Colossal dielectric behavior of semiconducting Sr2TiMnO6 ceramics

Manganitelike double perovskite Sr2TiMnO6 (STMO) ceramics fabricated from the powders synthesized via the solid-state reaction route, exhibited dielectric constants as high as similar to 10(5) in the low frequency range (100 Hz-10 kHz) at room temperature. The Maxwell-Wagner type of relaxation mechanism was found to be more appropriate to rationalize such high dielectric constant values akin to that observed in materials such as KxTiyNi(1-x-y)O and CaCu3Ti4O12. The dielectric measurements carried out on the samples with different thicknesses and electrode materials reflected the influence of extrinsic effects. The impedance studies (100 Hz-10 MHz) in the 180-300 K temperature range revealed the presence of two dielectric relaxations corresponding to the grain boundary and the electrode. The dielectric response of the grain boundary was found to be weakly dependent on the dc bias field (up to 11 V/cm). However, owing to the electrode polarization, the applied ac/dc field had significant effect on the low frequency dielectric response. At low temperatures (100-180 K), the dc conductivity of STMO followed a variable range hopping behavior. Above 180 K, it followed the Arrhenius behavior because of the thermally activated conduction process. The bulk conductivity relaxation owing to the localized hopping of charge carriers obeyed the typical universal dielectric response.

Colossal dielectric behavior of semiconducting $Sr_{2}TiMnO_{6}$ ceramics

Manganitelike double perovskite Sr2TiMnO6 (STMO) ceramics fabricated from the powders synthesized via the solid-state reaction route, exhibited dielectric constants as high as similar to 10(5) in the low frequency range (100 Hz-10 kHz) at room temperature. The Maxwell-Wagner type of relaxation mechanism was found to be more appropriate to rationalize such high dielectric constant values akin to that observed in materials such as KxTiyNi(1-x-y)O and CaCu3Ti4O12. The dielectric measurements carried out on the samples with different thicknesses and electrode materials reflected the influence of extrinsic effects. The impedance studies (100 Hz-10 MHz) in the 180-300 K temperature range revealed the presence of two dielectric relaxations corresponding to the grain boundary and the electrode. The dielectric response of the grain boundary was found to be weakly dependent on the dc bias field (up to 11 V/cm). However, owing to the electrode polarization, the applied ac/dc field had significant effect on the low frequency dielectric response. At low temperatures (100-180 K), the dc conductivity of STMO followed a variable range hopping behavior. Above 180 K, it followed the Arrhenius behavior because of the thermally activated conduction process. The bulk conductivity relaxation owing to the localized hopping of charge carriers obeyed the typical universal dielectric response.

Analysis Of The Dielectric Behavior Of Castor Oil Impregnated All-Paper Capacitors

Several new liquids impregnants for capacitors have been suggested as possible alternatives to PCB'S which are being replaced in view of their harmful effects.The application of castor oil, a vegetable product, has been studied in the authors laboratary with the same obejective.

Studies on dielectric behavior of insulator-conductor composites

This paper describes the dielectric behavior of an insulator-conductor composite, namely, the wax-graphite composite. The variation of specific capacitance of these composites with parameters such as volume fraction and grain size of the conducting particles and temperature has been studied. These observed variations have been explained using the same model [C. Rajagopal and M. Satyam, J. Appl. Phys. 49, 5536 (1978)] which explains electrical conduction in composites. The specific capacitance of these materials appears to be governed by the contact capacitance between the conducting particles and the number of contacts each particle has with its neighbors. The variation of specific capacitance with temperature is attributed to the change in contact area.

