Direct Current Electrical Conductivity Research Articles

Relationship between rheological and electrical percolation in a polymer nanocomposite with semiconductor inclusions

Microstructure, electrical conductivity, and rheological properties of nanocomposites based on isotactic polypropylene (iPP) containing semiconductor nanoparticles of TiO2 were studied. Compatibilized and uncompatibilized nanocomposites containing a wide range of TiO2 concentrations (up to 15 vol%) were prepared by melt compounding in a twin-screw extruder via a masterbatch method. An anhydride-modified PP (AMPP) was used as the compatibilizer. Atomic force microscopy (AFM), scanning electron microscopy (SEM), and image analysis techniques were utilized to study the morphology evolution in the samples. Analyzing the results of direct current (DC) electrical conductivity measurements showed a lower percolation threshold for the uncompatibilized samples, compared to the compatibilized ones. In order to estimate the percolation threshold, linear and nonlinear melt-state viscoelastic properties of the samples were studied. Liquid-solid transition and nonterminal behavior of the uncompatibilized samples were observed at relatively lower range of TiO2 loading, compared to the compatibilized samples. It was an indication of lower rheological percolation threshold in the uncompatibilized nanocomposites which was in agreement with the electrical percolation threshold. Scaling analysis of strain sweep tests above the percolation thresholds of the nanocomposites resulted in a lower fractal dimension for the uncompatibilized samples.

The effect of Fe substitution on the electrical and thermal conductivity and thermopower of Ca3(FexCo1−x)4O9 synthesised by a sol–gel process

The effect of Fe substitution for Co on direct current (DC) electrical and thermal conductivity and thermopower of Ca3(Co1−xFex)4O9 (x = 0, 0.05, 0.08), prepared by a sol–gel process, was investigated in the temperature range from 380 down to 5K. The results indicate that the substitution of Fe for Co results in an increase in thermopower and DC electrical resistivity and substantial (14.9–20.4% at 300K) decrease in lattice thermal conductivity. Experiments also indicated that the temperature dependence of electrical resistivity ρ for heavily substituted compounds Ca3(Co1−xFex)4O9 (x = 0.08) obeyed the relation lnρ ∝ T−1/3 at low temperatures, T < ~55K, in agreement with Mott’s two-dimensional (2D) variable range hopping model. The enhancement of thermopower and electrical resistivity was mainly ascribed to a decrease in hole carrier concentration caused by Fe substitution, while the decrease of thermal conductivity can be explained as phonon scattering caused by the impurity. The thermoelectric performance of Ca3Co4O9 was not improved in the temperature range investigated by Fe substitution largely due to great increase in electrical resistivity after Fe substitution.

Structural, electrical, magnetic and dielectric properties of rare-earth substituted cobalt ferrites nanoparticles synthesized by the co-precipitation method

Pure nanoparticles of the rare-earth substituted cobalt ferrites CoRExFe2−xO4 (where RE=Nd, Sm and Gd and x=0.1 and 0.2) were prepared by the chemical co-precipitation method. X-ray diffraction, Transmission electron microscopy (TEM), d.c. electrical conductivity, Magnetic hysteresis and Thermal analysis are utilized in order to study the effect of variation in the rare-earth substitution and its impact on particle size, magnetic properties like MS, HC and Curie temperature. The phase identification of the materials by X-ray diffraction reveals the single-phase nature of the materials. The lattice parameter increased with rare-earth content for x≤0.2. The Transmission electron micrographs of Nd-, Sm- and Gd-substituted CoFe2O4 exhibit the particle size 36.1 to 67.8nm ranges. The data of temperature variation of the direct current electrical conductivity showed definite breaks, which corresponds to ferrimagnetic to paramagnetic transitions. The thermoelectric power for all compound are positive over the whole range of temperature. The dielectric constant decreases with frequency and rare-earth content for the prepared samples. The magnetic properties of rare-earth substituted cobalt ferrites showed a definite hysteresis loop at room temperature. The reduction of coercive force, saturation magnetization, ratio MR/MS and magnetic moments may be due to dilution of the magnetic interaction.

