequency (42 Hz-5 MHz) at room temperature. The average particle size has been found between 8-17 nm. The dispersion in dielectric properties and ac conductivity ({sigma}{sub ac}), with frequency reveals that the dispersion is due to Maxwell-Wagner type of interfacial polarization in general and the hopping of charge between Fe{sup 2+} and Fe{sup 3+} as well as between Ni{sup 2+} and Ni{sup 3+} ions at B-sites. The dielectric loss tangent (tan {delta}) shows abnormal behavior for the compositions 0.3, 0.4 and 0.5 which has been explained in the light of Rezlescue model.

  5. Magnetic and dielectric properties of Bi3+ substituted SrFe12O19 hexaferrite

    NASA Astrophysics Data System (ADS)

    Auwal, I. A.; Erdemi, H.; Sözeri, H.; Güngüneş, H.; Baykal, A.

    2016-08-01

    In the present study, SrBixFe12-xO19 (0.0≤x≤1.0) nanomaterials were successfully synthesized by using chemical co-precipitation method. Products were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Vibrating sample magnetometer (VSM), Mössbauer spectroscopy, AC conductivity and dielectric measurements. The crystal structural information studied by X-ray diffraction (XRD) indicated the formation of single phase pure hexagonal structure, while electron-dispersive X-ray spectroscopy (EDX) revealed the stoichiometric ratio among Bi, Sr, Fe elements. The crystallite sizes of the products were in the range of 65-82 nm. VSM analysis showed a tendency in saturation magnetization as Bi2O3 concentration raises, which can be ascribed to preferential site occupied by Bi3+ ions. The frequency-dependent ac conductivity plots exhibited similar trends for all samples. A significant temperature-dependent behavior was only observed at low and medium frequencies. The replacement of non-magnetic Bi3+ ions by Fe3+ ones having magnetic moment of 5 μB decrease the magnetic moment of 4f1 site. The AC conductivity increases with frequency as hopping of the charge carriers increases between Fe2+and Fe3+. The DC conductivity exhibited an improvement with increasing temperature and Bi content, and the highest conductivity was measured as 2.84×10-9 S cm-1 for x=0.8 at 120 °C. The variation of dielectric constant, dielectric loss and tangent loss was observed with the frequency and temperature due to change of electrical conductivity as x changes.

  6. Effects of Heat-Treatment Time on the Structural, Dielectric, Electrical, and Magnetic Properties of BaM Hexaferrite

    NASA Astrophysics Data System (ADS)

    Ali, Ihsan; Islam, M. U.; Awan, M. S.; Ahmad, Mukhtar

    2013-07-01

    M-type hexaferrite (BaFe12O19) powders have been synthesized by means of the sol-gel autocombustion technique and is heat treated at 1000 °C for different times ( t = 1, 2, 3, and 4 h). Differential scanning calorimetry and thermogravimetric analyses are carried out to observe the weight loss and transformation of different phases during heat treatment. X-Ray diffraction patterns of the sample heat treated for 4 h confirms the formation of single phase M-type hexaferrite. The dielectric parameters and ac conductivityac) are measured in the high frequency range 1 MHz-3 GHz. The dielectric properties and ac conductivity are based on the space charge polarization according to the Maxwell-Wagner two-layer model and the Koop's phenomenological theory. The dielectric constant (ɛ') and dielectric loss (tan δ) decrease, while ac conductivity enhances with the increase of frequency. The room temperature DC electrical resistivity of the sample heat treated for 2 h enhances up to 2.93 × 109 (Ω-cm) and attributed to the migration of Fe2+ ions to the neighboring tetrahedral sites and lowering the Fe3+ contents on the octahedral sites. The temperature-dependent DC resistivity of samples shows a normal semiconducting behavior. The saturation magnetization, magnetic moment, and coercivity of the samples are observed to enhance with the increase of heat-treatment time. Owing to these qualities, the synthesized materials may be considered useful for high frequency applications, recording media, and permanent magnets.

  7. Optical, dielectric and electrical properties of PVA doped with Sn nanoparticles

    NASA Astrophysics Data System (ADS)

    Amin, G. A. M.; Abd-El Salam, M. H.

    2014-04-01

    Films of pure and doped polyvinyl alcohol (PVA) with different concentrations of Sn nanoparticles (≦̸100 nm) were prepared using casting technique. The effect of Sn addition on micro-structural, optical, electrical and dielectric properties of PVA was investigated. Microstructure of Sn/PVA nanocomposite films was characterized by scanning electron microscopy (SEM). Dielectric properties and ac conductivity measurements were carried out at room temperature over a wide range of frequencies ranging from 50 Hz to 5 MHz. AC conductivity was found to increase with frequency. Besides, addition of Sn nanoparticles to PVA leads to a change in conductivities of the films. Coulomb blockade effect was found to dominate at certain concentrations of Sn which may be used to explain the obtained results. The dielectric properties of the Sn/PVA films were also investigated and results were discussed in correlation with the relevant models. The frequency dependence of the imaginary part of complex electric modulus for the Sn/PVA composites shows a loss peak attributed to interfacial polarization at a certain frequency. Optical energy gap of Sn/PVA films was determined and found to decrease for Sn concentrations up to 20% due to the interaction between the Sn nanoparticles and the host polymeric network leading to the creation of new molecular dipoles. For higher Sn concentrations, the optical energy gap starts to increase which may be resulting from structural changes leading to passivation of localized states near the band edges and hence widening of the energy gap.

  8. Ferroelectric and dielectric properties of ferrite-ferroelectric ceramic composites

    SciTech Connect

    Elena Ciomaga, Cristina; Maria Neagu, Alexandra; Valentin Pop, Mihai; Mitoseriu, Liliana; Airimioaei, Mirela; Tascu, Sorin; Schileo, Giorgio; Galassi, Carmen

    2013-02-21

    Particulate composites of ferrite and ferroelectric phases with xNiFe{sub 2}O{sub 4} (NF) and (1 - x)Pb{sub 0.988}(Zr{sub 0.52}Ti{sub 0.48}){sub 0.976}Nb{sub 0.024}O{sub 3} (where x = 2, 10, 20, 30, 50, 70, and 100 wt. %) were prepared in situ by sol-gel method. The presence of a diphase composition was confirmed by X-ray diffraction while the microstructure of the composites was studied by scanning electron microscopy revealing a good mixing of the two phases and a good densification of the bulk ceramics. The dielectric permittivity shows usual dielectric dispersion behavior with increasing frequency due to Maxwell-Wagner interfacial polarization. AC conductivity measurements made in frequency range 1 Hz-1 MHz suggest that the conduction process is due to mixed polaron hopping. The effect of NF phase concentration on the P-E and M-H hysteresis behavior and dielectric properties of the composites was investigated. At low NF concentration a sharp ferro-paraelectric transition peak can be observed at around 360 Degree-Sign C while for higher NF concentrations a trend to a diffuse phase transition occurs. All the composite samples exhibit typical ferromagnetic hysteresis loops, indicating the presence of ordered magnetic structure.

  9. [Reduction of dielectric properties of rat gastrocnemius induced by loss of weight].

    PubMed

    Tang, Zhiynan; Zhao, Weihong; Wang, Lin; Ma, Qing

    2009-10-01

    In this experimental study, the AC impedance of isolated gastrocnemius was measured with an impendance analyzer of Agilent 4294A, and the effect of simulated weightlessness on the dielectric properties of the cells in isolated rat sural muscle was investigated by analyzing the dielectric numerical characters with the use of dielectric spectroscopy, the Cole-Cole plots, the spectrum of loss factor and loss tangent, as well as the spectrum of conductivity imaginary part. The results demonstrated that 10 weeks' simulated weightlessness caused some changes; for example, both permittivity at low frequency (epsilonL) and permittivity increment (deltaepsilon) were reduced, and conductivity at high frequency (kappa(h)) was also reduced; at the same time, conductivity increment (deltakappa) was reduced, too. The first characteristic frequency (f(C1)) decreased, while the second characteristic frequency(f(C2)) increased. All of the peak of loss factor, the peak of loss tangent, and the maximum of conductivity imaginary part were reduced. These data indicated that the reduction of dielectric properties of skeletal muscles was induced by weightlessness.

  10. Temperature switchable polymer dielectrics.

    SciTech Connect

    Kholwadwala, Fenil Manish; Johnson, Ross Stefan; Dirk, Shawn M.

    2010-06-01

    Materials with switchable states are desirable in many areas of science and technology. The ability to thermally transform a dielectric material to a conductive state should allow for the creation of electronics with built-in safety features. Specifically, the non-desirable build-up and discharge of electricity in the event of a fire or over-heating would be averted by utilizing thermo-switchable dielectrics in the capacitors of electrical devices (preventing the capacitors from charging at elevated temperatures). We have designed a series of polymers that effectively switch from a non-conductive to a conductive state. The thermal transition is governed by the stability of the leaving group after it leaves as a free entity. Here, we present the synthesis and characterization of a series of precursor polymers that eliminate to form poly(p-phenylene vinylene) (PPV's).

  11. Temperature switchable polymer dielectrics.

    SciTech Connect

    Johnson, Ross Stefan

    2010-08-01

    Materials with switchable states are desirable in many areas of science and technology. The ability to thermally transform a dielectric material to a conductive state should allow for the creation of electronics with built-in safety features. Specifically, the non-desirable build-up and discharge of electricity in the event of a fire or over-heating would be averted by utilizing thermo-switchable dielectrics in the capacitors of electrical devices (preventing the capacitors from charging at elevated temperatures). We have designed a series of polymers that effectively switch from a non-conductive to a conductive state. The thermal transition is governed by the stability of the leaving group after it leaves as a free entity. Here, we present the synthesis and characterization of a series of precursor polymers that eliminate to form poly(p-phenylene vinylene) (PPV's).

  12. The influence of interfaces on the dielectric properties of MnZn-based hybrid polymer composites

    NASA Astrophysics Data System (ADS)

    Moučka, R.; Vilčáková, J.; Kazantseva, N. E.; Lopatin, A. V.; Sáha, P.

    2008-11-01

    In the present paper we report on the specific features of the dielectric properties of a MnZn ferrite/Al based composite. Previously, it has been shown that high-frequency magnetic losses in such hybrid composites (HCs) can be enhanced due to the formation of a core-shell-like structure of a composite, in which ferrite particles are immersed into a conducting medium formed by a continuous network of conducting particles that spans throughout the polymer matrix. Simultaneously, one can vary the dielectric properties of HCs by changing the type and the concentration of conducting particles. Dielectric constant and ac conductivity measurements of MnZn-based composites have been made over the frequency range of 10 Hz-100 kHz in temperature interval from -30 to 100 °C and at ambient temperature up to 3 GHz. The results obtained show that addition of aluminum into the MnZn ferrite/polyurethane composite leads to a decrease in the dc conductivity due to the insulating barrier of Al-Al2O3. On the other hand, ac conductivity of MnZn ferrite and aluminum/polyurethane composite is greater than that of a two-component system due to the occurrence of Maxwell-Wagner-Sillars relaxation processes with a rather low value of activation energy and significantly higher relaxation time. Thus, on one side, aluminum provides sufficient conductivity of the "shell" and thus leads to the enhancement of effective permeability, but, on other side, it does not significantly contribute to the total conductivity (effective permittivity) of HCs. The analysis of the efficiency of HCs with different types of conducting filler as electromagnetic wave absorbers (EWAs) has shown that the matching frequency of EWAs can be effectively controlled in the radio-frequency range through an appropriate choice of the type of conducting filler.

  13. Pumping of dielectric liquids using non-uniform-field induced electrohydrodynamic flow

    NASA Astrophysics Data System (ADS)

    Kim, Wonkyoung; Chun Ryu, Jae; Kweon Suh, Yong; Hyoung Kang, Kwan

    2011-11-01

    We present a method of pumping dielectric (or non-polar) liquids. The pumping method relies on the electrohydrodynamic flow generated by field dependent electrical conductivity (Onsager effect). Adding a small amount of polar liquid increases the field-dependency of conductivity. Applying either dc or ac voltage produces a fast and regular flow around electrodes. Flow speed is proportional to cube of electric-field strength and inversely to applied frequency. The experimental results agreed well with numerical analysis based on our theoretical model.

  14. Relaxation processes in non-Debye dielectrics

    NASA Astrophysics Data System (ADS)

    Turik, A. V.; Bogatin, A. S.; Andreev, E. V.

    2011-12-01

    The specific features of the relaxation processes in non-Debye dielectrics have been investigated. The nature of the difference between the relaxation frequencies of the dielectric constant and dielectric loss (conductivity) has been explained. It has been shown that the average relaxation frequency of the conductivity is considerably (in some cases, by several orders of magnitude) higher than the relaxation frequency of the dielectric constant owing to an increase in the conductivity spectra of the statistical weight of the relaxation processes with short relaxation times.

  15. Opto-structural and dielectric properties of 80 MeV oxygen ion irradiated natural phlogopite mica

    NASA Astrophysics Data System (ADS)

    Kaur, Sukhnandan; Singh, Surinder; Singh, Lakhwant; Lochab, S. P.

    2013-04-01

    Ion beams of MeV energies produce latent tracks in most dielectrics. These ion tracks in turn produce various modifications in their structural, optical and dielectric properties. These modifications are monitored using various techniques such as Ultraviolet-visible spectrometry, X-ray Diffraction, LCR meter and Fourier Transform Infra red spectroscopy in natural phlogopite mica. Thin sheets (˜20 μm) of phlogopite mica were exposed to 80 MeV oxygen ions. A systematic decrease of the optical band gap with ion fluence was observed. An increase in the Urbach energy indicates an increase in the disorder in phlogopite mica. The dielectric constant was found to decrease with increasing fluence while measurements of tan δ, a.c. conductivity and dielectric loss show an increase. The measured data revealed that the value of a.c. conductivity depends linearly on the frequency, with slope n ranging between 0.62 and 0.77. X-ray Diffraction analysis of pristine and irradiated phlogopite mica demonstrated that the crystallite size decreases while strain and dislocation density increases with increasing fluence. Fourier Transform Infra red spectra showed the shifting of the OH stretching band and the disappearance of Si-H bands due to irradiation. Different causes of these modifications are discussed here.

  16. Effect of chromium substitution on the dielectric properties of mixed Ni-Zn ferrite prepared by WOWS sol–gel technique

    SciTech Connect

    Ashtar, M.; Munir, A.; Anis-ur-Rehman, M.; Maqsood, A.

    2016-07-15

    Graphical abstract: Variation of AC conductivity (σ{sub AC}) as a function of natural log of angular frequency (lnω) for Ni{sub 0.5}Zn{sub 0.5}Fe{sub 2-x}Cr{sub x}O{sub 4} nanoferrites at room temperature. - Highlights: • Cr doped mixed Ni-Zn ferrites were successfully synthesized by a newly developed WOWS sol gel technique. • The specific surface area and specific surface area to volume ratio increased with decrease in particle size. • The resonance peaks appeared in dielectric loss graphs, shifting towards low frequency with the increase in Cr concentration. • The prepared samples have the lowest values of the dielectric constant. • The dielectric constant were observed to be inversely proportional to square root of the AC resistivity. - Abstract: Cr{sup +3} doped Ni-Zn nanoferrite samples with composition Ni{sub 0.5}Zn{sub 0.5}Fe{sub 2-x}Cr{sub x}O{sub 4}(x = 0.1, 0.2, 0.3, 0.4) were synthesized With Out Water and Surfactant (WOWS) sol-gel technique. The structural, morphological and dielectric properties of the samples were investigated. The lattice constant, crystallite size, theoretical density and porosity of each sample were obtained from X-ray diffraction (XRD) data. The specific surface area and specific surface area to volume ratio increased with the decrease in the size of Cr{sup +3} doped Ni-Zn ferrite nanoparticles, as the concentration of Cr{sup +3} increased. The SEM analysis revealed that the particles were of nano size and of spherical shape. The dielectric parameters such as dielectric constant (ε′) and dielectric loss (tanδ) of all the samples as a function of frequency at room temperature were measured. The AC conductivity (σ{sub AC}) was determined from the dielectric parameters, which showed increasing trend with the rise in frequency.

  17. Effect of oxygen ion irradiation on dielectric, structural, chemical and thermoluminescence properties of natural muscovite mica.

    PubMed

    Kaur, Sukhnandan; Singh, Surinder; Singh, Lakhwant

    2017-03-01

    Thin cleaved samples (~18µm) of natural muscovite mica were irradiated with 80MeV oxygen ion beam at fluence ranging from 1×10(12) to 5×10(13)ion/cm(2). The alterations in dielectric, structural, chemical and thermoluminescence properties of irradiated as well as pristine samples have been investigated. Dielectric constant decreases while other dielectric parameters such as dielectric loss, tanδ, ac conductivity, real and imaginary parts of electric modulus increase with increase of ion fluence. Williamson Hall investigation has been utilized to ascertain crystallite size and micro strain of pristine and irradiated samples. The XRD analysis revealed a significant increase in micro strain and dislocation density with an increase of ion fluence. The variations in dielectric properties upon irradiation are collaborated with structural modifications in the muscovite. No appreciable changes in characteristic bands (FTIR) have been observed after irradiation, indicating that natural muscovite mica is chemically stable. Natural muscovite mica has eminent applications in heavy ions dosimetry due to observation of well defined single peak at 303°C with activation energy of 1.24eV in TL spectrum.

  18. A facile growth mechanism, structural, optical, dielectric and electrical properties of ZnSe nanosphere via hydrothermal process

    NASA Astrophysics Data System (ADS)

    Javed, Qurat-Ul-Ain; Baqi, Sabah; Abbas, Hussain; Bibi, Maryam

    2017-02-01

    Hydrothermal method was chosen as a convenient method to fabricate zinc selenide (ZnSe) nanoparticle materials. The prepared nanospheres were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM), where its different properties were observed using UV-visible spectroscopy and LCR meter. It was found that the pure ZnSe nanoparticles have a Zinc blende structure with crystallite size 10.91 nm and in a spherical form with average diameter of 35 nm (before sonication) and 18 nm (after sonication) with wide band gap of 4.28 eV. It was observed that there is inverse relation of frequency with dielectric constant and dielectric loss while AC conductivity grows up by increasing frequency. Such nanostructures were determined to be effectively used in optoelectronic devices as UV detector and in those devices where high-dielectric constant materials are required.

  19. Dynamic Properties of Dielectric Susceptibility in Ferroelectric Thin Films

    NASA Astrophysics Data System (ADS)

    Cui, Lian; Cui, Haiying; Wu, Chunmei; Yang, Guihua; He, Zelong; Wang, Yuling; Che, Jixin

    2016-02-01

    In this paper, frequency, temperature, film thickness, surface effects, and various parameters dependence of dielectric susceptibility is investigated theoretically for ferroelectric thin films by the modified Landau theory under an AC applied field. The dielectric susceptibility versus AC applied field shows butterfly-shaped behavior, and depends strongly on the frequency and amplitude of the field and temperature. Our study shows that the existence of the surface transition layer can depress the dielectric susceptibility of a ferroelectric thin film. These results are well consistent with the phenomena reported in experiments.

  20. Structural and optical characterization of Cr{sub 2}O{sub 3} nanostructures: Evaluation of its dielectric properties

    SciTech Connect

    Abdullah, M. M.; Rajab, Fahd M.; Al-Abbas, Saleh M.

    2014-02-15

    The structural, optical and dielectric properties of as-grown Cr{sub 2}O{sub 3} nanostructures are demonstrated in this paper. Powder X-ray diffractometry analysis confirmed the rhombohedral structure of the material with lattice parameter, a = b = 4.953 Å; c = 13.578 Å, and average crystallize size (62.40 ± 21.3) nm. FE-SEM image illustrated the mixture of different shapes (disk, particle and rod) of as-grown nanostructures whereas; EDS spectrum confirmed the elemental purity of the material. FTIR spectroscopy, revealed the characteristic peaks of Cr–O bond stretching vibrations. Energy band gap (3.2 eV) of the nanostructures has been determined using the results of UV-VIS-NIR spectrophotometer. The dielectric properties of the material were checked in the wide frequency region (100Hz-30 MHz). In the low frequency region, the matrix of the dielectric behaves like source as well as sink of electrical energy within the relaxation time. Low value of dielectric loss exhibits that the materials posses good optical quality with lesser defects. The ac conductivity of the material in the high frequency region was found according to frequency power law. The physical-mechanism and the theoretical-interpretation of dielectric-properties of Cr{sub 2}O{sub 3} nanostructures attest the potential candidature of the material as an efficient dielectric medium.

  1. Structural characterization and AC conductivity of bis tetrapropylammonium hexachlorado-dicadmate, [N(C{sub 3}H{sub 7}){sub 4}]{sub 2}Cd{sub 2}Cl{sub 6}

    SciTech Connect

    Hannachi, N.; Guidara, K.; Bulou, A.; Hlel, F.

    2010-11-15

    Synthesis, crystal structure, vibrational study, {sup 13}C, {sup 111}Cd CP-MAS-NMR analysis and electrical properties of the compound [N(C{sub 3}H{sub 7}){sub 4}]{sub 2}Cd{sub 2}Cl{sub 6}, are reported. The latter crystallizes in the triclinic system (space group P1-bar, Z = 2) with the following unit cell dimensions: a = 9.530(1) A, b = 11.744(1) A, c = 17.433(1) A, {alpha} = 79.31(1){sup o}, {beta} = 84.00(1){sup o} and {gamma} = 80.32(1){sup o}. Besides, its structure was solved using 6445 independent reflections down to R = 0.037. The atomic arrangement can be described by alternating organic and inorganic layers parallel to the (11-bar 0) plan, made up of tetrapropylammonium groups and Cd{sub 2}Cl{sub 6} dimers, respectively. In crystal structure, the inorganic layer, built up by Cd{sub 2}Cl{sub 6} dimers, is connected to the organic ones through van der Waals interaction in order to build cation-anion-cation cohesion. Impedance spectroscopy study, reported in the sample, reveals that the conduction in the material is due to a hopping process. The temperature and frequency dependence of dielectric constants of the single crystal sample has been investigated to determine some related parameters to the dielectric relaxation.

  2. Dielectric spectroscopy of polyaniline

    SciTech Connect

    Calleja, R.D.; Matveeva, E.M.

    1993-12-31

    Polyaniline films (PANI) are being considered as attractive new galvanic sources, electrochromic displays, chemical sensors, etc. So far much work has been done to study their optical, electrochemical and electrical properties. However, there are still doubts about the basic electric conductivity mechanisms of PANI. The aim of this paper is to study the influence of water molecules and acid anions on the properties of PANI films by dielectric spectroscopy.

  3. Disorder driven structural and dielectric properties of silicon substituted strontium titanate

    NASA Astrophysics Data System (ADS)

    Dugu, Sita; Pavunny, Shojan P.; Sharma, Yogesh; Scott, James F.; Katiyar, Ram S.

    2015-07-01

    A systematic study on structural, microstructural, optical, dielectric, and electrical properties of phase-pure silicon-modified SrTiO3 polycrystalline electroceramics synthesized using high energy solid state reaction techniques is presented. The asymmetry and splitting in the x-ray diffractometer spectra and the observation of first order transverse optical TO2 and longitudinal optical LO4 modes in Raman spectra (nominally forbidden) revealed the distortion in the cubic lattice as a result of breaking of inversion symmetry due to doping. A bandgap Eg of 3.27 eV was determined for the sample by diffuse reflectance spectroscopy. A high dielectric constant of ˜400 and very low dielectric loss of ˜0.03 were obtained at 100 kHz near ambient conditions. The temperature dependence of the dielectric data displayed features of high temperature relaxor ferroelectric behavior as evidence of existence of polar nano-regions. The ac conductivity as a function of frequency showed features typical of universal dynamic response and obeyed a power law σ a c = σ d c + A ω n . The temperature dependent dc conductivity followed an Arrhenius relation with activation energy of 123 meV in the 200-500 K temperature range. The linear dielectric response of Pt/SrSi0.03Ti0.97O3/Pt dielectric capacitors was well characterized. The measured leakage current was exceptionally low, 13 nA/cm2 at 8.7 kV/cm, revealing an interface blocked bulk conduction mechanism.

  4. Effect of 60Co gamma irradiation on dielectric and complex impedance properties of Dy3+ substituted Ni-Zn nanoferrites

    NASA Astrophysics Data System (ADS)

    Veena, M.; Somashekarappa, A.; Shankaramurthy, G. J.; Jayanna, H. S.; Somashekarappa, H. M.

    2016-12-01

    Nanocrystalline Ni1-xZnxFe2-yDyyO4 (x=0.0, 0.2, 0.4, 0.6, 0.8, 1.0; y=0.0 and 0.1) ferrites were synthesized by combustion method. Ni-Zn-Dy nanoferrites were investigated by X-ray diffraction, scanning electron microscopy, dielectric and impedance properties, before and after γ-irradiation process by 60Co γ-radiation with a dose rate of 310 kGy. The lattice parameter of irradiated samples increased attributed to the conversion of smaller size Fe3+ ions to larger size Fe2+ ions on ionizing effect of gamma radiation. Experimental results reveal that reduction in dielectric constant (ε‧), loss tangent (tan δ), real (Z‧) and imaginary (Z‧‧) impedance and increase in ac conductivityac) have been increased with increasing in frequency. It was found that ε‧, tan δ, σac increase, Z‧‧ and Z‧‧ reach a maximum value and thereafter decrease with further Zn ion substitution. The values of ε‧, tan δ and σac decrease with Dy3+ substitution and enhanced after irradiation. The complex impedance analysis suggesting predominant contribution to conduction was through the grain boundary.

  5. Photoacoustic and dielectric spectroscopic studies of 4-dimethylamino-n-methyl-4-stilbazolium tosylate single crystal: An efficient terahertz emitter

    NASA Astrophysics Data System (ADS)

    Manivannan, M.; Martin Britto Dhas, S. A.; Jose, M.

    2016-12-01

    Bulk terahertz emitting single crystal of 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) was synthesized by condensation method and grown by slow solvent evaporation technique from methanol. The structure and cell parameters of the grown crystals were derived from single crystal and powder X-ray diffraction analyses and the optical properties of the crystal were analyzed by UV-Vis Spectrophotometer. The presence of functional groups was identified by FTIR and FT-Raman spectroscopic studies. We demonstrated that in DAST crystal, the thermal transport properties such as thermal conductivity, thermal diffusivity and thermal effusivity are better than several well recognized standard materials using photoacoustic spectrophotometer. The dielectric measurement was made as a function of frequency (1 Hz-35 MHz) at different temperatures (30-200 °C). The dielectric constant and dielectric loss were found to be strongly dependent on temperature and frequency of the applied electric field. The semicircle in the cole-cole plot showed the presence of dielectric relaxation in the crystal with its diameter representing the resistance of the crystal. The resistivity and ac conductivity were calculated from the measured dielectric data.

  6. Weak ferromagnetism and temperature dependent dielectric properties of Zn{sub 0.9}Ni{sub 0.1}O diluted magnetic semiconductor

    SciTech Connect

    Ahmed, Raju; Moslehuddin, A.S.M.; Mahmood, Zahid Hasan; Hossain, A.K.M. Akther

    2015-03-15

    Highlights: • Single phase wurtzite structure was confirmed from XRD analysis. • Weak ferromagnetic behaviour at room temperature. • Pure semiconducting properties confirmed from temperature dependent conductivity. • Smaller dielectric properties at higher frequency. • Possible potential application in high frequency spintronic devices. - Abstract: In this study the room temperature ferromagnetic behaviour and dielectric properties of ZnO based diluted magnetic semiconductor (DMS) have been investigated using nominal chemical composition Zn{sub 0.9}Ni{sub 0.1}O. The X-ray diffraction analysis confirmed formation of single phase hexagonal wurtzite structure. An increase in grain size with increasing sintering temperature was observed from scanning electron microscopy. Field dependent DC magnetization values indicated dominant paramagnetic ordering along with a slight ferromagnetic behaviour at room temperature. Frequency dependent complex initial permeability showed some positive values around 12 at room temperature. In dielectric measurement, an increasing trend of complex permittivity, loss tangent and ac conductivity with increasing temperature were observed. The temperature dependent dispersion curves of dielectric properties revealed clear relaxation at higher temperature. Frequency dependent ac conductivity was found to increase with frequency whereas complex permittivity and loss tangent showed an opposite trend.

