scholarly journals Hopping Model for the Non-Debye Dielectric Response in Ionic Crystals

1988 ◽  
Vol 135 ◽  
Author(s):  
J. C. Wang ◽  
J. B. Bates
Keyword(s):  
Dielectric Loss ◽  
Phase Angle ◽  
Dielectric Response ◽  
Activation Energies ◽  
Interesting Property ◽  
Ionic Crystals ◽  
Loss Peak ◽  
Increasing Temperature ◽  
Double Wells ◽  
Hopping Model

AbstractA model based on ion hopping in potential double-wells is proposed to explain the non-Debye dielectric response in solids. Relying on some assumptions, an attempt is made to remove the “average” nature of previous diffusion theories. This results in a distribution of activation energies, G(E), which decays exponentially on both sides of some given value E0. It is shown that (a) the existence of a dielectric loss peak is a result of the decay of G(E) for E > E0, (b) the constant-phase-angle behavior above the loss peak is associated with the decay of G(E) for E < E0, and (c) G(E) can produce all the main features of the empirical Havriliak-Negami function. An interesting property of this G(E) is that it broadens with increasing temperature, consistent with many experimental observations.

Polarization Dynamics in La5/3Sr1/3NiO4

1999 ◽  
Vol 602 ◽  
Author(s):  
N. Hakim ◽  
Z. Zhai ◽  
C. Kusko ◽  
P.V. Parimi ◽  
S-W. Cheong ◽  
...  
Keyword(s):  
Dielectric Loss ◽  
Dielectric Response ◽  
Charge Ordering ◽  
Dielectric Susceptibility ◽  
Dynamic Susceptibility ◽  
Loss Peak ◽  
Relaxation Rates ◽  
Relaxation Mode ◽  
Microwave Frequencies ◽  
Charge Stripe

AbstractDynamic susceptibility measurements at microwave frequencies (2 – 10GHz) are a sensitive probe of charge dynamcis in La5/3Sr1/3NiO4. Below the charge ordering temperature of 240K, a dielectric loss peak due to a relaxation mode with a large dielectric susceptibility is observed, and is associated with charge stripe formation. The dielectric response for Hω∥b (Eω ⊥ b) is well represented by ε(T) = εo/(1 – iωτ(T)), with εo, ∼ 50, and τ(T) = 2 × 10−9(sec) exp(−T/37K). Parallel conductivity σ(T) contributions dominate at higher temperatures and for Hω∥c (Eω ⊥ c). The dielectric loss peak observed indicates that the charge relaxation rates lie in the GHz frequency ranges.

High Frequency Dielectric Response of the Ionic Liquid N-Methyl-N-ethylpyrrolidinium Dicyanamide

2007 ◽  
Vol 60 (1) ◽  
pp. 6 ◽  
Author(s):  
Simon Schrödle ◽  
Gary Annat ◽  
Douglas R. MacFarlane ◽  
Maria Forsyth ◽  
Richard Buchner ◽  
...  
Keyword(s):  
Ionic Liquid ◽  
Dielectric Loss ◽  
Dielectric Relaxation ◽  
High Frequency ◽  
Dielectric Response ◽  
Room Temperature ◽  
Room Temperature Ionic Liquid ◽  
Dielectric Relaxation Spectroscopy ◽  
Frequency Range ◽  
Fast Rotation

A study of the room-temperature ionic liquid N-methyl-N-ethylpyrrolidinium dicyanamide by dielectric relaxation spectroscopy over the frequency range 0.2 GHz ≤ ν ≤ 89 GHz has revealed that, in addition to the already known lower frequency processes, there is a broad featureless dielectric loss at higher frequencies. The latter is probably due to the translational (oscillatory) motions of the dipolar ions of the IL relative to each other, with additional contributions from their fast rotation.

Relaxation of Dielectric Loss Peak over Intermediate Temperature Range in Bi 5 TiNbWO 15 Intergrowth

2009 ◽  
Vol 26 (4) ◽  
pp. 047701 ◽  
Author(s):  
Wang Wei ◽  
Wang Xiao-Juan ◽  
Zhu Jun ◽  
Mao Xiang-Yu ◽  
Chen Xiao-Bing
Keyword(s):  
Dielectric Loss ◽  
Intermediate Temperature ◽  
Loss Peak ◽  
Temperature Range ◽  
Intermediate Temperature Range

scholarly journals Dielectric and electrical properties of Cr substituted Mg ferrites

