Electric Permittivity Measurements Research Articles

Comparison of dielectric properties of two isomorphous polymerizable single crystalline diacetylenes: pTS and pFBS

The results of measurements of relative electric permittivities in pure monomers and in fully polymerized crystals of pTS and pFBS diacetylenes are presented. The measurements were performed in the direction of growing polymer chains and in one direction perpendicular to it in the temperature range 80 to 333 K. In contrast to pTS, neither the monomer pFBS nor poly-pFBS crystals revealed any evidence of a phase transition. The difference is probably due to different dipole-dipole interaction energies of the side groups.

Electrical properties of PbTiO3single crystals doped with lanthanum

Abstract Results of electric conductivity, permittivity and spontaneous polarization measurements for PbTiO3 single crystals with La doping up to 0.44 at % are presented. Marked influence of lanthanum doping on dielectric parameters such as permittivity and Curie temperature has been found. Considerable changes of d.c. conductivity has been observed with La content increasing

Structural Phase Transitions in [(C2H5)4N]3Sb2Br9 and [(C2H5)4N]3Bi2Br9

Dielectric, DSC and preliminary X-ray diffraction studies on [(C2H5)4N]3Sb2Br9 (TEABA) and [(C2H5)4N]3Bi2Br9 (TEABB) are reported. The compounds are isomorphous, space group P6322. The static electric permittivity measurements on single crystals in the temperature range 220 - 290 K revealed that both compounds show two distinct dielectric anomalies; TEABA at Tc1 = 258 K and Tc2 = 252 K, while TEABB at Tc1= 265 K and Tc2 = 248 K. The DSC studies show only one anomaly of first order at Tc1 =258 K for TEABA, and Tc1 =266 K for TEABB. These transitions are presumably related to a freezing of the reorientational motion of the tetraethylammonium cations

Effect of hydrostatic pressure on the phase transitions in (CH 3NH 3) 3Bi 2Br 9

Effect of hydrostatic pressure on the phase transitions in (CH 3NH 3) 3 Bi 2Br 9 was studied by electric permittivity measurements at pressures up to 300 MPa. The (I→II) transition temperature decreases linearly with increasing pressure with a rate of −1.2 × 10 −2 degMPa −1. The region of phase (III) becomes narrower with increasing pressure and disappears at a triple point of 50 MPa and 128K. The new-induced (II→IV) phase transition temperature decreases with increasing pressure with a rate of −1.6 × 10 −2degMPa −1.

Gap exponents determined from temperature and pressure measurements of nonlinear electric permittivity for TGSe in the ferroelectric phase

Reported here are the results of measurements of the amplitude of the second harmonic obtained due to the nonlinear properties of electric permittivity in the ferroelectric phase of TGSe in the vicinity of the Curie temperature. From these measured values it was possible to determine the temperature and pressure dependences of coefficient α 1 ≈ (δ 3 G/δ E 3) E=0 where G is the Gibbs potential and E is the strength of the electric field. Basing on these measurements, values were found for the gap exponents Δ' 3 ≌ Δ' ∗ 3 ≌ 1.5.

Dielectric relaxation in the smectic-A and smectic-C phases of a ferroelectric liquid crystal.

The results of a study of the dielectric properties of a room-temperature ferroelectric liquid crystal in the frequency range from 5 Hz to 13 MHz are presented here. Measurements of complex electric permittivity versus temperature have been taken on aligned samples of different thicknesses with the electric measuring field being parallel or perpendicular to the layer planes. In homogeneously aligned samples two dielectric relaxation regions have been observed in the smectic-${C}^{\mathrm{*}}$ phase, one known as the Goldstone mode and the other showing up in the vicinity of the smectic-${C}^{\mathrm{*}}$\char21{}smectic-${A}^{\mathrm{*}}$ transition called the soft mode. In homeotropically aligned samples the low-frequency molecular relaxation was observed in both smectic phases. Temperature dependences of both dielectric increments and relaxation times suggest that the system studied exhibits a ferroelectric phase transition of the first-order type.