Exotic dielectric behavior of polar liquids

We present a report of our analysis of wave vector dependence of the static dielectric function of a dipolar liquid obtained by a microscopic calculation. At low values of the wave vector (k), the longitudinal dielectric function ϵ(k) increases with k, in contradiction to some assumptions reported in the literature. As the value of k is increased, ϵ(k) diverges at a critical value kc which depends on the value of the long wavelength static dielectric constant (ϵ0) of the liquid. The dielectric function is negative for values of k greater than kc. At large values of k, the calculated ϵ(k) fails to attain the limiting value of unity. We attribute this result to the failure of the point dipole assumption made in the evaluation of the polarization correlation function required by the theory. The behavior of ϵ(k) for the dipolar liquid is compared with that of one component plasma for which reliable results can be obtained over the full range of wave vectors. For both systems, the stability conditions are fulfilled at all values of k. A plausible explanation of this rather exotic behavior of ϵ(k) is given.

Anomalous dielectric behavior of some ferrites

The dielectric behavior of some powdered polycrystalline samples has been studied in the frequency range of 200 Hz–100 kHz. It is shown that the dielectric behavior in these systems below the Curie temperature is not purely relaxational in its character and cannot be described by any of the models of the dielectric relaxation hitherto put forward. It is also shown that ‘‘isolation’’ of the particles in the powder samples plays a very important role. The origin of this abnormality is thought to be due to the mechanical resonance arising out of the magnetostrictive property of the material.

On the High Frequency Dielectric Behavior of Castor Oil

The low frequency dielectric behavior of castor oil (a vegetable oil) has been analyzed quite exhaustively in the context of its application as impregnant in capacitors. For the sake of completeness and in order to understand the relaxation phenomena in this liquid dielectric, this high frequency dielectric study was undertaken. In order to compare its properties with a liquid dielectric used in similar application and whose high frequency behavior has been quite well analyzed, Arochlor 1476 was studied. It is observed that both liquids have distributed relaxation times. The distribution parameters together with the two distinct relaxation times have been calculated by measuring the average relaxation time. It has been found that the distinct relaxation times thus calculated represent the dielectric behavior quite satisfactorily. The average dipole moments, dipole radii and thermal activation energies for dipole relaxation have also been evaluated.

Studies on dielectric behavior of insulator‐conductor composites

This paper describes the dielectric behavior of an insulator‐conductor composite, namely, the wax‐graphite composite. The variation of specific capacitance of these composites with parameters such as volume fraction and grain size of the conducting particles and temperature has been studied. These observed variations have been explained using the same model [C. Rajagopal and M. Satyam, J. Appl. Phys. 49, 5536 (1978)] which explains electrical conduction in composites. The specific capacitance of these materials appears to be governed by the contact capacitance between the conducting particles and the number of contacts each particle has with its neighbors. The variation of specific capacitance with temperature is attributed to the change in contact area.

Nonlinear dielectric behavior in three-component ferroelectric superlattices

Three-component ferroelectric superlattices consisting of alternating layers of SrTiO3, BaTiO3, and CaTiO3 (SBC) with variable interlayer thickness were fabricated on Pt(111)/TiO2/SiO2/Si (100) substrates by pulsed laser deposition. The presence of satellite reflections in x-ray-diffraction analysis and a periodic concentration of Sr, Ba, and Ca throughout the film in depth profile of secondary ion mass spectrometry analysis confirm the fabrication of superlattice structures. The Pr (remnant polarization) and Ps (saturation polarization) of SBC superlattice with 16.4-nm individual layer thickness (SBC16.4) were found to be around 4.96 and 34 μC/cm2, respectively. The dependence of polarization on individual layer thickness and lattice strain were studied in order to investigate the size dependence of the dielectric properties. The dielectric constant of these superlattices was found to be much higher than the individual component layers present in the superlattice configuration. The relatively higher tunability ( ∼ 55%) obtained around 300 K indicates that the superlattice is a potential electrically tunable material for microwave applications at room temperature. The enhanced dielectric properties were thus discussed in terms of the interfacial strain driven polar region due to high lattice mismatch and electrostatic coupling due to polarization mismatch between individual layers.

