Dielectric relaxation in dipolar solid rotator phases

Dielectric relaxation in orientationally disordered dipolar solids often exhibits exotic features, such as a strong Cole-Cole relaxation for simple molecular solids. However, there does not seem to exist a detailed molecular theory of such phenomena. In this article, a molecular hydrodynamic theory of dielectric relaxation in solid rotator phases, such as plastic crystals, is presented.     

Dielectric relaxation in aqueous solutions and suspensions

A method is proposed for measuring the relaxational dielectric losses of liquids at radio frequencies on a background of large conductivity losses. The absorption of the electromagnetic field energy is explained by structural relaxation, i.e., by the processes of formation and destruction of clusters.Translated from Isvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 81–85, February, 1975.     

Dielectric relaxation of 1-propanol/water solutions

Time domain measurements of solutions at seven compositions and 25°C have been Fourier transformed to obtain complex permittivities in the range 50 MHz to 8 GHz. These can be represented by a sum of two Debye relaxation functions. The principal, slower, one has a relaxation time changing smoothly from 320 ps for 1-propanol to 8 ps for water (by extrapolation from 0.75 mole fraction of water). The second is quite small for 1-propanol, but increases with added water, and remarkably has a relaxation time of ca. 20 ps which is independent of concentration to within the accuracy of the data and fitting. The significance of the behavior is discussed in terms of diffusion like models for molecular reorientations and local conformational changes in hydrogen bonding, with the conclusion that the latter provides a more likely explanation, particularly of the faster relaxation.     

Grain boundary relaxation in fine-grained magnesium solid solutions

Grain boundary relaxation at elevated temperatures in fine-grained pure magnesium and Mg–Al solid solutions was investigated by measuring damping capacity at low frequencies. A sharp increase in damping capacity caused by grain boundary relaxation was observed at above a certain temperature. The onset temperature depended on aluminum content; the onset temperature increased with aluminum content. It was demonstrated that aluminum was effective in suppressing grain boundary relaxation in magnesium alloys. However, additional measurement of the damping capacity of a dilute Mg–Y alloy revealed that yttrium was more effective in suppressing grain boundary relaxation.     

Dielectric relaxation in aqueous solutions and suspensions I. Solutions and suspensions

The dielectric constants and dielectric loss factors of aqueous solutions and suspensions are measured as a function of the specific electrical conductivity, temperature, and electric field frequency. The dispersion of the dielectric constant and the dielectric loss factor in solutions is explained by the formation of a electric double layer at the electrodes and the redistribution of the electric field between the region adjoining the electrodes and the remaining volume of the measuring cell. An equivalent-circuit calculations for suspensions displays acceptable agreement with experiment.     

Dielectric strengths of monocrystals of solid solutions in the system KCl-KBr

The pulse dielectric strength of these monocrystals is plotted against composition. The results are compared with the composition-dependence of the defect concentration. The results are discussed in terms of collision ionization by electrons and the defect concentrations.     

Dielectric relaxation properties of tysonite-type solid solutions La1−xBaxF3−x

Dielectric relaxation properties of solid solutions La_1?xBa_xF_3?x (x ? 0105) have been studied by thermally stimulated depolanzation current (TSDC)- and a c. dielectric loss (DL) techniques.For x < 30 × 10^?3 the dielectric spectra show a relaxation peak which is ascribed to a simple associate of a substitutional dopant ion and a fluoride ion vacancy (Ba_LaV_F)^x in nearest-neighbour position, the vacancy being confined to the B sublattice For x values of about 1.3 × 10^?2 a relaxation peak appears which is tentatively attributed to a similar type of defect associate with the vacancy now confined to the A sublattice of the tysonite anion array One broad relaxation peak dominates the TSDC and DL spectra over the whole concentration range This peak is due to the relaxation of macroscopic space charge, i e ionic conductivity The low-temperature ion conductivity has been determined for several solid solutions, and extrapolates to the high-temperature conductivity determined previously with impedance spectroscopy Below liquid-nitrogen temperature three relaxations are observed, and ascribed to electronic transitions in cenum impurities. A computer programme has been developed to analyse TSDC relaxation peaks, taking dipole-dipole interactions into account Relaxation parameters and dipole concentrations are presented.     

Dielectric relaxation time and dipole moment of isometric butanols in benzene solutions.