Dependence of Site Occupancy and Structural and Electrical Properties on Successive Replacement of Co by Zn in CoFe2O4

The crystal structure and cation distribution at particular sites in the crystal lattice play the primary role in determining the properties of nanocrystalline transition-metal oxide materials. Nanocrystalline ferrite particles of Co1−xZnx Fe2O4 with x varying from 0.0 to 1.0 were synthesized by a coprecipitation method. Samples synthesized at the reaction temperature of 70°C were sintered at 600°C for 3 h. The face-centered cubic (FCC) spinel structure of the synthesized particles was confirmed by x-ray diffraction patterns. The grain sizes calculated from the most intense peak (311) using the Scherrer equation were found to be in the range from 10 nm to 35 nm. Extended x-ray absorption fine-structure and x-ray absorption near-edge structure spectroscopy is a powerful tool for structural study of metal oxide materials. These techniques are element specific and sensitive to the local structure. These techniques were used at Fe, Co, and Zn K-edges to investigate the cation distribution in the crystal structure. The dependence of the electrical transport properties on the shift in the crystal structure due to successive replacement of Co by Zn in CoFe2O4 was examined. Direct-current (dc) electrical conduction measurements were carried out as a function of temperature from 313 K to 700 K. Activation energy values indicated the polaron hopping conduction mechanism. The alternating-current (ac) electrical transport properties were studied by measuring the dielectric constant as a function of frequency. A regular shift␣in the electrical properties was observed depending upon the cation distribution.

Dielectric and microwave absorption properties of polymer derived SiCN ceramics annealed in N2 atmosphere

Abstract Porous SiCN ceramics were successfully fabricated by pyrolysis of a kind of polysilazane. The effects of annealing temperature on the microstructure evolution, direct-current electrical conductivity, dielectric properties, and microwave absorption properties of SiCN in the frequency range 8.2–12.4 GHz (X-band) were investigated. With the increase of annealing temperature, SiC, Si3N4 and free carbon nanodomains are gradually formed in the SiCN. Both the SiC and free carbon nanodomains lead to the increases of the complex relative permittivity and loss tangent of SiCN. With the increase of the annealing temperature, the average real permittivity, imaginary permittivity and loss tangent increase from 4.4, 0.2 and 0.05 to 13.8, 6.3 and 0.46, respectively. The minimum reflection coefficient and the frequency bandwidth below −10 dB for SiCN annealed at 1500 °C are −53 dB and 3.02 GHz, indicating good microwave absorption properties.

Effect of iodine doping on the electrical transport mechanism in plasma polymerized 2,6-diethylaniline thin films

The current density–voltage characteristics of pure and iodine doped plasma polymerized 2,6-diethylaniline (PPDEA) thin films of different thicknesses ranging from 150 to 450nm with aluminum (Al)/PPDEA/Al structure have been investigated at room temperature. The direct current electrical conductivity has showed a higher value due to iodine doping of PPDEA thin film. In contrast to pure PPDEA thin films where the most probable conduction mechanism is electrode limited Schottky type, Poole–Frenkel (PF) conduction mechanism is found to be operative in iodine doped PPDEA thin films. The PF conduction mechanism in iodine doped PPDEA thin films may have generated due to the charge transfer complex formation through donor type monomer and acceptor type iodine. The presence of charge transfer complex is confirmed by a new absorption shoulder/peak in ultraviolet–visible spectrum of iodine doped PPDEA thin film.

Electrical and thermal studies on poly(3-methyl thiophene) and in situ polymerized poly(3-methyl thiophene)[sbnd]cerium(IV)phosphate cation exchange nanocomposite