2015 ◽  
Vol 39 (1) ◽  
pp. 1-12 ◽  
Author(s):  
AKM Zakaria ◽  
Faizun Nesa ◽  
MA Saeed Khan ◽  
SM Yunus ◽  
NI Khan ◽  
...  
Keyword(s):  
Dielectric Constant ◽  
Dielectric Loss ◽  
Loss Tangent ◽  
Dielectric Loss Tangent ◽  
Lattice Parameter ◽  
Activation Energies ◽  
X Ray Diffraction ◽  
Constant E ◽  
Cr Concentration ◽  
Academy Of Sciences

The spinel ferrites MgCrxFe2-xO4 (0.0 ? × ?1.0) were prepared through the solid state reaction using conventional ceramic method at 1300°C in air. The homogeneous phase of the ferrite samples was observed from the X-ray diffraction study. Lattice parameter of the samples was found to decrease with increasing Cr concentration in the system obeying Vegard’s law. The ac electrical resistivity, measured as a function of temperature, decreases with the increase of temperature indicating the semiconducting nature of all the samples. The activation energies were calculated and found to decrease with increasing Cr content. The lower activation energies are associated with higher electrical conductivity. With the increase of temperature, dielectric constant (e`) and dielectric loss tangent are observed to be increased; while with the increase of frequency, dielectric constant (e`) and dielectric loss tangent decrease for all the samples.Journal of Bangladesh Academy of Sciences, Vol. 39, No. 1, 1-12, 2015

scholarly journals Photophysical Investigatigation of Poly [N-isopropylacrylamide-co-Acrylic Acid] Copolymers

2013 ◽  
Vol 28 ◽  
pp. 67-73
Author(s):  
Megh Raj Pokhrel
Keyword(s):  
Acrylic Acid ◽  
Chemical Society ◽  
Interesting Property ◽  
Independent Study ◽  
Increasing Temperature

Poly[n-isopropylacrylamide], Poly[NIPAM], and Poly[n-isopropylacrylamide-co-acrylic acid], poly[NIPAM-co-AA] copolymers exhibit the interesting property of size contraction with increasing temperature. Photophysical probe, ruthenium-tris-phenanthroline has been used to monitor the above changes and the studies are correlated with independent study state fluorescence data. DOI: http://dx.doi.org/10.3126/jncs.v28i0.8109 Journal of Nepal Chemical Society Vol. 28, 2011 Page: 67-73 Uploaded Date: May 24, 2013

Frequency Dependence of Dielectric Parameters and A. C. Conductivity of Mg-Co-Zn Nanoferrites Synthesized via Combustion Method

2012 ◽  
Vol 584 ◽  
pp. 295-298 ◽  
Author(s):  
B.J. Madhu ◽  
M. Kavya ◽  
S. Razika Banu ◽  
B. Shruthi ◽  
C.P. Sowmya ◽  
...  
Keyword(s):  
Dielectric Loss ◽  
Combustion Method ◽  
Cobalt Nitrate ◽  
Zinc Nitrate ◽  
Magnesium Nitrate ◽  
X Ray Diffraction ◽  
Dielectric Parameters ◽  
X Ray ◽  
Wide Range ◽  
Hopping Model

Mg-Co-Zn nanoferrite particles were prepared by combustion method using stoichiometric compositions of magnesium nitrate, cobalt nitrate and zinc nitrate as oxidizers and urea as a fuel. The structure of the sample is studied with X-ray diffraction (XRD) using Cu-Kα radiation. The X-ray diffraction analysis revealed the nanocrystalline nature in the prepared ferrite samples. Dielectric and a. c. conductivity studies have been undertaken over a wide range of frequencies (100-5MHz) for Mg-Co-Zn nanoferrites at room temperature. The dielectric properties such as dielectric loss tangent (D), dielectric constant (ε′) and dielectric loss factor (ε″) were found to decrease with an increase in the frequency. Further, a. c. conductivity of the Mg-Co-Zn nanoferrite was found to increase with the increase in the frequency. The electrical conduction mechanism in the Mg-Co-Zn nanoferrite has been understood on the basis of the electron hopping model.