  7. Frequency Dependent Electrical and Dielectric Properties of Au/P3HT:PCBM:F4-TCNQ/n-Si Schottky Barrier Diode

    NASA Astrophysics Data System (ADS)

    Taşçıoğlu, İ.; Tüzün Özmen, Ö.; Şağban, H. M.; Yağlıoğlu, E.; Altındal, Ş.

    2017-04-01

    In this study, poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester: 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (P3HT:PCBM:F4-TCNQ) organic film was deposited on n-type silicon (n-Si) substrate by spin coating method. The electrical and dielectric analysis of Au/P3HT:PCBM:F4-TCNQ/n-Si Schottky barrier diode was conducted by means of capacitance-voltage ( C- V) and conductance-voltage ( G/ ω- V) measurements in the frequency range of 10 kHz-2 MHz. The C- V- f plots exhibit fairly large frequency dispersion due to excess capacitance caused by the presence of interface states ( N ss). The values of N ss located in semiconductor bandgap at the organic film/semiconductor interface were calculated by Hill-Coleman method. Experimental results show that dielectric constant ( ɛ') and dielectric loss ( ɛ″) decrease with increasing frequency, whereas loss tangent (tan δ) remains nearly the same. The decrease in ɛ' and ɛ″ was interpreted by the theory of dielectric relaxation due to interfacial polarization. It is also observed that ac electrical conductivity ( σ ac) and electric modulus ( M' and M″) increase with increasing frequency.

  8. Inhibiting electro-thermal breakdown of acrylic dielectric elastomer actuators by dielectric gel coating

    NASA Astrophysics Data System (ADS)

    La, Thanh-Giang; Lau, Gih-Keong

    2016-01-01

    Electrical breakdown of dielectric elastomer actuators (DEA) is very localized; a spark and a pinhole (puncture) in dielectric ends up with short-circuit. This letter shows that prevention of electrothermal breakdown helps defer failure of DEAs even with conductive-grease electrodes. Dielectric gel encapsulation or coating (Dow Corning 3-4170) helps protect acrylic elastomer (VHB 4905), making it thermally more stable and delaying its thermal oxidation (burn) from 218 °C to 300 °C. Dielectric-gel-coated acrylic DEAs can withstand higher local leak-induced heating and thus achieve higher dielectric strengths than non-coated DEAs do.

  9. Comprehensive analysis of human cells motion under an irrotational AC electric field in an electro-microfluidic chip.

    PubMed

    Vaillier, Clarisse; Honegger, Thibault; Kermarrec, Frédérique; Gidrol, Xavier; Peyrade, David

    2014-01-01

    AC electrokinetics is a versatile tool for contact-less manipulation or characterization of cells and has been widely used for separation based on genotype translation to electrical phenotypes. Cells responses to an AC electric field result in a complex combination of electrokinetic phenomena, mainly dielectrophoresis and electrohydrodynamic forces. Human cells behaviors to AC electrokinetics remain unclear over a large frequency spectrum as illustrated by the self-rotation effect observed recently. We here report and analyze human cells behaviors in different conditions of medium conductivity, electric field frequency and magnitude. We also observe the self-rotation of human cells, in the absence of a rotational electric field. Based on an analytical competitive model of electrokinetic forces, we propose an explanation of the cell self-rotation. These experimental results, coupled with our model, lead to the exploitation of the cell behaviors to measure the intrinsic dielectric properties of JURKAT, HEK and PC3 human cell lines.

  10. Comprehensive Analysis of Human Cells Motion under an Irrotational AC Electric Field in an Electro-Microfluidic Chip

    PubMed Central

    Kermarrec, Frédérique; Gidrol, Xavier; Peyrade, David

    2014-01-01

    AC electrokinetics is a versatile tool for contact-less manipulation or characterization of cells and has been widely used for separation based on genotype translation to electrical phenotypes. Cells responses to an AC electric field result in a complex combination of electrokinetic phenomena, mainly dielectrophoresis and electrohydrodynamic forces. Human cells behaviors to AC electrokinetics remain unclear over a large frequency spectrum as illustrated by the self-rotation effect observed recently. We here report and analyze human cells behaviors in different conditions of medium conductivity, electric field frequency and magnitude. We also observe the self-rotation of human cells, in the absence of a rotational electric field. Based on an analytical competitive model of electrokinetic forces, we propose an explanation of the cell self-rotation. These experimental results, coupled with our model, lead to the exploitation of the cell behaviors to measure the intrinsic dielectric properties of JURKAT, HEK and PC3 human cell lines. PMID:24736275

  11. Broadband local dielectric spectroscopy

    NASA Astrophysics Data System (ADS)

    Labardi, M.; Lucchesi, M.; Prevosto, D.; Capaccioli, S.

    2016-05-01

    A route to extend the measurement bandwidth of local dielectric spectroscopy up to the MHz range has been devised. The method is based on a slow amplitude modulation at a frequency Ω of the excitation field oscillating at a frequency ω and the coherent detection of the modulated average electric force or force gradient at Ω. The cantilever mechanical response does not affect the measurement if Ω is well below its resonant frequency; therefore, limitations on the excitation field frequency are strongly reduced. Demonstration on a thin poly(vinyl acetate) film is provided, showing its structural relaxation spectrum on the local scale up to 45 °C higher than glass temperature, and nanoscale resolution dielectric relaxation imaging near conductive nanowires embedded in the polymer matrix was obtained up to 5 MHz frequency, with no physical reason to hinder further bandwidth extension.

  12. Calculation of Dielectric Response in Molecular Solids for High Capacitance Organic Dielectrics

    NASA Astrophysics Data System (ADS)

    Heitzer, Henry Matthew

    with experiment. This method is then used to help design new high-capacitance molecular dielectrics by determining what materials and chemical properties are important in maximizing dielectric response in Self-Assembled Monolayers (SAMs). Highly (hyper)polarizable Donor-Bridge-Acceptor (DBA) molecular materials are shown to have remarkable dielectric responses. Lastly, the interplay between charge conduction and dielectric constant is examined and it is demonstrated that high dielectric constant materials with low conductance are achievable through molecular design. This technique is a powerful tool for understanding and designing molecular dielectric systems, whose properties are fundamental in many scientific pursuits.

  13. Characterization of the dielectric properties and alternating current conductivity of the SrBi5-xLaxTi4FeO18 (x=0, 0.2) compound

    NASA Astrophysics Data System (ADS)

    Almodovar, N. S.; Portelles, J.; Raymond, O.; Heiras, J.; Siqueiros, J. M.

    2007-12-01

    Lanthanum-doped bismuth layer-structured ferroelectric ceramics SrBi5-xLaxTi4FeO18 (x =0,0.2) were prepared by the solid-state reaction method. X-ray diffraction patterns indicate that single phases were formed. Hysteresis loops at room temperature (20 °C) show that the La-doped ceramic presents a slightly lower spontaneous polarization than the undoped compound. Measurements of relative permittivity and dielectric loss versus temperature were performed from room temperature to 700 °C in the 100 Hz-1 MHz frequency range. Three anomalies were observed in the thermal behavior of the relative permittivity in both samples. Anomalies around the temperatures of 465 and 430 °C have been identified as the ferroelectric-paraelectric transition temperatures for the x =0 and 0.2 compounds, respectively. The sizable shift of the transition temperatures toward lower temperatures with the La doping is interpreted as a manifestation of the La ion incorporation into the crystal structure. From the conductivity studies, the activation energies as functions of frequency for three different temperature zones are obtained. It is found that activation energies are strongly frequency dependent, particularly in the low-frequency region. The frequency dependence of the conductivity at different temperatures was analyzed using Jonscher's power law and the Almond-West conductivity formalism.

  14. Dielectric properties of solutions of oil materials solubilized by sodium dodecyl sulfate in aqueous solutions

    SciTech Connect

    Abe, M.; Shimizu, A.; Ogino, K.

    1982-08-01

    One of the most important properties of micellar systems is their ability to solubilize a variety of species. For aqueous micelles, solubilization is related closely to the hydrophobic and hydrophilic properties of the solubilizate. Different sites of solubilization and orientations may be involved, depending on the structure of the solubilizate. A number of studies on solubilization have been performed experimentally and theoretically. Dielectric constant measurement has proved to be a powerful tool for the investigation of permanent dipole moments of various molecules and of the behavior in solution of various substances, and has been applied in various fields. This technique has been used to determine the chemical structure of surfactants, but not to investigate the solubilization of oily materials in aqueous solution. The dielectric constants and ac electric conductivities observed when a solubilizate is added to an aqueous solution of an anionic surfactant and the differences in the solubilizing behavior due to different kinds of polar groups are discussed. 30 references.

  15. Synthesis and dielectric properties of zinc oxide nanoparticles using a biotemplate

    SciTech Connect

    P, Sharmila P; Tharayil, Nisha J.

    2014-10-15

    Zinc Oxide nanoparticles are synthesized using DNA as capping agent. Zinc oxide nanoparticles are synthesized using DNA as a capping agent. Structural and morphological characterizations are done using SEM, FTIR and XRD. The particle size and lattice parameters are calculated from the diffraction data. The optical properties are studied using UV-Vis absorption spectroscopy and bandgap variation with temperature is determined. The dielectric property of nanoparticles is studied by varying temperature and frequency. The dielectric constant and dispersion parameters are found out. Method of Cole-Cole analysis is used to study the high temperature dispersion of relaxation time. The variation of both AC and DC conductivity are studied and activation energy calculated.

  16. Role of Zn substitution on structural, magnetic and dielectric properties of Cu-Cr spinel ferrites

    NASA Astrophysics Data System (ADS)

    Anjum, S.; Nazli, H.; Khurram, R.; Zeeshan, Talat; Riaz, S.; Usman, A.

    2016-08-01

    The Zn substituted copper chromium spinel ferrites with the chemical formula ZnxCu1-xCr0.5Fe1.5O4 (x = 0-0.8) have been fabricated using powder metallurgical route. The synthesized powders have been investigated by thermal analysis, X-ray diffraction, Fourier transform infrared spectroscopy, Field emission scanning electron microscopy, magnetic and electrical measurement. The X-ray diffraction has confirmed the formation of spinel structure. It has been observed that lattice parameter increases but both the bulk and X-ray density decrease with the increase of Zn concentration. FTIR spectra show two prominent bands in the range of 400-800 cm-1 confirming the formation of spinel ferrites. The saturation magnetization increases up to x = 0.4. As the concentration of Zn increases further, the saturation magnetization decreases. The dielectric tangent loss and dielectric constant (ɛ) decreases while the ac conductivity increases with increasing frequency.

  17. Studies on structural, thermal and AC conductivity scaling of PEO-LiPF6 polymer electrolyte with added ionic liquid [BMIMPF6

    NASA Astrophysics Data System (ADS)

    Chaurasia, S. K.; Saroj, A. L.; Shalu, Singh, V. K.; Tripathi, A. K.; Gupta, A. K.; Verma, Y. L.; Singh, R. K.

    2015-07-01

    Preparation and characterization of polymer electrolyte films of PEO+10wt.% LiPF6 + xwt.% BMIMPF6 (1-butyl-3-methylimidazolium hexafluorophosphate) containing dopant salt lithium hexafluorophosphate (LiPF6) and ionic liquid (BMIMPF6) having common anion PF6 - are reported. The ionic conductivity of the polymer electrolyte films has been found to increase with increasing concentration of BMIMPF6 in PEO+10 wt.% LiPF6 due to the plasticization effect of ionic liquid. DSC and XRD results show that the crystallinity of polymer electrolyte decreases with BMIMPF6 concentration which, in turn, is responsible for the increase in ionic conductivity. FTIR spectroscopic study shows the complexation of salt and/or ionic liquid cations with the polymer backbone. Ion dynamics behavior of PEO+LiPF6 as well as PEO+LiPF6 + BMIMPF6 polymer electrolytes was studied by frequency dependent conductivity, σ(f) measurements. The values σ(f) at various temperatures have been analyzed in terms of Jonscher power law (JPL) and scaled with respect to frequency which shows universal power law characteristics at all temperatures.

  18. AC photovoltaic module magnetic fields

    SciTech Connect

    Jennings, C.; Chang, G.J.; Reyes, A.B.; Whitaker, C.M.

    1997-12-31

    Implementation of alternating current (AC) photovoltaic (PV) modules, particularly for distributed applications such as PV rooftops and facades, may be slowed by public concern about electric and magnetic fields (EMF). This paper documents magnetic field measurements on an AC PV module, complementing EMF research on direct-current PV modules conducted by PG and E in 1993. Although not comprehensive, the PV EMF data indicate that 60 Hz magnetic fields (the EMF type of greatest public concern) from PV modules are comparable to, or significantly less than, those from household appliances. Given the present EMF research knowledge, AC PV module EMF may not merit considerable concern.

  19. Nanostructured high-performance dielectric block copolymers.

    PubMed

    Liu, Wenmei; Liao, Xiaojuan; Li, Yawei; Zhao, Qiuhua; Xie, Meiran; Sun, Ruyi

    2015-10-25

    A new type of insulating-conductive block copolymer was synthesized by metathesis polymerization. The copolymer can self-assemble into unique nanostructures of micelles or hollow spheres. It exhibits a high dielectric constant, low dielectric loss, and high stored/released energy density due to the strong dipolar and nano-interfacial polarization contributions.

  20. AC Electrokinetics of Physiological Fluids for Biomedical Applications.

    PubMed

    Lu, Yi; Liu, Tingting; Lamanda, Ariana C; Sin, Mandy L Y; Gau, Vincent; Liao, Joseph C; Wong, Pak Kin

    2015-12-01

    Alternating current (AC) electrokinetics is a collection of processes for manipulating bulk fluid mass and embedded objects with AC electric fields. The ability of AC electrokinetics to implement the major microfluidic operations, such as pumping, mixing, concentration, and separation, makes it possible to develop integrated systems for clinical diagnostics in nontraditional health care settings. The high conductivity of physiological fluids presents new challenges and opportunities for AC electrokinetics-based diagnostic systems. In this review, AC electrokinetic phenomena in conductive physiological fluids are described followed by a review of the basic microfluidic operations and the recent biomedical applications of AC electrokinetics. The future prospects of AC electrokinetics for clinical diagnostics are presented.

  1. AC Electrokinetics of Physiological Fluids for Biomedical Applications

    PubMed Central

    Lu, Yi; Liu, Tingting; Lamanda, Ariana C.; Sin, Mandy L Y; Gau, Vincent; Liao, Joseph C.; Wong, Pak Kin

    2016-01-01

    AC electrokinetics is a collection of processes for manipulating bulk fluid mass and embedded objects with AC electric fields. The ability of AC electrokinetics to implement the major microfluidic operations, such as pumping, mixing, concentration and separation, makes it possible to develop integrated systems for clinical diagnostics in non-traditional healthcare settings. The high conductivity of physiological fluids presents new challenges and opportunities for AC electrokinetics based diagnostic systems. In this review, AC electrokinetic phenomena in conductive physiological fluids are described followed by a review of the basic microfluidic operations and the recent biomedical applications of AC electrokinetics. The future prospects of AC electrokinetics for clinical diagnostics are presented. PMID:25487557

  2. Microstructure, AC impedance and DC electrical conductivity characteristics of NiFe2-xGdxO4 (x = 0, 0.05 and 0.075)

    NASA Astrophysics Data System (ADS)

    Kamala Bharathi, K.; Markandeyulu, G.; Ramana, C. V.

    2012-03-01

    The structure and electrical characteristics of Gd doped Ni ferrite materials, namely NiFe1.95Gd0.05O4 and NiFe1.925Gd0.075O4, are reported to demonstrate their improved electrical properties compared to that of pure NiFe2O4. NiFe1.95Gd0.05O4 and NiFe1.925Gd0.075O4 compounds crystallize in the cubic inverse spinel phase with a very small amount of GdFeO3 additional phase while pure NiFe2O4 crystallize in inverse spinel phase without any impurity phase. The back scattered electron imaging analysis indicate the primary and secondary formation in NiFe1.95Gd0.05O4 and NiFe1.925Gd0.075O4 compounds. Atomic force microscopy measurements indicate that the bulk grains are ˜2-5 micron size while the grain boundaries are thin compared to bulk grains. Impedance spectroscopic analysis at different temperature indicates the different relaxation mechanisms and their variation with temperature, bulk grain and grain-boundary contributions to the electrical conductivity (Rg) and capacitance (Cg) of these materials. The conductivity in pure NiFeO4 is found to be predominantly due to intrinsic bulk contribution (Rg=213 kΩ and Cg=4.5 x 10-8 F). In the case of NiFe1.95Gd0.05O4 and NiFe1.925Gd0.075O4 compounds, grain and grain-boundary contributions to the conductivity are clearly observed. The DC conductivity values (at 300 K) of NiFe2O4, NiFe1.95Gd0.05O4 and NiFe1.925Gd0.075O4 compounds are found to be 1.06 x 10-7 Ω-1 cm-1, 5.73 x 10-8 Ω-1 cm-1 and 1.28 x 10-8 Ω-1 cm-1 respectively.

  3. 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.

  4. Structural, dielectric and magnetic properties of Ni substituted zinc ferrite

    NASA Astrophysics Data System (ADS)

    Kumbhar, S. S.; Mahadik, M. A.; Mohite, V. S.; Rajpure, K. Y.; Kim, J. H.; Moholkar, A. V.; Bhosale, C. H.

    2014-08-01

    NixZn1-xFe2O4 ferrite has been synthesized by the ceramic method using Ni CO3, ZnO, Fe2O3 precursors. The influence of Ni content on the structural, morphological, electrical and magnetic properties of NixZn1-xFe2O4 ferrites is studied. The X-ray diffraction (XRD) analysis reveals that the samples are polycrystalline with spinel cubic structure. The SEM images of NixZn1-xFe2O4 ferrite show that the grain size decreases with an increase in the Ni content. The tetrahedral and octahedral vibrations in the samples are studied by IR spectra. Frequency dependence of dielectric constant shows dielectric dispersion due to the Maxwell-Wagner type of interfacial polarization. Conduction mechanism due to polarons has been analyzed by measuring the AC conductivity. Impedance spectroscopy is used to study the electrical behavior. Magnetic properties of NixZn1-xFe2O4 are studied by using hysteresis loop measurement. The maximum value of saturation magnetization of 132.8 emu/g obtained for the composition, x=0.8, is attributed to magnetic moment of Fe3+ ions.

  5. Thermal conductivity and dielectric properties of a TiO2-based electrical insulator for use with high temperature superconductor-based magnets

    NASA Astrophysics Data System (ADS)

    Ishmael, S. A.; Slomski, M.; Luo, H.; White, M.; Hunt, A.; Mandzy, N.; Muth, J. F.; Nesbit, R.; Paskova, T.; Straka, W.; Schwartz, J.

    2014-09-01

    Quench protection is a remaining challenge impeding the implementation of high temperature superconductor (HTS)-based magnet applications. This is due primarily to the slow normal zone propagation velocity (NZPV) observed in Bi2Sr2CaCu2OX (Bi2212) and (RE)Ba2Cu3O7 - x (REBCO) systems. Recent computational and experimental findings reveal significant improvements in turn-to-turn NZPV, resulting in a magnet that is more stable and easier to protect through three-dimensional normal zone growth (Phillips M 2009; Ishmael S et al 2013 IEEE Trans. Appl. Supercond. 23 7201311). These improvements are achieved by replacing conventional insulation materials, such as Kapton and mullite braid, with a thin, thermally conducting, electrically-insulating ceramic oxide coating. This paper reports on the temperature-dependent thermal properties, electrical breakdown limits and microstructural characteristics of a titanium oxide (TiO2) insulation and a doped-TiO2-based proprietary insulation (doped-TiO2) shown previously to enhance quench behavior (Ishmael S et al 2013 IEEE Trans. Appl. Supercond. 23 7201311). Breakdown voltages at 77 K ranging from ˜1.5 kV to over 5 kV are reported. At 4.2 K, the TiO2 increases the thermal conductivity of polyimide by about a factor of 10. With the addition of a dopant, thermal conductivity is increased by an additional 13%, and a high temperature heat treatment increases it by nearly an additional 100%. Similar increases are observed at 77 K and room temperature. These results are understood in the context of the various microstructures observed.

  6. Tunneling conduction in graphene/(poly)vinyl alcohol composite

    NASA Astrophysics Data System (ADS)

    Mitra, Sreemanta; Banerjee, Sourish; Chakravorty, Dipankar

    2013-04-01

    Graphene/(Poly)vinyl alcohol (PVA) composite film with thickness 60μm was synthesized by solidification of a PVA solution comprising of dispersed graphene nanosheets. The close proximity of the graphene sheets enables the fluctuation induced tunneling of electrons to occur from one sheet to another. The dielectric data show that the present system can be simulated to a parallel resistance-capacitor network. The high frequency exponent of the frequency variation of the ac conductivity indicates that the charge carriers move in a two-dimensional space. The sample preparation technique will be helpful for synthesizing flexible conductors.

  7. Dielectric metasurfaces

    NASA Astrophysics Data System (ADS)

    Valentine, Jason

    While plasmonics metasurfaces have seen much development over the past several years, they still face throughput limitations due to ohmic losses. On the other hand, dielectric resonators and associated metasurfaces can eliminate the issue of ohmic loss while still providing the freedom to engineer the optical properties of the composite. In this talk, I will present our recent efforts to harness this freedom using metasurfaces formed from silicon and fabricated using CMOS-compatible techniques. Operating in the telecommunications band, I will discuss how we have used this platform to realize a number of novel functionalities including wavefront control, near-perfect reflection, and high quality factor resonances. In many cases the optical performance of these silicon-based metasurfaces can surpass their plasmonic counterparts. Furthermore, for some cases the surfaces are more amenable to large-area fabrication techniques.

  8. Electrical characteristics and conduction mechanisms of amorphous subnanometric Al2O3-TiO2 laminate dielectrics deposited by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Kahouli, Abdelkader; Lebedev, Oleg; Dao, Vu Hung; Elbahri, Marwa Ben; Prellier, Wilfrid; Lüders, Ulrike

    2016-11-01

    Electric conduction mechanisms of amorphous Al2O3/TiO2 (ATO)-laminates deposited by atomic layer deposition with sub-nanometer individual layer thicknesses were studied in a large temperature range. Two characteristic field regions are identified. In the low field region (E ≤ 0.31 MV/cm), the leakage current is dominated by the trap-assisted tunneling through oxygen vacancies occurring in the TiO2, while in the high electric field region (E > 0.31 MV/cm) the Poole Frenkel (PF) hopping is the appropriate conduction process with energy levels depending on the temperature and the electric field. It is shown that the PF potential levels decrease with the applied ATO field due to the overlapping of the Coulomb potential. Amorphous ATO-laminates show the presence of two intrinsic potential energy levels ϕi, which are 0.18 eV for low temperature region and 0.4 eV at high temperature region. Oxygen vacancies are the main origin of traps, which is consistent with the principal mechanisms for leakage in ATO-laminates.

  9. The effects of Bi4Ti3O12 interfacial ferroelectric layer on the dielectric properties of Au/n-Si structures

    NASA Astrophysics Data System (ADS)

    Gökçen, Muharrem; Yıldırım, Mert

    2015-06-01

    Au/n-Si metal-semiconductor (MS) and Au/Bi4Ti3O12/n-Si metal-ferroelectric-semiconductor (MFS) structures were fabricated and admittance measurements were held between 5 kHz and 1 MHz at room temperature so that dielectric properties of these structures could be investigated. The ferroelectric interfacial layer Bi4Ti3O12 decreased the polarization voltage by providing permanent dipoles at metal/semiconductor interface. Depending on different mechanisms, dispersion behavior was observed in dielectric constant, dielectric loss and loss tangent versus bias voltage plots of both MS and MFS structures. The real and imaginary parts of complex modulus of MFS structure take smaller values than those of MS structure, because permanent dipoles in ferroelectric layer cause a large spontaneous polarization mechanism. While the dispersion in AC conductivity versus frequency plots of MS structure was observed at high frequencies, for MFS structure it was observed at lower frequencies.

  10. Effect of gamma irradiation on opto-structural, dielectric, and thermoluminescence properties of natural phlogopite mica

    SciTech Connect

    Kaur, Sukhnandan; Singh, Surinder; Singh, Lakhwant; Lochab, S. P.

    2013-09-07

    Gamma ray induced modifications in natural phlogopite mica have been studied in the dose range of 1–2000 kGy. These modifications were monitored using different techniques viz: ultraviolet-visible spectroscopy, Fourier Transform Infrared spectroscopy, dielectric measurements, X-ray diffraction, and thermoluminescence dosimeter. The analysis of the results reveals that the dose of 100 kGy produces significant change in the natural phlogopite mica as compared to pristine and other exposed samples. Ultraviolet-visible analysis provides the value of optical indirect, direct band gap, and Urbach energy. Cody model was used to calculate structural disorder from Urbach energy. Different dielectric parameters such as dielectric constant, dielectric loss, ac conductivity, and real and imaginary parts of electric modulus were calculated for pristine and irradiated samples at room temperature. Williamson Hall analysis was employed to calculate crystallite size and micro-strain of pristine and irradiated sheets. No appreciable changes in characteristic bands were observed after irradiation, indicating that natural phlogopite mica is chemically stable. The natural phlogopite mica may be recommended as a thermoluminescent dosimeter for gamma dose within 1 kGy–300 kGy.

  11. Optical, Dielectric Characterization and Impedance Spectroscopy of Ni-Substituted MgTiO3 Thin Films

    NASA Astrophysics Data System (ADS)

    Gogoi, Pallabi; Srinivas, P.; Sharma, Pramod; Pamu, D.

    2016-02-01

    We report the effects of oxygen mixing percentage (OMP) and annealing temperature on surface morphology, optical, dielectric and electrical properties of (Mg0.95Ni0.05)TiO3 (MNT) thin films deposited onto amorphous SiO2 and platinized silicon (Pt/TiO2/SiO2/Si) substrates by radio frequency (RF) magnetron sputtering. The annealed films exhibited the highest refractive index, 2.05, at 600 nm with an optical bandgap value of 4.33 eV. The metal-insulator-metal (MIM) capacitors of the MNT thin films were fabricated under different OMPs and the dielectric properties were analyzed by using Maxwell-Wagner two-layer theory and Koop's phenomenological theory. MNT films prepared under 50% OMP displayed the highest dielectric constant (11.21) and minimum loss tangent (0.0114) at 1 MHz. The impedance spectroscopy of the films deposited under 50% OMP has been studied. The Nyquist plots of MNT films revealed two semi-circular arcs and is explained on the basis of an equivalent circuit model. The frequency-dependent alternative current (AC) conductivity followed the Jonscher's power law. The activation energies are calculated using the Arrhenius relationship. The hopping frequency of the charged species was calculated, and the correlation between AC and direct current (DC) conduction mechanisms established in accordance with the Barton-Nakajima-Namikawa (BNN) relationship.

  12. Polycarbonate based three-phase nanocomposite dielectrics

    NASA Astrophysics Data System (ADS)

    Sain, P. K.; Goyal, R. K.; Prasad, Y. V. S. S.; Bhargava, A. K.

    2016-08-01

    Three-phase polycarbonate (PC) matrix nanocomposites are prepared using the solution method. One of the nanocomposite fillers is dielectric and the other is conducting. Lead zirconate titanate (PZT) is used as the dielectric filler. The conducting fillers, nano-Cu and multi-walled carbon nanotubes (MWCNTs), are used to make two different nanocomposites, MWCNT-PZT-PC and Cu-PZT-PC. The prepared nanocomposites are characterized using density measurement, x-ray diffractometry, scanning electron microscopy, energy dispersive x-ray spectroscopy, and differential scanning calorimetry. Percolation is absent in both three-phase nanocomposites within the study’s concentration window of conducting fillers. The dielectric properties of the nanocomposites are evaluated using a precision impedance analyser. The dielectric constant of the Cu-PZT-PC nanocomposite increases to 14 (a dissipation factor of 0.17), whereas in the case of the MWCNT-PZT-PC nanocomposite it increases to 8.5 (a dissipation factor of 0.002). The melting point of both nanocomposites decreases with respect to the control PC. The frequency (1 kHz to 1 MHz) and temperature (room temperature to 200 °C) dependence of the dielectric constant and dissipation factor are examined. For the Cu-PZT-PC nanocomposites, the dielectric constant decreases with increasing frequency, whereas in the case of the MWCNT-PZT-PC nanocomposites the dielectric constant is almost constant. The dielectric constant and dissipation factor exhibit a slight temperature dependence.

