Dielectric relaxation of PrFeO3 nanoparticles

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.     

Impedance and electric modulus approaches to investigate four origins of giant dielectric constant in CaCu3Ti4O12 ceramics

The frequency dependence of electric modulus of polycrystalline CaCu₃Ti₄O₁₂ (CCTO) ceramics has been investigated. The experimental data have also been analyzed in the complex plane of impedance and electric modulus, and a suitable equivalent circuit has been proposed to explain the dielectric response. Four dielectric responses are first distinguished in the impedance and modulus spectroscopies. The results are well interpreted in terms of a triple insulating barrier capacitor model. Using this model, these four dielectric relaxations are attributed to the domain, domain-boundary, grain-boundary, and surface layer effects with three Maxwell–Wagner relaxations. Moreover, the values of the resistance and capacitance of bulk CCTO phase, domain-boundary, grain-boundary and surface layer contributions have been calculated directly from the peak characteristics of spectroscopic plots.     

Nearly constant dielectric loss behavior in ionomers

The electrical conductivity of a series of ionomers has been characterized by measuring the electrical conductivity in a relatively broad range of frequencies and temperatures. At low frequencies, the conductivity of the ionomers exhibits a universal Jonscher power law (JPL), and at higher frequencies a nearly constant loss (NCL) behavior. The NCL for the ionomers is qualitatively similar to that observed for other inorganic ionic conductors. However, the magnitude of NCL for ionomers is lower than that observed for inorganic ionic conductors. The analysis of the conductivity master curves suggests that the conduction mechanism, which includes both the NCL and the JPL behaviors, is governed by ion hopping of the mobile ions.     

Some polymers of high dielectric constant

A class of highly conjugated macromolecules exhibiting extraordinarily high effective dielectric constants (DK = 50–900) is described. These polymers are of the polyacene radical quinone type, are highly purified, and exhibit electronic semiconduction. The dielectric constant varies only slightly with pressure (up to 20 Kbar), but strongly with frequency (300–300,000 cps) and moderately with temperature and field strength. The latter effect of field strength on the effective dielectric constant (and on the conductivity) required the development of special measurement techniques which are described. The unusual dielectric behavior can be accounted for assuming the presence of what amounts to a thermally generated plasma of electrons and holes, each locally mobile on extended regions of associated π-orbitals on the molecules. The postulated resulting “hyperelectronic” polarization of the locally mobile charges in external fields fits the observed high magnitude of the polarizability, as well as its field, frequency, and temperature dependence.     

The dielectric constant and oscillometric measurement

Summary New evidence is given that the characteristic conductance and susceptance curves of high frequency measurements, expressed as a function of the log of the electrolyte concentration, depend only on the physical parameters of the measuring cell, and the Debye effect plays only an insignificant role.

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Zusammenfassung Wie neuerlich gezeigt wurde, sind die Konduktanz- und Susceptibilitäts. kurven bei Hochfrequenzmessungen, ausgedrückt als Funktion des Logarithmus der Elektrolytkonzentration nur von den physikalischen Parametern der Meßzelle abhängig. Der Debye-Effekt spielt keine signifikante Rolle.

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Résumé On donne une nouvelle preuve que les courbes caractéristiques de la conductance et de la susceptance des mesures en haute fréquence, exprimées en fonction du log de la concentration de l'électrolyte, ne dépendent que des paramètres physiques de la cellule de mesure, et que l'effet Debye ne joue qu'un rôle minime.

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Presented at the Symposium on Analytical Chemistry, Graz, 29th September–1st October 1965.     

Phthalocyanine with a giant dielectric constant

Compound 1 has been prepared by the reaction of 4-nitrophthalonitrile and trans-2-methoxy-4-(2-nitrovinil)phenol by the common method of nucleophilic substitution of an activated nitro group in an aromatic ring. The metallophthalocyanines 2, 3 were prepared by the reaction of a dinitrile derivative with Co(OAc)(2) or Zn(OAc)(2) in DMSO. The lutetium bis-(phthalocyaninato) complex 4 was obtained by treating the dinitrile derivative with lutetium acetate and DBU in 1-hexanol. The new compounds were characterized by elemental analyses, FT-IR, (1)H-NMR, MALDI-TOF MS and UV/Vis spectral data. The spectroscopic data of the new compounds were in accordance with the structures. The temperature and frequency dependence of dielectric and conduction properties of the spin coated film of compounds (2-4) have been studied by fabricating metal-Pc-metal structures. The results show that compound 2 has giant dielectric constant. At a low range of frequency and room temperature, ε' is found to be equal to 2.33 × 10(6), 1.53 × 10(4) and 1.03 × 10(4) for 2, 3 and 4, respectively. The giant dielectric behavior of 2 is mainly attributed to Maxwell-Wagner polarization. The obtained results also indicated that the frequency dependence of the dielectric permittivity, ε'(ω), exhibits non-Debye type relaxation for all temperatures investigated. The ac conductivity results gave a temperature dependent frequency exponent s. The results were compared with the prediction of the Quantum Mechanical Tunneling and Correlated Barrier Hopping models.     

