Electric Permittivity Measurements Research Articles

Destruction and formation of a carbon nanotube network in polymer melts: Rheology and conductivity spectroscopy

Destruction and formation of the carbon nanotube network in polymer melts have been investigated by a combination of conductivity spectroscopy and dynamic-mechanical analysis for polycarbonate (PC) containing multiwalled carbon nanotubes. The combined setup allows simultaneous time-resolved measurements of electrical conductivity, dielectric permittivity and dynamic shear modulus. Furthermore, well-defined shear deformations can be applied to the samples. After annealing the samples well above glass transition short shear deformations were applied to the melt. These deformations lead to a decrease of the conductivity by about 6 orders of magnitude and of the real part of the shear modulus (G′) by a factor of 20. In the rest time after the shear deformation a complete recovery of the conductivity and G′ modulus was observed. The changes in conductivity and G′ were assigned to destruction and reformation of agglomerates, which are assumed to be conductive spherical objects containing loosely packed nanotubes. For a quantitative description of the time dependent electrical conductivity a simple model combining cluster aggregation and electrical percolation is applied.

Synthesis, characterization, electrical and dielectric permittivity measurements of 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyanines

2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyanines were synthesized from 4-(4-amino-3-nitrophenoxy)phthalonitrile which was obtained from 4-nitro-1,2-dicyanobenzene and 4-amino-3-nitrophenol. 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyanine and 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyaninatocobalt(II) were synthesized in a one-step condensation reaction of ferrocenylaldehyde with 2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyanine and 2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyaninatocobalt(II), respectively. The novel compounds were characterized by elemental analysis, Inductively Coupled Plasma (ICP-MS), UV-vis, IR and 1 H NMR spectroscopy. The effects of temperature and frequency on the conduction properties (a.c. and d.c.) and the dielectric constant were studied on pellet samples of 2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyanine, 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyanine, 2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyaninatocobalt(II) and 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyaninatocobalt(II), with evaporated, ohmic gold electrodes in the frequency range 40-105 Hz. and within the temperature range 290-400 K. Unlike many metallophthalocyanines, a variable-range hopping model is found to most appropriately fit the experimental conductivity data of 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyanine and 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyaninatocobalt(II), while for 2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyanine and 2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyaninatocobalt(II), thermally activated conduction with single activation energy is valid. Frequency and temperature dependence of the a.c conductivity were analyzed in terms of existing theory for 2,9,16,23-tetra-(4-amino-3-nitrophenoxy)phthalocyanine, 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyanine, 2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyaninatocobalt(II) and 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyaninatocobalt(II). It was found that the a.c. conductivity of the compounds depends on the frequency, obeying the empirical formula, σ ac = A ( T )ωs. The model parameters calculated are reasonable and consistent with the prediction of the correlated barrier hopping model for 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyanine and 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyaninatocobalt(II) and the quantum mechanical tunneling model for 2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyanine and 2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyaninatocobalt(II). The dielectric constant of the compounds increased with temperature and decreased with frequency in the investigated range.

Influence of the dc and ac field intensity on electric permittivities of (Na0.5Bi0.5)0.88Ba0.12TiO3 ceramics

The electric permittivity measurements under different ac or dc field amplitudes on lead-free (Na0.5Bi0.5)0.88Ba0.12TiO3 ceramics were performed. A significant increase or decrease in permittivities was observed with increasing ac or dc fields intensity, respectively. It was found that temperature T m decreases or increases with increasing ac or dc fields, respectively. When ac field amplitude increased, stronger frequency relaxation around T m and greater shift in T m was observed. This was in opposite to the effect of dc field intensity. The obtained results were discussed in terms of polar region behaviour in external electric fields.