  13. Interrelationship between Number of Mobile Protons, Diffusion Coefficient, and AC Conductivity in Superprotonic Conductors, CsHSO4 and Rb3H(SeO4)2

    NASA Astrophysics Data System (ADS)

    Kamazawa, Kazuya; Harada, Masashi; Araki, Toru; Matsuo, Yasumitsu; Tyagi, Madhusudan; Sugiyama, Jun

    2014-07-01

    Using quasielastic neutron scattering (QENS), we investigated the proton dynamics for two superprotonic conductors, CsHSO4 and Rb3H(SeO4)2. To evaluate the self-diffusion coefficients and the number of mobile protons on both superprotonic and normal phases, we focused on proton dynamics not only in the phase above Tc, but also in the phase below Tc. In Rb3H(SeO4)2, the self-diffusion of protons was observed even below the Tc phase. In contrast to popular belief, no large changes in the self-diffusion coefficients were observed across Tc. Nevertheless, the increase in the number of mobile protons across Tc was about 14.5 times, which was estimated from the integrated intensity of QENS spectra, and this change could not account for the increased magnitude of proton conductivity, which is about 500 times. As a large translational self-diffusion coefficient has not been reported in previous works by QENS experiments, there are still unknown factors that contribute to the Nernst-Einstein relation that need to be discovered.

  14. Dielectric and transport properties of magnetic insulators irradiated with GeV heavy ions

    SciTech Connect

    Costantini, J.M.; Salvetat, J.P.; Brisard, F.

    1997-11-01

    The dielectric and ac/dc transport properties of single crystals of yttrium iron garnet (Y{sub 3}Fe{sub 5}O{sub 12} and Y{sub 3}Fe{sub 5}O{sub 12}:Si), and barium hexaferrite (BaFe{sub 12}O{sub 19} and BaFe{sub 12}O{sub 1 9}:Co,Ti) were investigated after irradiations with Xe and Pb ions in the GeV range. In the virgin n-type samples (Y{sub 3}Fe{sub 5}O{sub 12}:Si and BaFe{sub 12}O{sub 19}:Co,Ti), the strong dielectric relaxation below 100 kHz is found to correspond to a space-charge polarization at the blocking metal/insulator contacts yielding a nonohmic dc conductivity. The relaxation frequency decreases with increasing amorphization yield in relation to the decrease of the insulators bulk dc conductivity which becomes ohmic in the amorphous phases. The ac conductivity data of both crystalline and amorphous Y{sub 3}Fe{sub 5}O{sub 12}:Si above 100 kHz and for 100K{lt}T{lt}300K exhibit two contributions: (i) that of carrier transport in a disordered or inhomogeneous medium varying as {nu}{sup s}, with s{approx_equal}0.8, (ii) and that of a two-site polaron hopping process of charge transfer between Fe{sup 2+} and Fe{sup 3+} with an activation energy of 0.29 eV for T{gt}180K. The dc conductivity data of crystalline Y{sub 3}Fe{sub 5}O{sub 12}:Si for 80K{lt}T{lt}300K are discussed on the basis of a small polaron hopping conduction mechanism between Fe{sup 2+} and Fe{sup 3+} with an activation energy around 0.28 eV for T{gt}125K, in agreement with the activation energy around 0.28 eV of the space-charge dielectric relaxation frequency for T{gt}180K. All amorphous phases data are consistent with the picture of hopping conduction between gap states in a disordered medium with (i) an {nu}{sup s} dependence for the ac conductivity above a critical frequency proportional to the dc conductivity, (ii) and an exp({minus}T{sup {minus}1/4}) law for the dc conductivity. {copyright} {ital 1997 American Institute of Physics.}

  15. Transport and dielectric properties of dense ionized matter from the average-atom RESEOS model

    NASA Astrophysics Data System (ADS)

    Ovechkin, A. A.; Loboda, P. A.; Falkov, A. L.

    2016-09-01

    Electron transport properties of warm and hot dense matter are calculated using two versions of the average-atom approach: Liberman's model and the neutral Wigner-Seitz-sphere model. Electrical conductivity calculations employed the extended Ziman formula, the relaxation-time approximation, the Zubarev method, and the Kubo-Greenwood formula. Thermal conductivities were evaluated in the relaxation-time approximation. The results obtained are in good agreement with experimental data and ab initio calculations. The origin of nonphysical features appearing in the DC electrical and thermal conductivities calculated with the relaxation-time approximation and the Zubarev method is analyzed. AC conductivity and dielectric properties of dense ionized matter are obtained from the radiative opacity data calculated using the RESEOS model.

  16. Analyses of temperature-dependent interface states, series resistances, and AC electrical conductivities of Al/p—Si and Al/Bi4Ti3O12/p—Si structures by using the admittance spectroscopy method

    NASA Astrophysics Data System (ADS)

    Mert, Yıldırım; Perihan, Durmuş; Şemsettin, Altındal

    2013-10-01

    In this study, Al/p—Si and Al/Bi4Ti3O12/p—Si structures are fabricated and their interface states (Nss), the values of series resistance (Rs), and AC electrical conductivityac) are obtained each as a function of temperature using admittance spectroscopy method which includes capacitance—voltage (C—V) and conductance—voltage (G—V) measurements. In addition, the effect of interfacial Bi4Ti3O12 (BTO) layer on the performance of the structure is investigated. The voltage-dependent profiles of Nss and Rs are obtained from the high-low frequency capacitance method and the Nicollian method, respectively. Experimental results show that Nss and Rs, as strong functions of temperature and applied bias voltage, each exhibit a peak, whose position shifts towards the reverse bias region, in the depletion region. Such a peak behavior is attributed to the particular distribution of Nss and the reordering and restructuring of Nss under the effect of temperature. The values of activation energy (Ea), obtained from the slope of the Arrhenius plot, of both structures are obtained to be bias voltage-independent, and the Ea of the metal-ferroelectric-semiconductor (MFS) structure is found to be half that of the metal—semiconductor (MS) structure. Furthermore, other main electrical parameters, such as carrier concentration of acceptor atoms (NA), built-in potential (Vbi), Fermi energy (EF), image force barrier lowering (Δ Φb), and barrier height (Φb), are extracted using reverse bias C-2—V characteristics as a function of temperature.

  17. The importance of including conductivity and dielectric permittivity information when processing low-frequency GPR and high-frequency EMI data sets

    NASA Astrophysics Data System (ADS)

    Hatch, Michael A.; Heinson, Graham; Munday, Tim; Thiel, Stephan; Lawrie, Ken; Clarke, Jonathan D. A.; Mill, Philip

    2013-09-01

    The full solution for the wavenumber equation in electromagnetic (EM) theory is available, but not routinely used when processing ground penetrating radar (GPR), and electromagnetic induction (EMI) data. The wavenumber approach is important as it is used for the development of concepts such as skin depth and phase velocity, as well as being the basis for more complete interpretation of EM data sets. Approximations that make the solution simpler are common, and sufficiently accurate, provided that the underlying assumptions are not grossly violated. With the advent of lower-frequency GPR systems (25 MHz and below) and higher-frequency EMI systems (greater than 100 kHz) such approximations need to be re-examined. This paper reviews the full wavenumber expression and then compares phase velocity and skin depth equations based on approximations with the equations for the same parameter based on the full solution. This comparison allows the conditions under which the assumptions are valid to be refined. In this paper it is shown that for GPR surveys conducted under transition band conditions, the error in phase velocity estimates based on low-loss assumptions may be 40%. Similarly, for EMI surveys the skin depth estimation errors may be more than 30% when the equation based on quasi-static assumptions is used instead of the full solution.

  18. Dielectric Barrier Discharge Plasma Actuator for Flow Control

    NASA Technical Reports Server (NTRS)

    Opaits, Dmitry, F.

    2012-01-01

    This report is Part II of the final report of NASA Cooperative Agreement contract no. NNX07AC02A. It includes a Ph.D. dissertation. The period of performance was January 1, 2007 to December 31, 2010. Part I of the final report is the overview published as NASA/CR-2012- 217654. Asymmetric dielectric barrier discharge (DBD) plasma actuators driven by nanosecond pulses superimposed on dc bias voltage are studied experimentally. This produces non-self-sustained discharge: the plasma is generated by repetitive short pulses, and the pushing of the gas occurs primarily due to the bias voltage. The parameters of ionizing pulses and the driving bias voltage can be varied independently, which adds flexibility to control and optimization of the actuators performance. The approach consisted of three elements coupled together: the Schlieren technique, burst mode of plasma actuator operation, and 2-D numerical fluid modeling. During the experiments, it was found that DBD performance is severely limited by surface charge accumulation on the dielectric. Several ways to mitigate the surface charge were found: using a reversing DC bias potential, three-electrode configuration, slightly conductive dielectrics, and semi conductive coatings. Force balance measurements proved the effectiveness of the suggested configurations and advantages of the new voltage profile (pulses+bias) over the traditional sinusoidal one at relatively low voltages. In view of practical applications certain questions have been also addressed, such as electrodynamic effects which accompany scaling of the actuators to real size models, and environmental effects of ozone production by the plasma actuators.

  19. Electrical conduction through DNA molecule.

    PubMed

    Abdalla, S

    2011-09-01

    Several disorder parameters, inside the DNA molecule, lead to localization of charge carriers inside potential wells in the lowest unoccupied and highest occupied molecular orbits (LUMO and HOMO) which affects drastically the electrical conduction through the molecule, and demonstrates that the band carriers play an essential role in the conduction mechanism. So, a model is presented to shed light on the role of electrons of the LUMO in the electrical conduction through the DNA molecule. DC-, AC-conductivity and dielectric permittivity experimental data are well fitted with the presented model giving evidence that the free carriers in the LUMO and HOMO are responsible to make the DNA molecule conductor, insulator or semiconductor. The obtained results show that the localized charge carriers in the DNA molecule are characterized by four different types of relaxation phenomena which are thermally activated by corresponding four activation energies at 0.56 eV, 0.33 eV, 0.24 eV, and 0.05 eV respectively. Moreover, the calculations after the model, at room temperature, show that the time of the relaxation times of the current carriers are in the order of 5 × 10(-2)s, 1.74 × 10(-4)s, 5 × 10(-7)s, and 1.6 × 10(-10)s, respectively.

  20. Correlation of dielectric, electrical and magnetic properties near the magnetic phase transition temperature of cobalt zinc ferrite.

    PubMed

    Pradhan, Dhiren K; Kumari, Shalini; Puli, Venkata S; Das, Proloy T; Pradhan, Dillip K; Kumar, Ashok; Scott, J F; Katiyar, Ram S

    2016-12-21

    Multiferroic composite structures, i.e., composites of magnetostrictive and piezoelectric materials, can be envisioned to achieve the goal of strong room-temperature ME coupling for real practical device applications. Magnetic materials with high magnetostriction, high Néel temperature (TN), high resistivity and large magnetization are required to observe high ME coupling in composite structures. In continuation of our investigations on suitable magnetic candidates for multiferroic composite structures, we have studied the crystal structure, dielectric, transport, and magnetic properties of Co0.65Zn0.35Fe2O4 (CZFO). Rietveld refinement of X-ray diffraction patterns confirms the phase purity with a cubic crystal structure with the (Fd3[combining macron]m) space group; however, we have found a surprisingly large magneto-dielectric anomaly at the Néel temperature, unexpected for a cubic structure. The presence of mixed valences of Fe(2+)/Fe(3+) cations is probed by X-ray photoelectron spectroscopy (XPS), which supports the catonic ordering-mediated large dielectric response. Large dielectric permittivity dispersion with a broad anomaly is observed in the vicinity of the magnetic phase transition temperature (TN) of CZFO suggesting a strong correlation between dielectric and magnetic properties. The evidence of strong spin-polaron coupling has been established from temperature dependent dielectric, ac conductivity and magnetization studies. The ferrimagnetic-paramagnetic phase transition of CZFO has been found at ∼640 K, which is well above room temperature. CZFO exhibits low loss tangent, a high dielectric constant, large magnetization with soft magnetic behavior and magnetodielectric coupling above room temperature, elucidating the possible potential candidates for multiferroic composite structures as well as for multifunctional and spintronics device applications.

  1. Myoblast differentiation of human mesenchymal stem cells on graphene oxide and electrospun graphene oxide-polymer composite fibrous meshes: importance of graphene oxide conductivity and dielectric constant on their biocompatibility.

    PubMed

    Chaudhuri, Biswadeep; Bhadra, Debabrata; Moroni, Lorenzo; Pramanik, Krishna

    2015-02-18

    Recently graphene and graphene based composites are emerging as better materials to fabricate scaffolds. Addition of graphene oxide (GO) nanoplatelets (GOnPs) in bioactive polymers was found to enhance its conductivity (σ) and, dielectric permittivity (ϵ) along with biocompatibility. In this paper, human cord blood derived mesenchymal stem cells (CB-hMSCs) were differentiated to skeletal muscle cells (hSkMCs) on spin coated thin GO sheets composed of GOnPs and on electrospun fibrous meshes of GO-PCL (poly-caprolactone) composite. Both substrates exhibited excellent myoblast differentiations and promoted self-alignedmyotubesformation similar to natural orientation. σ, ϵ, microstructural and vibration spectroscopic studies were carried out for the characterizations of GO sheet and the composite scaffolds. Significantly enhanced values of both σ and ϵ of the GO-PCL composite were considered to provide favourable cues for the formation of superior multinucleated myotubes on the electrospun meshes compared to those on thin GO sheets. The present results demonstrated that both substrates might be used as potential candidates for CB-hMSCs differentiation and proliferation for human skeletal muscle tissue regeneration.

  2. Local electrical and dielectric properties of nanocrystalline solid oxide fuel cell electrolytes

    NASA Astrophysics Data System (ADS)

    Perry, Nicola Helen

    Reducing the operating temperature of solid oxide fuel cells (SOFCs), to improve durability and lower cost, requires an increase in the low temperature oxygen-ion conductivity of the electrolyte. This work investigates whether the electrolyte conductivity could be increased by decreasing the grain size into the nanoscale. Bulk electrolytes - cubic yttria-stabilized zirconia (YSZ, with 8mol% Y2O3), tetragonal zirconia polycrystal (TZP, with 3mol% Y2O3), and Sr- and Mg- co-doped LaGaO3 (LSGM) - were fabricated with grain sizes ranging from 10nm to 3mum, using commercial or sol-gel-derived nanopowders and various sintering techniques. Local grain boundary and grain core conductivities and dielectric constants were analyzed over a range of temperatures and atmospheres using AC-impedance spectroscopy and our novel nano-Grain Composite Model, and interpreted in terms of grain-size dependent defect chemistry (e.g. space charge models, local thermodynamics, and impurity/ acceptor segregation). All three oxides exhibited qualitatively similar electrical/ dielectric behavior. Their single crystal/ grain core dielectric constants exhibited an upturn with temperature, which was attributed to the onset of dipolar relaxation. Grain boundary dielectric constants were consistently higher than grain core dielectric constants at the nanoscale. n-GCM-derived electrical grain boundary half-widths agreed well with measured acceptor dopant segregation widths at grain boundaries. The local grain boundary conductivity was consistently increased in nanocrystalline vs. microcrystalline samples, although the mechanisms responsible for this behavior differed in each material. Grain core conductivity did not change with grain size in each case. Despite the increase in local grain boundary conductivity at the nanoscale, the total conductivity decreased monotonically with decreasing grain size in all three electrolytes; the grain boundaries remain barriers to transport (relative to grain cores

  3. Dielectric relaxation and optical properties of 4-amino-3-mercapto-6-(2-(2-thienyl)vinyl)-1,2,4-triazin-5(4 H)-one donor

    NASA Astrophysics Data System (ADS)

    El-Nahass, M. M.; Ashour, Ahmed; Atta, A. A.; Saad, Hosam A.; Hassanien, A. M.; Al-Baradi, Ateyyah M.; M El-Zaidia, E. F.

    2017-01-01

    Structural, optical, electrical conductivity and dielectric relaxation properties of bulk 4-amino-3-mercapto-6-(2-(2-thienyl)vinyl)-1,2,4-triazin-5(4 H)-one donor (AMT) are studied. The structure of AMT in its powder form was analysed by X-ray diffraction (XRD), infrared spectroscopy (FT-IR) and atomic force microscopy (AFM). AC measurements (impedance, capacitance and phase angle) are done over the temperature range 303-373 K and in the frequency range from 42 Hz to 5 MHz. Analytical approaches for the experimental results of the σ AC( ω, T) and the temperature behaviour of the frequency exponent show that the correlated barrier hopping (CBH) model is a good model to explain the AC electrical conductivity of bulk AMT organic semiconductor material. Application of the dielectric modulus formulism gives a simple method for evaluating the activation energy of the dielectric relaxation. The activation energy from the DC conductivity and the relaxation time are quite similar suggesting a hopping mechanism for AMT. The optical band gap of AMT is investigated using spectrophotometric measurement of transmittance at normal incidence of light in the wavelength range 300-1100 nm.

  4. Dielectric relaxation and Maxwell-Wagner interface polarization in Nb2O5 doped 0.65BiFeO3-0.35BaTiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Wang, Tong; Hu, Jiacong; Yang, Haibo; Jin, Li; Wei, Xiaoyong; Li, Chunchun; Yan, Fei; Lin, Ying

    2017-02-01

    Electrical characterizations of Nb2O5 doped 0.65BiFeO3-0.35BaTiO3 (0.65BF-0.35BT) ceramic were carried out over broad temperature and frequency ranges through dielectric spectroscopy, impedance spectroscopy, and ac conductivity measurements. The dielectric constant and loss tangent are drastically reduced with introducing Nb2O5 into the 0.65BF-0.35BT system. Two dielectric anomalies are detected in the temperature regions of 100 °C ≤ T ≤ 280 °C and 350 °C ≤ T ≤ 480 °C, and the Curie temperature (TC) was confirmed in higher temperature region. A dielectric relaxation with large dielectric constants was detected near the TC. This dielectric relaxation becomes even stronger with the gradual increase in the Nb2O5 content. Impedance spectroscopy results clearly show the contributions of grains and grain boundaries in the frequency range of 100 Hz ≤ f ≤ 1 MHz, and the relaxation processes for grains and grain boundaries are non-Debye-type. The grain boundaries are more resistive than that of the grains, revealing the inhomogeneity in samples. The experimental results are well fitted based on a Maxwell-Wagner (MW) interfacial polarization model below 100 kHz, and the MW interfacial polarization effect becomes more and more obvious with the increase in the Nb2O5 content. The increase in dielectric constant is possibly related to space charge polarization, which is caused by charges accumulated at the interface between the grain and grain boundaries. Frequency dependence of the ac conductivity confirms the MW interfacial polarization effect below 100 kHz.

  5. Optical properties and dielectric relaxation of polyvinylidene fluoride thin films doped with gadolinium chloride

    NASA Astrophysics Data System (ADS)

    El-Sayed, Somyia

    2014-12-01

    In this study, the properties of pure and GdCl3-doped polyvinylidene fluoride (PVDF) films were investigated. X-ray diffraction revealed that the PVDF was composed of mixed α and β phases. Adding GdCl3 to PVDF decreased the crystallinity of the polymer matrix. At room temperature, in the ultraviolet-visible range both the absorbance (a) and extinction coefficient (k) of PVDF decreased with GdCl3 content, demonstrating that the optical response of the doped films improved because of increasing optical energy gap (Eg). We also measured the dielectric loss (ɛ″), electric modulus (M″), and ac conductivityac) at 300-450 K and 0.1-3000 kHz. The pure and doped PVDF exhibited different relaxation processes. The activation energy (Ea) of the αc relaxation decreased with increasing GdCl3 content, following an Arrhenius relationship. The behavior of the ac conductivity revealed that the conduction mechanism for studied films followed correlated barrier hopping model. The hopping distance (R) was calculated at different temperatures for all investigated samples.

  6. Temperature and Frequency Dependent Dielectric Properties of Cu0.5Tl0.5Ba2Ca3(Cu4- y Cd y )O12- δ Bulk Superconductor

    NASA Astrophysics Data System (ADS)

    Rahim, M.; Khan, Nawazish A.; Mumtaz, M.

    2013-07-01

    The temperature and frequency dependent dielectric properties of polycrystalline Cd-doped Cu0.5Tl0.5Ba2Ca3(Cu4- y Cd y )O12- δ ( y=0,0.25,0.5,0.75) bulk superconductor samples are investigated. The zero resistivity critical temperature { T c( R=0)} has decreased and normal state resistivity has increased with the increase of Cd-doping in Cu0.5Tl0.5Ba2Ca3(Cu4- y Cd y )O12- δ samples. The dielectric properties such as dielectric constants ( ɛ', ɛ″), dielectric loss tangent (tan δ) and ac-conductivity ( σ ac ) are investigated by measuring the capacitance (C) and conductance (G) in the frequency range of 10 KHz to 10 MHz at different temperature from 80 K to 300 K. The negative capacitance (NC) is observed in all Cu0.5Tl0.5Ba2Ca3(Cu4- y Cd y )O12- δ samples. The large values of NC observed at lower frequencies and temperatures may be due to reduced thermal vibrations and enhanced polarizability of the material. The effect of Cd-doping on bulk properties, dc-resistivity ( ρ) and ac-electrical conductivity ( σ ac ) of these superconductor samples are investigated. The polarization in Cu0.5Tl0.5Ba2Ca3(Cu4- y Cd y )O12- δ samples is most likely arising from the displacement of charges in CuO2/CdO2 planes relative to the static charges at Ba2+, Tl3+, and Cu2+ sites in Cu0.5Tl0.5Ba2O4- δ charge reservoir layers by external applied field.

  7. Correlation between ionic radii of metal azodye complexes and electrical conductivity.

    PubMed

    El-Ghamaz, N A; El-Sonbati, A Z; Diab, M A; El-Bindary, A A; Mohamed, G G; Morgan, Sh M

    2015-08-05

    5-(2,3-Dimethyl-1-phenylpyrazol-5-one azo)-2-thioxo-4-thiazolidinone (HL) and its metal complexes with copper(II) (1), cobalt(II) (2) and nickel(II) (3) are synthesized and characterized by physico-chemical techniques. The thermal properties of the ligand (HL) and its metal complexes (1-3) are discussed. The thermal activation energies of decomposition (Ea) of HL and its metal complexes with Cu(II), Co(II) and Ni(II) are found to be 48.76, 36.83, 30.59 and 40.45 kJ/mol, respectively. The frequency and temperature dependence of ac conductivity, dielectric constants for HL and its complexes (1-3) are investigated in the temperature range 300-356 K and frequency range 0.1-100 kHz. Both of the ac conductivity and the values of the thermal activation energy for conduction, as well as the dielectric properties of the complexes of HL are found to depend on the nature of the metallic ions. The values of the thermal activation energies of electrical conductivity decrease with increasing the value of test frequency. The small polarons tunneling (SPT) is the dominant conduction mechanism for the ligand (HL), while for complex (2) the overlapping large tunneling model (OLPT) is the dominant conduction mechanism. The correlated barrier hopping (CBH) is the dominant conduction mechanism for both of the complexes (1) and (3).

  8. Structural, Optical and AC Electrical Properties of Ce3+-Doped TiO2-SiO2 Matrices

    NASA Astrophysics Data System (ADS)

    Vidyadharan, Viji; Vasudevan, Prathibha; Karthika, S.; Joseph, Cyriac; Unnikrishnan, N. V.; Biju, P. R.

    2015-08-01

    We report the structural, photoluminescence and alternating current (AC) electrical properties of Ce3+-doped titanosilicate matrices prepared by nonhydrolytic sol-gel method, with different annealing temperatures. The structural characterization of the prepared samples was done by x-ray diffraction, energy dispersive spectrum and Fourier transform infrared spectroscopy measurements. The thermal stability of the prepared matrices was studied by the differential scanning calorimetric analysis. The photoluminescence spectrum shows two luminescence bands centered at 360 nm and 464 nm corresponding to the transitions 2D3/2 to 2F7/2 and 2F5/2, respectively. The dielectric responses of the samples were investigated for the frequency range 1 kHz-3 MHz at room temperature. The variation of AC conductivity, real part of dielectric constant ɛ' and imaginary part of dielectric constant ɛ″ with frequency were also studied. The Cole-Cole parameters were calculated and the semicircles observed in the plots indicate a single relaxation process which can be modelled by an equivalent parallel resistor-capacitor circuit.

  9. Electrical properties of AC{sub 3}B{sub 4}O{sub 12}-type perovskite ceramics with different cation vacancies

    SciTech Connect

    Li, Guizhong; Chen, Zhi; Sun, Xiaojun; Liu, Laijun; Fang, Liang; Elouadi, Brahim

    2015-05-15

    Highlights: • AC{sub 3}B{sub 4}O{sub 12} perovskite with different concentration cation vacancies were prepared. • Cell parameter decreases with the increase of concentration of cation vacancies. • PTCO and CTO remain high dielectric permittivity but depress loss greatly. • Dielectric loss associates with cation vacancies and motion of oxygen vacancies. - Abstract: AC{sub 3}B{sub 4}O{sub 12}-type perovskite CaCu{sub 3}Ti{sub 4}O{sub 12} (CCTO), □{sub 0.34}Pr{sub 0.67}Cu{sub 3}Ti{sub 4}O{sub 12} (PCTO), □{sub 1}Cu{sub 3}Ta{sub 2}Ti{sub 2}O{sub 12} (CTTO), □{sub 2}Cu{sub 2}Ta{sub 4}O{sub 12} (CTO) ceramics with different concentration cation vacancies were prepared through traditional solid state reaction method. X-ray diffraction analysis indicated that CCTO and PCTO are perovskite cubic with space group Im-3 (no. 204) while CTTO and CTO are Pm-3 (no. 200). Cell parameter of the samples dramatically increases with the increase of cation vacancies. Dielectric permittivity of them maintains very high value of ∼10{sup 4} from room temperature to 550 K but the dielectric loss is depressed with the increase of cation vacancies in the same space group. The dielectric properties and conductivity behavior were described by the Debye relaxation and the universal dielectric response, respectively. The effect mechanism of cation vacancy and crystal structure on carrier transposition were discussed.

  10. Deuterium isotope effects on the ionization constant of acetic acid in H2O and D2O by AC conductance from 368 to 548 K at 20 MPa.

    PubMed

    Erickson, K M; Arcis, H; Raffa, D; Zimmerman, G H; Tremaine, P R

    2011-03-31

    Values of the ionization constant of acetic acid in H(2)O and D(2)O (K(HAc) and K(DAc)) and the deuterium isotope effect, ΔpK = pK(DAc) - pK(HAc), have been determined from T = 368 K to T = 548 K at p = 20 MPa, using a flow-through ac conductance cell built at the University of Delaware. Measurements were made on dilute (ionic strength ∼ 10(-4) mol·kg(-1)) solutions of acetic acid, sodium acetate, hydrochloric acid, and sodium chloride in H(2)O and D(2)O, injected in sequence at each temperature and pressure, so that systematic errors in the measured conductance of each solution would cancel. Experimental values for the molar conductivity, Λ, of the strong electrolytes were used to calculate the molar conductivity at infinite dilution, Λ°, using the Fuoss-Hsia-Fernández-Prini (FHFP) equation. These were used to calculate the molar conductivity at infinite dilution for acetic acid which was in turn used to calculate the degree of dissociation and finally the ionization constants of acetic acid. This same procedure was done for the pertinent deuterated solutes in D(2)O. Measured values of log K(HAc), log K(DAc), and ΔpK were obtained to a precision of ±0.008. The present results are in agreement with the only other accurate study at high temperatures and pressures (Mesmer, R. E.; Herting, D. L. J. Solution Chem.1978, 7, 901-913). The deuterium isotope effects, ΔpK, become independent of temperature above ∼420 K, at a value approximately 0.1 unit lower than that at 298 K. These values are ΔpK = 0.43 ± 0.01 and ΔpK = 0.51 ± 0.01, respectively. The temperature dependence of the Walden product ratio, (λ°η)(D(2)O)/(λ°η)(H(2)O), indicates a change in the relative hydration behavior of ions, whereby the effective Stokes radii of the sodium, chloride, and acetate ions in D(2)O relative to H(2)O reverse above ∼423 K. The results also suggest that the greater efficiency of the well-established proton-hopping transport mechanisms for OH(-) and H(3)O

  11. Optical and dielectrical properties of 2-hydroxy-1-naphthylideneaniline and its derivatives

    NASA Astrophysics Data System (ADS)

    El-Ghamaz, N. A.; Shoair, A. F.; El-Shobaky, A. R.; Abo-Yassin, H. R.