Dipole moments and dielectric properties of fluorine substituted nematic liquid crystals

Abstract The effect of lateral fluorine substituents on the dielectric properties of a range of nematic liquid crystals is reported. Measurements of dipole moments and electric permittivities have been made and used to calculate Kirkwood correlation factors over a range of temperature. The results show that the extent and nature of dipole correlations are important considerations in determining the magnitude of the dielectric anisotropy in these materials. Correlation factors up to 1.4 are found, providing good evidence for the presence of parallel dipole associations.

Electric permittivity measurements as a method for detection of helix unwinding process

Abstract We present the method for determination of the azimuthal angle φ distribution in helicoidal smectics from electric permittivity measurements performed as a function of the DC electric field. The results are confronted with the theoretical predictions by Dmitrienko and Bielyakov [1].

Electric properties of PbTiO3single crystals doped with lanthanum

Abstract Results of electric conductivity, permittivity and spontaneous polarization measurements for Pb1−xLaxTiO3 single crystals are presented. The x values range from 0 to 0. 0044.

Electrical conductivity and permittivity measurements near the percolation transition in a microemulsion: I. Experiment.

We have made conductivity and permittivity measurements from 5--13 MHz on the microemulsion system toluene--brine--sodium-dodecyl-sulfate--butanol in the region where, by varying the brine salinity, the volume fraction of brine in the microemulsion varies from 0.1 to 0.9 as the system passes from one two-phase region to another via a three-phase region. In the two-phase region at high salinities, where the microemulsion consists of brine droplets dispersed in oil, a percolation transition, identified by a steep rise in the electrical conductivity, and a peak in the permittivity, is observed at brine volume fraction ${f}_{p}$=0.130\ifmmode\pm\else\textpm\fi{}0.001. This transition, although very close to the boundary between the two-phase and three-phase regions, clearly lies inside the two-phase region. The data also suggest that there is a discontinuity in the conductivity at the phase boundary, and we argue that the microemulsion undergoes a change in structure at the phase boundary.

Electrical conductivity and permittivity measurements near the percolation transition in a microemulsion. II. Interpretation.

In this paper I compare the conductivity and permittivity measurements reported in the previous paper near the percolation transition in a microemulsion to (i) the predictions of the Bruggeman theory and suitable extensions of this theory, and (ii) models for percolation in dynamic systems. Consideration of the frequency dependence and also an earlier comparison between conductivity and molecular diffusion data show that the stirred percolation model of M. Lagu\"es [J. Phys. Lett. 40, L331 (1979)] cannot explain the raised conductivity exponent observed below the percolation transition in the microemulsion studied here. The Bruggeman theory predicts most of the features of the conductivity and permittivity near the percolation transition, in particular, the frequency dependence, observed in this microemulsion. G. S. Grest, I. Webman, S. A. Safran, and A. L. R. Bug [Phys. Rev. A 33, 2842 (1986)] have attributed the frequency dependence of the conductivity observed in microemulsions with a spherical-droplet structure to dynamic effects. Dynamic effects have little effect on the frequency dependence of the conductivity in the microemulsion studied here. Although this microemulsion is structurally different from that studied by Grest et al., the analysis presented here provides a critical test of their dynamic percolation model.

Spin ordering in the ion-radical salt MPht(TCNQ) 2

Static magnetic susceptibility and e.s.r. studies of a highly-conducting TCNQ salt with an N-methyl-phthalazinium cation in the temperature range 6 – 300 K are reported. The magnetic studies are supplemented by an analysis of i.r. absorption as well as a.c. conductivity and electric permittivity measurements. Two phase transitions are observed in MPht(TCNQ) 2. The susceptibility of the highly conducting, high-temperature phase of the salt is determined by both acceptor and donor chains. The susceptibility of the TCNQ· − chains comes from the free electrons of the finite linear magnetic chains, whereas that of the MPht + chains is determined by the properties of finite linear magnetic chains with anisotropic coupling. The magnetic properties below the phase transition at 72 K are mainly determined by the triplet excitons of the TCNQ chains. The distortion of the crystal lattice at 20 K leads to a change in the dipolar interactions; a contribution of Curie-like spins is also seen. Some conclusions are drawn about the spin ordering and the nature of the phase changes in the salt MPht(TCNQ) 2.