Nonlinear dielectric properties and temperature stabilization effect near the ferroelectricphase transition in sodium trihydrogen selenite

The ferroelectric phase transition of crystalline sodium trihydrogen selenite has beencharacterized by domain observations and measurements of electric permittivity,pyroeffect and spontaneous polarization. The first-order character of the phasetransition is clearly demonstrated by the phase coexistence and temperatureautostabilization. The considerable heating effect at 50 Hz ac field is described. Theelectric field effect on the temperature variation of the electric permittivity, inthe phase transition region, shows a considerable domain structure contributionto the permittivity value. It is demonstrated that the dielectric properties ofx- andy-samples can be described by classical dielectric state equations: theset of coefficients has been determined. It is concluded that thex-component of spontaneous polarization plays a predominant role in the phase transition.

Compositional and Pressure Effects on the Phase Transition in Ferroelectric NH4H(ClH2CCOO)2

The effects of pressure and of the substitution of Rb+ for the ammonium cations on the dielectric responce in NH 4 H(ClH 2 CCOO) 2 (AHCA) crystals have been studied using electric permittivity measurements. The transition temperature (T c ) decreases with the pressure increasing up to 800 MPa and pressure coefficient dT c /dp = −1.4*10− 2 [K/MPa] has been experimentally determined. In mixed crystals with different Rb+ admixture proportion, T c lowers considerably and additional electric permittivity anomaly is clearly evidenced. The results are discussed assuming a model which combines polarizability effects related to the heavy ion units with the pseudospin tunnelling model.

Decoupling of the order–disorder and displacive contributions to the phase transition in NH 4H(ClH 2CCOO) 2

The effects of hydrostatic pressure and substitution of Rb +for the ammonium cations on the ferroelectric phase transition temperature in NH 4H(ClH 2CCOO) 2 have been studied by electric permittivity measurements. The transition temperature ( T c) decreases with increasing pressure up to 800 MPa and the pressure coefficient d T c/d p=−1.4×10 −2 [K/MPa] has been experimentally determined. The substitution of Rb + for the ammonium cations has been shown to considerably lower the ferroelectric phase transition temperature T c. In mixed crystals, additional electric permittivity anomaly has been clearly evidenced. The results are discussed assuming a model, which combines polarizability effects, related to the heavy ion units, with the pseudo-spin tunnelling.

Dielectric and optical studies of phase transitions in [(CH3)2NH2]5Cd2CuCl11 crystal

AbstractSingle crystals of [(CH3)2 NH2]5Cd2CuCl11 have been grown and their dielectric and optical properties have been studied. Electric permittivity, losses and linear optic birefringence measurements have shown that the obtained new crystal is isomorphous with the original one – [(CH3)2 NH2]5Cd3Cl11. Phase transitions were observed at 175 K (continuous) and 120 K (first order). It means that partial replacing of cadmium atoms by copper ones does not change the structure and the heavy Cd2CuCl11–2 anions do not influence significantly the interaction of dimethylammonium cations. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Investigation of dielectric anomalies at cryogenic temperatures in (1−x)[Pb(Mg1∕3Nb2∕3)O3]–xPbTiO3 system

Complex electrical permittivity measurements in (1−x)[Pb(Mg1∕3Nb2∕3)O3]–xPbTiO3 ceramics for 0.10⩽x⩽0.40 were performed in the frequency and temperature range from 1to100kHz and from 15to600K, respectively. Unexpected dielectric anomalies, which were frequency dependent, were found at cryogenic temperatures. It was verified that this dielectric behavior is always observed, independent of whether the composition presents a “normal” ferroelectric or a relaxor characteristic. The results were analyzed within the framework of two current models found in the literature. It was concluded that none of the proposed mechanisms uniquely satisfies the experimental results in the composition range investigated here.

The effect of hydrostatic pressure on the ferroelectric phase transition in [NH 2(CH 3) 2] 3[Sb 2Cl 9

The effect of hydrostatic pressure on the ferroelectric phase transition temperature in [NH 2(CH 3) 2] 3[Sb 2Cl 9] (DMACA) has been studied by electric permittivity measurements at pressures up to 400 MPa. The pressure–temperature phase diagram is given. The phase transition temperature ( T c) increases with increasing pressure up to 150 MPa, passes through a maximum and then decreases with a further increase of pressure. The unexpected nonlinear decrease in T c with pressure increasing above 150 MPa suggests that the mechanism of ferroelectric phase transition in DMACA is different from hitherto assumed.