    2016-08-01

    The optical and electrical properties of 2-Hydroxy-1-naphthylideneaniline and its derivatives (HLn) have been investigated. The spectral distribution of absorption (α) coefficient for the ligands HL1 and HL4 showed five absorption peaks and shoulders which are assigned as π-π* and n-π* transitions. The optical energy gap (Eg) for HL1 and HL4 is investigated and found to be in the range of 2.09-2.27 eV depending on the function group and the type of electronic transition. The ac conductivity measurements showed a semiconductor behavior. The electrical conduction mechanism was also investigated and found to be correlated barrier-hopping (CBH) and quantum mechanical tunneling (QMT) mechanisms depending on the function group. The effect of adsorbed NH3 gas on the electrical conductivity and dielectric constants of ligand HL3 was also investigated.

  12. Dielectric Actuation of Polymers

    NASA Astrophysics Data System (ADS)

    Niu, Xiaofan

    Dielectric polymers are widely used in a plurality of applications, such as electrical insulation, dielectric capacitors, and electromechanical actuators. Dielectric polymers with large strain deformations under an electric field are named dielectric elastomers (DE), because of their relative low modulus, high elongation at break, and outstanding resilience. Dielectric elastomer actuators (DEA) are superior to traditional transducers as a muscle-like technology: large strains, high energy densities, high coupling efficiency, quiet operation, and light weight. One focus of this dissertation is on the design of DE materials with high performance and easy processing. UV radiation curing of reactive species is studied as a generic synthesis methodology to provide a platform for material scientists to customize their own DE materials. Oligomers/monomers, crosslinkers, and other additives are mixed and cured at appropriate ratios to control the stress-strain response, suppress electromechanical instability of the resulting polymers, and provide stable actuation strains larger than 100% and energy densities higher than 1 J/g. The processing is largely simplified in the new material system by removal of the prestretching step. Multilayer stack actuators with 11% linear strain are demonstrated in a procedure fully compatible with industrial production. A multifunctional DE derivative material, bistable electroactive polymer (BSEP), is invented enabling repeatable rigid-to-rigid deformation without bulky external structures. Bistable actuation allows the polymer actuator to have two distinct states that can support external load without device failure. Plasticizers are used to lower the glass transition temperature to 45 °C. Interpenetrating polymer network structure is established inside the BSEP to suppress electromechanical instability, providing a breakdown field of 194 MV/m and a stable bistable strain as large as 228% with a 97% strain fixity. The application of BSEP

  13. Capacitance and conductance characterization of nano-ZnGa{sub 2}Te{sub 4}/n-Si diode

    SciTech Connect

    Fouad, S.S.; Sakr, G.B.; Yahia, I.S.; Abdel-Basset, D.M.; Yakuphanoglu, F.

    2014-01-01

    Graphical abstract: - Highlights: • XRD and DTA micrographs were used to study the structure of ZnGa{sub 2}Te{sub 4}. • C–V, G–V and R{sub s}–V of the diode characteristics have been analyzed for the first time. • Dielectric constant, dielectric loss, loss tangent and ac conductivity were determined. • The interfaces states were determined using conductance–voltage technique. • ZnGa{sub 2}Te{sub 4} is a good candidate for electronic device applications. - Abstract: Capacitance–voltage (C–V) and conductance–voltage (G–V) characteristics of p-ZnGa{sub 2}Te{sub 4}/n-Si HJD were studied over a wide frequency and temperature. Both the interface states density N{sub ss} and series resistance R{sub s} were strongly frequency and temperature dependent. The interface states density N{sub ss} is decreased with increasing frequency and increase with increasing temperature. The values of the built-in potential (V{sub bi}) were calculated and found to increase with increasing temperature and frequency. The values of capacitance C, conductance G, series resistance R{sub s}, corrected capacitance C{sub ADJ}, corrected conductance G{sub ADJ}, dielectric constant (ε′), dielectric loss (ε″), loss tangent (tan δ) and the AC conductivity (σ{sub ac}) are strongly dependent on the applied frequency, voltage and temperature. The obtained results show that the locations of N{sub ss} and R{sub s} have a significant effect on the electrical characteristics of the studied diode.

  14. Rutile-type Co doped SnO2 diluted magnetic semiconductor nanoparticles: Structural, dielectric and ferromagnetic behavior

    NASA Astrophysics Data System (ADS)

    Mehraj, Sumaira; Shahnawaze Ansari, M.; Alimuddin

    2013-12-01

    Nanoparticles of basic composition Sn1-xCoxO2 (x=0.00, 0.01, 0.03, 0.05 and 0.1) were synthesized through the citrate-gel method and were characterized for structural properties using X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDS) and Fourier transform infrared spectroscopy (FT-IR). XRD analysis of the powder samples sintered at 500 °C for 12 h showed single phase rutile type tetragonal structure and the crystallite size decreased as the cobalt content was increased. FT-IR spectrum displayed various bands that came due to fundamental overtones and combination of O-H, Sn-O and Sn-O-Sn entities. The effect of Co doping on the electrical and magnetic properties was studied using dielectric spectroscopy and vibrating sample magnetometer (VSM) at room temperature. The dielectric parameters (ε, tan δ and σac) show their maximum value for 10% Co doping. The dielectric loss shows anomalous behavior with frequency where it exhibits the Debye relaxation. The variation of dielectric properties and ac conductivity with frequency reveals that the dispersion is due to the Maxwell-Wagner type of interfacial polarization in general and hopping of charge between Sn2+ and Sn4+ as well as between Co2+ and Co3+ ions. The complex impedance analysis was used to separate the grain and grain boundary contributions in the system which shows that the conduction process in grown nanoparticles takes place predominantly through grain boundary volume. Hysteresis loops were observed clearly in M-H curves from 0.01 to 0.1% Co doped SnO2 samples. The saturation magnetization of the doped samples increased slightly with increase of Co concentration. However pure SnO2 displayed paramagnetism which vanished at higher values of magnetic field.

  15. Microstructure, electrical conductivity and modulus spectra of CdI2 doped nanocomposite-electrolytes

    NASA Astrophysics Data System (ADS)

    Kundu, Ranadip; Roy, Debasish; Bhattacharya, Sanjib

    2017-02-01

    Ionic conductivity and dielectric behavior of Ag2O-CdI2-CdO nanocomposite system have been studied. X-ray diffraction has been carried out to obtain the crystallite sizes and the growth of CdO dispersed in glass-matrices. Total conductivity of them shows thermally activated nature. It is observed that total conductivity decreases and corresponding activation energy for conduction follows opposite behavior. The high-frequency ac conductivity may correspond to a nonrandom, correlated and sub-diffusive motion of Ag+ ions. Conductivity relaxation time is found to increase. The nature of scaling of the conductivity as well as modulus spectra indicates that the electrical relaxation of Ag+ is temperature independent but depends upon composition.

  16. Dielectric Metamaterials

    DTIC Science & Technology

    2015-05-29

    approach to reducing the antenna size and achieving an electrically resistive and magnetically conducting metasurface are shown in (f) and (g...currents generated by the incident radiation. This metasurface can be designed for the chosen compact antenna frequency. 3.3 Polarizer Our...demonstrated near-unity polarization conversion over a 200-nm bandwidth (Figure 18c). However, one drawback of such metasurfaces is that they must operate

  17. Effect of exceeding the concentration limit of solubility of silver in perovskites on the dielectric and electric properties of half doped lanthanum-calcium manganite

    NASA Astrophysics Data System (ADS)

    Rahmouni, H.; Cherif, B.; Smari, M.; Dhahri, E.; Moutia, N.; Khirouni, K.

    2015-09-01

    Dielectric and electric properties of La0.5Ca0.2Ag0.3MnO3 (LCMO-Ag) manganite have been investigated using admittance spectroscopy technique. AC conductivity analysis shows that the conductivity verifies the Jonscher universal power law. The deduced exponent 's' values prove that hopping model is the dominating mechanism in the material. From dc-electrical resistivity study, conduction process is found to be dominated by thermally activated small polaron hopping (SPH) mechanism. Complex impedance analysis (CIA) indicates the presence of relaxation phenomenon and allows to modelize the sample in terms of an electrical equivalent circuit. Also, impedance study confirms the contribution of grain boundary in the electrical properties. Dielectric studies indicate that the La0.5Ca0.2Ag0.3MnO3 compound has a Debye-like relaxation. The temperature dependence of permittivity is well fitted by the modified Curie-Weiss law. It is found that dielectric permittivity behavior and the estimated relaxation parameter value (γ≈2), support the evidence of the relaxor nature of La0.5Ca0.2Ag0.3MnO3 material. The high dielectric constant and the low loss tangent indicate the material is promising for tunable capacitor applications.

  18. Influence of Te doping on the dielectric and optical properties of InBi crystals grown by directional freezing

    NASA Astrophysics Data System (ADS)

    Ajayakumar, C. J.; Kunjomana, A. G.

    2014-05-01

    Stoichiometric pure and tellurium (Te) doped indium bismuthide (InBi) were grown using the directional freezing technique in a fabricated furnace. The X-ray diffraction profiles identified the crystallinity and phase composition. The surface topographical features were observed by scanning electron microscopy and atomic force microscopy. The energy dispersive analysis by X-rays was performed to identify the atomic proportion of elements. Studies on the temperature dependence of dielectric constant ( ɛ), loss tangent (tan δ), and AC conductivity ( σ ac) reveal the existence of a ferroelectric phase transition in the doped material at 403 K. When InBi is doped with tellurium (4.04 at%), a band gap of 0.20 eV can be achieved, and this is confirmed using Fourier transform infrared studies. The results thus show the conversion of semimetallic InBi to a semiconductor with the optical properties suitable for use in infrared detectors.

  19. Numerical investigation of dielectric barrier discharges

    NASA Astrophysics Data System (ADS)

    Li, Jing

    1997-12-01

    A dielectric barrier discharge (DBD) is a transient discharge occurring between two electrodes in coaxial or planar arrangements separated by one or two layers of dielectric material. The charge accumulated on the dielectric barrier generates a field in a direction opposite to the applied field. The discharge is quenched before an arc is formed. It is one of the few non-thermal discharges that operates at atmospheric pressure and has the potential for use in pollution control. In this work, a numerical model of the dielectric barrier discharge is developed, along with the numerical approach. Adaptive grids based on the charge distribution is used. A self-consistent method is used to solve for the electric field and charge densities. The Successive Overrelaxation (SOR) method in a non-uniform grid spacing is used to solve the Poisson's equation in the cylindrically-symmetric coordinate. The Flux Corrected Transport (FCT) method is modified to solve the continuity equations in the non-uniform grid spacing. Parametric studies of dielectric barrier discharges are conducted. General characteristics of dielectric barrier discharges in both anode-directed and cathode-directed streamer are studied. Effects of the dielectric capacitance, the applied field, the resistance in external circuit and the type of gases (O2, air, N2) are investigated. We conclude that the SOR method in an adaptive grid spacing for the solution of the Poisson's equation in the cylindrically-symmetric coordinate is convergent and effective. The dielectric capacitance has little effect on the g-factor of radical production, but it determines the strength of the dielectric barrier discharge. The applied field and the type of gases used have a significant role on the current peak, current pulse duration and radical generation efficiency, discharge strength, and microstreamer radius, whereas the external series resistance has very little effect on the streamer properties. The results are helpful in

  20. Frequency and voltage-dependent electrical and dielectric properties of Al/Co-doped PVA/p-Si structures at room temperature

    NASA Astrophysics Data System (ADS)

    Ibrahim, Yücedağ; Ahmet, Kaya; Şemsettin, Altındal; Ibrahim, Uslu

    2014-04-01

    In order to investigate of cobalt-doped interfacial polyvinyl alcohol (PVA) layer and interface trap (Dit) effects, Al/p-Si Schottky barrier diodes (SBDs) are fabricated, and their electrical and dielectric properties are investigated at room temperature. The forward and reverse admittance measurements are carried out in the frequency and voltage ranges of 30 kHz-300 kHz and -5 V-6 V, respectively. C-V or ɛ'-V plots exhibit two distinct peaks corresponding to inversion and accumulation regions. The first peak is attributed to the existence of Dit, the other to the series resistance (Rs), and interfacial layer. Both the real and imaginary parts of dielectric constant (ɛ' and ɛ″) and electric modulus (M' and M″), loss tangent (tan δ), and AC electrical conductivityac) are investigated, each as a function of frequency and applied bias voltage. Each of the M' versus V and M″ versus V plots shows a peak and the magnitude of peak increases with the increasing of frequency. Especially due to the Dit and interfacial PVA layer, both capacitance (C) and conductance (G/w) values are strongly affected, which consequently contributes to deviation from both the electrical and dielectric properties of Al/Co-doped PVA/p-Si (MPS) type SBD. In addition, the voltage-dependent profile of Dit is obtained from the low-high frequency capacitance (CLF-CHF) method.

  1. Dielectric and magnetic properties of Zn-substituted Co2Y barium hexaferrite prepared by sol-gel auto combustion method

    NASA Astrophysics Data System (ADS)

    Odeh, I.; El Ghanem, H. M.; Mahmood, S. H.; Azzam, S.; Bsoul, I.; Lehlooh, A.-F.

    2016-08-01

    This work describes the synthesis, structural, dielectric, and magnetic properties of Y-type Ba2Co2-xZnxFe12O22 hexaferrites prepared by the sol-gel n method. X-ray diffraction (XRD) results revealed a structure of the Zn-substituted samples consistent with the standard patterns for Y-type hexaferrites. The saturation magnetization at room temperature increased with Zn-substitution. Further, the coercive field for the sample with x=2.0 was found to have the lowest value. The results of the dielectric measurements indicated that all samples are insulators, and that the ac conductivity decreased with increasing zinc content. However, the ac conductivity increased with increasing dc bias. The effect of the dc bias was more pronounced on samples with low zinc content. The real part of the dielectric constant decreased markedly with increasing frequency at constant applied bias voltage. Further, the activation energy for the prepared samples depends strongly on the Zn concentration.

  2. Dielectric Relaxation Behavior of Exfoliated Graphite Nanoplatelet-Filled EPDM Vulcanizates

    NASA Astrophysics Data System (ADS)

    Dash, Bikash Kumar; Achary, P. Ganga Raju; Nayak, Nimai C.; Choudhary, R. N. P.

    2017-01-01

    The present study investigates the dielectric relaxation and mechanical behavior of exfoliated graphite nanoplatelet (XgnP)-filled ethylene-propylene-diene terpolymer (EPDM) vulcanizates with variation in frequency, temperature and xGnP loading. The samples were prepared by a solution-cast method using toluene as the solvent followed by compression molding. The enhanced permittivity and ac conductivity which sharply changes above 20 wt.% of xGnP loading shows the conducting behavior of the composites. The real parts of the impedance for the vulcanizates were continuously decreased up to 40 wt.% whereas the complex part shows an increasing tendency at the same loading expressing the increase in the conductivity of the vulcanizates. The percolation threshold of the xGnP-loaded EPDM vulcanizates was at 25 wt.% of xGnP loading. A more prominent effect of temperature on dielectric loss tangent is observed at 85°C, and 100°C. The ac conductivity increases with the rise in temperature. The Nyquist plots of xGnP-reinforced EPDM show the small intercepts on the Z' axis at 85°C, and 100°C for the 40 wt.% loading. The experimental complex impedance plots were in good agreement with the model-fitted plots. The tensile strength of 15 wt.% xGnP-filled vulcanizate increases up to 12 times more than the unfilled EPDM whereas the elongation at break (%) increases up to 700% at the same loading of xGnP. Young's modulus has been doubled and quadrupled for the vulcanizates with 20 and 40 wt.% of xGnPs, respectively, compared to the pure EPDM samples. The results indicate that the xGnP-EPDM conductive composite can find applications in the area of antistatic material, electrostatic discharge gaskets, etc.

  3. Dielectric and Pyroelectric Properties of La- and Pr-Modified Tungsten-Bronze Ferroelectrics

    NASA Astrophysics Data System (ADS)

    Parida, B. N.; Das, Piyush R.; Padhee, R.; Choudhary, R. N. P.

    2013-08-01

    The polycrystalline materials Li2Pb2R2W2Ti4Nb4O30 (R = La, Pr) of the tungsten-bronze structural family have been synthesized using a high- temperature mixed-oxide method. Room-temperature x-ray diffraction (XRD) analysis confirms the formation of single-phase compounds. Room-temperature scanning electron micrography of the pellet samples shows a uniform distribution of well-defined different sizes of grains on the surface of the samples, confirming the formation of single-phase compounds. Study of the frequency and temperature dependence of the dielectric constant and loss tangent suggests the existence of dielectric dispersion in the materials. The ferroelectric phase transition in the samples has been studied based on the variation of fitting parameters (calculated from a theoretical model) with temperature. Studies of pyroelectric properties [figure of merit (FOM) and coefficient] show that the materials have reasonably high FOM useful for pyroelectric detectors. The variation of alternating-current (AC) and direct-current (DC) conductivity with inverse absolute temperature (obtained from dielectric data) follows a typical Arrhenius relation. The low leakage current and negative temperature coefficient of resistance behavior of the samples have been verified from J- E plots.

  4. Dynamic electromechanical instability of a dielectric elastomer balloon

    NASA Astrophysics Data System (ADS)

    Chen, Feifei; Zhu, Jian; Wang, Michael Yu

    2015-11-01

    Electromechanical instability, a significant phenomenon in dielectric elastomers, has been well studied in the literature. However, most previous work was based on the assumption that dielectric elastomers undergo quasi-static deformation. This letter investigates the dynamic electromechanical instability of a dielectric elastomer balloon which renders four types of oscillation subject to a parametric combination of DC and AC voltages. The simulated oscillations show that dynamic electromechanical instability occurs within quite a large range of excitation frequency, in the form of snap-through or snap-back, when the DC and AC voltages reach critical values. The balloon is at its most susceptible to dynamic electromechanical instability when the superharmonic, harmonic or subharmonic resonance is excited. Taking all excitation parameters into account, this letter analyzes the global critical condition which triggers the dynamic electromechanical instability of the balloon.

  5. Structural and dielectric studies of lead-free ceramics: Na1/2Y1/2TiO3

    NASA Astrophysics Data System (ADS)

    Barik, Subrat K.; Choudhary, Ram N. P.; Mahapatra, Prasanta K.

    2008-12-01

    The polycrystalline samples of Na1/2Y1/2TiO3 were prepared by the mixed-oxide method. A preliminary X-ray structural analysis was shown to exhibit the formation of a single-phase compound with an orthorhombic structure. Microstructural analysis by scanning electron microscopy (SEM) exhibits well defined grains distributed uniformly through out the sample suggesting the compactness and homogeneity of the sample. Detailed studies of dielectric properties of Na1/2Y1/2TiO3 in a wide frequency range (102 106 Hz) at different temperatures (31 500°C) show a dielectric anomaly at 105°C, which may be related to a ferroelectricparaelectric phase transition as suggested by hysteresis loop at room temperature. An ac conductivity ( σ ac) of the material is mainly governed by the polaron hopping mechanism, which is also influenced by both frequency and temperature. The activation energy was obtained from the plot of temperature with a.c. conductivity.

  6. Structural and dielectric studies of lead-free ceramics: Na1/2Y1/2TiO3

    NASA Astrophysics Data System (ADS)

    Barik, Subrat; Choudhary, Ram; Mahapatra, Prasanta

    2008-12-01

    The polycrystalline samples of Na1/2Y1/2TiO3 were prepared by the mixed-oxide method. A preliminary X-ray structural analysis was shown to exhibit the formation of a single-phase compound with an orthorhombic structure. Microstructural analysis by scanning electron microscopy (SEM) exhibits well defined grains distributed uniformly through out the sample suggesting the compactness and homogeneity of the sample. Detailed studies of dielectric properties of Na1/2Y1/2TiO3 in a wide frequency range (102-106 Hz) at different temperatures (31-500°C) show a dielectric anomaly at 105°C, which may be related to a ferroelectricparaelectric phase transition as suggested by hysteresis loop at room temperature. An ac conductivityac) of the material is mainly governed by the polaron hopping mechanism, which is also influenced by both frequency and temperature. The activation energy was obtained from the plot of temperature with a.c. conductivity.

  7. Correlation between AC and DC transport properties of Mn substituted cobalt ferrite

    NASA Astrophysics Data System (ADS)

    Supriya, Sweety; Kumar, Sunil; Kar, Manoranjan

    2016-12-01

    The CoFe2-xMnxO4 compound is prepared by following the sol gel technique. The structural analysis through XRD and Rietveld has been confirmed for the single cubic phase having F d 3 ¯ m space group for CoFe2-xMnxO4 and also verified it through Raman spectroscopy measurements. The tetrahedral site observed to be red shifted with increase in Mn concentration in cobalt ferrite. All the XRD patterns have been analyzed by employing the Rietveld refinement technique. The particle size was found to be in the range of 30-40 nm. The electrical properties of polycrystalline CoFe2-xMnxO4 for x = 0.00, 0.10, 0.15, and 0.2, spinel ferrite was investigated by impedance spectroscopy. The influence of doping, frequency and temperature on the electrical transport properties of the CoFe2-xMnxO4 for x = 0.00, 0.10, 0.15, and 0.20 were investigated. The magnitude of Z' and Z″ decreases with increase in temperature. Only one semicircle is observed in each Cole Cole plot which reveals that ac conductivity is dominated by grains. The grain resistance and grain boundary resistance both were found to decrease as a function of temperature. Temperature variation of DC electrical conductivity follows the Arrhenius relationship. A detailed analysis of electrical parameters provides assistance in connecting information regarding the conduction mechanism as well as determination of both dielectric and magnetic transition temperatures in the substituted cobalt ferrite. Detailed analysis of ac impedance and DC resistivity measurement reveals that, the magnetic ordering temperature in the Mn substituted cobalt ferrite does not respond to the frequency of ac electrical signal; however, it responds to the DC resistivity. The correlation between ac impedance and DC resistivity has been established.

  8. Dielectric Heaters for Testing Spacecraft Nuclear Reactors

    NASA Technical Reports Server (NTRS)

    Sims, William Herbert; Bitteker, Leo; Godfroy, Thomas

    2006-01-01

    A document proposes the development of radio-frequency-(RF)-driven dielectric heaters for non-nuclear thermal testing of the cores of nuclear-fission reactors for spacecraft. Like the electrical-resistance heaters used heretofore for such testing, the dielectric heaters would be inserted in the reactors in place of nuclear fuel rods. A typical heater according to the proposal would consist of a rod of lossy dielectric material sized and shaped like a fuel rod and containing an electrically conductive rod along its center line. Exploiting the dielectric loss mechanism that is usually considered a nuisance in other applications, an RF signal, typically at a frequency .50 MHz and an amplitude between 2 and 5 kV, would be applied to the central conductor to heat the dielectric material. The main advantage of the proposal is that the wiring needed for the RF dielectric heating would be simpler and easier to fabricate than is the wiring needed for resistance heating. In some applications, it might be possible to eliminate all heater wiring and, instead, beam the RF heating power into the dielectric rods from external antennas.

  9. Microwave dielectric behavior of vegetation material

    NASA Technical Reports Server (NTRS)

    Elrayes, Mohamed A.; Ulaby, Fawwaz T.

    1987-01-01

    The microwave dielectric behavior of vegetation was examined through the development of theoretical models involving dielectric dispersion by both bound and free water and supported by extensive dielectric measurements conducted over a wide range of conditions. The experimental data were acquired using an open-ended coaxial probe that was developed for sensing the dielectric constant of thin layers of materials, such as leaves, from measurements of the complex reflection coefficient using a network analyzer. The probe system was successfully used to record the spectral variation of the dielectric constant over a wide frequency range extending from 0.5 to 20.4 GHz at numerous temperatures between -40 to +40 C. The vegetation samples were measured over a wide range of moisture conditions. To model the dielectric spectrum of the bound water component of the water included in vegetation, dielectric measurements were made for several sucrose-water solutions as analogs for the situation in vegetation. The results were used in conjunction with the experimental data for leaves to determine some of the constant coefficients in the theoretical models. Two models, both of which provide good fit to the data, are proposed.

  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. 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 conductivityac) 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.

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

    SciTech Connect

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

    2012-07-01

    M-type hexaferrites with compositions BaFe{sub 12}O{sub 19} (BFO), SrFe{sub 12}O{sub 19} (SFO), Ba{sub 0.5}Sr{sub 0.5}Fe{sub 12}O{sub 19} (BSFO), and Ba{sub 0.5}Pb{sub 0.5}Fe{sub 12}O{sub 19} (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 P6{sub 3}/mmc for BFO, SFO, and BSFO samples, whereas BPFO sample contains hematite ({alpha}-Fe{sub 2}O{sub 3}) phase with space group R3c along with the M-type main phase. All the samples show dispersion in dielectric constant ({epsilon} Prime ) and dielectric loss (tan {delta}) values with frequency. The values of {epsilon} Prime and tan {delta} 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 ({sigma}{sub ac}) and the most probable relaxation time ({tau}{sub M Double-Prime }) 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{sup *} (M Double-Prime vs M Prime ) indicate that dc conductivity dominates in the region below the M Double-Prime {sub max} point. Above M Double-Prime {sub max}, the variations follow Jonscher power law ({sigma} = A{omega}{sup s}) implying that ac conductivity is dominating in this region. Among the prepared samples, SFO hexaferrite has lowest values of {sigma}{sub ac}, {epsilon} Prime , and tan {delta} making it suitable for use in microwave devices.

  13. Effects of oxygen vacancies on dielectric, electrical, and ferroelectric properties of Ba{sub 4}Nd{sub 2}Fe{sub 2}Nb{sub 8}O{sub 30} ceramics

    SciTech Connect

    Fei Liu, Shu; Jun Wu, Yong; Li, Juan; Ming Chen, Xiang

    2014-02-24

    Effects of oxygen vacancies on the dielectric, electrical, and ferroelectric properties of Ba{sub 4}Nd{sub 2}Fe{sub 2}Nb{sub 8}O{sub 30} ceramics were investigated. A dielectric relaxation above T{sub c} can be ascribed to the trap-controlled ac conduction around doubly ionized oxygen vacancies. The dc conductivity of the N{sub 2}-annealed and O{sub 2}-annealed samples is attributed to the long-range motion of the V{sub o}{sup ⋅⋅}, and that of the as-sintered sample is considered to be governed by the electronic and oxygen-vacancy ionic mixed conduction mechanism. Low concentration and random distributed oxygen vacancies are propitious to the domain switching, while high concentration and allied oxygen defects hinder the domain-wall movement.

  14. Resonant dielectric metamaterials

    DOEpatents

    Loui, Hung; Carroll, James; Clem, Paul G; Sinclair, Michael B

    2014-12-02

    A resonant dielectric metamaterial comprises a first and a second set of dielectric scattering particles (e.g., spheres) having different permittivities arranged in a cubic array. The array can be an ordered or randomized array of particles. The resonant dielectric metamaterials are low-loss 3D isotropic materials with negative permittivity and permeability. Such isotropic double negative materials offer polarization and direction independent electromagnetic wave propagation.

  15. Study of the dielectric properties of weathered granite, basalt and quartzite by means of broadband dielectric spectroscopy over a wide range of frequency and temperature.

    NASA Astrophysics Data System (ADS)

    Araujo, Steven; Delbreilh, Laurent; Antoine, Raphael; Dargent, Eric; Fauchard, Cyrille

    2016-04-01

    Broadband Dielectric Spectroscopy (BDS) allows the measurement of the complex impedance of various materials over a wide range of frequency (0.1 Hz to 2 MHz) and temperature (-150 to 400°C). Other properties can be assessed from this measurement such as permittivity and conductivity. In this study, the BDS is presented to figure out the complex behaviour of several rock parameters as a function of the temperature and frequency. Indeed, multiple processes might occur such as interfacial polarization, AC and DC conductivity. The measurements of a weathered granite, basalt and quartzite were performed. The activation energy associated to each process involved during the measurement can be calculated by following the relaxation time as a function of the temperature, taking into account the Havriliak-Négami model. The principle of the technique and the whole study is presented here and several hypothesis are advanced to explain the dielectric behaviour of rocks. Finally, as the range of frequency and temperature of the BDS method is common to several electromagnetic and electrical techniques applied in subsurface geophysics, some perspectives are proposed to better understand geophysical measurements in hydrothermal systems.

