scholarly journals Low-Frequency Dielectric Relaxation in Structures Based on Macroporous Silicon with Meso-Macroporous Skin-Layer

Materials ◽  
2021 ◽  
Vol 14 (10) ◽  
pp. 2471
Author(s):  
Rene Castro ◽  
Yulia Spivak ◽  
Sergey Shevchenko ◽  
Vyacheslav Moshnikov
Keyword(s):  
Dielectric Relaxation ◽  
Pore Diameter ◽  
Relaxation Times ◽  
Low Frequency ◽  
Skin Layer ◽  
Macroporous Silicon ◽  
Linear Sections ◽  
Relaxation Curves ◽  
Cole Model ◽  
Probable Relaxation Time

The spectra of dielectric relaxation of macroporous silicon with a mesoporous skin layer in the frequency range 1–106 Hz during cooling (up to 293–173 K) and heating (293–333 K) are presented. Macroporous silicon (pore diameter ≈ 2.2–2.7 μm) with a meso-macroporous skin layer was obtained by the method of electrochemical anodic dissolution of monocrystalline silicon in a Unno-Imai cell. A mesoporous skin layer with a thickness of about 100–200 nm in the form of cone-shaped nanostructures with pore diameters near 13–25 nm and sizes of skeletal part about 35–40 nm by ion-electron microscopy was observed. The temperature dependence of the relaxation of the most probable relaxation time is characterized by two linear sections with different slope values; the change in the slope character is observed at T ≈ 250 K. The features of the distribution of relaxation times in meso-macroporous silicon at temperatures of 223, 273, and 293 K are revealed. The Havriliak-Negami approach was used for approximation of the relaxation curves ε″ = f(ν). The existence of a symmetric distribution of relaxers for all temperatures was found (Cole-Cole model). A discussion of results is provided, taking into account the structure of the studied object.

Dielectric Relaxation Studies of Silver Nanoparticles dispersed Liquid Crystal

2015 ◽  
Vol 8 (3) ◽  
pp. 2176-2188 ◽  
Author(s):  
Keisham Nanao Singh
Keyword(s):  
Activation Energy ◽  
Silver Nanoparticles ◽  
Liquid Crystal ◽  
Dielectric Relaxation ◽  
Relaxation Process ◽  
Relaxation Times ◽  
Low Frequency ◽  
Bulk Liquid ◽  
Molecular Rearrangement ◽  
Relaxation Studies

This article reports on the Dielectric Relaxation Studies of two Liquid Crystalline compounds - 7O.4 and 7O.6 - doped with dodecanethiol capped Silver Nanoparticles. The liquid crystal molecules are aligned homeotropically using CTAB. The low frequency relaxation process occurring above 1 MHz is fitted to Cole-Cole formula using the software Dielectric Spectra fit. The effect of the Silver Nanoparticles on the molecular dipole dynamics are discussed in terms of the fitted relaxation times, Cole-Cole distribution parameter and activation energy. The study indicate a local molecular rearrangement of the liquid crystal molecules without affecting the order of the bulk liquid crystal molecules but these local molecules surrounding the Silver Nanoparticles do not contribute to the relaxation process in the studied frequency range. The observed effect on activation energy suggests a change in interaction between the nanoparticles/liquid crystal molecules.

Niederfrequente dielektrische Relaxation von K+-Ionen in der zweidimensionalen Tunnel-Struktur von K3Sb5O14 / Low-Frequency Dielectric Relaxation of K+-lons in the Two-Dimensional Tunnel Structure of Ka5Sb5O14

1975 ◽  
Vol 30 (3) ◽  
pp. 385-387
Author(s):  
Günter Schön ◽  
Ulrich Staudt
Keyword(s):  
Dielectric Relaxation ◽  
Dielectric Spectroscopy ◽  
Single Phase ◽  
Relaxation Times ◽  
Low Frequency ◽  
Two Dimensional ◽  
Tunnel Structure ◽  
Compound K ◽  
Kcal Mole ◽  
Dielectric Absorption

The compound K3Sb5O14 was synthetisized single-phase and examined by means of dielectric spectroscopy from 30 Hz to 10 MHz. Three separate regions of dielectric absorption with broad distributions of relaxation times have been found. Temperature-dependend measurements up to 200 °C yielded enthalpies of activation between 15 and 20 kcal/mole.