Electric and magnetic properties of sol–gel silica powders doped with ferrofluid

SiO2 powders with magnetic properties have been prepared via the sol–gel method. Morphology of the magnetic powders has been investigated by scanning electron microscope (SEM). The magnetic susceptibility and electric permittivity measurements of the obtained materials have been performed by means of the lumped-capacitance method. The complex magnetic permeability measurements have been performed by means of the inductance method using toroidal-shaped samples.

In-situ Measurements of Electrorheological Response and Electric Properties of Ferroelectric Barium Titanate/Silicone Oil Suspension.

Electrorheological response of ferroelectric BaTiO3 / silicone oil suspension was experimentally studied with in-situ measurements of electric conductivity and dielectric permittivity in ranges of electric field strength (0-2kV/mm) and field frequency (100-5000Hz) under steady shear and shear stress sweep. In steady shear experiments, conducted at shear rates of 100 and 200s-1, shear stress increased with time accompanied by increases in the conductivity and the permittivity. The evolution of these electric properties suggested the growth of particle aggregation in the suspension. The shear stress at each time increased with field frequency, reached maximum value around 103Hz, and then declined. The change in the shear stress well corresponded to the change in the permittivity. An empirical relation of Δτ ∝(Δε rΕ )2 , observed for silica particle / silicone oil (Saimoto et al.,1999), was applicable to the present suspension, where Δτ is generated shear stress, Δεr generated dielectric permittivity, and Ε electric field strength. In the shear stress sweep experiments, hysteresis behavior was observed. Longer sweep period induced larger yield stress due to the growth of the aligned particles during the application of electric field. A drastic decrease in the permittivity around a yield point indicated collapse of the aggregative structure. A correlative behavior was observed between changes in the yield stress and the value of ΔεrΕ.

Copper ordering in lamellar CuMP2S6(M= Cr, In): Transition to an antiferroelectric or ferroelectric phase

Abstract The transition to an antiferroelectric or ferroelectric phase in the lamellar compound CuMP2S6 (M= Cr or In) is shown to be triggered by the appearance of an ordered copper sublattice. Cu(I) ions in CuCrP2S6, which are distributed over several sites at room temperature, freeze into an intermediate quasi-antipolar state between 190 and 175K, and then form an array of alternating up and down dipoles below 150K. Evidence for these transitions were obtained using calorimetry, diffraction and electric permittivity measurements. CuInP2S6 at 298K contains antiparallel polar sublattices of Cu(I) and In(III) which yield a Ps =2.6 μC-cm−2, as calculated from crystallographic results. The existence of copper disorder and the central octahedral location of In(III) in the paraelectric phase (T>315K) were also confirmed.

Changes of polarization in the range of phase transition for SbSJ-modified

Abstract Temperature measurements of electric permittivity, pyroelectric current as well as temperature and time studies of electric hysteresis loop have been performed in modified SbSJ. The appropriate measurements have been performed in the temperature range from 190K to 370K. The undertaken investigations have shown a complex character of ferroelectric phase transition in the samples. A change of the sign of pyroelectric current, observed in the temperature of 330K, corresponds to the temperature of the phase transition determined from dielectric measurements. Additionally a deformation of the shape of electric hysteresis loop has been observed close to 330K. The above behaviour of the investigated samples may be directly related to the changes in the ordering of spontaneous and induced polarization which take place in the region close to the phase transition.

5427116 Device for maintaining a desired load on a joint during observation under magnetic resonance imaging

SiO2 powders with magnetic properties have been prepared via the sol–gel method. Morphology of the magnetic powders has been investigated by scanning electron microscope (SEM). The magnetic susceptibility and electric permittivity measurements of the obtained materials have been performed by means of the lumped-capacitance method. The complex magnetic permeability measurements have been performed by means of the inductance method using toroidal-shaped samples.