Electrically conductive poly(3-methythiophene)cerium(IV)phosphate cation exchange nanocomposites have been synthesized for the first time by in situ chemical oxidative polymerization of 3-methythiophene in the presence of cerium(IV)phosphate. FTIR, SEM, TEM and XRD analysis were used to characterize P3MThcerium(IV)phosphate cation exchange nanocomposites. The characterization results confirmed that there is a strong interaction between poly(3-methythiophene) and cerium(IV)phosphate particles. The thermal behavior of poly(3-methythiophene), cerium(IV)phosphate and poly(3-methythiophene)cerium(IV)phosphate nanocomposite were also investigated by thermogravimetric analysis (TGA), differential thermal analysis (DTA) and differential thermal gravimetry (DTG) at heating rate 10°Cmin−1 under nitrogen atmosphere and the P3MThcerium(IV)phosphate nanocomposite was found thermally more stable than pure P3MTh. Isothermal stability of P3MTh and P3MThcerium(IV)phosphate nanocomposite in terms of direct-current electrical conductivity retention was also studied in ambient air. The P3MThcerium(IV)phosphate nanocomposite showed better ion-exchange capacity, electrical conductivity and isothermal stability in terms of direct-current electrical conductivity retention under ambient condition than pure poly(3-methythiophene).

Thickness Dependent Direct Current Electrical Conduction in Plasma Polymerized Pyrrole Monolayer Thin Films

The thickness dependent direct current electrical conduction mechanism in plasma polymerized pyrrole (PPPy) monolayer thin films has been discussed in this paper. A parallel plate capacitively coupled glow discharge reactor was used to deposit PPPy thin films at room temperature onto glass substrates. The Fourier Transform Infrared (FTIR) analyses showed that the spectrum of PPPy is very much different than that of the pyrrole monomer and indicated that the monomer has undergone the re-organization during the plasma polymerization. The current density-voltage (J-V) characteristics of PPPy monolayer thin films of different thicknesses indicated an increase in electrical conductivity in the thin films of lower thickness. It is seen that in the low voltage region, the current conduction obeys Ohms law while the charge transport phenomenon appears to be the space charge limited conduction (SCLC) in the higher voltage region. The permittivity, free charge carrier density, and the mobility of the charges of the PPPy monolayer thin films have been calculated from the experimental data of J-V characteristics and found to be 1.07 × 10-10 C2N-1m-2, (3.56 ± 0.01) × 1022 m-3, (4.4 ± 0.01) × 10-19 m2 V-1s-1 respectively.

Optical, electrical and photovoltaic properties of thermally evaporated 3-amino-2-[(2-nitrophenyl)diazinyl]-3-(piperidin-1-yl)acrylonitrile thin films

Thin films with various thickness of 3-amino-2-[(2-nitrophenyl)diazinyl]-3-(piperidin-1-yl)acrylonitrile (ANPA) were produced by conventional thermal evaporation. The dependence of the optical, electrical, and photovoltaic properties on the film thickness was investigated. X-ray diffraction showed that the films have an amorphous structure. The optical properties were investigated in terms of transmittance and reflectance in the spectral range 200–2500nm. Spectral distribution analysis of the absorption coefficient revealed that the films have an indirect allowed electronic interband transition. The optical bandgap decreased from 2.47 to 2.1eV for an increase in film thickness from 105 to 265nm. The direct current electrical conductivity of the films was measured for sandwich-structured samples as a function of the heating temperature and film thickness. The films exhibited semiconductor behavior and electrical conduction was attributed to hopping of charge carriers in localized states. ANPA films of differing thickness were deposited on p-type Si single-crystal substrates. The influence of film thickness on the electrical and photovoltaic parameters of Au/ANPA/p-Si/Al heterojunction solar cells was investigated.

Associating oriented polyaniline and eumelanin in a reactive layer-by-layer manner: Composites with high electrical conductivity

Eumelanin like coatings, often called “polydopamine” films are a new class of universal coatings allowing to coat almost all kinds of materials in a straightforward and one step reaction. To broaden the range of applications of such coatings particularly for biomedical applications and for the design of new biosensors, it is mandatory to provide an increased electrical conductivity to such coatings. Herein we produce composite films made of oriented polyaniline (PANI) and eumelanin (“polydopamine”) using a reactive layer-by-layer deposition approach. In this approach, the two constitutive components of the films are not deposited from solutions containing particles thereof but are produced through successive oxidation of aniline and dopamine in the appropriate reaction conditions. The composite films contain about 24% by weight of eumelanin and display a direct current (DC) electrical conductivity similar to that of oriented PANI, namely of the order of 1Scm−1. An increase in the mass fraction of eumelanin in the composite films can be easily achieved by two successive deposition steps of eumelanin and leads to a significant reduction in the electrical conductivity of the whole material.