Slow Dielectric Relaxation of Supercooled Liqutos Investigated by Nonresonant Spectral Hole Burning

1996 ◽  
Vol 455 ◽  
Author(s):  
R. V. Chamberlin ◽  
B. Schiener ◽  
R. Böhmer
Keyword(s):  
Dielectric Relaxation ◽  
Degrees Of Freedom ◽  
Relaxation Times ◽  
Low Frequency ◽  
Hole Burning ◽  
Thermal Bath ◽  
Spectral Hole Burning ◽  
General Shape ◽  
Spectral Hole ◽  
Bulk Response

ABSTRACTWhen supercooled propylene carbonate and glycerol are subjected to a large-amplitude, low-frequency electric field, a spectral hole develops in their dielectric relaxation that is significantly narrower than their bulk response. This observation of nonresonant spectral hole burning establishes that the non-Debye response is due to a distribution of relaxation times. Refilling of the spectral hole occurs abruptly, indicative of a single recovery rate that corresponds to the peak in the distribution. The general shape of the spectral hole is preserved during recovery, indicating negligible interaction between the degrees of freedom that responded to the field. All relevant features in the behavior can be characterized by a model for independently relaxing domains that are selectively heated by the large oscillation, and which recover via connection to a common thermal bath, with no direct coupling between the domains.

Developments in a model to describe low‐frequency electrical polarization of rocks

Geophysics ◽  
2000 ◽  
Vol 65 (2) ◽  
pp. 437-451 ◽  
Author(s):  
Carlos A. Dias
Keyword(s):  
Single Phase ◽  
Relaxation Times ◽  
Low Frequency ◽  
Frequency Range ◽  
Electrical Polarization ◽  
Classical Models ◽  
Conductivity Function ◽  
Basic Characteristics ◽  
Cole Model ◽  
Model Circuit

The author reworks his total current conductivity function introduced in a previous paper, related to electrical polarization of rocks in the frequency range of 1 MHz to 10−3 Hz. The original five parameters in this function are replaced by new ones, which from the beginning have clear petrophysical and electrochemical meanings and well‐defined ranges of variation. Some classical models are derived as particular cases of it. The main existing models proposed to describe induced polarization (IP) are analyzed, and most of them are grouped together under a common circuit analog representation and a respective generating function. A circuit analog is assigned to each model. The multi‐Cole‐Cole model circuit analog reveals intrinsic constraints involving the values of its circuit elements. Because of these constraint relations and the relaxation times ratio (τ1/τ2)—usually many orders of magnitude from unity—the model has no physical validation to represent single‐phase material systems (in the sense of the polarization). The performance and analysis of the various models to describe a few well‐selected experimental data show that only two of the models, the multi‐Cole‐Cole and Dias models, can provide a function structure capable of fitting these data. This fact, the associated petrophysical interpretation consistency, and the basic characteristics of these two models, such as the way they were derived (empirically, the former; phenomenologically, the latter) and the number of coefficients in the function (directly related to the degree of ambiguity of their determination), make the author’s model attractive and promising.

scholarly journals AC – Conductivity Study of CdSe Nanorods

2018 ◽  
Vol 2 (1) ◽  
Keyword(s):  
Dielectric Relaxation ◽  
Relaxation Times ◽  
Complex Impedance ◽  
Relaxation Mechanism ◽  
Electrical Equivalent Circuit ◽  
Chemical Route ◽  
Polaron Hopping ◽  
Transmission Electron ◽  
Complex Impedance Plane Plot ◽  
Cole Model

The nanorods of cadmium selenide (CdSe) have been synthesized by soft chemical route using mercapto ethanol as a capping agent. The sample forms a rod like shape, confirmed by transmission electron microscope (TEM) measurement. Impedance spectroscopy is applied to investigate the dielectric relaxation of the sample at a various temperature region with varying frequency range. Grain and grain boundary effects both are present in the complex impedance plane plot and is analyzed by an electrical equivalent circuit consisting of a resistance and a constantphase element. Dielectric relaxation mechanism shows peak positions in the imaginary parts of the spectra and that is analyzed by Cole–Cole model. The temperature-dependent relaxation times obeys Arrhenius law having activation energy of 0.391 eV, which indicates that polaron hopping is responsible for conduction or dielectric relaxation in this material. The presence of two plateaus in the frequency-dependent conductivity spectra follows double-power law