  16. Magnetic, dielectric properties, and scaling behaviors of Aurivillius compounds Bi{sub 6−x∕3}Fe{sub 2}Ti{sub 3−2x}(WCo){sub x}O{sub 18} (0 ≤ x ≤ 0.15)

    SciTech Connect

    Zuo, X. Z.; Yang, J. Yuan, B.; Tang, X. W.; Zhang, K. J.; Zhu, X. B.; Song, W. H.; Dai, J. M.; Song, D. P.; Sun, Y. P.

    2015-03-21

    We investigate the structural, magnetic, dielectric properties, and scaling behaviors of Aurivillius compounds Bi{sub 6−x∕3}Fe{sub 2}Ti{sub 3−2x}(WCo){sub x}O{sub 18} (0 ≤ x ≤ 0.15). The room-temperature weak ferromagnetism is observed for the W/Co co-doped samples. The results of the dielectric constant ε{sub r}, complex impedance Z″, the dc conductivity σ{sub dc}, and hopping frequency f{sub H} manifest that the dielectric relaxation of the x = 0 sample and the doped samples in the dielectric anomaly region (450–750 K) can be ascribed to the trap-controlled ac conduction around the doubly ionized oxygen vacancies and the localized hopping process of oxygen vacancies, respectively. The scaling behaviors reveal that the dynamic process of both electrons in the x = 0 sample and oxygen vacancies in the doped samples is temperature independent. The ferroelectric Curie-temperature T{sub c} decreases slightly from 973 K to 947 K with increasing the doping level of W/Co. In addition, the dielectric loss exhibits a dielectric relaxation above 800 K with the rather large activation energies (1.95 eV ≤ E{sub a} ≤ 2.72 eV)

  17. Effects of Heat-Treatment Temperature on the Microstructure, Electrical and Dielectric Properties of M-Type Hexaferrites

    NASA Astrophysics Data System (ADS)

    Ali, Ihsan; Islam, M. U.; Awan, M. S.; Ahmad, Mukhtar

    2014-02-01

    M-type hexaferrite BaCr x Ga x Fe12-2 x O19 ( x = 0.2) powders have been synthesized by use of a sol-gel autocombustion method. The powder samples were pressed into 12-mm-diameter pellets by cold isostatic pressing at 2000 bar then heat treated at 700°C, 800°C, 900°C, and 1000°C. X-ray diffraction patterns of the powder sample heat treated at 1000°C confirmed formation of the pure M-type hexaferrite phase. The electrical resistivity at room temperature was significantly enhanced by increasing the temperature of heat treatment and approached 5.84 × 109 Ω cm for the sample heat treated at 1000°C. Dielectric constant and dielectric loss tangent decreased whereas conductivity increased with increasing applied field frequency in the range 1 MHz-3 GHz. The dielectric properties and ac conductivity were explained on the basis of space charge polarization in accordance with the Maxwell-Wagner two-layer model and Koop's phenomenological theory. The single-phase synthesized materials may be useful for high-frequency applications, for example reduction of eddy current losses and radar absorbing waves.

  18. 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

  19. 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.

  20. The electrical characteristics of the dielectric barrier discharges

    NASA Astrophysics Data System (ADS)

    Yehia, Ashraf

    2016-06-01

    The electrical characteristics of the dielectric barrier discharges have been studied in this paper under different operating conditions. The dielectric barrier discharges were formed inside two reactors composed of electrodes in the shape of two parallel plates. The dielectric layers inside these reactors were pasted on the surface of one electrode only in the first reactor and on the surfaces of the two electrodes in the second reactor. The reactor under study has been fed by atmospheric air that flowed inside it with a constant rate at the normal temperature and pressure, in parallel with applying a sinusoidal ac voltage between the electrodes of the reactor. The amount of the electric charge that flows from the reactors to the external circuit has been studied experimentally versus the ac peak voltage applied to them. An analytical model has been obtained for calculating the electrical characteristics of the dielectric barrier discharges that were formed inside the reactors during a complete cycle of the ac voltage. The results that were calculated by using this model have agreed well with the experimental results under the different operating conditions.

  1. Terahertz Artificial Dielectric Lens

    NASA Astrophysics Data System (ADS)

    Mendis, Rajind; Nagai, Masaya; Wang, Yiqiu; Karl, Nicholas; Mittleman, Daniel M.

    2016-03-01

    We have designed, fabricated, and experimentally characterized a lens for the THz regime based on artificial dielectrics. These are man-made media that mimic properties of naturally occurring dielectric media, or even manifest properties that cannot generally occur in nature. For example, the well-known dielectric property, the refractive index, which usually has a value greater than unity, can have a value less than unity in an artificial dielectric. For our lens, the artificial-dielectric medium is made up of a parallel stack of 100 μm thick metal plates that form an array of parallel-plate waveguides. The convergent lens has a plano-concave geometry, in contrast to conventional dielectric lenses. Our results demonstrate that this lens is capable of focusing a 2 cm diameter beam to a spot size of 4 mm, at the design frequency of 0.17 THz. The results further demonstrate that the overall power transmission of the lens can be better than certain conventional dielectric lenses commonly used in the THz regime. Intriguingly, we also observe that under certain conditions, the lens boundary demarcated by the discontinuous plate edges actually resembles a smooth continuous surface. These results highlight the importance of this artificial-dielectric technology for the development of future THz-wave devices.

  2. Aging dynamics in the polymer glass of poly(2-chlorostyrene): Dielectric susceptibility and volume

    NASA Astrophysics Data System (ADS)

    Fukao, Koji; Tahara, Daisuke

    2009-11-01

    Aging dynamics was investigated in the glassy states of poly(2-chlorostyrene) by measuring the complex electrical capacitance during aging below the glass transition temperature. The variations with time and temperature of the ac dielectric susceptibility and volume could be determined by simply measuring the variation in the complex electrical capacitance. Isothermal aging at a given temperature for several hours after an intermittent stop in constant-rate cooling is stored in the deviations of both the real and imaginary parts of the complex ac dielectric susceptibility and volume. During cooling after isothermal aging, the deviation of the ac dielectric susceptibility from the reference value decreases and almost vanishes at room temperature. By contrast, the deviation in volume induced during isothermal aging remains almost constant during cooling. The simultaneous measurement of ac dielectric susceptibility and volume clearly revealed that the ac dielectric susceptibility exhibits a full rejuvenation effect, whereas the volume does not show any rejuvenation effects. We discuss a plausible model that can reproduce the present experimental results.

  3. Thermal, optical and dielectric properties of phase stabilized δ - Dy-Bi2O3 ionic conductors

    NASA Astrophysics Data System (ADS)

    Bandyopadhyay, Swagata; Dutta, Abhigyan

    2017-03-01

    In this work, we have investigated the thermal, structural, optical and dielectric properties of Bi1-xDyxO1.5-δ (0.10≤x≤0.40) ionic conductors prepared by citrate auto-ignition method. The Thermo gravimetric-DTA analysis and X-Ray Diffraction pattern confirm the single δ-phase stabilization of doped system beyond 25 mol% doping concentration. XRD analysis also indicates that average crystallite size is maximum and micro strain is minimum for Bi0.75Dy0.25O1.5-δ composition. The optical band gap of the prepared compositions is obtained from the Ultraviolet- Visible spectroscopy that shows a red shift with the increase in Dy content. The presence of different structural bonds is confirmed from FT-IR spectroscopy analysis. Ionic transport property of the prepared compositions has been analyzed using Nyquist plot for dc conduction and Nernst-Einstein relation for ac conduction mechanism. This analysis indicates that the composition Bi0.75Dy0.25O1.5-δ shows highest conductivity. The dielectric properties of these ionic conductors have been analyzed using Havriliak-Negami (HN) formalism. The dielectric permittivity ε' (ω) of all the prepared compositions is found to be within the range 1.61-3.63(x102) in S.I. unit. Analysis of electric modulus data reveals that dielectric and modulus relaxation follows same mechanism. The time-temperature superposition principle has been verified from the scaling of modulus spectra.

  4. ACS: ALMA Common Software

    NASA Astrophysics Data System (ADS)

    Chiozzi, Gianluca; Šekoranja, Matej

    2013-02-01

    ALMA Common Software (ACS) provides a software infrastructure common to all ALMA partners and consists of a documented collection of common patterns and components which implement those patterns. The heart of ACS is based on a distributed Component-Container model, with ACS Components implemented as CORBA objects in any of the supported programming languages. ACS provides common CORBA-based services such as logging, error and alarm management, configuration database and lifecycle management. Although designed for ALMA, ACS can and is being used in other control systems and distributed software projects, since it implements proven design patterns using state of the art, reliable technology. It also allows, through the use of well-known standard constructs and components, that other team members whom are not authors of ACS easily understand the architecture of software modules, making maintenance affordable even on a very large project.

  5. Photoelectric charging of partially sunlit dielectric surfaces in space

    NASA Technical Reports Server (NTRS)

    De, B. R.; Criswell, D. R.

    1977-01-01

    Sunlight-shadow effects may substantially alter the charging situation for a dielectric surface. The sunlight-shadow boundary tends to be the site of intense multipole electric fields. Charges on a sunlit dielectric surface have a finite effective mobility. The charge distribution tends to resemble that on a conducting surface. A boundary between a conducting and a dielectric surface may not represent a conductivity discontinuity when this boundary is sunlit; charges may migrate at a nontrivial rate across the boundary. A contracting or expanding sunlit area may experience a supercharging.

  6. Microtubule alignment and manipulation using AC electrokinetics.

    PubMed

    Uppalapati, Maruti; Huang, Ying-Ming; Jackson, Thomas N; Hancock, William O

    2008-09-01

    The kinesin-microtubule system plays an important role in intracellular transport and is a model system for integrating biomotor-driven transport into microengineered devices. AC electrokinetics provides a novel tool for manipulating and organizing microtubules in solution, enabling new experimental geometries for investigating and controlling the interactions of microtubules and microtubule motors in vitro. By fabricating microelectrodes on glass substrates and generating AC electric fields across solutions of microtubules in low-ionic-strength buffers, bundles of microtubules are collected and aligned and the electrical properties of microtubules in solution are measured. The AC electric fields result in electro-osmotic flow, electrothermal flow, and dielectrophoresis of microtubules, which can be controlled by varying the solution conductivity, AC frequency, and electrode geometry. By mapping the solution conductivity and AC frequency over which positive dielectrophoresis occurs, the apparent conductivity of taxol-stabilized bovine-brain microtubules in PIPES buffer is measured to be 250 mS m(-1). By maximizing dielectrophoretic forces and minimizing electro-osmotic and electrothermal flow, microtubules are assembled into opposed asters. These experiments demonstrate that AC electrokinetics provides a powerful new tool for kinesin-driven transport applications and for investigating the role of microtubule motors in development and maintenance of the mitotic spindle.

  7. Synthesis, crystal structure, spectroscopic, thermal and dielectric properties of a novel semi-organic pentachloroantimonate (III)

    NASA Astrophysics Data System (ADS)

    Lahbib, Ikram; Rzaigui, Mohamed; Smirani, Wajda

    2016-09-01

    A new organic-inorganic hybrid material of formula (C10H15N2F)5(SbCl5)5.2H2O was synthesized and characterized by X-Ray diffraction analysis. It crystallizes in the monoclinic space group P21/c with the following unit cell parameters a = 15.819(4) Å, b = 17.685(3) Å, c = 30.529(4) Å, Z = 4 and V = 8540(3) Å3. The examination of the structure shows that the three-dimensional frameworks are produced by Nsbnd H⋯Cl, Nsbnd H⋯O, Csbnd H⋯Cl and Nsbnd H⋯F, Csbnd H⋯F hydrogen bonding and Cl⋯Cl interactions. IR, Raman and UV-Visible spectroscopies were also used to characterize this compound. In addition, the fluorescent properties of this compound have been investigated in the liquid state at room temperature. Differential scanning calorimetry (DSC) has revealed a structural phase transition of the order-disorder type around 370 K. Dielectric investigations revealed a step-wise change of the electric permittivity at Ttr characteristic of the crystal in the high-temperature phase. The evolution of dielectric constant as a function of temperature of the sample has been investigated in order to determine some related parameters. Measurements of AC conductivity as a function of frequency at different temperatures indicated a hopping conduction mechanism and/or reorientational motion.

  8. Structural, thermal and dielectric properties of cobaltous malonate single crystals grown in limited diffusion media

    NASA Astrophysics Data System (ADS)

    Lincy, A.; Mahalakshmi, V.; Tinto, A. J.; Thomas, J.; Saban, K. V.

    2010-11-01

    Well-faceted crystals of cobaltous malonate (C 6 H 12 Co 2 O 12) have been grown by the controlled diffusion of ionic species in hydrosilica gel. Single crystal X-ray diffraction studies show that the crystal belongs to the monoclinic system with space group C2/m. The unit cell dimensions are a=12.6301(9) Å, b=7.3857(9) Å, c=7.2945(7) Å, α= γ=90°, β=120.193(9)°. The functional groups, elucidated from the FT-IR spectrum, are in conformity with the information derived from the X-ray diffraction studies. The thermal behaviour of the material has been investigated using TG-DTA in the temperature range 30-1050 °C. The optical band gap of the sample is estimated using diffuse reflectance spectroscopy (DRS). The dielectric constant and dielectric loss of the crystal have been studied over wide temperature and frequency ranges. AC conductivity measurements reveal a thermally activated process and the mechanism behind the conduction process has been discussed.

  9. Synthesis and controlling the optical and dielectric properties of CMC/PVA blend via γ-rays irradiation

    NASA Astrophysics Data System (ADS)

    El Sayed, A. M.

    2014-02-01

    Carboxymethyl cellulose (CMC)/Polyvinyl alcohol (PVA) blend films were prepared by solution casting method. Then, these films were irradiated with γ-rays from a Co-60 source at doses over the range 0-70 kGy to investigate the modifications induced in the optical and dielectric properties. The dielectric constant (ɛ‧) was measured in the temperature range 303-408 K and in the frequency range 10 kHz-1 MHz. The indirect optical band gap was found to increase within the dose range 0-10 kGy, and to decrease at the higher doses. The refractive index values, however, showed a reversed behavior. The highest transmittance percentage was obtained at 10 kGy dose. According to the frequency and temperature dependence of ɛ‧, α- relaxation peaks were observed in all samples and assigned to the micro-Brownian motion of the blend chains. The values of ɛ‧ showed a decrease in the dose range 0-10 kGy and an increase in the dose range 10-70 kGy. The ac conductivity σac (T) showed an Arrhenius type behavior separated into two distinct regions. The results of the present system are compared with those of similar materials.

  10. Improved Dielectric Films For Capacitors

    NASA Technical Reports Server (NTRS)

    Yen, Shiao-Ping S.; Lewis, Carol R.; Cygan, Peter J.; Jow, T. Richard

    1994-01-01

    Dielectric films made from blends of some commercially available high-dielectric-constant cyanoresins with each other and with cellulose triacetate (CTA) have both high dielectric constants and high breakdown strengths. Dielectric constants as high as 16.2. Films used to produce high-energy-density capacitors.

  11. Fabrication of Polyurethane Dielectric Actuators

    DTIC Science & Technology

    2005-01-01

    a summary of a 3 year Technology Investment Fund Project entitled “Dielectric Polymer Actuators for Active/ Passive Vibration Isolation”, which was...completed in March 2005. The purpose of this project was to investigate dielectric polymer materials for potential use in active/ passive vibration...devices and systems based on dielectric polymer actuators. Keywords: dielectric actuators, electroactive polymers , Technology Investment Fund 1

  12. Dielectric cure monitoring: Preliminary studies

    NASA Technical Reports Server (NTRS)

    Goldberg, B. E.; Semmel, M. L.

    1984-01-01

    Preliminary studies have been conducted on two types of dielectric cure monitoring systems employing both epoxy resins and phenolic composites. An Audrey System was used for 23 cure monitoring runs with very limited success. Nine complete cure monitoring runs have been investigated using a Micromet System. Two additional measurements were performed to investigate the Micromet's sensitivity to water absorption in a post-cure carbon-phenolic material. While further work is needed to determine data significance, the Micromet system appears to show promise as a feedback control device during processing.

  13. Nonlinear electroelastic deformations of dielectric elastomer composites: II - Non-Gaussian elastic dielectrics

    NASA Astrophysics Data System (ADS)

    Lefèvre, Victor; Lopez-Pamies, Oscar

    2017-02-01

    This paper presents an analytical framework to construct approximate homogenization solutions for the macroscopic elastic dielectric response - under finite deformations and finite electric fields - of dielectric elastomer composites with two-phase isotropic particulate microstructures. The central idea consists in employing the homogenization solution derived in Part I of this work for ideal elastic dielectric composites within the context of a nonlinear comparison medium method - this is derived as an extension of the comparison medium method of Lopez-Pamies et al. (2013) in nonlinear elastostatics to the coupled realm of nonlinear electroelastostatics - to generate in turn a corresponding solution for composite materials with non-ideal elastic dielectric constituents. Complementary to this analytical framework, a hybrid finite-element formulation to construct homogenization solutions numerically (in three dimensions) is also presented. The proposed analytical framework is utilized to work out a general approximate homogenization solution for non-Gaussian dielectric elastomers filled with nonlinear elastic dielectric particles that may exhibit polarization saturation. The solution applies to arbitrary (non-percolative) isotropic distributions of filler particles. By construction, it is exact in the limit of small deformations and moderate electric fields. For finite deformations and finite electric fields, its accuracy is demonstrated by means of direct comparisons with finite-element solutions. Aimed at gaining physical insight into the extreme enhancement in electrostriction properties displayed by emerging dielectric elastomer composites, various cases wherein the filler particles are of poly- and mono-disperse sizes and exhibit different types of elastic dielectric behavior are discussed in detail. Contrary to an initial conjecture in the literature, it is found (inter alia) that the isotropic addition of a small volume fraction of stiff (semi-)conducting

  14. Electrical Conductivity Mechanism in Unconventional Lead Vanadate Glasses

    NASA Astrophysics Data System (ADS)

    Abdel-Wahab, F.; Merazga, A.; Montaser, A. A.

    2017-03-01

    Lead vanadate glasses of the system (V2O5)_{1-x}(PbO)x with x = 0.4, 0.45, 0.5, 0.55, 0.6 have been prepared by the press-quenching technique. The dc (σ (0)) and ac (σ (ω )) electrical conductivities were measured in the temperature range from 150 to 420 K and the frequency range from 102 to 106 Hz. The electrical properties are shown to be sensitive to composition. The experimental results have been analyzed within the framework of different models. The dc conductivity is found to be proportional to Tp with the exponent p ranging from 8.2 to 9.8, suggesting that the transport is determined by a multi-phonon process of weak electron-lattice coupling. The ac conductivity is explained by the percolation path approximation (PPA). In this model, σ (ω ) is closely related to the σ (0) and fitting the experimental data produces a dielectric relaxation time τ in good agreement with the expected value in both magnitude and temperature dependence.

  15. Interfacial effects in oxide-polymer laminar composite thin film dielectrics for capacitor applications

    NASA Astrophysics Data System (ADS)

    Tewari, Pratyush

    enhanced segmental chain mobility or reduced degree of co-operative chain motion in comparison to Parylene C itself. These effects were found to be more pronounced for Parylene C in the vicinity of SiO2. AC electric field dependant impedance spectroscopy analysis of SiO 2-Parylene C laminar composites showed gradual reduction in segmental chain motion relaxation rate in Parylene C with an increase in AC oscillation amplitude. Reduced segmental chain motion relaxation rate at a fixed temperature, suggesting higher stability of glassy phase at high AC oscillation amplitude, was explained based on its similar dependence on external pressure, previously shown for polyisoprene and PMMA. Lesser effect of AC oscillation amplitude on interfacial polymer segmental chain motion relaxation rate in comparison to bulk polymer was found to be consistent with reported higher activation energy for segmental chain motion for thicker film in comparison to thinner. With an increase in AC oscillation amplitude a new sub-ohmic AC conduction mechanism associated with minority carrier injection was found to be dominant at lower frequency. The relaxation associated minority carrier injection was found to be strongly coupled with AC electric field amplitude. Thermally stimulated depolarization current measurements (TSDC) of SiO 2-Parylene C laminar composites revealed the presence of interfacial dipolar energy state with activation energy in the range of 1.05 to 1.30 eV. Surface functionalization of thermally grown SiO2 with various organosilane was carried out to control the polarity of SiO2 surface and modify interfacial characteristics of laminar composites. Shift in TSDC interfacial peak maxima, signifying presence of deeper interfacial state, with surface functionalization was found to be directly related to surface polarity of functionalized SiO2. Overall increase in polarizibility of SiO2-Parylene C laminar composite dielectric with surface functionalization was found to be controlled by

  16. Growth, thermal, dielectric and mechanical properties of L-phenylalanine-benzoic acid: A nonlinear optical single crystal

    NASA Astrophysics Data System (ADS)

    Tamilselvan, S.; Vimalan, M.; Vetha Potheher, I.; Rajasekar, S.; Jeyasekaran, R.; Antony Arockiaraj, M.; Madhavan, J.

    2013-10-01

    An efficient amino acid family nonlinear optical single crystal L-phenylalanine-benzoic acid (LPB) was conveniently grown by slow evaporation technique at room temperature. The crystal system and the lattice parameters were analyzed by single crystal X-ray diffraction studies. The grown crystal has excellent transmission in the entire visible region and its lower cut-off wavelength was found to be 248 nm. The SHG efficiency of the grown crystal was found to be 1.6 times higher than that of KDP crystal. The Laser damage threshold value of LPB has been found to be 6.5 GW/cm2. The sample was thermally stable up to 134 °C. Microhardness, dielectric and AC/DC conductivity measurements were made along (0 0 1) plane and reported for the first time. Microhardness studies revealed that the sample belongs to hard nature. Frequency dependent dielectric constant was measured for different temperatures and found maximum dielectric constant of 14 for 363 K. Photoconductivity studies of LPB divulged its negative photoconducting nature.

  17. Growth, thermal, dielectric and mechanical properties of L-phenylalanine-benzoic acid: a nonlinear optical single crystal.

    PubMed

    Tamilselvan, S; Vimalan, M; Potheher, I Vetha; Rajasekar, S; Jeyasekaran, R; Arockiaraj, M Antony; Madhavan, J

    2013-10-01

    An efficient amino acid family nonlinear optical single crystal L-phenylalanine-benzoic acid (LPB) was conveniently grown by slow evaporation technique at room temperature. The crystal system and the lattice parameters were analyzed by single crystal X-ray diffraction studies. The grown crystal has excellent transmission in the entire visible region and its lower cut-off wavelength was found to be 248 nm. The SHG efficiency of the grown crystal was found to be 1.6 times higher than that of KDP crystal. The Laser damage threshold value of LPB has been found to be 6.5 GW/cm(2). The sample was thermally stable up to 134°C. Microhardness, dielectric and AC/DC conductivity measurements were made along (001) plane and reported for the first time. Microhardness studies revealed that the sample belongs to hard nature. Frequency dependent dielectric constant was measured for different temperatures and found maximum dielectric constant of 14 for 363 K. Photoconductivity studies of LPB divulged its negative photoconducting nature.

  18. Induced Charge Electrokinetics Over ``Controllably Contaminated'' Surfaces: The Effects of Dielectric Thin Films and Surface Chemistry on Slip Velocity

    NASA Astrophysics Data System (ADS)

    Pascall, Andrew; Squires, Todd

    2009-11-01

    Microfluidics has renewed interest in utilizing electrokinetics (EK) for transporting fluids on small scales, and has subjected EK theories and understanding to new challenges. For example, induced-charge electro-osmosis (ICEO), a non-linear EK effect in which an externally applied AC electric field both induces and drives a layer of charged fluid near an electrically conductive surface, could provide an on-chip means to drive high pressures with low voltage [1]. Experimental data on ICEO and related phenomena have shown that the standard theory consistently overpredicts slip velocities by up to a factor of 1000[2]. Here we present experiments in which we controllably ``contaminate'' the metallic surface with a thin dielectric film or Au-thiol self assembled monolayer, and derive a theory for ICEO that incorporates both dielectric effects and surface chemistry, which both act to decrease the slip velocity relative to a `clean' metal. Data for over a thousand combinations of electric field strength and frequency, electrolyte composition, dielectric thickness and surface chemistry show essentially unprecedented quantitative agreement with our theory. [1] Squires & Bazant. J. Fluid Mech. 2004 [2] Bazant, et al. arXiv. 0903.4790

  19. Study of structural, electrical, and dielectric properties of phosphate-borate glasses and glass-ceramics

    NASA Astrophysics Data System (ADS)

    Melo, B. M. G.; Graça, M. P. F.; Prezas, P. R.; Valente, M. A.; Almeida, A. F.; Freire, F. N. A.; Bih, L.

    2016-08-01

    In this work, phosphate-borate based glasses with molar composition 20.7P2O5-17.2Nb2O5-13.8WO3-34.5A2O-13.8B2O3, where A = Li, Na, and K, were prepared by the melt quenching technique. The as-prepared glasses were heat-treated in air at 800 °C for 4 h, which led to the formation of glass-ceramics. These high chemical and thermal stability glasses are good candidates for several applications such as fast ionic conductors, semiconductors, photonic materials, electrolytes, hermetic seals, rare-earth ion host solid lasers, and biomedical materials. The present work endorses the analysis of the electrical conductivity of the as-grown samples, and also the electrical, dielectric, and structural changes established by the heat-treatment process. The structure of the samples was analyzed using X-Ray powder Diffraction (XRD), Raman spectroscopy, and density measurements. Both XRD and Raman analysis confirmed crystals formation through the heat-treatment process. The electrical ac and dc conductivities, σac and σdc, respectively, and impedance spectroscopy measurements as function of the temperature, varying from 200 to 380 K, were investigated for the as-grown and heat-treated samples. The impedance spectroscopy was measured in the frequency range of 100 Hz-1 MHz.

  20. Cast dielectric composite linear accelerator

    DOEpatents

    Sanders, David M.; Sampayan, Stephen; Slenes, Kirk; Stoller, H. M.

    2009-11-10

    A linear accelerator having cast dielectric composite layers integrally formed with conductor electrodes in a solventless fabrication process, with the cast dielectric composite preferably having a nanoparticle filler in an organic polymer such as a thermosetting resin. By incorporating this cast dielectric composite the dielectric constant of critical insulating layers of the transmission lines of the accelerator are increased while simultaneously maintaining high dielectric strengths for the accelerator.

  1. The AC-120: The advanced commercial transport

    NASA Technical Reports Server (NTRS)

    Duran, David; Griffin, Ernest; Mendoza, Saul; Nguyen, Son; Pickett, Tim; Noernberg, Clemm

    1993-01-01

    The main objective of this design was to fulfill a need for a new airplane to replace the aging 100 to 150 passenger, 1500 nautical mile range aircraft such as the Douglas DC9 and Boeing 737-100 airplanes. After researching the future aircraft market, conducting extensive trade studies, and analysis on different configurations, the AC-120 Advanced Commercial Transport final design was achieved. The AC-120's main design features include the incorporation of a three lifting surface configuration which is powered by two turboprop engines. The AC-120 is an economically sensitive aircraft which meets the new FM Stage Three noise requirements, and has lower NO(x) emissions than current turbofan powered airplanes. The AC-120 also improves on its contemporaries in passenger comfort, manufacturing, and operating cost.

  2. Dielectric Properties of BaTiO3-Based Ceramics under High Electric Field

    NASA Astrophysics Data System (ADS)

    Tsurumi, Takaaki; Adachi, Hiroshige; Kakemoto, Hirofumi; Wada, Satoshi; Mizuno, Youichi; Chazono, Hirokazu; Kishi, Hiroshi

    2002-11-01

    The dielectric properties under a high electric field (ac-field) of BaTiO3-based ceramics with core grains, shell grains and core-shell grains were compared with those of multilayer ceramic capacitors (MLCCs) with these three kinds of grains. The MLCCs with the X7R specification had a core-shell structure, and the relative dielectric permittivity (\\varepsilonr) of the dielectric layers in the MLCCs increased with increasing ac-field. Similar behavior was observed in the MLCCs consisting of only cores, indicating that the core predominantly determined the dielectric properties of MLCCs under high ac-fields. The dielectric properties of MLCCs and ceramic plates consisting of only shell grains showed that the shell was the relaxor ferroelectrics. A slight change in the shell composition yielded a large shift of the peak temperature of \\varepsilonr. The shell improved the temperature stability of \\varepsilonr at low temperatures under low ac-fields. In a ceramic plate with relatively large BaTiO3 grains (approximately 3 μm), the maximum \\varepsilonr was observed at a moderate ac-field, which was explained from the electric displacement vs electric field hysteresis curves of ferroelectric BaTiO3. The MLCCs and ceramics plates with fine BaTiO3 grains (0.4 to 0.5 μm) showed similar dielectric behavior to the MLCC with the core-shell structure. The size effect of BaTiO3 played an important role in determining the temperature stability of \\varepsilonr. For future MLCCs with very thin dielectric layers, a microstructure with fine BaTiO3 grains and grain boundary layers of the shell was proposed.

