Temperature dependent dc and ac electrical transport properties of the composite of a polyaniline nanorod with copper chloride

We have prepared the composite of polyaniline nanorods with copper chloride by chemical oxidative polymerization of aniline. Introduction of copper chloride in polyaniline significantly increases the conductivity of the nanocomposite. Temperature dependence of resistivity for our sample is best fitted with the quasi-one-dimensional hopping model and also the tunneling model. Negative magnetoconductivity is obtained for the samples at room temperature. Temperature variation of ac conductivity can be explained in terms of correlated barrier hopping model. Frequency dependence of the real part of impedance is explained by the Maxwell-Wagner capacitor model. Two activation behaviors are observed from the analysis of grain and grain boundary contributions.     

Investigation of electrical properties (ac and dc) of organic zinc phthalocyanine,ZnPc, semiconductor thin films

We report measurements on the electrical properties of thermally evaporated zinc phthalocyanine, ZnPc, semiconductor thin films. Aluminum and gold metal electrodes were used and both proved to act as ohmic contacts. A relative permittivity, ε_r, of 1.56 was estimated from the dependence of capacitance on film thickness. The room temperature current density–voltage measurements indicated an ohmic conduction at low voltages, while a space–charge-limited conduction at higher voltages. An average value of a thermally generated hole concentration of the order 10¹³ m⁻³ was estimated at room temperature.The ac conductivity, capacitance and loss tangent were measured over a wide range of temperature (from 170 to 430 K) and frequency (between 0.1 and 20 kHz). The ac conductivity of ZnPc films was observed to be proportional to ω^s, where ω is the angular frequency, and the index s is a temperature and frequency-dependent constant. At low temperatures and for higher frequencies the ac conduction was due to hopping. The capacitance, as well as the loss tangent, was found to be dependent on both temperature and frequency, but was constant for all frequencies at low temperatures. Such dependences were accounted for the equivalent-circuit model consisting of inherent capacitance in parallel with a temperature dependent resistive element.     

Electrical properties (dc and ac) of vanadium-borate glass

The results of an investigation into the temperature and frequency dependence of the electrical conductivity [dc and ac (10²–10⁵ Hz)] of glass of the composition 35% B₂O₃-15% CaO-20% V₂O₄-30% V₂O₅ (weight %) are discussed. The resistivity of the glass at T=300°K is =1.2·10¹¹ ·cm. The activation energy of the dc conductivity is E=(0.652±0.004) eV and equal to E for ₂ at high temperatures. The temperature-frequency dependences of the polarization component _p, the dielectric loss coefficient, and the permittivity are explained on the basis of the Fröhlich model proposed for uncoupled relaxation oscillators for which the heights of the potential barriers are uniformly distributed in some range of energies.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika. No. 3, pp. 35–38, March, 1981.     

Biasing effects on thallium and silver chlorides with dc/ac voltage

Comparison was made between crystals of thallium chloride and silver chloride on their biasing effects with dc/ac voltage. Previous reports say that, although their electrical conductivities are similar, the dominant charge carriers in the former are the Cl⁻ ions while the Ag⁺ ions in the latter. The present dc/ac study demonstrates the following: for thallium chloride, although Cl⁻ conduction may be dominant under low bias field, Tl⁺ conduction supercedes Cl⁻ conduction when the bias field is enhanced. For silver chloride, Ag⁺ conduction is overwhelming within wide temperature range, to cause easy dielectric breakdown on dc biasing. Concerning the extrinsic conductivity seen at temperatures below 60 °C (thallium chloride) or below 150 °C (silver chloride), it is ascribed to grain-boundary related electron conduction, not to grain-boundary related Tl⁺ or Ag⁺ conduction as reported earlier.     

Lifetime statistics for a Bloch particle in ac and dc fields

We study the statistics of the Wigner delay time and resonance width for a Bloch particle in ac and dc fields in the regime of quantum chaos. It is shown that after appropriate rescaling the distributions of these quantities have a universal character predicted by the random matrix theory of chaotic scattering.     

Surface treatment of nanoporous silicon with noble metal ions and characterizations

A very large surface to volume ratio of nanoporous silicon (PS) produces a high density of surface states, which are responsible for uncontrolled oxidation of the PS surface. Hence it disturbs the stability of the material and also creates difficulties in the formation of a reliable electrical contact. To passivate the surface states of the nanoporous silicon, noble metals (Pd, Ru, and Pt) were dispersed on the PS surface by an electroless chemical method. GIXRD (glancing incidence X-ray diffraction) proved the crystallinity of PS and the presence of noble metals on its surface. While FESEM (field emission scanning electron microscopy) showed the morphology, the EDX (energy dispersive X-ray) line scans and digital X-ray image mapping indicated the formation of the noble metal islands on the PS surface. Dynamic SIMS (secondary ion mass spectroscopy) further confirmed the presence of noble metals and other impurities near the surface of the modified PS. The variation of the surface roughness after the noble metal modification was exhibited by AFM (atomic force microscopy). The formation of a thin oxide layer on the modified PS surface was verified by XPS (X-ray photoelectron spectroscopy).     