The Goldstone mode in mixtures containing ferroelectric liquid crystals

Abstract Measurements of complex electric permittivity of room temperature ferroelectric liquid crystal mixtures have been made on aligned samples with the electric measuring field being parallel to the layer planes. The spontaneous polarization, the tilt angles and pitch have been measured in these mixtures. By theoretical fitting of the experimental points of electric permittivity for the Cole–Cole modification of the Debye equation dielectric parameters, the dielectric strength, relaxation frequency, and distribution parameter for the Goldstone mode have been computed. The dielectrically observed Goldstone mode in our mixtures is shown to have both DC bias field and AC field dependences.

Native Oxide Films of In0.53Ga0.47As Formed Using Plasma Anodization

DC plasma anodization has been used to form insulating native oxide films on epitaxial layers supported on semi‐insulating and conducting substrates. Anodizations at constant current density have been compared with those which were limited by a preset voltage. Rutherford back scattering showed that the composition was for both anodization processes. There was a loss of about 11% In in comparison with the aggregate of the Ga and As fractions. The absolute losses of In and were 20 and 6%, respectively. The volume increase on oxidation was imperceptible. Auger electron spectroscopy showed that the oxide‐semiconductor interface width was less than 40 Å. When current limited growth was used, the composition within 200 Å of the interface was particularly uniform. Measurements of electrical resistivity, breakdown field, permittivity, and etch rate are reported and point to the usefulness of the plasma native oxide as a device insulator material.

Dielectric relaxation in a high-tilt-angle chiral-nematic–smectic-C*ferroelectric liquid crystal

The dielectric properties of a high-tilt-angle chiral-nematic--smectic-${\mathit{C}}^{\mathrm{*}}$ phase ferroelectric liquid crystal are studied in the frequency range of 30 Hz to 1 MHz. Measurements of electric permittivity at different temperatures and biasing fields were taken in thin homogeneously aligned samples with the electric measuring field being parallel to the layer planes. In the smectic-${\mathit{C}}^{\mathrm{*}}$ phase two relaxation mechanisms have been found, viz., the Goldstone mode originating due to the phase fluctuations of the director and 180\ifmmode^\circ\else\textdegree\fi{} flip of the molecular relaxation connected with the reorientation of the liquid-crystal molecule around its short axis. Temperature and bias-field dependence of the dielectric permittivity and the critical relaxation frequency of the molecular mode in the smectic-${\mathit{C}}^{\mathrm{*}}$ phase are studied and discussed.

Dielectric and calorimetric study of phase transitions in mixed diacetylene single crystals polymerizing in the solid state

Dielectric and calorimetric experiments were performed on a series of pTS-pFBS mixed diacetylene single crystals. The electric permittivity measurements were carried out in the direction of growing polymer chains in the temperature range 80-333 K, as a function of the degree of polymerization of the samples. The specific heat measurements were performed on monomeric and fully polymerized samples in the temperature range 120-220 K. Phase transitions, already described in the literature for pure pTS crystals, were found to shift toward lower temperatures upon increasing the pFBS content in mixed crystals

Kinetics of polymerization of mixed diacetylene single crystals determined from dielectric measurements

AbstractResults of investigations on the kinetics of thermal polymerization of mixed single‐crystalline diacetylenes are reported. The polymerization was studied at 333 K on a series of mixed 1 (pTS)–3 (pFBS) crystals of various compositions. The polymer contents were determined from the measurements of electric permittivities of the samples during polymerization. A simple qualitative model was put forward to explain changes in the kinetics of polymerization as function of the composition of mixed crystals. At early stages of polymerization, the process of initiation of the growth of polymer chains seems to be dependent on the concentration of defects associated with a misfit between pTS and pFBS molecules.

Dielectric Studies of the Structure in Some Homologous Series of Esters and Their Mixtures

Abstract The results of electric permittivity and conductivity measurements for mesogens from the CBnAB (n = 5−8) homologous series and for the mixtures of CB7AB with 10XPCHB (X = F or COCH3), are presented.