  3. Pattern formation in dielectric barrier discharges with different dielectric materials

    SciTech Connect

    Dong, L. F.; Fan, W. L.; Wang, S.; Ji, Y. F.; Liu, Z. W.; Chen, Q.

    2011-03-15

    The influence of dielectric material on the bifurcation and spatiotemporal dynamics of the patterns in dielectric barrier discharge in argon/air at atmospheric pressure is studied. It is found that pattern bifurcation sequences are different with different dielectric materials. The spatiotemporal dynamics of the hexagonal pattern in dielectric barrier discharge depends on the dielectric material. The hexagon pattern with glass dielectric is an interleaving of two rectangular sublattices appearing at different moments. The hexagon pattern with quartz dielectric is composed of one set of hexagonal lattice discharging twice in one half cycle of the applied voltage, one is at the rising edge and the other at the falling edge. It results in that the accumulation of wall charges in individual microdischarges in a hexagon pattern with quartz dielectric is greater than that with glass dielectric, which is in agreement with the electron density measurement by Stark broadening of Ar I 696.54 nm.

  4. Residual ferroelectricity in barium strontium titanate thin film tunable dielectrics

    SciTech Connect

    Garten, L. M. Trolier-McKinstry, S.; Lam, P.; Harris, D.; Maria, J.-P.

    2014-07-28

    Loss reduction is critical to develop Ba{sub 1−x}Sr{sub x}TiO{sub 3} thin film tunable microwave dielectric components and dielectric energy storage devices. The presence of ferroelectricity, and hence the domain wall contributions to dielectric loss, will degrade the tunable performance in the microwave region. In this work, residual ferroelectricity—a persistent ferroelectric response above the global phase transition temperature—was characterized in tunable dielectrics using Rayleigh analysis. Chemical solution deposited Ba{sub 0.7}Sr{sub 0.3}TiO{sub 3} films, with relative tunabilities of 86% over 250 kV/cm at 100 kHz, demonstrated residual ferroelectricity 65 °C above the ostensible paraelectric transition temperature. Frequency dispersion observed in the dielectric temperature response was consistent with the presence of nanopolar regions as one source of residual ferroelectricity. The application of AC electric field for the Rayleigh analysis of these samples led to a doubling of the dielectric loss for fields over 10 kV/cm at room temperature.

  5. DIELECTRIC-LOADED WAVE-GUIDES

    DOEpatents

    Robertson-Shersby-Harvie, R.B.; Mullett, L.B.

    1957-04-23

    This patent presents a particular arrangement for delectric loading of a wave-guide carrying an electromagnetic wave in the E or TM mode of at least the second order, to reduce the power dissipated as the result of conduction loss in the wave-guide walls. To achieve this desirabie result, the effective dielectric constants in the radial direction of adjacent coaxial tubular regions bounded approximateiy by successive nodai surfaces within the electromagnetic field are of two different values alternating in the radial direction, the intermost and outermost regions being of the lower value, and the dielectric constants between nodes are uniform.

  6. Method for producing high dielectric strength microvalves

    DOEpatents

    Kirby, Brian J.; Reichmuth, David S.; Shepodd, Timothy J.

    2006-04-04

    A microvalve having a cast-in-place and lithographically shaped mobile, polymer monolith for fluid flow control in microfluidic devices and method of manufacture. The microvalve contains a porous fluorinated polymer monolithic element whose pores are filled with an electrically insulating, high dielectric strength fluid, typically a perfluorinated liquid. This combination provides a microvalve that combines high dielectric strength with extremely low electrical conductivity. These microvalves have been shown to have resistivities of at least 100 G.OMEGA. and are compatible with solvents such as water at a pH between 2.7 and 9.0, 1-1 propanol, acetonitrile, and acetone.

  7. Dielectric investigations of polycrystalline samarium bismuth ferrite ceramic

    NASA Astrophysics Data System (ADS)

    Palaimiene, E.; Macutkevic, J.; Karpinsky, D. V.; Kholkin, A. L.; Banys, J.

    2015-01-01

    Results of broadband dielectric investigations of samarium doped bismuth ferrite ceramics are presented in wide temperature range (20-800 K). At temperatures higher than 400 K, the dielectric properties of samarium bismuth ferrite ceramics are governed by Maxwell-Wagner relaxation and electrical conductivity. The DC conductivity increases and activation energy decreases with samarium concentration. In samarium doped bismuth ferrite, the ferroelectric phase transition temperature decreases with samarium concentration and finally no ferroelectric order is observed at x = 0.2. At lower temperatures, the dielectric properties of ferroelectric samarium doped bismuth ferrite are governed by ferroelectric domains dynamics. Ceramics with x = 0.2 exhibit the relaxor-like behaviour.

  8. Dielectric elastomer actuators for facial expression

    NASA Astrophysics Data System (ADS)

    Wang, Yuzhe; Zhu, Jian

    2016-04-01

    Dielectric elastomer actuators have the advantage of mimicking the salient feature of life: movements in response to stimuli. In this paper we explore application of dielectric elastomer actuators to artificial muscles. These artificial muscles can mimic natural masseter to control jaw movements, which are key components in facial expressions especially during talking and singing activities. This paper investigates optimal design of the dielectric elastomer actuator. It is found that the actuator with embedded plastic fibers can avert electromechanical instability and can greatly improve its actuation. Two actuators are then installed in a robotic skull to drive jaw movements, mimicking the masseters in a human jaw. Experiments show that the maximum vertical displacement of the robotic jaw, driven by artificial muscles, is comparable to that of the natural human jaw during speech activities. Theoretical simulations are conducted to analyze the performance of the actuator, which is quantitatively consistent with the experimental observations.

  9. Structural, microstructural, optical, and dielectric properties of Mn2+: Willemite Zn2SiO4 nanocomposites obtained by a sol-gel method

    NASA Astrophysics Data System (ADS)

    Chandra Babu, B.; Rao, B. Vengla; Ravi, M.; Babu, S.

    2017-01-01

    The synthesis of Zn2SiO4 doped with Mn2+ ions at different concentrations have been successfully achieved by a conventional sol-gel method. The structure and morphology of the obtained samples were characterized by XRD, FTIR, Raman spectroscopy, EDAX, and FE-SEM, TEM. The XRD results of Zn2SiO4 samples with different Mn concentrations showed no obvious differences from the willemite structure. The SEM and TEM results showed the ceramic powders are nanometer sized spherical grains spherical forms and EDAX results confirmed the successful doping of Mn2+ ions into Zn2SiO4 matrix. The optical and dielectric properties of Mn2+ ions doped Zn2SiO4 show an appreciable difference between the levels of Mn2+ doping. The luminescence spectra showed that 0.25mol% Mn2+ in Zn2SiO4 gives a maximum intensity a in the green emission corresponding to the 4T1 (4G) → 6A1(6S) transition for tetrahedral-coordinated Mn2+ (weak crystal field) and at higher levels of Mn2+ doping the green band intensity decreases. The 0.25mol% Mn2+ in Zn2SiO4 also gives the highest ionic conductivity at 373 K. The dielectric constant (ε‧), loss tangent (tan δ) and AC conductivityac) properties as the function of frequency have also been analyzed and those are strongly dependent on Mn ion concentrations.

  10. Microfabricated AC impedance sensor

    DOEpatents

    Krulevitch, Peter; Ackler, Harold D.; Becker, Frederick; Boser, Bernhard E.; Eldredge, Adam B.; Fuller, Christopher K.; Gascoyne, Peter R. C.; Hamilton, Julie K.; Swierkowski, Stefan P.; Wang, Xiao-Bo

    2002-01-01

    A microfabricated instrument for detecting and identifying cells and other particles based on alternating current (AC) impedance measurements. The microfabricated AC impedance sensor includes two critical elements: 1) a microfluidic chip, preferably of glass substrates, having at least one microchannel therein and with electrodes patterned on both substrates, and 2) electrical circuits that connect to the electrodes on the microfluidic chip and detect signals associated with particles traveling down the microchannels. These circuits enable multiple AC impedance measurements of individual particles at high throughput rates with sufficient resolution to identify different particle and cell types as appropriate for environmental detection and clinical diagnostic applications.

  11. Evaluation of high temperature capacitor dielectrics

    NASA Technical Reports Server (NTRS)

    Hammoud, Ahmad N.; Myers, Ira T.

    1992-01-01

    Experiments were carried out to evaluate four candidate materials for high temperature capacitor dielectric applications. The materials investigated were polybenzimidazole polymer and three aramid papers: Voltex 450, Nomex 410, and Nomex M 418, an aramid paper containing 50 percent mica. The samples were heat treated for six hours at 60 C and the direct current and 60 Hz alternating current breakdown voltages of both dry and impregnated samples were obtained in a temperature range of 20 to 250 C. The samples were also characterized in terms of their dielectric constant, dielectric loss, and conductivity over this temperature range with an electrical stress of 60 Hz, 50 V/mil present. Additional measurements are underway to determine the volume resistivity, thermal shrinkage, and weight loss of the materials. Preliminary data indicate that the heat treatment of the films slightly improves the dielectric properties with no influence on their breakdown behavior. Impregnation of the samples leads to significant increases in both alternating and direct current breakdown strength. The results are discussed and conclusions made concerning their suitability as high temperature capacitor dielectrics.

  12. PREFACE: Dielectrics 2011

    NASA Astrophysics Data System (ADS)

    Vaughan, Alun; Lewin, Paul

    2011-08-01

    In 2011, the biennial meeting of the Dielectrics Group of the IOP, Dielectrics 2011, was held for the first time in a number of years at the University of Kent at Canterbury. This conference represents the most recent in a long standing series that can trace its roots back to a two-day meeting that was held in the spring of 1968 at Gregynog Hall of the University of Wales. In the intervening 43 years, this series of meetings has addressed many topics, including dielectric relaxation, high field phenomena, biomaterials and even molecular electronics, and has been held at many different venues within the UK. However, in the early 1990s, a regular venue was established at the University of Kent at Canterbury and, it this respect, this year's conference can be considered as "Dielectrics coming home". The format for the 2011 meeting followed that established at Dielectrics 2009, in breaking away from the concept of a strongly themed event that held sway during the mid 2000s. Rather, we again adopted a general, inclusive approach that was based upon four broad technical areas: Theme 1: Insulation/HV Materials Theme 2: Dielectric Spectroscopy Theme 3: Modelling Dielectric Response Theme 4: Functional Materials The result was a highly successful conference that attracted more than 60 delegates from eight countries, giving the event a truly international flavour, and which included both regular and new attendees; it was particularly pleasing to see the number of early career researchers at the meeting. Consequently, the organizing committee would like to thank our colleagues at the IOP, the invited speakers, our sponsors and all the delegates for making the event such a success. Finally, we look forward to convening again in 2013, when we will be returning to The University of Reading. Prof Alun Vaughan and Prof Paul Lewin, Editors

  13. A single dielectric nanolaser

    NASA Astrophysics Data System (ADS)

    Huang, Tsung-Yu; Yen, Ta-Jen

    2016-09-01

    To conquer Ohmic losses from metal and enhance pump absorption efficiency of a nanolaser based on surface plasmon polariton, we theoretically calculate the first magnetic and electric scattering coefficient of a dielectric sphere under a plane wave excitation with a dielectric constant of around 12. From this calculation, we could retrieve both negative effective permittivity and permeability of the sphere simultaneously at frequencies around 153 THz in the aids of Lewin's theory and the power distribution clearly demonstrate the expected negative Goos-Hänchen effect, which usually occurred in a negative refractive waveguide, thus creating two energy vortices to trap incident energy and then promoting the pump absorption efficiency. Meanwhile, a magnetic lasing mode at 167.3 THz is demonstrated and reveals a magnetic dipole resonance mode and a circulating energy flow within the dielectric sphere, providing a possible stopped light feedback mechanism to enable the all-dielectric nanolaser. More importantly, the corresponding mode volume is reduced to 0.01λ3 and a gain threshold of 5.1×103 is obtained. To validate our design of all-dielectric nanolaser, we employ finite-difference-time-domain simulation software to examine the behavior of the nanolaser. From simulation, we could obtain a pinned-down population inversion of 0.001 and a lasing peak at around 166.5 THz, which is very consistent with the prediction of Mie theory. Finally, according to Mie theory, we can regard the all-dielectric nanolaser as the excitation of material polariton and thus could make an analogue between lasing modes of the dielectric and metallic nanoparticles.

  14. Virtual gap dielectric wall accelerator

    DOEpatents

    Caporaso, George James; Chen, Yu-Jiuan; Nelson, Scott; Sullivan, Jim; Hawkins, Steven A

    2013-11-05

    A virtual, moving accelerating gap is formed along an insulating tube in a dielectric wall accelerator (DWA) by locally controlling the conductivity of the tube. Localized voltage concentration is thus achieved by sequential activation of a variable resistive tube or stalk down the axis of an inductive voltage adder, producing a "virtual" traveling wave along the tube. The tube conductivity can be controlled at a desired location, which can be moved at a desired rate, by light illumination, or by photoconductive switches, or by other means. As a result, an impressed voltage along the tube appears predominantly over a local region, the virtual gap. By making the length of the tube large in comparison to the virtual gap length, the effective gain of the accelerator can be made very large.

  15. Regular structures in 5CB liquid crystals under the joint action of ac and dc voltages

    NASA Astrophysics Data System (ADS)

    Aguirre, Luis E.; Anoardo, Esteban; Éber, Nándor; Buka, Ágnes

    2012-04-01

    A nematic liquid crystal with high, positive dielectric anisotropy (5CB) has been studied under the influence of the combined action of a dc and an ac electric field. Broad frequency, voltage, and cell thickness ranges were considered. Pattern morphologies were identified; the thresholds and critical wave numbers were measured and analyzed as a function of frequency, dc-to-ac voltage ratio, and thickness. The current-voltage characteristics were simultaneously detected.

  16. Low temperature dielectric properties of YMn0.95Ru0.05O3

    NASA Astrophysics Data System (ADS)

    Thakur, Rajesh K.; Thakur, Rasna; Okram, G. S.; Kaurav, N.; Gaur, N. K.

    2013-02-01

    The single phase hexagonal YMn0.95Ru0.05O3 compound has been synthesized via solid state reaction method at sintering temperature 1280°C with space group P63cm (25-1079). The detailed dielectric properties were evaluated over broad temperature and frequency ranges. An obvious dielectric relaxation was observed near the antiferromagnetic (AFM) transition temperature. The temperature dependence of the ac resistivity at low frequency infers the semiconducting behavior and favored the variable range hopping conduction model. The obtained experimental data in the temperature range of our study can be described by the equation ρ(T) = ρ0exp[(T*/T)1/4]. The fitting results are used for the calculation of the temperature scale T* ˜ 0.8 × 104 K and finally the density of state at Fermi level N(EF). The activation energy Ea ˜ 0.0314 eV is calculated from the plot, peak temperature of the loss tangent near the magnetic transition region versus frequency using Arrhenius law.

  17. Dielectric-spectroscopy approach to ferrofluid nanoparticle clustering induced by an external electric field.

    PubMed

    Rajnak, Michal; Kurimsky, Juraj; Dolnik, Bystrik; Kopcansky, Peter; Tomasovicova, Natalia; Taculescu-Moaca, Elena Alina; Timko, Milan

    2014-09-01

    An experimental study of magnetic colloidal particles cluster formation induced by an external electric field in a ferrofluid based on transformer oil is presented. Using frequency domain isothermal dielectric spectroscopy, we study the influence of a test cell electrode separation distance on a low-frequency relaxation process. We consider the relaxation process to be associated with an electric double layer polarization taking place on the particle surface. It has been found that the relaxation maximum considerably shifts towards lower frequencies when conducting the measurements in the test cells with greater electrode separation distances. As the electric field intensity was always kept at a constant value, we propose that the particle cluster formation induced by the external ac electric field accounts for that phenomenon. The increase in the relaxation time is in accordance with the Schwarz theory of electric double layer polarization. In addition, we analyze the influence of a static electric field generated by dc bias voltage on a similar shift in the relaxation maximum position. The variation of the dc electric field for the hysteresis measurements purpose provides understanding of the development of the particle clusters and their decay. Following our results, we emphasize the utility of dielectric spectroscopy as a simple, complementary method for detection and study of clusters of colloidal particles induced by external electric field.

  18. Dielectric Properties of Boron Nitride-Ethylene Glycol (BN-EG) Nanofluids

    NASA Astrophysics Data System (ADS)

    Fal, Jacek; Cholewa, Marian; Gizowska, Magdalena; Witek, Adam; ŻyŁa, GaweŁ

    2017-02-01

    This paper presents the results of experimental investigation of the dielectric properties of ethylene glycol (EG) with various load of boron nitride (BN) nanoparticles. The nanofuids were prepared by using a two-step method on the basis of commercially available BN nanoparticles. The measurements were carried out using the Concept 80 System (NOVOCONTROL Technologies GmbH & Co. KG, Montabaur, Germany) in a frequency range from 10 Hz to 10 MHz and temperatures from 278.15 K to 328.15 K. The frequency-dependent real (ɛ ^' }) and imaginary (ɛ ^' ' }) parts of the complex permittivity (ɛ ^*) and the alternating current (AC) conductivity are presented. Also, the effect of temperature and mass concentrations on the dielectric properties of BN-EG nanofluids are demonstrated. The results show that the most significant increase can be achieved for 20 wt.% of BN nanoparticles at 283.15 K and 288.15 K, that is eleven times larger than in the case of pure EG.

  19. Dielectric interpretation of Lei-Ting nonlinear force-momentum-balance transport equation for isothermal resistivity

    NASA Astrophysics Data System (ADS)

    Horing, N. J. M.; Lei, X. L.; Cui, H. L.

    1986-05-01

    A dielectric interpretation of the nonlinear Lei-Ting force-momentum-balance transport equation for steady-state dc current flow is developed here in correspondence with standard techniques for calculating fast-particle energy loss to a plasmalike medium. In conjunction with this we interpret the result to be an isothermal resistivity calculated to lowest order in the impurity scattering potentials, isothermal in the sense that all energy dissipated is removed from the system, essentially instantaneously as it is generated, by a heat bath in contact with the system which maintains it at constant temperature throughout the nonlinear dc conduction process. On the basis of its isothermal character, we argue that the Lei-Ting dc resistivity calculated to lowest order in the impurity scattering potentials-whose linear limit is significantly different from the corresponding linear resistivity of an adiabatic character (for a system admitting no drainoff of dissipated energy, developing under a purely mechanical Hamiltonian)-is immune to serious critical objections of the type brought by Argyres and Sigel against similar lowest-order adiabatic linear resistivity calculations some time ago. Moreover, we also show that a dielectric Lei-Ting type formulation of linearized ac resistivity leads to the standard high-frequency linear resistivity formula, and that its zero-frequency limit naturally yields the isothermal dc linear Lei-Ting resistivity.

  20. Structural, magnetic and dielectric properties of polyaniline/MnCoFe2O4 nanocomposites

    NASA Astrophysics Data System (ADS)

    Chitra, Palanisamy; Muthusamy, Athianna; Jayaprakash, Rajan

    2015-12-01

    Ferromagnetic PANI containing MnCoFe2O4 nanocomposites were synthesized by in-situ chemical polymerization of aniline incorporated MnCoFe2O4 nanoparticles (20%, 10% w/w of fine powders) with and without ultrasonic treatment. The MnCoFe2O4 nanoparticles were synthesized by auto combustion method. The PANI/MnCoFe2O4 nanocomposites were characterized with Fourier transform infrared (FTIR), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The average particle size of the resulting PANI/MnCoFe2O4 nanocomposites was confirmed from the TEM and XRD analysis. The structure and morphology of the composites were confirmed by FT-IR spectroscopy, XRD and SEM. In addition, the electrical and magnetic properties of the nanocomposites were investigated. The PANI/MnCoFe2O4 nanocomposites under applied magnetic field exhibited the hysteresis loops of ferromagnetic nature at room temperature. The variation of Dielectric constant, Dielectric loss, and AC conductivity of PANI/MnCoFe2O4 nanocomposites at room temperature as a function of frequency in the range 50 Hz-5 MHz has been studied. Effect of ultrasonication on the PANI/MnCoFe2O4 nanocomposites was also investigated.

  1. AC magnetohydrodynamic microfluidic switch

    SciTech Connect

    Lemoff, A V; Lee, A P

    2000-03-02

    A microfluidic switch has been demonstrated using an AC Magnetohydrodynamic (MHD) pumping mechanism in which the Lorentz force is used to pump an electrolytic solution. By integrating two AC MHD pumps into different arms of a Y-shaped fluidic circuit, flow can be switched between the two arms. This type of switch can be used to produce complex fluidic routing, which may have multiple applications in {micro}TAS.

  2. Electrostatic measurement system. [for contact-electrifying a dielectric

    NASA Technical Reports Server (NTRS)

    Johnston, J. E. (Inventor)

    1975-01-01

    A system for and method of contact-electrifying a dielectric to determine its electrostatic properties is described. The dielectric is placed in contact with a contact plate means, and connected to a voltage source means to charge the contact plate and to contact-electrify the dielectric. The contact plate means is disconnected from the voltage source and a charge sensor means monitors the rate of decay of the charge on the dielectric. If a conductive path from the contact plate to ground is desired, a lead may be connected between the conductor and ground. Automatic timing and charge monitoring are preferred for maximum accuracy, especially where dielectrics treated with antistatic agents are tested.

  3. 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.

  4. 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.

  5. Role of ambient dielectric in propagation of Ar atmospheric pressure nonequilibrium plasma jets

    SciTech Connect

    Song, Jian; Wang, Youyin; Yu, Daren; Tang, Jingfeng Wei, Liqiu; Ren, Chunsheng

    2015-05-15

    A single-electrode atmospheric pressure nonequilibrium plasma jet surrounded with different ambient dielectrics is investigated driven by AC power supply. Another three ambient dielectrics, distilled water, ethanol, and carbon tetrachloride, are adopted to compare with air. By examining electrical and optical characteristics, it was found that the molecular polarity of ambient dielectrics had its significant effect on the propagation of atmospheric pressure nonequilibrium plasma jets. When the polarization of molecules was enhanced, the discharge current and the bullet velocity were also increased. For nonpolar dielectric of carbon tetrachloride, this was mainly resulted from the electron polarization in the built-in electric field. For polar dielectrics of ethanol and distilled water, in addition to the electron polarization, orientation polarization was the main cause for the further increase in discharge current and bullet velocity.

  6. The radar cross section of dielectric disks

    NASA Technical Reports Server (NTRS)

    Levine, D. M.

    1982-01-01

    A solution is presented for the backscatter (nonstatic) radar cross section of dielectric disks of arbitrary shape, thickness and dielectric constant. The result is obtained by employing a Kirchhoff type approximation to obtain the fields inside the disk. The internal fields induce polarization and conduction currents from which the scattered fields and the radar cross section can be computed. The solution for the radar cross section obtained in this manner is shown to agree with known results in the special cases of normal incidence, thin disks and perfect conductivity. The solution can also be written as a product of the reflection coefficient of an identically oriented slab times the physical optics solution for the backscatter cross section of a perfectly conducting disk of the same shape. This result follows directly from the Kirchhoff type approximation without additional assumptions.

  7. The radar cross section of dielectric disks

    NASA Technical Reports Server (NTRS)

    Le Vine, D. M.

    1984-01-01

    A solution is presented for the backscatter (monostatic) radar cross section of dielectric disks of arbitrary shape, thickness, and dielectric constant. The result is obtained by employing a Kirchhoff-type approximation to obtain the fields inside the disk. The internal fields induce polarization and conduction currents from which the scattered fields and the radar cross section can be computed. The solution for the radar cross section obtained in this manner will be shown to agree with known results in the special cases of normal incidence, thin disks, and perfect conductivity. It will also be shown that the solution can be written as a product of the reflection coefficient of an identically oriented slab times the physical optics solution for the backscatter cross section of a perfectly conducting disk of the same shape. This result follows directly from the Kirchhoff-type approximation without additional assumptions.

  8. High dielectric constant polymer nanocomposites for embedded capacitor applications

    NASA Astrophysics Data System (ADS)

    Lu, Jiongxin

    Driven by ever growing demands of miniaturization, increased functionality, high performance and low cost for microelectronic products and packaging, embedded passives will be one of the key emerging techniques for realizing the system integration which offer various advantages over traditional discrete components. Novel materials for embedded capacitor applications are in great demand, for which a high dielectric constant ( k), low dielectric loss and process compatibility with printed circuit boards are the most important prerequisites. To date, no available material satisfies all these prerequisites and research is needed to develop materials for embedded capacitor applications. Conductive filler/polymer composites are likely candidate material because they show a dramatic increase in their dielectric constant close to the percolation threshold. One of the major hurdles for this type of high-k composites is the high dielectric loss inherent in these systems. In this research, material and process innovations were explored to design and develop conductive filler/polymer nanocomposites based on nanoparticles with controlled parameters to fulfill the balance between sufficiently high-k and low dielectric loss, which satisfied the requirements for embedded capacitor applications. This work involved the synthesis of the metal nanoparticles with different parameters including size, size distribution, aggregation and surface properties, and an investigation on how these varied parameters impact the dielectric properties of the high-k nanocomposites incorporated with these metal nanoparticles. The dielectric behaviors of the nanocomposites were studied systematically over a range of frequencies to determine the dependence of dielectric constant, dielectric loss tangent and dielectric strength on these parameters.

  9. Superdirective dielectric nanoantennas

    NASA Astrophysics Data System (ADS)

    Krasnok, Alexander E.; Simovski, Constantin R.; Belov, Pavel A.; Kivshar, Yuri S.

    2014-06-01

    We introduce the novel concept of superdirective nanoantennas based on the excitation of higher-order magnetic multipole moments in subwavelength dielectric nanoparticles. Our superdirective nanoantenna is a small Si nanosphere containing a notch, and is excited by a dipole located within the notch. In addition to extraordinary directivity, this nanoantenna demonstrates efficient radiation steering at the nanoscale, resulting from the subwavelength sensitivity of the beam radiation direction to variation of the source position inside the notch. We compare our dielectric nanoantenna with a plasmonic nanoantenna of similar geometry, and reveal that the nanoantenna's high directivity in the regime of transmission is not associated with strong localization of near fields in the regime of reception. Likewise, the absence of hot spots inside the nanoantenna leads to low dissipation in the radiation regime, so that our dielectric nanoantenna has significantly smaller losses and high radiation efficiency of up to 70%.

  10. PREFACE: Dielectrics 2013

    NASA Astrophysics Data System (ADS)

    Hadjiloucas, Sillas; Blackburn, John

    2013-11-01

    This volume records the 42nd Dielectrics Group Proceedings of the Dielectrics Conference that took place at the University of Reading UK from 10-12 April 2013. The meeting is part of the biennial Dielectrics series of the Dielectrics Group, and formerly Dielectrics Society, and is organised by the Institute of Physics. The conference proceedings showcase some of the diversity and activity of the Dielectrics community worldwide, and bring together contributions from academics and industrial researchers with a diverse background and experiences from the Physics, Chemistry and Engineering communities. It is interesting to note some continuing themes such as Insulation/HV Materials, Dielectric Spectroscopy, Dielectric Measurement Techniques and Ferroelectric materials have a growing importance across a range of technologically important areas from the Energy sector to Materials research, Semiconductor and Electronics industries, and Metrology. We would like to thank all of our colleagues and friends in the Dielectrics community who have supported this event by contributing manuscripts and participating in the event. The conference has provided excellent networking opportunities for all delegates. Our thanks go also to our theme chairs: Dr Stephen Dodd (University of Leicester) on Insulation/HV Materials, Professor Darryl Almond (University of Bath) on Dielectric Spectroscopy, Dr John Blackburn (NPL) on Dielectric Measurement Techniques and Professor Anthony R West (University of Sheffield) on Ferroelectric Materials. We would also like to thank the other members of the Technical Programme Committee for their support, and refereeing the submitted manuscripts. Our community would also like to wish a full recovery to our plenary speaker Prof John Fothergill (City University London) who was unexpectedly unable to give his talk as well as thank Professor Alun Vaughan for stepping in and giving an excellent plenary lecture in his place at such very short notice. We are also

  11. Controlling birefringence in dielectrics

    NASA Astrophysics Data System (ADS)

    Danner, Aaron J.; Tyc, Tomáš; Leonhardt, Ulf

    2011-06-01

    Birefringence, from the very essence of the word itself, refers to the splitting of light rays into two parts. In natural birefringent materials, this splitting is a beautiful phenomenon, resulting in the perception of a double image. In optical metamaterials, birefringence is often an unwanted side effect of forcing a device designed through transformation optics to operate in dielectrics. One polarization is usually implemented in dielectrics, and the other is sacrificed. Here we show, with techniques beyond transformation optics, that this need not be the case, that both polarizations can be controlled to perform useful tasks in dielectrics, and that rays, at all incident angles, can even follow different trajectories through a device and emerge together as if the birefringence did not exist at all. A number of examples are shown, including a combination Maxwell fisheye/Luneburg lens that performs a useful task and is achievable with current fabrication materials.