Aerodynamic noise from an asymmetric airfoil with perforated extension plates at the trailing edge

2020 ◽  
pp. 1475472X2097838
Author(s):  
CK Sumesh ◽  
TJS Jothi
Keyword(s):  
High Frequency ◽  
Sound Pressure ◽  
Pore Diameter ◽  
Low Frequency ◽  
Aerodynamic Noise ◽  
Frequency Noise ◽  
Low Frequency Noise ◽  
Trailing Edge ◽  
High Frequency Noise ◽  
Displacement Thickness

This paper investigates the noise emissions from NACA 6412 asymmetric airfoil with different perforated extension plates at the trailing edge. The length of the extension plate is 10 mm, and the pore diameters ( D) considered for the study are in the range of 0.689 to 1.665 mm. The experiments are carried out in the flow velocity ( U∞) range of 20 to 45 m/s, and geometric angles of attack ( αg) values of −10° to +10°. Perforated extensions have an overwhelming response in reducing the low frequency noise (<1.5 kHz), and a reduction of up to 6 dB is observed with an increase in the pore diameter. Contrastingly, the higher frequency noise (>4 kHz) is observed to increase with an increase in the pore diameter. The dominant reduction in the low frequency noise for perforated model airfoils is within the Strouhal number (based on the displacement thickness) of 0.11. The overall sound pressure levels of perforated model airfoils are observed to reduce by a maximum of 2 dB compared to the base airfoil. Finally, by varying the geometric angle of attack from −10° to +10°, the lower frequency noise is seen to increase, while the high frequency noise is observed to decrease.

scholarly journals Determination of the Distribution of Relaxation Times by Means of Pulse Evaluation for Offline and Online Diagnosis of Lithium-Ion Batteries

Batteries ◽  
2021 ◽  
Vol 7 (2) ◽  
pp. 36
Author(s):  
Erik Goldammer ◽  
Julia Kowal
Keyword(s):  
Lithium Ion Batteries ◽  
Electrochemical Impedance ◽  
Sampling Rate ◽  
Relaxation Times ◽  
Low Frequency ◽  
Lithium Ion ◽  
Battery Management ◽  
Time Constants ◽  
Time Domain Data ◽  
Aging Study

The distribution of relaxation times (DRT) analysis of impedance spectra is a proven method to determine the number of occurring polarization processes in lithium-ion batteries (LIBs), their polarization contributions and characteristic time constants. Direct measurement of a spectrum by means of electrochemical impedance spectroscopy (EIS), however, suffers from a high expenditure of time for low-frequency impedances and a lack of general availability in most online applications. In this study, a method is presented to derive the DRT by evaluating the relaxation voltage after a current pulse. The method was experimentally validated using both EIS and the proposed pulse evaluation to determine the DRT of automotive pouch-cells and an aging study was carried out. The DRT derived from time domain data provided improved resolution of processes with large time constants and therefore enabled changes in low-frequency impedance and the correlated degradation mechanisms to be identified. One of the polarization contributions identified could be determined as an indicator for the potential risk of plating. The novel, general approach for batteries was tested with a sampling rate of 10 Hz and only requires relaxation periods. Therefore, the method is applicable in battery management systems and contributes to improving the reliability and safety of LIBs.

Relaxation processes of some simple aliphatic molecules in dilute solutions

1977 ◽  
Vol 55 (4) ◽  
pp. 297-301 ◽  
Author(s):  
M. P. Madan
Keyword(s):  
Carbon Tetrachloride ◽  
Dielectric Relaxation ◽  
Thermodynamic Parameters ◽  
Relaxation Times ◽  
Relaxation Processes ◽  
Dilute Solutions ◽  
Microwave Region ◽  
Nonpolar Solvents ◽  
Dielectric Data ◽  
Intramolecular Rotation

The dielectric relaxation processes of acetone, cyclohexanone, 4-methyl-2-pentanone, and 4-heptanone in dilute nonpolar solvents, n-heptane, cyclohexane, benzene, and carbon tetrachloride have been studied in the microwave region over a temperature range 10 to 60 °C. The relaxation times and the thermodynamic parameters for the activated states have been determined using the measured dielectric data. The results have been discussed in terms of dipole reorientation by molecular and intramolecular rotation and compared, wherever possible, with other similar studies on aliphatic molecules.

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