Implications of a high dielectric constant in proteins

Solvation of protein surface charges plays an important role for the protonation states of titratable surface groups and is routinely incorporated in low dielectric protein models using surface accessible areas. For many-body protein simulations, however, such dielectric boundary methods are rarely tractable and a greater level of simplification is desirable. In this work, we scrutinize how charges on a high dielectric surface are affected by the nonpolar interior core of the protein. A simple dielectric model, which models the interior as a low dielectric sphere, combined with Monte Carlo simulations, shows that for small, hydrophilic proteins the effect of the low dielectric interior is largely negligible and that the protein (and solution) can be approximated with a uniform high dielectric constant equal to that of the solvent. This is verified by estimates of titration curves and acidity constants for four different proteins (BPTI, calbindin D(9k), ribonuclease A, and turkey ovomucoid third domain) that all correlate well with experimental data. Furthermore, the high dielectric approximation follows as a natural consequence of the multipole expansion of the potential due to embedded protein charges in the presence of the low dielectric core region.     

Anisotropy of the dielectric constant of polyacetylene

The dielectric constant ? of polyacetylene films oriented by rolling was measured. The variation of ? and also that of the proton nuclear magnetic resonance line shape indicate that rolling partially isomerizes cis(CH)_x. For oriented trans(CH)_x we find ?_∥ = 5.7 and ?_? = 4.0 in the plane of the film. A calculation based on bond polarizabilities leads to qualitative agreement with experiment.     

Theory of the dielectric constant of ice

The first result of this paper is to show that the Onsager—Slater theory of the dielectric constant is consistent for some reasoable model of ice in the limit of no intrinsic defects. Accordingly, a model is presented, called the unit model, which has unit cells with no dipole moments for which the Onsager—Slater theory is exact. The second result of this paper is to show that the unit model is physically and chemically realistic. Bjerrum defects are introduced into the model and the relation between the dielectric constant and the Bjerrum defect charge found by Onsager and Dupuis for a less realistic model continues to hold and is satisfied by the experimental values. In a simple point charge approximation the charge distribution determined by the model requirements and the experimentally determined Bjerrum fault charge are found and seem reasonble. Higher order multipole interaction energies are consistent with eviations from pure 1/T dependence of the dielectric constant of real ice with intrinsic defects, can be derived in the context of the unit model. This formula interpolates between the Onsager—Slater formula in the limit of no intrinsic defects and the Kirkwood—Frohlich formula in the limit of many intrinsic defects. For the concentration of defects in real ice the interpolation formula is practically the same as the Onsager—Slater formula and differs from the Kirkwood—Frohlich formula by a factor of nearly $\text{3}\text{2}$.     

The dielectric constant of lamellar semicrystalline polymers

The problem of representing the dielectric constant of semicrystalline polymers in terms of the dielectric constants and volume fractions of the constitutent crystalline and amorphous phases is considered. For locally lamellar morphology, bounds based on uniform electric and displacement fields are derived. The equations also include the degree of crystal orientation as a parameter. For unoriented polymers the bounds are considerably tighter than the Hashin–Shtrikman bounds, the latter being the best possible without knowledge of phase geometries. The bounds presented here are sufficiently tight to represent the dielectric constant with practical accuracy for a number of examples of semicrystalline polymers. A treatment is also given of the dielectric constant where the lamellar morphology is further specified as being organized into spherulite-like structures. These bounds are somewhat tighter than the lamellar bounds.     