The dc and ac properties of potassium trioxalatoferrate (III) trihydrate

The complex potassium trioxalatoferrate (III) trihydrate {K₃(Fe(C₂O₄)₃ · 3H₂O)} was synthesised and characterised by energy dispersion X-ray fluorescence (XRF) and X-ray diffraction (XRD). The electrical and dielectric properties of the complex pellet were studied by ac- and dc-techniques in room temperature and in a temperature range of 293–373 K. The data of the ac conductivity as a function of frequency in a frequency range of 1–100 kHz follow the correlated barrier hopping CBH model and the parameters of the model were determined and connecting them with the optical properties. The temperature dependence of dc conductivity shows that the semiconducting behaviour of conduction phenomenon in the complex is realised by hopping mechanism between localised states and the minimum hopping distance was determined. High relative permittivity of about 30 at 100 kHz was obtained for the complex, which can find technological applications like alternative for the SiO₂ insulator in MOS devices.     

Experimental observation of further frequency upshift from dc to ac radiation converter with perpendicular dc magnetic field

A frequency upshift of a short microwave pulse is generated by the interaction between a relativistic underdense ionization front and a periodic electrostatic field with a perpendicular dc magnetic field. When the dc magnetic field is applied, further frequency upshift of 3 GHz is observed with respect to an unmagnetized case which has typically a GHz range. The radiation frequency depends on both the plasma density and the strength of the dc magnetic field, i.e., the plasma frequency and the cyclotron frequency. The frequency of the emitted radiation is in reasonable agreement with the theoretical values.     

Resistance oscillations in two-dimensional electron systems induced by both ac and dc fields

We report on magnetotransport measurements in a high-mobility two-dimensional electron system subject simultaneously to ac (microwave) and dc (Hall) fields. We find that dc excitation affects microwave photoresistance in a nontrivial way. Photoresistance maxima (minima) evolve into minima (maxima) and back, reflecting strong coupling and interplay of ac- and dc-induced effects. Most of our observations can be explained in terms of indirect electron transitions using a new, combined resonant condition. Observed quenching of microwave-induced zero resistance by a dc field cannot be unambiguously linked to a domain model, at least before a systematic theory treating both excitation types within a single framework is developed.     

Electrical and thermoelectric properties of nanoporous carbon

This paper reports on a study of the temperature dependences of the electrical resistivity, Hall coefficient, and thermopower of nanoporous carbon prepared from polycrystalline carbides (α-SiC, TiC, Mo₂C) and 6H-SiC single crystals in the temperature range 1.5–300 K. The structural units responsible for the character of charge transport in these materials are carbon nanoclusters measuring ～10–30 Å. The conductivity in all the samples studied was found to be p type with a high carrier concentration (n_h ～ 10²⁰ cm^?3). The behavior of the transport coefficients at low temperatures is discussed.     

Resonant two-wave mixing in photorefractive materials with the aid of dc and ac fields

A recently predicted resonant effect for the enhancement of two-wave mixing in photorefractive materials is investigated. The resonance occurs when the frequency of the applied ac field agrees with the eigenfrequency of the excited space-charge wave. Experimentally a clear resonance is found, as predicted by the theory, for high dc electric fields, but the resonance is smeared out for lower fields. A modified theory, taking into account the second temporal harmonic of the space-charge wave, shows good agreement with the experimental results.     

Nonuniversal features of the ac conductivity in ion conducting glasses

Recently, Sidebottom [Phys. Rev. Lett. 82, 3653 (1999)] proposed a new scaling approach for the conductivity spectra of ion conducting glasses. This approach is based on the condition that the shape of the spectra is universal. In this Letter, we show that this condition is generally not fulfilled, but that the shape depends on the glass composition. In single alkali glasses, the frequency dependence of the conductivity varies with the alkali oxide content. Furthermore, the mixing of dissimilar alkali ions leads to pronounced changes in the shape of the conductivity spectra.     

Mechanical properties and structures of bulk nanomaterials based on carbon nanopolymorphs

Bulk nanomaterials based on sp² carbon nanopolymorphs are promising candidates for supercapacitors due to their unique properties such as extremely high specific surface area, high conductivity and stability against graphitization. However, the mechanical response of such materials to external loading is not understood well. This Letter studies the effect of hydrostatic pressure on the mechanical properties and structures of these materials via molecular dynamics simulations. Three types of nanopolymorphs‐based nanomaterials that are composed of bended graphene flakes, short carbon nanotubes and fullerenes are considered. It is found that these three materials show a distinct relation between the pressure and volume strain. Moreover, their resistance to graphitization depends on the structure of their constituent components. The phenomena are explained by analysing the radial distribution function and coordination numbers of the atoms. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of carbon blacks with various structures on electrical properties of filled ethylene-propylene-diene rubber

The effect of carbon blacks on the electrical properties of filled EPDM is investigated by comparing five types of carbon blacks. Electrical tests show that EPDM filled with carbon black having a large value of surface area (conductive carbon black, CCB) displays the low volume and surface resistivities, and easily succumbs to dielectric breakdown. EPDM/CCB composites show the lowest dielectric constant and highest dissipation factor. Hence, a CCB with large surface area and high content of sulphur on the surface is suitable for conductive polymers; whereas, EPDM filled with other carbon blacks is useful for insulation applications.