  12. Influence of Eu impurity on the dielectric properties of Sr{sub x}Ba{sub 1−x}Nb{sub 2}O{sub 6} crystals

    SciTech Connect

    Malyshkina, O. V. Pedko, B. B.; Lisitsin, V. S.

    2015-03-15

    The dielectric characteristics of barium-strontium niobate crystals with Eu impurities of 2000, 4000, 8000, and 16 000 ppm are presented. The dielectric hysteresis loops observed during heating and exposure to an electric field at room temperature are compared. It is shown that the evolution of the loops in time occurs as a result of sample heating under an ac electric field.

  13. Energy deposition characteristics of nanosecond dielectric barrier discharge plasma actuators: Influence of dielectric material

    NASA Astrophysics Data System (ADS)

    Correale, G.; Winkel, R.; Kotsonis, M.

    2015-08-01

    An experimental study aimed at the characterization of energy deposition of nanosecond Dielectric Barrier Discharge (ns-DBD) plasma actuators was carried out. Special attention was given on the effect of the thickness and material used for dielectric barrier. The selected materials for this study were polyimide film (Kapton), polyamide based nylon (PA2200), and silicone rubber. Schlieren measurements were carried out in quiescent air conditions in order to observe density gradients induced by energy deposited. Size of heated area was used to qualify the energy deposition coupled with electrical power measurements performed using the back-current shunt technique. Additionally, light intensity measurements showed a different nature of discharge based upon the material used for barrier, for a fixed thickness and frequency of discharge. Finally, a characterisation study was performed for the three tested materials. Dielectric constant, volume resistivity, and thermal conductivity were measured. Strong trends between the control parameters and the energy deposited into the fluid during the discharge were observed. Results indicate that efficiency of energy deposition mechanism relative to the thickness of the barrier strongly depends upon the material used for the dielectric barrier itself. In general, a high dielectric strength and a low volumetric resistivity are preferred for a barrier, together with a high heat capacitance and a low thermal conductivity coefficient in order to maximize the efficiency of the thermal energy deposition induced by an ns-DBD plasma actuator.

  14. Rietveld refinement and dielectric studies of Bi{sub 0.8}Ba{sub 0.2}Fe{sub 0.95}V{sub 0.05}O{sub 3} ceramic

    SciTech Connect

    Priyanka, Agarwal, A. Ahlawat, N. Sanghi, S. Rani, S.

    2014-04-24

    Polycrystalline Bi{sub 0.8}Ba{sub 0.2}Fe{sub 0.95}V{sub 0.05}O{sub 3} ceramic has been prepared by the conventional solid state reaction technique. The Rietveld refinement of x-ray powder diffraction revealed that the sample has a rhombohedral crystal structure (space group R3c) with average particle size of 29 nm. The values of dielectric constant (ε′) and dielectric loss (tan δ) increases with increasing temperature at different frequencies which may be the result of increase in the number of charge carriers and their mobilities due to the thermal activation. The Jonscher’s universal power law used to analyze the ac conductivity. In the measured temperature range, the values of frequency exponent ‘s’ are less than one and shows a continous decrease which is attributed to the short range translational hopping assisted by large polaron hopping mechanisms.

  15. Experimental realization of a terahertz all-dielectric metasurface absorber.

    PubMed

    Liu, Xinyu; Fan, Kebin; Shadrivov, Ilya V; Padilla, Willie J

    2017-01-09

    Metamaterial absorbers consisting of metal, metal-dielectric, or dielectric materials have been realized across much of the electromagnetic spectrum and have demonstrated novel properties and applications. However, most absorbers utilize metals and thus are limited in applicability due to their low melting point, high Ohmic loss and high thermal conductivity. Other approaches rely on large dielectric structures and / or a supporting dielectric substrate as a loss mechanism, thereby realizing large absorption volumes. Here we present a terahertz (THz) all dielectric metasurface absorber based on hybrid dielectric waveguide resonances. We tune the metasurface geometry in order to overlap electric and magnetic dipole resonances at the same frequency, thus achieving an experimental absorption of 97.5%. A simulated dielectric metasurface achieves a total absorption coefficient enhancement factor of FT=140, with a small absorption volume. Our experimental results are well described by theory and simulations and not limited to the THz range, but may be extended to microwave, infrared and optical frequencies. The concept of an all-dielectric metasurface absorber offers a new route for control of the emission and absorption of electromagnetic radiation from surfaces with potential applications in energy harvesting, imaging, and sensing.

  16. The electrical breakdown of thin dielectric elastomers: thermal effects

    NASA Astrophysics Data System (ADS)

    Zakaria, Shamsul; Morshuis, Peter H. F.; Benslimane, Mohamed Y.; Gernaey, Krist V.; Skov, Anne L.

    2014-03-01

    Dielectric elastomers are being developed for use in actuators, sensors and generators to be used in various applications, such as artificial eye lids, pressure sensors and human motion energy generators. In order to obtain maximum efficiency, the devices are operated at high electrical fields. This increases the likelihood for electrical breakdown significantly. Hence, for many applications the performance of the dielectric elastomers is limited by this risk of failure, which is triggered by several factors. Amongst others thermal effects may strongly influence the electrical breakdown strength. In this study, we model the electrothermal breakdown in thin PDMS based dielectric elastomers in order to evaluate the thermal mechanisms behind the electrical failures. The objective is to predict the operation range of PDMS based dielectric elastomers with respect to the temperature at given electric field. We performed numerical analysis with a quasi-steady state approximation to predict thermal runaway of dielectric elastomer films. We also studied experimentally the effect of temperature on dielectric properties of different PDMS dielectric elastomers. Different films with different percentages of silica and permittivity enhancing filler were selected for the measurements. From the modeling based on the fitting of experimental data, it is found that the electrothermal breakdown of the materials is strongly influenced by the increase in both dielectric permittivity and conductivity.

  17. Dielectric Behavior of Biomaterials at Different Frequencies on Room Temperature

    NASA Astrophysics Data System (ADS)

    Shrivastava, B. D.; Barde, Ravindra; Mishra, A.; Phadke, S.

    2014-09-01

    Propagation of electromagnetic (EM) waves in radiofrequency (RF) and microwave systems is described mathematically by Maxwell's equations with corresponding boundary conditions. Dielectric properties of lossless and lossy materials influence EM field distribution. For a better understanding of the physical processes associated with various RF and microwave devices, it is necessary to know the dielectric properties of media that interact with EM waves. For telecommunication and radar devices, variations of complex dielectric permittivity (referring to the dielectric property) over a wide frequency range are important. For RF and microwave applicators intended for thermal treatments of different materials at ISM (industrial, scientific, medical) frequencies, one needs to study temperature and moisture content dependencies of the Permittivity of the treated materials. Many techniques have been developed for the measurement of materials. In the present paper authors used Bones and scales of Fish taken from Narmada River (Rajghat Dist. Barwani) as biomaterials. Dielectric properties of Biomaterials with the frequency range from 1Hz to 10 MHz at room temperature with low water content were measured by in-situ performance dielectric kit. Analysis has been done by Alpha high performance impedance analyzer and LCR meters. The experimental work were carried out in Inter University Consortium UGC-DAE, CSR center Indore MP. Measured value indicates the dielectric constant (ɛ') dielectric loss (ɛ") decreases with increasing frequency while conductivity (σ) increases with frequency increased.

  18. Structural, dielectric and magnetic properties of Gd substituted manganese ferrite nanoparticles

    NASA Astrophysics Data System (ADS)

    Murugesan, C.; Sathyamoorthy, B.; Chandrasekaran, G.

    2015-08-01

    Gd3+ ion-substituted manganese ferrite nanoparticles with the chemical formula MnGdxFe2-xO4 (x = 0.0, 0.05, and 0.1) were synthesized by sol-gel auto combustion method. Thermal stability of the as-prepared sample was analyzed using thermo gravimetric and differential thermal analysis (TG-DTA) and the result reveals that the prepared sample is thermally stable above 300 °C. Structural and morphology studies were performed using powder x-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Indexed PXRD patterns confirm the formation of pure cubic spinel structure. The average crystallite sizes calculated using Sherrer’s formula decreased from 47 nm to 32 nm and lattice constant was enhanced from 8.407 Å to 8.432 Å. The FTIR spectrum of manganese ferrite shows a high frequency vibrational band at 564 cm-1 assigned to tetrahedral site and a low frequency vibrational band at 450 cm-1 assigned to octahedral site which are shifted to 556 cm-1 and 439 cm-1 for Gd3+ substitution and confirm the incorporation of Gd3+ into manganese ferrite. SEM analysis shows the presence of agglomerated spherical shaped particles at the surface. Room temperature dielectric and magnetic properties were studied using broadband dielectric spectroscopy (BDS) and vibrating sample magnetometry (VSM). Frequency dependent dielectric constant, ac conductivity and tan delta were found to increase with Gd3+ ion substitution. The measured values of saturation magnetization decrease from 46.6 emu g-1 to 41 emu g-1 with increase in Gd3+ concentration and coercivity decreases from 179.5 Oe to 143 Oe.

  19. Synthesis, structural, dielectric and magnetic properties of polyol assisted copper ferrite nano particles

    NASA Astrophysics Data System (ADS)

    Pavithradevi, S.; Suriyanarayanan, N.; Boobalan, T.

    2017-03-01

    Nanocrystalline copper ferrite CuFe2O4 is synthesized by co-precipitation method in ethylene glycol as chelating agent, using sodium Hydroxide as precipitator at pH 8. The as synthesized CuFe2O4 is annealed at temperatures of 350 °C, 700 °C, and 1050 °C for 2 h respectively. The thermal analysis of the synthesized sample is done by TG technique. It is shown that at 260 °C ethylene glycol has evaporated completely and after 715 °C, spinel ferrite is formed with a cubic structure. The calculated lattice parameters are in agreement with the reported values. FTIR spectra of CuFe2O4 nano particles are as synthesized and annealed at 1050 °C and recorded between 400 cm-1 and 4000 cm-1. It shows that when the temperature increases ethylene glycol gradually evaporates. Finally, nano crystalline single phase spinel ferrite is obtained. X-ray diffraction (XRD) and electron diffraction (EDS) studies show that the sample is indexed as the face centered cubic spinel structure. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicated that the particles are flaky and spherical with the crystallite size in the range of 25-34 nm. From the dielectric studies, the dielectric constant decreases as the frequency increases. Low value of dielectric loss at higher frequencies suggests that the material is suitable for high frequency applications. AC conductivity increases with frequency. The magnetic properties of the samples are measured using a vibrating sample magnetometer (VSM) at room temperature, which shows that the sample exhibited a typical super paramagnetic behavior at low temperature. The saturation magnetization, remanant magnetism, and coercivity increases with applied field.

  20. Thermally switchable dielectrics

    DOEpatents

    Dirk, Shawn M.; Johnson, Ross S.

    2013-04-30

    Precursor polymers to conjugated polymers, such as poly(phenylene vinylene), poly(poly(thiophene vinylene), poly(aniline vinylene), and poly(pyrrole vinylene), can be used as thermally switchable capacitor dielectrics that fail at a specific temperature due to the non-conjugated precursor polymer irreversibly switching from an insulator to the conjugated polymer, which serves as a bleed resistor. The precursor polymer is a good dielectric until it reaches a specific temperature determined by the stability of the leaving groups. Conjugation of the polymer backbone at high temperature effectively disables the capacitor, providing a `built-in` safety mechanism for electronic devices.

  1. A dielectric affinity microbiosensor

    NASA Astrophysics Data System (ADS)

    Huang, Xian; Li, Siqi; Schultz, Jerome S.; Wang, Qian; Lin, Qiao

    2010-01-01

    We present an affinity biosensing approach that exploits changes in dielectric properties of a polymer due to its specific, reversible binding with an analyte. The approach is demonstrated using a microsensor comprising a pair of thin-film capacitive electrodes sandwiching a solution of poly(acrylamide-ran-3-acrylamidophenylboronic acid), a synthetic polymer with specific affinity to glucose. Binding with glucose induces changes in the permittivity of the polymer, which can be measured capacitively for specific glucose detection, as confirmed by experimental results at physiologically relevant concentrations. The dielectric affinity biosensing approach holds the potential for practical applications such as long-term continuous glucose monitoring.

  2. Multilayer dielectric diffraction gratings

    DOEpatents

    Perry, Michael D.; Britten, Jerald A.; Nguyen, Hoang T.; Boyd, Robert; Shore, Bruce W.

    1999-01-01

    The design and fabrication of dielectric grating structures with high diffraction efficiency used in reflection or transmission is described. By forming a multilayer structure of alternating index dielectric materials and placing a grating structure on top of the multilayer, a diffraction grating of adjustable efficiency, and variable optical bandwidth can be obtained. Diffraction efficiency into the first order in reflection varying between 1 and 98 percent has been achieved by controlling the design of the multilayer and the depth, shape, and material comprising the grooves of the grating structure. Methods for fabricating these gratings without the use of ion etching techniques are described.

  3. Multilayer dielectric diffraction gratings

    DOEpatents

    Perry, M.D.; Britten, J.A.; Nguyen, H.T.; Boyd, R.; Shore, B.W.

    1999-05-25

    The design and fabrication of dielectric grating structures with high diffraction efficiency used in reflection or transmission is described. By forming a multilayer structure of alternating index dielectric materials and placing a grating structure on top of the multilayer, a diffraction grating of adjustable efficiency, and variable optical bandwidth can be obtained. Diffraction efficiency into the first order in reflection varying between 1 and 98 percent has been achieved by controlling the design of the multilayer and the depth, shape, and material comprising the grooves of the grating structure. Methods for fabricating these gratings without the use of ion etching techniques are described. 7 figs.

  4. Thermoplastic-based conductive composites containing multi-wall carbon nanotubes aligned under the application of external electric fields

    NASA Astrophysics Data System (ADS)

    Osazuwa, Osayuki

    The objective of this thesis is to prepare thermoplastic/multi-wall carbon nanotubes (MWCNTs) and to apply external alternating current (AC) electric fields to achieve enhanced conductivity and dielectric properties. The first part of the thesis focuses on preparing polyolefin-based composites containing welldispersed MWCNTs. MWCNTs are functionalized with a hyperbranched polyethylene (HBPE) using a non-covalent, non-specific functionalization approach and melt compounded with an ethylene-octene copolymer (EOC) matrix. The improved filler dispersion in the functionalized EOC/MWCNT composite results in higher elongation at break compared to the non-functionalized composite. However, the electrical percolation threshold and the ultimate conductivity of the composites are not affected considerably, suggesting that this functionalization approach leaves the inherent properties of the nanotubes intact. EOC/HBPE-functionalized MWCNT composites are further subjected to external AC electric fields (35 -- 212 kV/m), which induce the formation of aligned columnar structures, as evidenced by Scanning Electron Microscopy. Experimentally acquired resistivity data are used to derive correlations between the characteristic insulator-to-conductor transition times of the composites and the electric field strength (E), polymer viscosity (eta) and MWCNT volume fraction (φ). A criterion for the selection of (eta, E, φ) conditions that enable MWCNT assembly under an electric field controlled regime (minimal Brownian motion-driven aggregation effects) is developed. The dielectric properties of the solidified aligned EOC/MWCNT composites are further studied using dielectric spectroscopy. Annealing of the composites at 160 °C results in the formation of interconnected structures, whereas electrification, using AC field of 71 and 212 kV/m induces the formation of aligned columnar structures. The electrified and annealed composites have increased real and imaginary permittivity compared

  5. Spectroscopic and dielectric study of iodine chloride doped PVA/PVP blend

    NASA Astrophysics Data System (ADS)

    Abdelrazek, E. M.; Ragab, H. M.

    2015-06-01

    Optical and dielectric properties of Poly (vinyl alcohol)/ Poly (vinyl pyrrolidone) blend and blend loaded with different concentrations of ICl2 were studied. UV-Vis spectral analysis before and after γ-irradiation suggested that the addition of iodine led to complete complexation between ICl2 and polymer blend were observed. The values of optical parameters λ o , S o and n ∞ were determined from by reflection and transmission spectra in the range of 200-800 nm. The refractive index was found to change non-monotonically with the increase of iodine. Infrared analysis revealed the formation of new species between blend and iodine content. There were some changes in IR absorption bands, position and their intensities. The AC conductivity ( σ ac ) behavior of all prepared films was investigated in the frequency range 42 Hz-5 MHz and under different isothermal stabilization in the temperature range 300-400 K. The dependence of the imaginary modulus ( M″) on frequency at lower frequencies was estimated. The increasing values of M″ may be attributed to the bulk effect with the increase in temperature.

  6. Dielectric Response of a Quantum Dot Measured with an Aluminum Single Electron Transistor

    NASA Astrophysics Data System (ADS)

    Berman, D.; Zhitenev, N. B.; Ashoori, R. C.; Melloch, M. R.

    1997-03-01

    We demonstrate the first use of an aluminum single electron transistor (SET) as a charge sensor coupled to a semiconductor structure. A quantum dot is electrostatically defined with metal gates on top of a GaAs/AlGaAs heterostructure. The SET functions both as one of the defining gates for the quantum dot and as an electrometer. The quantum dot acts as a dielectric between two capacitor plates, one of which is the SET, and the other is an opposing gate to which we apply an ac excitation and a dc voltage V_g. We vary the conductance of a single tunnel barrier (resistances in the range of 10^3-10^12 Ω) which connects the dot to a charge reservoir and measure the capacitance C between the opposing gate and the SET. Due to the effect of screening, C(V_g) displays periodically occurring dips for those Vg at which a single electron can move in and out of the dot. The oscillations are gradually washed out as the coupling strength to the lead increases beyond 2e^2/h. For sufficiently small couplings, electrons do not tunnel into the dot during one cycle of ac excitation. Surprisingly, the capacitance of such an effectively sealed dot also displays oscillations with electron number. These however are opposite in sign to the oscillations seen for moderate coupling.

  7. Note: Optimization of the numerical data analysis for conductivity percolation studies of drying moist porous systems

    SciTech Connect

    Moscicki, J. K.; Sokolowska, D.; Dziob, D.; Nowak, J.; Kwiatkowski, L.

    2014-02-15

    A simplified data analysis protocol, for dielectric spectroscopy use to study conductivity percolation in dehydrating granular media is discussed. To enhance visibility of the protonic conductivity contribution to the dielectric loss spectrum, detrimental effects of either low-frequency dielectric relaxation or electrode polarization are removed. Use of the directly measurable monofrequency dielectric loss factor rather than estimated DC conductivity to parameterize the percolation transition substantially reduces the analysis work and time.

  8. Note: optimization of the numerical data analysis for conductivity percolation studies of drying moist porous systems.

    PubMed

    Moscicki, J K; Sokolowska, D; Kwiatkowski, L; Dziob, D; Nowak, J

    2014-02-01

    A simplified data analysis protocol, for dielectric spectroscopy use to study conductivity percolation in dehydrating granular media is discussed. To enhance visibility of the protonic conductivity contribution to the dielectric loss spectrum, detrimental effects of either low-frequency dielectric relaxation or electrode polarization are removed. Use of the directly measurable monofrequency dielectric loss factor rather than estimated DC conductivity to parameterize the percolation transition substantially reduces the analysis work and time.

  9. ac electroosmosis in rectangular microchannels.

    PubMed

    Campisi, Michele; Accoto, Dino; Dario, Paolo

    2005-11-22

    Motivated by the growing interest in ac electroosmosis as a reliable no moving parts strategy to control fluid motion in microfluidic devices for biomedical applications, such as lab-on-a-chip, we study transient and steady-state electrokinetic phenomena (electroosmosis and streaming currents) in infinitely extended rectangular charged microchannels. With the aid of Fourier series and Laplace transforms we provide a general formal solution of the problem, which is used to study the time-dependent response to sudden ac applied voltage differences in case of finite electric double layer. The Debye-Huckel approximation has been adopted to allow for an algebraic solution of the Poisson-Boltzmann problem in Fourier space. We obtain the expressions of flow velocity profiles, flow rates, streaming currents, as well as expressions of the complex hydraulic and electrokinetic conductances. We analyze in detail the dependence of the electrokinetic conductance on the extension of linear dimensions relative to the Debye length, with an eye on finite electric double layer effects.

  10. ac electroosmosis in rectangular microchannels

    NASA Astrophysics Data System (ADS)

    Campisi, Michele; Accoto, Dino; Dario, Paolo

    2005-11-01

    Motivated by the growing interest in ac electroosmosis as a reliable no moving parts strategy to control fluid motion in microfluidic devices for biomedical applications, such as lab-on-a-chip, we study transient and steady-state electrokinetic phenomena (electroosmosis and streaming currents) in infinitely extended rectangular charged microchannels. With the aid of Fourier series and Laplace transforms we provide a general formal solution of the problem, which is used to study the time-dependent response to sudden ac applied voltage differences in case of finite electric double layer. The Debye-Hückel approximation has been adopted to allow for an algebraic solution of the Poisson-Boltzmann problem in Fourier space. We obtain the expressions of flow velocity profiles, flow rates, streaming currents, as well as expressions of the complex hydraulic and electrokinetic conductances. We analyze in detail the dependence of the electrokinetic conductance on the extension of linear dimensions relative to the Debye length, with an eye on finite electric double layer effects.

  11. AC plasma anemometer—characteristics and design

    NASA Astrophysics Data System (ADS)

    Marshall, Curtis; Matlis, Eric; Corke, Thomas; Gogineni, Sivaram

    2015-08-01

    The characteristics and design of a high-bandwidth flow sensor that uses an AC glow discharge (plasma) as the sensing element is presented. The plasma forms in the air gap between two protruding low profile electrodes attached to a probe body. The output from the anemometer is an amplitude modulated version of the AC voltage input that contains information about the mean and fluctuating velocity components. The anemometer circuitry includes resistance and capacitance elements that simulate a dielectric-barrier to maintain a diffuse plasma, and a constant-current feedback control that maintains operation within the desired glow discharge regime over an extended range of air velocities. Mean velocity calibrations are demonstrated over a range from 0 to 140 m s-1. Over this velocity range, the mean output voltage varied linearly with air velocity, providing a constant static sensitivity. The effect of the electrode gap and input AC carrier frequency on the anemometer static sensitivity and dynamic response are investigated. Experiments are performed to compare measurements obtained with a plasma sensor operating at two AC carrier frequencies against that of a constant-temperature hot-wire. All three sensors were calibrated against the same known velocity reference. An uncertainty based on the standard deviation of the velocity calibration fit was applied to the mean and fluctuating velocity measurements of the three sensors. The motivation is not to replace hot-wires as a general measurement tool, but rather as an alternative to hot-wires in harsh environments or at high Mach numbers where they either have difficulty in surviving or lack the necessary frequency response.

  12. Optimization of structural and dielectric properties of CdSe loaded poly(diallyl dimethyl ammonium chloride) polymer in a desired frequency and temperature window

    SciTech Connect

    Tyagi, Chetna Sharma, Ambika

    2016-01-07

    In the present paper, investigations of CdSe loaded poly(diallyl dimethyl ammonium chloride) (PDADMAC) nanocomposites and pure PDADMAC synthesized by wet chemical technique have been carried out. Fourier transform infrared and X-ray diffraction analysis have been performed to reveal the structural details of pure polymer and polymer nanocomposite (PNC). The dielectric behavior of pure polymer and PNC has been recorded, which results in higher value of the real and imaginary part of dielectric constant for PNC, as compared with pure PDADMAC. The increase is attributed to the addition of CdSe quantum dots to the pure polymer. The contribution of ionic and electronic polarization has been observed at higher frequency. The theoretical fitting of Cole-Cole function to the experimental data of dielectric constant of PNC and pure PDADMAC results in the determination of relaxation time and conductivity of space charge carriers. The CdSe loaded polymer nanocomposite has been used as an electrolyte in the battery fabrication with configuration Al/PNC/Ag{sub 2}O. The ac conductivity measurements have been carried out for both samples in a frequency window of 1 kHz–5 MHz and at different temperatures varying from 298 K to 523 K. Activation energy (E{sub a}) has been determined for pure polymer as well as PNC and is found to be less for PNC, as compared with pure polymer. Further, impedance measurement at different temperatures results in two frequency ranges corresponding to ionic conduction and blocking electrode effect. The value of bulk resistance for pure polymer and PNC has been found to be 3660 Ω and 442 Ω, respectively, at 298 K temperature. Electric modulus has been determined and is observed to support the dielectric constant data; it further reveals the deviation from Debye behavior at a higher frequency.

  13. Optimization of structural and dielectric properties of CdSe loaded poly(diallyl dimethyl ammonium chloride) polymer in a desired frequency and temperature window

    NASA Astrophysics Data System (ADS)

    Tyagi, Chetna; Sharma, Ambika

    2016-01-01

    In the present paper, investigations of CdSe loaded poly(diallyl dimethyl ammonium chloride) (PDADMAC) nanocomposites and pure PDADMAC synthesized by wet chemical technique have been carried out. Fourier transform infrared and X-ray diffraction analysis have been performed to reveal the structural details of pure polymer and polymer nanocomposite (PNC). The dielectric behavior of pure polymer and PNC has been recorded, which results in higher value of the real and imaginary part of dielectric constant for PNC, as compared with pure PDADMAC. The increase is attributed to the addition of CdSe quantum dots to the pure polymer. The contribution of ionic and electronic polarization has been observed at higher frequency. The theoretical fitting of Cole-Cole function to the experimental data of dielectric constant of PNC and pure PDADMAC results in the determination of relaxation time and conductivity of space charge carriers. The CdSe loaded polymer nanocomposite has been used as an electrolyte in the battery fabrication with configuration Al/PNC/Ag2O. The ac conductivity measurements have been carried out for both samples in a frequency window of 1 kHz-5 MHz and at different temperatures varying from 298 K to 523 K. Activation energy (Ea) has been determined for pure polymer as well as PNC and is found to be less for PNC, as compared with pure polymer. Further, impedance measurement at different temperatures results in two frequency ranges corresponding to ionic conduction and blocking electrode effect. The value of bulk resistance for pure polymer and PNC has been found to be 3660 Ω and 442 Ω, respectively, at 298 K temperature. Electric modulus has been determined and is observed to support the dielectric constant data; it further reveals the deviation from Debye behavior at a higher frequency.

  14. Effect of Mn2+ substitution on structural, magnetic, electric and dielectric properties of Mg-Zn ferrites

    NASA Astrophysics Data System (ADS)

    Ghodake, U. R.; Chaudhari, N. D.; Kambale, R. C.; Patil, J. Y.; Suryavanshi, S. S.