Radiation-Sensitized Thermal Cracking of n-Butane. II. Ionic Reactions

1975 ◽  
Vol 53 (1) ◽  
pp. 92-97 ◽  
Author(s):  
Shingo Matsuoka ◽  
Takaaki Tamura ◽  
Keichi Oshima ◽  
Yunosuke Oshima
Keyword(s):  
Room Temperature ◽  
Material Balance ◽  
Thermal Cracking ◽  
Activation Energies ◽  
Chain Reactions ◽  
Ionic Reactions ◽  
Cracking Mechanism ◽  
High Yields ◽  
Increasing Temperature ◽  
First Time

Ionic reactions in the radiolysis of n-butane were studied at temperatures ranging from 17 to 548 °C. Ionic chain reactions were found for the first time to take part in the radiation-sensitized thermal cracking mechanism of hydrocarbon system.The isobutane and isobutene yields increased with increasing temperature and at 548 °C their G-values reached 31.2 and 12.1, respectively, though they were not formed by the thermal cracking of n-butane. The formation was completely suppressed by the addition of 0.15 mol% ammonia. They were produced with high yields irrespective of the kind of wall of the irradiation cells. It was concluded from these results that isobutane and isobutene were formed by homogeneous ionic chain reactions with activation energies. Part of the propane product was also found to have been formed by ionic chain reactions. From the effect of adding n-pentane on the yields of the ionic products, C4H9+ ion was inferred as the carrier ion.In the vicinity of room temperature, formation by ionic reactions of polymers with more than 14 carbon atoms was inferred from the material balance of the products from H2 to C14.

scholarly journals Dielectric and Conductivity Properties of Some Wood Composites

2016 ◽  
Vol 8 ◽  
pp. 51-60
Author(s):  
K.Ch. Varada Rajulu ◽  
B.N. Mohanty
Keyword(s):  
Dielectric Constant ◽  
Dielectric Properties ◽  
Dielectric Loss ◽  
Low Temperature ◽  
Temperature Region ◽  
Loss Factor ◽  
Wood Composites ◽  
Frequency Range ◽  
Increasing Temperature ◽  
Coaxial Probe

This study presents the dielectric and conductivity properties as function of temperature and frequency of wood based composites. These properties were measured by an open-ended coaxial probe at frequency range between 100 kHz to 100MHz, temperature from 30OC to 200OC which is fully computer interfaced. It has been observed that dielectric constant (ε') and dielectric loss factor (ε") increase with increasing temperature and decrease with increasing frequency. At low temperature region, the conductivity depends significantly on the frequency. However, with the increase in temperature dielectric relaxation takes place and the dependency of the conductivity on frequency get reduced. The patterns of variation were established for the studied specimens and discrepancies were discussed. The study of dielectric properties will help in improving the drying, heating and gluing processes of wood and wood based products.

Non-Debye and CPA Behaviors of Ionic Materials

1997 ◽  
Vol 500 ◽  
Author(s):  
J. C Wang
Keyword(s):  
Dielectric Loss ◽  
Complex Impedance ◽  
Thermal Fluctuations ◽  
Wide Frequency Range ◽  
Loss Peak ◽  
Warburg Impedance ◽  
Interfacial Processes ◽  
Wide Range ◽  
Ionic Materials ◽  
Hopping Models

ABSTRACTNon-Debye and constant-phase-angle (CPA) behaviors associated with the bulk and interfacial processes involving ionic materials are discussed in terms of complex impedance, admittance, and dielectric spectra. The yielding of a CPA and/or a broad non-Debye dielectric loss peak in a spectrum from fractal, pore, and ion-hopping models are compared and reviewed. The observed wide frequency ranges of the CPA behavior suggest that the fractal and pore models, which require a wide range of special structures down to very fine scales, may not be realistic. The ion-hopping model treats the bulk and interfacial processes as a chemical reaction having a thermally-activated Arrhenius form. Because of thermal fluctuations, the activation energies for ion hopping (e.g., in a potential double-well) have a double-exponential distribution which yields a non-Debye dielectric loss peak and a CPA spectrum over a wide frequency range above the loss peak. The distribution also has a special temperature dependence which may explain the invariance of dielectric spectral shapes with temperature, an observation by Joscher. The construction of CPA elements (in a generalized Warburg impedance form) using three distinct types of resistor-capacitor networks are presented and used to aid the discussion.

Permeability of Elastic Polymers to Hydrogen

1941 ◽  
Vol 14 (2) ◽  
pp. 444-448
Author(s):  
Theron P. Sager
Keyword(s):  
Molecular Structure ◽  
Natural Rubber ◽  
Activation Energies ◽  
Energy Requirements ◽  
Synthetic Materials ◽  
Lower Permeability ◽  
Increasing Temperature

Abstract The permeabilities to hydrogen of natural rubber, Perbunan, Neoprene G, Vistanex, Thiokol DX, and Pliofilm diminished in the order mentioned. The increase in rate of permeation with increasing temperature was exponential in all cases. Values for the activation energies or permeability for hydrogen were found to be 6,800 calories per mole for natural rubber and 8,400 to 9,500 calories per mole for the synthetic materials. The greater magnitude of the energy requirements of the latter indicates that their lower permeability may be attributed to differences in their molecular structure.

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