Structural and dielectric behavior of pulsed laser ablated Sr(0.6)Ca(0.4)TiO(3) thin film and asymmetric multilayer of SrTiO(3) and CaTiO(3)

Homogeneous thin films of Sr(0.6)Ca(0.4)TiO(3) (SCT40) and asymmetric multilayer of SrTiO(3) (STO) and CaTiO(3) (CTO) were fabricated on Pt/Ti/SiO(2)/Si substrates by using pulsed laser deposition technique. The electrical behavior of films was observed within a temperature range of 153 K-373 K. A feeble dielectric peak of SCT40 thin film at 273 K is justified as paraelectric to antiferroelectric phase transition. Moreover, the Curie-Weiss temperature, determined from the epsilon'(T) data above the transition temperature is found to be negative. Using Landau theory, the negative Curie-Weiss temperature is interpreted in terms of an antiferroelectric transition. The asymmetric multilayer exhibits a broad dielectric peak at 273 K. and is attributed to interdiffusion at several interfaces of multilayer. The average dielectric constants for homogeneous Sr(0.6)Ca(0.4)TiO(3) films (similar to 650) and asymmetric multilayered films (similar to 350) at room temperature are recognized as a consequence of grain size effect. Small frequency dispersion in the real part of the dielectric constants and relatively low dielectric losses for both cases ensure high quality of the films applicable for next generation integrated devices. (C) 2011 Elsevier B.V. All rights reserved.

Dielectric Behavior of Natural Rubber Composites in Microwave Fields

In this article, we report the preparation of conducting natural rubber (NR) with polyaniline (Pani). NR was made into a conductive material by the compounding of NR with Pani in powder form. NR latex was made into a conductive material by the in situ polymerization of aniline in the presence of NR latex. Different compositions of Pani- NR semi-interpenetrating networks were prepared, and the dielectric properties of all of the samples were determined in microwave frequencies. The cavity perturbation techpique was used for this study. A HP8510 vector network analyzer with a rectangular cavity resonator was used for this study. S bands 2-4 GHz in frequency were used. Thermal studies were also carried out with thermogravimetric analysis and differential scanning calorimetry.

Dielectric Behavior of Natural Rubber Composites in Microwave Fields

In this article, we report the preparation of conducting natural rubber (NR) with polyaniline (Pani). NR was made into a conductive material by the compounding of NR with Pani in powder form. NR latex was made into a conductive material by the in situ polymerization of aniline in the presence of NR latex. Different compositions of Pani- NR semi-interpenetrating networks were prepared, and the dielectric properties of all of the samples were determined in microwave frequencies. The cavity perturbation techpique was used for this study. A HP8510 vector network analyzer with a rectangular cavity resonator was used for this study. S bands 2-4 GHz in frequency were used. Thermal studies were also carried out with thermogravimetric analysis and differential scanning calorimetry.

Electric and dielectric behavior of CaCu3Ti4O12-based thin films obtained by soft chemical method

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Dielectric behavior of PVDF/POMA blends that have a low doped POMA content

The real (epsilon') and imaginary (epsilon) components of the complex permittivity of blends of PVDF [poly(vinylidene fluoride)] with POMA [poly(o-methoxyaniline)] doped with toluenosulfonic acid (TSA) containing 1, 2.5, and 5 wt % POMA-TSA were determined in the frequency interval between 10(2) and 3 X 10(6) Hz and in the temperature range from -120 up to 120degreesC. It was observed that the values of epsilon' and epsilon had a greater increase with the POMA-TSA content and with a temperature in the region of frequencies below 10 kHz. This effect decreased with frequency and it was attributed to interfacial polarization. This polarization was caused by the blend heterogeneity, formed by conductive POMA-TSA agglomerates dispersed in an insulating matrix of PVDF. The equation of Maxwell-Garnett, modified by Cohen, was used to evaluate the permittivity and conductivity behavior of POMA-TSA in the blends. A strong decrease was observed in POMA-TSA conductivity in the blend, which was bigger the lower the POMA-TSA content in the blend. This decrease could have been caused either by the POMA dedoping during the blend preparation process or by its dispersion into the insulating matrix. (C) 2002 Wiley Periodicals, Inc.