Dielectric studies on the reaction of the intracellular matter of fish red blood cells to detergent toxicity

Results from dielectric studies on the freshwater fish Cyprinus carpio exposed to a sublethal concentration of sodium alkyl benzene sulphonate were compared with those from untreated control fish; recovery from the test solution was also checked. The influence of the anionic detergent on the intracellular matter of fish red blood cells was investigated by measurement of electrical conductivity and permittivity using a method that did not harm the cell membrane. The results were compared with a calculation using Wagner's and Hanai's equation. It has been found that electrical conductivity and permittivity increase with time of exposure to detergent and the results indicate an almost linear relationship. The dielectric data, however, reveal anomalous behaviour for both conductivity and permittivity on the 16th and 30th, and 12th and 30th days, respectively. This may be associated with a structural change in the red blood cells.

Ferroelectric phase transitions in NH 4HSeO 4 crystals

Results are presented of measurements of spontaneous polarization, electric permittivity and electrical conductance of NH 4HSeO 4 crystals in three principal crystallographic directions from liquid nitrogen temperature to 320 K. NH 4HSeO 4 crystals exhibit ferroelectric properties in the a-axis direction between 106–250 K, whereas in the b-direction they are pyroelectrie over the entire temperature range. The calculated activation energy (1.42 eV) is indicative of semiconducting behavior.

The Elastic Constants and Electric Permittivities of Mixtures Containing Terminally Cyano Substituted Nematogens

Abstract Measurements of electric permittivities and elastic constants for various terminally cyano substituted nematics and their mixtures with terminally dialkyl substituted nematogens are reported. The mixtures showed a considerably reduced ratio of the bend to splay elastic constants (k 33/k 11) compared with the pure p-cyano substituted nematics. Also the large diversity in k 33/k 11 observed for the p-cyano substituted nematics was found to converge upon dilution. It is suggested that these results can be attributed to the reduced anti-parallel local ordering observed in the mixtures.

Rubber-modified epoxy resins: 2. Dielectric and ultrasonic relaxation studies

Dielectric and ultrasonic relaxation measurements are reported on a series of rubber-modified epoxy resins over a temperature range from 190 to 423K. The resins were prepared by the reaction of the diglycidyl ether of bisphenol A with a chain-extender formed from carboxyl-terminated acrylonitrile-butadiene copolymer and cured with either triethylene tetramine or diethylene glycol bis-propyl amine. At low temperature, a dielectric relaxation was detected which was also active ultrasonically and can be associated with molecular motion of the acrylonitrile-butadiene chain extender. Changes in the concentration of the rubbery phase and type of curing agent used have marked effects on both the activation energy for molecular relaxation and in the breadth of the relaxation curves. Extensive studies of the dielectric properties at higher temperatures failed to reveal a resolvable relaxation associated with either of the higher temperature transitions observed using equilibrium measurements. Electrical conductivity, permittivity and acoustic velocity measurements performed as a function of temperature, however, indicate the existence of a change in slope at approximately the value of the glass transition of the epoxy phase. A further change in slope at approximately the temperature of the highest temperature transition was detected. The observed relaxation properties are compatible with the resins being phase-separated at low rubber concentrations and changing to a semicontinuous interpenetrating network structure at higher rubber concentrations.

Dielectric Study of Ferroelectric Properties in Chiral Smectic C

Abstract Measurements of electric permittivity, and polarization are reported for chiral liquid crystal DOBAMBC. Dielectric hysteresis was found. Temperature-variations of spontaneous polarization and relaxation time are studied. The dielectric properties of chiral smectic C and those of crystalline ferroelectrics are compared.

Differential thermal analysis of phase transitions in (Bi 1− xLa x)FeO 3 solid solution

(Bi 1− x La x )FeO 3 solid solution, a material exhibiting simultaneously electric and magnetic long range dipole order, is studied by the method of differential thermal analysis. The results confirm the data on ferroelectric phase transitions obtained from electric permittivity and dilatometric measurements above 500°C. The endothermal effect observed about 820°C is related to the ferroelectric phase transition of BiFeO 3.

Phase diagram of (Bi 1− xLa x)FeO 3 solid solution

From electric permittivity, magnetic susceptibility, dilatometric and derivatographic measurements as well as X-ray and EPR data for (Bi 1- xLa x )FeO 3 solid solution exhibiting simultaneously ordering of electric and magnetic dipoles, phase diagrams are constructed.