Low dielectric constant polyimide nanomats by electrospinning

The proper combination of material (i.e. fluorinated polyimides) and processing technique (electrospinning) could lead to the formation of polyimides with low dielectric constant, high thermo‐oxidative stability and glass transition temperature, and high hydrophobicity. The polyimides in this work were based on 4, 4‐bis [3′‐trifluoromethyl‐4′ (4′‐amino benzoxy) benzyl] biphenyl (Q) and various fluorinated and non‐fluorinated dianhydrides namely benzene‐1,2,4,5‐tetracarboxylic dianhydride, 3,3′,4,4′‐biphenyltetracarboxylic dianhydride, benzophenone‐3,3′,4,4′‐tetracarboxylic dianhydride, and 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA). Processing of the polyimides was carried out in poly(amic acid) stage by two different methods—electrospinning and solution casting for comparison purposes. The processing of polyimides by electrospinning led to enhancement in mechanical properties (dianhydride‐structure dependent) and hydrophobicity without sacrificing thermo‐oxidative stability and glass transition temperatures significantly. Also, low dielectric constants (as low as 1.43) could be attained by suitable combination of dianhydride (6FDA) with 4, 4‐bis [3′‐trifluoromethyl‐4′ (4′‐amino benzoxy) benzyl] biphenyl diamine. Copyright © 2011 John Wiley & Sons, Ltd.     

On the dielectric constant of nonpolar fluids

Referring to a recent paper in this journal of Stell and Rushbrooke the deviation from the Clausius-Mossotti relation for the static dielectric constant of a nonpolar fluid is discussed. In particular a number of coefficients in the dielectric virial expansion have been evaluated for a hard-sphere system.     

On the dielectric constant of nonpolar fluids

We discuss the recent work of Wertheim on the dielectric constant of nonpolar fluids, and also present some new calculations on the Kirkwood-Yvon theory. These serve to emphasise the prime importance of the state dependence of the effective polarisability in interpreting deviations from the Clausius-Mossotti theory for real dense fluids.     

A low dielectric constant polyimide/polyoxometalate composite

A silane‐modified mono‐lacunary Keggin‐type polyoxometalate (POM), (Bu₄N)₄[SiW₁₁O₃₉{(CH₂?CH? Si)₂O}] (SiW₁₁? CH?CH₂), was obtained by reaction of vinyltrimethoxysilane with K₈(SiW₁₁O₃₉) in acidic MeCN/H₂O mixed solutions. Then, the modified polyoxometalate was physically blended with the pyromellitic dianhydride (PMDA)‐4,4′‐oxydianiline (ODA) poly(amic acid) and the blends were thermally imidized to form polyimide/ polyoxometalate composites. The X‐ray diffraction (XRD) analysis indicates that the polyoxometalate clusters cannot form crystalline structures in the composite, suggesting that the blending leads to improved compatibility between the polymer matrix and the modified polyoxometalate. The EDS (W‐mapping) studies on the composite films reveal that the polyoxometalate clusters are well dispersed in the polyimide matrix. The physical incorporation of modified POM into polyimide remarkably reduced the dielectric constant of the latter from 3.29 to 2.05 when 20 wt% of SiW₁₁? CH?CH₂ was used. Besides, the addition of the modified POM into polyimide increased the storage modulus of polyimide without severely affecting its thermal properties. Copyright © 2009 John Wiley & Sons, Ltd.     

Ferroelectric metal-organic framework with a high dielectric constant

Hydrothermal reaction of (l)-N-(4'-cyanobenzy)-(S)-proline with CdCl2 as a Lewis acid catalyst and NaN3 gives colorless block compound 1, in which 1 displays a complicated 3D framework. Ferroelectric and dielectric property measurements reveal that 1 exhibits physical properties comparable to that of a typical ferroelectric compound with a dipole relaxation process and a dielectric constant of ca. 38.6 that makes it, by definition, a high dielectric material.     

Controllable porous fluorinated polyimide thin films for ultralow dielectric constant interlayer dielectric applications

In this paper, silica microspheres were used as template to prepare porous fluorinated polyimide (FPI) thin films from polyamic acid (PAA, precursor of FPI) and silica colloid solution. The strong hydrogen-bonding interaction between silica microspheres and PAA chains have improved the dispersion of silica microspheres in N,N-Dimethylformamide (DMF) solution, resulting in the high weight content of silica template in PAA/silica colloid solution, and thus giving rise to the formation of porous FPI films with maximum porosity of 35%. The interior microstructures of the resultant porous FPI thin films were investigated. It is found that the porous FPI thin films have interconnected “ink-bottle-type” porous structure, and the pore size, porosity could be precisely controlled by the diameter and weight content of silica microspheres, respectively. Although both the tensile strength and young modules declined with the increasing porosity, the high level void of the porous FPI films endowed the FPI ultralow dielectric constant of 1.84 when the porosity increased to 35%. Furthermore, the mechanical and dielectric properties of the porous FPI films were closely related to the microstructures and porosity, indicating the desired properties could be controlled to meet the application in the microelectronics.