Measurements of static permittivity at 100 KHz, refractive index (for Sodium D line) and complex permittivity at 7.73 GHz have been made for Butane 1-01, Iso-butyl alcohol, Sec. butyl alcohol and Tert. butyl alcohol at 35°C. in dilute solutions of benzene. Dielectric relaxation time (τ) have been determined following the three methods, viz., method of Higasi et al, Gopal Krishna's method and Higasi's method. The value of τ and the distribution parameter (α) show evidence for existence of morethan one relaxation mechanism. This has been interpreted in terms of intramolecular orientation of O-H. group occuring simultaneously with the end over end molecular orientation. The > values for all these compounds have been found much larger than the corresponding compounds of similar structure. This behaviour has been explained as due to the formation of dimers by association and solute solvent interaction. This is also confirmed from the tan δ concentration curves. The values of the dipole moments determined from the Higasi's method, Gopal Krishna's method and Guggenheim's method are found to be in good agreement.     

Dielectric relaxation studies of some aliphatic alcohols and their mixtures in benzene solutions

Dielectric absorption of four aliphatic alcohols, viz., methyl alcohol, ethyl alcohol, n-propyl alcohol, tert-butyl alcohol and their binary mixtures, mixtures of these alcohols with dimethyl formamide and 2-fluoroaniline has been studied in the 3 cm microwave region at a temperature of 30°C in benzene. In alcohols and their mixtures the tan σ - concentration curve shows a marked increase in the concentration range 0.02 – 0.05 weight fraction. This behaviour has been explained as due to the formation of complex via self and hetero-association. The alcohols + DMF systems show complex formation at a very low concentration range. The study of systems alcohols + 2 - fluoroaniline indicate that the 2-fluoroaniline produces dissociating effects in these alcohols.     

Dielectric response function of GaPAs solid solutions in the vibrational absorption region

By taking spectra of IR transmission and reflection, attenuated total reflection, and Raman scattering, different models of the dielectric response function of GaPAs solid solutions are tested. It is demonstrated that the models accounting for the difference in the times of transverse and longitudinal vibrational relaxations, as well as the frequency distribution of TO phonons, make possible the prediction of the experimental spectra with a reasonable accuracy.     

Dielectric relaxation studies of alkanols solubilized by sodium dodecyl sulphate aqueous solutions

Considerable attention has been paid in recent years to the influence of alcohols on ionic micellar structures, alcohol co-surfactants most commonly employed in the preparation of microemulsions. Dielectric relaxation spectroscopy (DRS) is a versatile tool to monitor the dynamic process of such micellar systems. We report here the changes in the dielectric constant of the medium and the relaxation time of micellar solutions of sodium dodecyl sulphate (SDS) in water in the presence and absence of alkanols—hexan-1-ol, octan-l-ol, decan-l-ol and 1,2-ethanediol. The time domain dielectric data were obtained in the reflection mode in the frequency range of 10 MHz to 20 GHz using a HP54750A sampling oscilloscope and HP 54754A TDR plug-in-module. The sample is held at 303 K in a SMA cell with an effective pin length of 1.35 mm. We have determined the relaxation time (τ) using the Cole–Cole method. The relative viscosity ηr on the micellar solutions were also determined. The result shows that the dielectric constant increases linearly with SDS concentration in pure aqueous solutions up to 400 mM and decreases thereafter. The relaxation times are of the order of 15 ps to 25 ps and are far greater than that of Debye rotational relaxation of the monomer species. It is assigned to the dispersion step to water molecules surrounding to hydrophobic particles or the “bound water”. The addition of alcohols results in a linear increase in relaxation time in all the systems. As the concentration of SDS increases τ/ηr attains a near constant value showing that solubilization becomes more difficult at these concentrations. Our results show that the alcohol molecules are solubilized at the surface of the SDS micelle (i.e.) the micelle–water interface.     

Dielectric relaxation in Ih ice

Relaxation processes in Ih ice are studied in the temperature interval 77–27G°K and frequency band 5 Hz–500 kHz. A new maximum in thermally stimulated currents was found at 97°K, clarifying the nature of the relaxing defects. The parameters of the peaks of the thermally stimulated currents at 97, 127, 139, and 158°K are determined, and the concentrations of L defects and oriented H₂O dipoles are evaluated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 72–76, October, 1986.     

Dielectric relaxation in LuFeO3 ceramics

LuFeO₃ ceramics were prepared, and the dielectric characteristics were investigated together with the structure. A giant dielectric constant step (8000 at 10 kHz, 7200 at 100 kHz, and 4000 at 1 MHz) very similar to that in LuFe₂O₄ was observed. The dielectric constant dropped quickly when the temperature decreased through a critical temperature which increased significantly when the frequency increased. A very high relaxor-like dielectric peak with strong frequency dispersion was also observed in a higher temperature range. Two obvious corresponding dielectric relaxation peaks were observed on the curve of dielectric loss vs temperature, and all these dielectric relaxations followed the Arrhenius law. The Fe²⁺/Fe³⁺ mixed-valence structure and the oxygen vacancy primarily governed these relxor-like dielectric behaviors. However, the present ceramics are not relaxor ferroelectric.     