    2016-06-01

    In this work, Mn substituted Mg-Zn spinel ferrites having general formula Zno.4Mg0.6-xMnxFe2O4 (0≤x≤0.30) have been synthesized by oxalate precursor chemical method and investigated their structural, magnetic and electric properties. X-ray diffraction (XRD) is used to study the crystal structure of synthesized materials. XRD study reveals the formation of polycrystalline cubic spinel lattice structure without any impurity phase having crystallite size in the range from 39.97 nm to 45.62 nm. Scanning electron micrographs revealed, increase in grain size (D) with increase in Mn2+ content up to x=0.10; then it decreases for x>0.10. Energy dispersive x-ray analysis (EDAX) confirms the presence of Mg2+, Mn2+, Fe3+, Zn2+ and O2- ions as per the stoichiometry. The magnetic moment (nB), with Mn2+ substitution is found to increase initially up to x=0.10 and then it deceases with further Mn2+ substitution. The observed variation in the magnetic moment (nB) is explained by considering the variation of saturation magnetization, anisotropy constant, density values and exchange interaction. The d.c. electrical resistivity decreased with increase in temperature in accordance with semiconducting behavior. Furthermore, the conductivity was found to obey the Arrhenius relation with a change in slope at critical temperature (i.e. the Curie temperature). The increase in d.c. resistivity is attributed to the hindering of Verwey mechanism between Fe2+⇔Fe3+ ions and Mn2+⇔Mn3+. The dielectric constant (ε‧) measurement revealed the dielectric dispersion behavior in accordance with the Maxwell-Wagner model and Koops phenomenological theory, which is responsible for conduction and polarization. The dielectric characteristics (ε‧, ε″ and tan δ) exhibit dispersion due to Maxwell-Wagner type interfacial polarization. The values of dielectric constant (ε‧) and a.c. resistivity (ρac) exhibit highest magnitude at x=0.10 and decreases further with Mn2+ substitution.

  15. The effects of vacuum ultraviolet radiation on low-k dielectric films

    SciTech Connect

    Sinha, H.; Ren, H.; Nichols, M. T.; Lauer, J. L.; Shohet, J. L.; Tomoyasu, M.; Russell, N. M.; Jiang, G.; Antonelli, G. A.; Fuller, N. C.; Engelmann, S. U.; Lin, Q.; Ryan, V.; Nishi, Y.

    2012-12-01

    Plasmas, known to emit high levels of vacuum ultraviolet (VUV) radiation, are used in the semiconductor industry for processing of low-k organosilicate glass (SiCOH) dielectric device structures. VUV irradiation induces photoconduction, photoemission, and photoinjection. These effects generate trapped charges within the dielectric film, which can degrade electrical properties of the dielectric. The amount of charge accumulation in low-k dielectrics depends on factors that affect photoconduction, photoemission, and photoinjection. Changes in the photo and intrinsic conductivities of SiCOH are also ascribed to the changes in the numbers of charged traps generated during VUV irradiation. The dielectric-substrate interface controls charge trapping by affecting photoinjection of charged carriers into the dielectric from the substrate. The number of trapped charges increases with increasing porosity of SiCOH because of charge trapping sites in the nanopores. Modifications to these three parameters, i.e., (1) VUV induced charge generation, (2) dielectric-substrate interface, and (3) porosity of dielectrics, can be used to reduce trapped-charge accumulation during processing of low-{kappa} SiCOH dielectrics. Photons from the plasma are responsible for trapped-charge accumulation within the dielectric, while ions stick primarily to the surface of the dielectrics. In addition, as the dielectric constant was decreased by adding porosity, the defect concentrations increased.

  16. Optimal Super Dielectric Material

    DTIC Science & Technology

    2015-09-01

    electrically insulating materials filled to the point of incipient wetness (paste consistency) with liquids containing dissolved ions. This work...109. This strongly supports the fundamental hypothesis of SDM: In the presence of an electric field any electrically insulating, porous material...ABSTRACT The results of this study establish that powder-based super dielectric materials (SDM) are a large family of porous electrically

  17. Dielectric properties of albumin and yolk of avian egg.

    PubMed

    Lokhande, M P; Arbad, B R; Landge, M G; Mehrotra, S C

    1996-04-01

    The dielectric properties of albumin and yolk of eggs of hen and duck have been investigated using the time domain reflectometry (TDR) technique in the frequency range 10 MHz to 10 GHz at room temperature. The conductivity and pH values were also measured. It has been found that the values of dielectric constant (epsilon s) is lower, while the values of relaxation time tau(ps) are higher than that of pure water possibly due to the bound water present in the yolk and albumin of the avian egg. The dielectric constant for albumin is more than that for yolk of eggs, while reverse is found with the values of relaxation time. Also albumin shows approximately three times higher conductivity than that of yolk. In the case of relatively older (by 2 days) eggs, the dielectric parameters tend to be slightly increased.

  18. Structural and dielectric properties of barium-modified SrBi4Ti4O15 ceramics

    NASA Astrophysics Data System (ADS)

    Nayak, P.; Badapanda, T.; Anwar, S.; Panigrahi, S.

    2015-04-01

    Barium-modified strontium bismuth titanate ceramics with chemical formula Sr1-xBaxBi4Ti4O15 (x = 0.00, 0.02, 0.06, 0.08 and 0.1) (SBBT) have been prepared by means of solid-state reaction technique and their structural and electrical properties were investigated. X-ray diffraction data confirm that all the compositions show orthorhombic structure without any deleterious phase. Scanning electron micrographs show plate like grain morphology with random orientation of platelets. The temperature-dependent dielectric study shows that the phase transition temperature decreases, but the dielectric constant increases with increase in Ba content. Complex impedance plots show that both grain and grain boundary effect on the resistance mechanisms in all the compositions. The values of the activation energy confirm that the oxygen vacancies play an important role in the conduction. The ac conductivity of SBBT ceramics increases as a function of frequency due to relaxation phenomenon which arises due to mobile charge carriers.

  19. TiO2 nanoparticles and silicon nanowires hybrid device: Role of interface on electrical, dielectric, and photodetection properties

    NASA Astrophysics Data System (ADS)

    Rasool, Kamran; Rafiq, M. A.; Ahmad, Mushtaq; Imran, Z.; Hasan, M. M.

    2012-12-01

    We report ˜12, 5, 12, 100, and 70 times enhancement of external quantum efficiency, detectivity, responsivity, AC conductivity, and overall dielectric constant (ɛ'), respectively of hybrid silicon nanowires (SiNWs) and titania (TiO2) nanoparticles (NPs) device as compared to SiNWs only device. Devices show persistent photoconductivity. Metal assisted chemical etching and co-precipitation method were used to prepare SiNWs (length ˜40 μm, diameter ˜30-400 nm) and TiO2 NPs (diameter ˜50 nm), respectively. Formation of acceptor like states at NPs and SiNWs interface improves electrical properties. Presence of low refractive index TiO2 around SiNWs causing funneling of photon energy into SiNWs improves photodetection.

  20. Tevatron AC dipole system

    SciTech Connect

    Miyamoto, R.; Kopp, S.E.; Jansson, A.; Syphers, M.J.; /Fermilab

    2007-06-01

    The AC dipole is an oscillating dipole magnet which can induce large amplitude oscillations without the emittance growth and decoherence. These properties make it a good tool to measure optics of a hadron synchrotron. The vertical AC dipole for the Tevatron is powered by an inexpensive high power audio amplifier since its operating frequency is approximately 20 kHz. The magnet is incorporated into a parallel resonant system to maximize the current. The use of a vertical pinger magnet which has been installed in the Tevatron made the cost relatively inexpensive. Recently, the initial system was upgraded with a more powerful amplifier and oscillation amplitudes up to 2-3{sigma} were achieved with the 980 GeV proton beam. This paper discusses details of the Tevatron AC dipole system and also shows its test results.

  1. Evaluation of DC electric field distribution of PPLP specimen based on the measurement of electrical conductivity in LN2

    NASA Astrophysics Data System (ADS)

    Hwang, Jae-Sang; Seong, Jae-Kyu; Shin, Woo-Ju; Lee, Jong-Geon; Cho, Jeon-Wook; Ryoo, Hee-Suk; Lee, Bang-Wook

    2013-11-01

    High temperature superconducting (HTS) cable has been paid much attention due to its high efficiency and high current transportation capability, and it is also regarded as eco-friendly power cable for the next generation. Especially for DC HTS cable, it has more sustainable and stable properties compared to AC HTS cable due to the absence of AC loss in DC HTS cable. Recently, DC HTS cable has been investigated competitively all over the world, and one of the key components of DC HTS cable to be developed is a cable joint box considering HVDC environment. In order to achieve the optimum insulation design of the joint box, analysis of DC electric field distribution of the joint box is a fundamental process to develop DC HTS cable. Generally, AC electric field distribution depends on relative permittivity of dielectric materials but in case of DC, electrical conductivity of dielectric material is a dominant factor which determines electric field distribution. In this study, in order to evaluate DC electric field characteristics of the joint box for DC HTS cable, polypropylene laminated paper (PPLP) specimen has been prepared and its DC electric field distribution was analyzed based on the measurement of electrical conductivity of PPLP in liquid nitrogen (LN2). Electrical conductivity of PPLP in LN2 has not been reported yet but it should be measured for DC electric field analysis. The experimental works for measuring electrical conductivity of PPLP in LN2 were presented in this paper. Based on the experimental works, DC electric field distribution of PPLP specimen was fully analyzed considering the steady state and the transient state of DC. Consequently, it was possible to determine the electric field distribution characteristics considering different DC applying stages including DC switching on, DC switching off and polarity reversal conditions.

  2. Dielectric and spectroscopic properties of PbO-Nb2O5-P2O5:V2O5 glass system

    NASA Astrophysics Data System (ADS)

    Krishna Mohan, N.; Sahaya Baskaran, G.; Veeraiah, N.

    2006-06-01

    PbO-Nb2O5-P2O5 glasses containing different concentrations of V2O5 ranging from 0 to 1.0 mol% were prepared. A number of studies, viz. differential thermal analysis, infrared, optical absorption, Raman and ESR spectra and dielectric properties (dielectric constant , loss tan δ, a.c. conductivity ac over a range of frequency and temperature), of these glasses have been carried out. The results have been analysed in the light of different oxidation states of vanadium ions. The analysis indicates that when the concentration of V2O5 is increased gradually, vanadium ions are observed to exist mostly in the V4+ state, occupy network-modifying positions and decrease the rigidity of the glass network. A transformation of NbO4 to NbO6 structural units and a decrease in the concentration of PO4 structural units have also been observed with an increase in the concentration of V2O5 in the glass network.

  3. ACS CCDs daily monitor

    NASA Astrophysics Data System (ADS)

    Sirianni, Marco

    2006-07-01

    This program consists of a set of basic tests to monitor, the read noise, thedevelopment of hot pixels and test for any source of noise in ACS CCDdetectors. The files, biases and dark will be used to create referencefiles for science calibration. This programme will be for the entire lifetime of ACS.For cycle 15 the program will cover 18 months 12.1.06->05.31.08and it has been divied into three different proposal each covering six months.The three poroposal are 11041-11042-11043.

  4. ac bidirectional motor controller

    NASA Technical Reports Server (NTRS)

    Schreiner, K.

    1988-01-01

    Test data are presented and the design of a high-efficiency motor/generator controller at NASA-Lewis for use with the Space Station power system testbed is described. The bidirectional motor driver is a 20 kHz to variable frequency three-phase ac converter that operates from the high-frequency ac bus being designed for the Space Station. A zero-voltage-switching pulse-density-modulation technique is used in the converter to shape the low-frequency output waveform.

  5. Dielectric measurements of selected ceramics at microwave frequencies

    NASA Technical Reports Server (NTRS)

    Dahiya, J. N.; Templeton, C. K.

    1994-01-01

    Dielectric measurements of strontium titanate and lead titanate zirconate ceramics are conducted at microwave frequencies using a cylindrical resonant cavity in the TE(sub 011) mode. The perturbations of the electric field are recorded in terms of the frequency shift and Q-changes of the cavity signal. Slater's perturbation equations are used to calculate e' and e" of the dielectric constant as a function of temperature and frequency.

  6. Spacecraft dielectric material properties and spacecraft charging

    NASA Technical Reports Server (NTRS)

    Frederickson, A. R.; Wall, J. A.; Cotts, D. B.; Bouquet, F. L.

    1986-01-01

    The physics of spacecraft charging is reviewed, and criteria for selecting and testing semiinsulating polymers (SIPs) to avoid charging are discussed and illustrated. Chapters are devoted to the required properties of dielectric materials, the charging process, discharge-pulse phenomena, design for minimum pulse size, design to prevent pulses, conduction in polymers, evaluation of SIPs that might prevent spacecraft charging, and the general response of dielectrics to space radiation. SIPs characterized include polyimides, fluorocarbons, thermoplastic polyesters, poly(alkanes), vinyl polymers and acrylates, polymers containing phthalocyanine, polyacene quinones, coordination polymers containing metal ions, conjugated-backbone polymers, and 'metallic' conducting polymers. Tables summarizing the results of SIP radiation tests (such as those performed for the NASA Galileo Project) are included.

  7. Model of dissipative dielectric elastomers

    NASA Astrophysics Data System (ADS)

    Chiang Foo, Choon; Cai, Shengqiang; Jin Adrian Koh, Soo; Bauer, Siegfried; Suo, Zhigang

    2012-02-01

    The dynamic performance of dielectric elastomer transducers and their capability of electromechanical energy conversion are affected by dissipative processes, such as viscoelasticity, dielectric relaxation, and current leakage. This paper describes a method to construct a model of dissipative dielectric elastomers on the basis of nonequilibrium thermodynamics. We characterize the state of the dielectric elastomer with kinematic variables through which external loads do work, and internal variables that measure the progress of the dissipative processes. The method is illustrated with examples motivated by existing experiments of polyacrylate very-high-bond dielectric elastomers. This model predicts the dynamic response of the dielectric elastomer and the leakage current behavior. We show that current leakage can be significant under large deformation and for long durations. Furthermore, current leakage can result in significant hysteresis for dielectric elastomers under cyclic voltage.

  8. Dielectric breakdown strength of magnetic nanofluid based on insulation oil after impulse test

    NASA Astrophysics Data System (ADS)

    Nazari, M.; Rasoulifard, M. H.; Hosseini, H.

    2016-02-01

    In this study, the dielectric breakdown strength of magnetic nanofluids based on transformer mineral oil for use in power systems is reviewed. Nano oil samples are obtained from dispersion of the magnetic nanofluid within uninhibited transformer mineral oil NYTRO LIBRA as the base fluid. AC dielectric breakdown voltage measurement was carried out according to IEC 60156 standard and the lightning impulse breakdown voltage was obtained by using the sphere-sphere electrodes in an experimental setup for nano oil in volume concentration of 0.1-0.6%. Results indicate improved AC and lightning impulse breakdown voltage of nano oil compared to the base oil. AC test was performed again after applying impulse current and result showed that nano oil unlike the base oil retains its dielectric properties. Increase the dielectric strength of the nano oil is mainly due to dielectric and magnetic properties of Fe3O4 nanoparticles that act as free electrons snapper, and reduce the rate of free electrons in the ionization process.

  9. Raman, dielectric and variable range hopping nature of Gd2O3-doped K0.5N0.5NbO3 piezoelectric ceramics

    NASA Astrophysics Data System (ADS)

    Peddigari, Mahesh; Dobbidi, Pamu

    2015-10-01

    (K0.5Na0.5)NbO3 (KNN) + x wt% Gd2O3 (x = 0 -1.5) ceramics have been prepared by conventional solid state reaction method. The effect of Gd2O3 on the structural, microstructural and dielectric properties of KNN ceramics were studied systematically. The effect of Gd2O3 on phase transformation from orthorhombic to psuedocubic structure is explained interms of changes in the internal vibration modes of NbO6 octahedra. The Raman intensity of the stretching mode v1 enhanced and shifted toward higher wavenumber with Gd2O3 concentration, which is attributed to the increase in polarizability and change in the O-Nb-O bond angles. Microstructural analysis revealed that the grain size of the KNN ceramics decreases from 2.26 ± 1.07 μm to 0.35 ± 0.13 μm and becomes homogenous with an increase in Gd2O3 concentration. The frequency dependent dielectric spectra are analyzed by using Havriliak-Negami function. The fitted symmetry parameter and relaxation time (τ) are found to be 0.914 and 8.78 × 10-10 ± 5.5 × 10-11 s, respectively for the sample doped with x = 1.0. The addition of Gd2O3 to the KNN shifted the polymorphic phase transition orthorhombic to tetragonal transition temperature (TO-T) from 199oC to 85oC with enhanced dielectric permittivity (ɛ' = 1139 at 1 MHz). The sample with x = 1.0, shown a high dielectric permittivity (ɛ' = 879) and low dielectric loss (<5%) in the broad temperature range (-140oC - 150oC) with the Curie temperature 307 oC can have the potential for high temperature piezoelectric and tunable RF circuit applications. The temperature dependent AC-conductivity follows the variable range hopping conduction mechanism by obtaining the slope -0.25 from the ln[ln(ρac)] versus ln(T) graph in the temperature range of 133 K-308 K. The effect of Gd2O3 on the Mott's parameters such as density of states (N(EF)), hopping length (RH), and hopping energy (WH) have been discussed.

  10. Numerical simulation of ac plasma arc thermodynamics

    NASA Astrophysics Data System (ADS)

    Wu, Han-Ming; Carey, G. F.; Oakes, M. E.

    1994-05-01

    A mathematical model and approximate analysis for the energy distribution of an ac plasma arc with a moving boundary is developed. A simplified electrical conductivity function is assumed so that the dynamic behavior of the arc may be determined, independent of the gas type. The model leads to a reduced set of non-linear partial differential equations which governs the quasi-steady ac arc. This system is solved numerically and it is found that convection plays an important role, not only in the temperature distribution, but also in arc disruptions. Moreover, disruptions are found to be influenced by convection only for a limited frequency range. The results of the present studies are applicable to the frequnecy range of 10-10(exp 2) Hz which includes most industry ac arc frequencies.

  11. Numerical Simulation of AC Plasma Arc Thermodynamics

    NASA Astrophysics Data System (ADS)

    Wu, Han-Ming; Carey, G. F.; Oakes, M. E.

    1994-05-01

    A mathematical model and approximate analysis for the energy distribution of an ac plasma arc with a moving boundary is developed. A simplified electrical conductivity function is assumed so that the dynamic behavior of the arc may be determined, independent of the gas type. The model leads to a reduced set of non-linear partial differential equations which governs the quasi-steady ac arc. This system is solved numerically and it is found that convection plays an important role, not only in the temperature distribution, but also in arc disruptions. Moreover, disruptions are found to be influenced by convection only for a limited frequency range. The results of the present studies are applicable to the frequency range of 10-102 Hz which includes most industry ac arc frequencies.

  12. Open-access dielectric elastomer material database

    NASA Astrophysics Data System (ADS)

    Vertechy, R.; Fontana, M.; Stiubianu, G.; Cazacu, M.

    2014-03-01

    Dielectric Elastomer Transducers (DETs) are deformable capacitors that can be used as sensors, actuators and generators. The design of effective and optimized DETs requires the knowledge of a set of relevant properties of the employed Dielectric Elastomer (DE) material, which make it possible to accurately predict their electromechanical dynamic behavior. In this context, an open-access database for DE materials has been created with the aim of providing the practicing engineer with the essential information for the design and optimization of new kinds of DET. Among the electrical properties, dielectric susceptibility, dielectric strength and conductivity are considered along with their dependence on mechanical strain. As regards mechanical behavior, experimental stress-strain curves are provided to predict hyperelasticity, plasticity, viscosity, Mullins effect and mechanical rupture. Properties of commercial elastomeric membranes have been entered in the database and made available to the research community. This paper describes the instrumentations, experimental setups and procedures that have been employed for the characterization of the considered DE materials. To provide an example, the experimental data acquired for a commercially available natural rubber membrane (OPPO Band Red 8012) are presented.

  13. Metallic magnetism and change of conductivity in the nano to bulk transition of cobalt ferrite

    NASA Astrophysics Data System (ADS)

    Arunkumar, A.; Vanidha, D.; Oudayakumar, K.; Rajagopan, S.; Kannan, R.

    2013-11-01

    Variations in conductivity with particle size have been observed in cobalt ferrite, when synthesized by solgel auto-combustion method. Impedance analysis reveals metallic and semiconducting behavior at room temperature for a particle size of 6 nm and 52 nm, respectively. Upon thermal activation, metallic to semiconducting phase transition has been observed as a function of particle size and vice-versa. Grainboundary Resistance (Rgb), increased drastically with particle size (19 MΩ for 6 nm and 259 MΩ for 52 nm) at room temperature. AC conductivity and dielectric constants exhibit similar metallic to semiconducting phase transition at 6 nm and semiconducting behavior at 52 nm with temperature in the selected frequencies. Enhanced magnetic moment with an increase in the grain size along with decreased coercivity (1444 G to 1146 G) reveals transition from single domain to multi-domain. Increased inter-particle interaction is responsible for metallicity at the nano level and on the contrary semiconductivity is attributed to bulk.

  14. AC/DC converter

    NASA Astrophysics Data System (ADS)

    Jain, Praveen K.

    1992-08-01

    In a system such as a 20 kHz space station primary electrical power distribution system, power conversion from AC to DC is required. Some of the basic requirements for this conversion are high efficiency, light weight and small volume, regulated output voltage, close to unity input power factor, distortionless input current, soft-starting, low electromagnetic interference, and high reliability. An AC-to-DC converter is disclosed which satisfies the main design objectives of such converters for use in space. The converter of the invention comprises an input transformer, a resonant network, a current controller, a diode rectifier, and an output filter. The input transformer is for connection to a single phase, high frequency, sinusoidal waveform AC voltage source and provides a matching voltage isolating from the AC source. The resonant network converts this voltage to a sinusoidal, high frequency bidirectional current output, which is received by the current controller to provide the desired output current. The diode rectifier is connected in parallel with the current controller to convert the bidirectional current into a unidirectional current output. The output filter is connected to the rectifier to provide an essentially ripple-free, substantially constant voltage DC output.

  15. AC/RF Superconductivity

    SciTech Connect

    Ciovati, Gianluigi

    2015-02-01

    This contribution provides a brief introduction to AC/RF superconductivity, with an emphasis on application to accelerators. The topics covered include the surface impedance of normal conductors and superconductors, the residual resistance, the field dependence of the surface resistance, and the superheating field.

  16. Study of the effect of substitution by MnO2 and V2O5 on the microstructure, electrical and dielectric characteristics of zinc oxide ceramics

    NASA Astrophysics Data System (ADS)

    Rady, K. E.; Desouky, Osama A.

    2016-12-01

    As a consequence of their established properties in varistors, V2O5 and MnO2 dopants were added to ZnO ceramics to improve their microstructural, non-linear electrical as well as their dielectric properties. Samples of the general chemical formula (100-2 x) ZnO- x V2O5- x MnO2, x = 0, 0.5, 0.7, 1, 1.25 mol%, were prepared using the conventional ceramic technique at five sintering temperatures, namely 800 °C, 900 °C, 1000 °C, 1100 °C and 1200 °C, for 2 hours. The maximum shrinkage and minimum water absorption percentages were recorded at the sintering temperature 1200 °C. This temperature was selected as the appropriate sintering temperature for all the samples. The structure of the prepared samples was examined using XRD and EDAX measurements. SEM micrographs revealed that the selected sintering temperature improved the microstructure of the samples and strongly affected the non-linear behavior of the prepared samples. The values of the non-linear coefficient (α) improved with the increase of V2O5 and MnO2 mol%. Upon studying the frequency and compositional dependence of the dielectric constant (\\varepsilon{^') and ac conductivity ( σ), a significant improvement in the dielectric properties was detected with increasing V2O5 and MnO2 mol%.

  17. Effects of ultrasonication and conventional mechanical homogenization processes on the structures and dielectric properties of BaTiO3 ceramics.

    PubMed

    Akbas, Hatice Zehra; Aydin, Zeki; Yilmaz, Onur; Turgut, Selvin

    2017-01-01

    The effects of the homogenization process on the structures and dielectric properties of pure and Nb-doped BaTiO3 ceramics have been investigated using an ultrasonic homogenization and conventional mechanical methods. The reagents were homogenized using an ultrasonic processor with high-intensity ultrasonic waves and using a compact mixer-shaker. The components and crystal types of the powders were determined by Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analyses. The complex permittivity (ε('), ε″) and AC conductivity (σ') of the samples were analyzed in a wide frequency range of 20Hz to 2MHz at room temperature. The structures and dielectric properties of pure and Nb-doped BaTiO3 ceramics strongly depend on the homogenization process in a solid-state reaction method. Using an ultrasonic processor with high-intensity ultrasonic waves based on acoustic cavitation phenomena can make a significant improvement in producing high-purity BaTiO3 ceramics without carbonate impurities with a small dielectric loss.

  18. Understanding Ion Transport in Polymerized Ionic Liquids using Dielectric Spectroscopy

    NASA Astrophysics Data System (ADS)

    Hyeok Choi, U.; Chen, Hong; Liu, Wenjuan; Elabd, Yossef A.; Colby, Ralph H.

    2009-03-01

    In order to deduce the mechanism of ion conduction in ion-containing polymers, not only the conductivity needs to be measured but also the number density and mobility of conducting ions must be determined using broadband dielectric spectroscopy, covering broad frequency and temperature ranges. To obtain a transference number of unity, one ionic charge is covalently bonded to the polymer so that only the counterions can contribute to ion conduction. In this study, imidazolium-containing monomer was synthesized and polymerized to make a cationic homopolymer with either tetrafluoroborate or bis(trifluoromethanesulfonyl)imide anionic counterions. These ions can associate into pairs and larger aggregates. The degree of ion pairing can be estimated from the temperature dependence of the dielectric constant and knowledge of the dipole moment of the ion pair, using the 1936 Onsager equation. Using the 1953 Macdonald model makes it possible to determine concentration and mobility of mobile counterions from analysis of electrode polarization in dielectric spectroscopy.

  19. Reactance and resistance: main properties to follow the cell differentiation process in Bacillus thuringiensis by dielectric spectroscopy in real time.

    PubMed

    Dinorín-Téllez-Girón, Jabel; Delgado-Macuil, Raúl Jacobo; Larralde Corona, Claudia Patricia; Martínez Montes, Francisco Javier; de la Torre Martínez, Mayra; López-Y-López, Víctor Eric

    2015-07-01

    During growth, Bacillus thuringiensis presents three phases: exponential phase (EP), transition state (TS), and sporulation phase (SP). In order to form a dormant spore and to synthesize delta-endotoxins during SP, bacteria must undergo a cellular differentiation process initiated during the TS. Dielectric spectroscopy is a technique that can be utilized for continuous and in situ monitoring of the cellular state. In order to study on-line cell behavior in B. thuringiensis cultures, we conducted a number of batch cultures under different conditions, by scanning 200 frequencies from 42 Hz to 5 MHz and applying fixed current and voltage of 20 mA and 5 V DC, respectively. The resulting signals included Impedance (Z), Angle phase (Deg), Voltage (V), Current (I), Conductance (G), Reactance (X), and Resistance (R). Individual raw data relating to observed dielectric property profiles were correlated with the different growth phases established using data from cellular growth, cry1Ac gene expression, and free spores obtained with conventional techniques and fermentation parameters. Based on these correlations, frequencies of 0.1, 0.5, and 1.225 MHz were selected for the purpose of measuring dielectric properties in independent batch cultures, at a fixed frequency. X and R manifest more propitious behavior in relation to EP, TS, SP, and spore release, due to particular changes in their signals. Interestingly, these profiles underwent pronounced changes during EP and TS that were not noticed when using conventional methods, but were indicative of the beginning of the B. thuringiensis cell differentiation process.

  20. Structural and dielectric studies of Co doped MgTiO3 thin films fabricated by RF magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Kumar, T. Santhosh; Gogoi, P.; Thota, S.; Pamu, D.

    2014-06-01

    We report the structural, dielectric and leakage current properties of Co doped MgTiO3 thin films deposited on platinized silicon (Pt/TiO2/SiO2/Si) substrates by RF magnetron sputtering. The role of oxygen mixing percentage (OMP) on the growth, morphology, electrical and dielectric properties of the thin films has been investigated. A preferred orientation of grains along (110) direction has been observed with increasing the OMP. Such evolution of the textured growth is explained on the basis of the orientation factor analysis followed the Lotgering model. (Mg1-xCox)TiO3 (x = 0.05) thin films exhibits a maximum relative dielectric permittivity of ɛr = 12.20 and low loss (tan δ ˜ 1.2 × 10-3) over a wide range of frequencies for 75% OMP. The role of electric field frequency (f) and OMP on the ac-conductivity of (Mg0.95Co0.05)TiO3 have been studied. A progressive increase in the activation energy (Ea) and relative permittivity ɛr values have been noticed up to 75% of OMP, beyond which the properties starts deteriorate. The I-V characteristics reveals that the leakage current density decreases from 9.93 × 10-9 to 1.14 × 10-9 A/cm2 for OMP 0% to 75%, respectively for an electric field strength of 250 kV/cm. Our experimental results reveal up to that OMP ≥ 50% the leakage current mechanism is driven by the ohmic conduction, below which it is dominated by the schottky emission.