Dielectric relaxation in thin-film metal-PZT-ferroelectric-metal structures

The parameters of the Colle-Colle-type distribution function for the time constant of Pb(Zr_0.52Ti_0.48)O₃ thin-film layers and the pattern of the bulk resistivity distribution through the film thickness have been derived from measured frequency dependences of the complex capacitance of metal-PZT-ferroelectric-metal thin-film structures within the 100 Hz to 100 MHz range. Fiz. Tverd. Tela (St. Petersburg) 40, 1915–1918 (October 1998)     

Dielectric relaxation in PEO-based polymer electrolytes

Dielectric properties of cross-linked poly(ethylene oxide) (PEO) with different mesh sizes, doped with lithium salt lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), have been studied in frequency region between 0.1 and 10⁷ Hz and in broad temperature range. Results were compared with linear PEO of 1000 g/mol. Dielectric responses of the systems are dependent on frequency and thermally activated. Systems exhibit different responses in semi-crystalline and molten state. Increase of temperature promotes polarization; whereas, increase of frequency lessens it. In other words, polarization is thermally activated and local conductivity reduced. Generally, one observes enhanced dc conductivity in linear PEO as compared to cross-linked PEO at high temperature and the opposite at low temperature. Resonance responses are observed in low-molecular cross-linked PEO and in linear PEO at low temperature. These responses lead to splitting of polarization relaxation at frequencies beyond low-frequency range. Salt-comprising systems display only relaxation-type dielectric response. Imaginary parts of response spectra show distribution of relaxation times. It turns out that this distribution is independent of temperature in the low-frequency range, but depends on concentration of salt in the cross-linked polymer. In both systems, neat cross-linked and linear polymer of low-molecular mass, one observes coexistence of non-local and local motions of charged entities even at very low temperature.     

The relaxation peak in the internal friction of kbr and KBr-KCl solid solutions

It is considered that this peak is due to rapidly changing fluctuations in the distribution of bends in dislocation lines. The internal friction is found to vary for a time after plastic deformation or X-irradiation.I am indebted to Professor E. K. Zavadovskaya for direction in this work and to Professor A. A. Vorob'ev for discussion of the results.     

Dielectric relaxation in vanadium phosphate glasses

An asymmetric distribution of relaxation times has been inferred from an increase in the Cole-Cole distribution parameter α with increasing values of ωτ in 62% v₂O₅–38% P₂O₂ glass. The conventional Debye type relaxation loss peaks in the frequency range 10²–10⁵ Hz are observed in this sample above 85°K. The extrapolated values of dielectric constant and relaxation time below 100°K seem unexpectedly large while the high temperature extrapolated values of ?' are close to ?_∞ as expected. Probably the conventional dielectric loss peaks are observed only above a critical temperature at which the carriers gain sufficient energy to be excited to the conduction band edge. Below this temperature hopping of carriers within kT of the Fermi level may dominate and conventional Debye type dielectric loss peaks may lose their significance as envisaged in the models of frequency dependent ac conductivity.     

Dielectric relaxation in liquid trimethylsilane carbonitrile

Measurements of the complex electric permittivity and viscosity of liquid trimethylsilane carbonitrile (TMSiCN) in the range from 500 MHz to 36 GHz are reported at three temperatures (293 K, 303 K and 313 K). The dipole moment at 293 K was also determined, in neat liquid and in benzene solutions. The relaxation times and activation parameters were determined and interpreted in terms of the molecular reorientation of TMSiCN molecules. The reorientational correlation function was determined from dielectric data. Combining this function with IR data the vibrational correlation functions and vibrational correlation times for two fully-symmetrical, parallel type vibrations of liquid TMSiCN i.e. the ν_s (CN) and sym-ν_s[Si(CH₃)₃] stretching vibrations were determined and compared with Raman data.     

Dielectric relaxation effect in MIM systems

On applying voltage to a thin film Al-Al₂O₃-M system, one observes a decrease of the leakage current with time. After a long period (10³–10⁴ s) the current settles at a new value, lower by several orders of magnitude. After shortcircuiting the sample, there appears a discharge current of reversed polarity, with decay time again of the order of 10³ s. This effect has been reproducibly observed in the temperature range 80–500 K. The present paper is devoted to the experimental study of this relaxation phenomenon in dependence on the parameters of the system (thickness of the dielectric layer, temperature, and material of the upper electrode).The paper is based on RNDr Thesis of the first author.