Synthesis, Structure, and Electrochemistry of Sm-Modified LiMn2O4 Cathode Materials for Lithium-Ion Batteries

Spinel lithium manganese oxide and a series of Sm/LiMn2O4 spinels with different Sm additive contents (x = 0.02%, 0.05%) were prepared for the first time via a coprecipitation method for rechargeable lithium-ion batteries. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive analysis of x-rays (EDAX), infrared (IR), and electron spin resonance spectral studies as well as various electrochemical measurements were used to examine the structural and electrochemical characteristics of LiMn2−xSmxO4 (x = 0.00%, 0.02%, 0.05%). XRD and SEM studies confirmed the nano materials size for all prepared spinels. From cyclic voltammetry studies, in terms of peak splitting, electrochemical active surface area, and intensity of the peaks, the LiMn1.98Sm0.02O4 sample possesses better electrochemical performance compared with the LiMn1.95Sm0.05O4 sample. Hence, limited addition of a rare-earth dopant is preferable to obtain better efficiency. Direct-current (DC) electrical conductivity measurements indicated that these samples are semiconducting and their activation energies decrease with increasing rare-earth Sm3+ content.

Electrical, dielectric and microwave-absorption properties of polymer derived SiC ceramics in X band

Porous silicon carbide ceramics were successfully fabricated by pyrolysis of a polycarbosilane precursor. The direct-current electrical conductivity, dielectric and microwave absorption properties over the frequency range of 8.2–12.4GHz (X band) were investigated. Polymer derived silicon carbide is composed of SiC nano-crystals and free carbon nanodomains. The high-temperature direct-current conductivities of samples indicate the transformation of amorphous semiconductor into polycrystalline semiconductor with the increase of the annealing temperature. After annealed at 1500°C, the real permittivity, imaginary permittivity and the loss tangent increase from 3.6, 0.17 and 0.05 to 8.49, 10.01 and 1.18, respectively. The increases of the relative complex permittivity and loss tangent are ascribed to the appearance of SiC nano-crystals and free carbon nanodomains. The average reflectivity of the polymer derived SiC ceramics annealed at 1400°C is −9.9dB, which exhibits a promising prospect as microwave absorbing materials.

Effect of magnetic field treatment on the electrical conductivity of low-density polyethylene and its composites with CNTs

Low-density polyethylene (LDPE) and carbon nanotube (CNT) composites (CNT/LDPE) were treated during their hot-press molding using a strong static magnetic field. The effect of the magnetic field on the direct current electrical conductivity of these materials was investigated and the mechanism for the effect was analyzed by differential scanning calorimetry, polarized light microscopy and atomic force microscopy. Results indicate that the magnetic field treatment increases the degree of crystallization and the volume resistivity of the composites. The induced magnetic moment in the CNTs caused by the magnetic field leads to an improved orientation of the CNTs in LDPE along the magnetic field direction during molding, which causes an increase in the electrical conductivity of the CNT/LDPE composites in the magnetic field direction and an increase of nonlinear conductivity characteristics. The increased amplitude of electrical conductivity of the composites increases with the increasing amount of CNTs added. [New Carbon Materials 2013, 28(1): 20–25]

Effects of thermal oxidation on electromagnetic interference shielding properties of SiCf/SiC composites

Abstract SiC f /SiC composites containing PyC interphase were prepared by chemical vapor infiltration and their properties were investigated for electromagnetic interference (EMI) shielding applications in the frequency of 8.2–12.4 GHz. The room temperature direct current electrical conductivity ( σ dc ) and EMI shielding effectiveness (SE) were tested after thermal oxidation for various time at 900 °C. It was found that the EMI was shielded mainly by absorption for both as-received and oxidized SiC f /SiC composites. Both σ dc and SE of SiC f /SiC composites decrease after thermal oxidation at 900 °C. It was proposed that the free carbon, including PyC interphase and free carbon in matrix and fibers, mainly determines the EMI SE of composites. The decrease of σ dc and SE of composites after oxidation are attributed to the consumption of free carbon. The SE of SiC f /SiC composites with a thickness of 2 mm remains above 15 dB after thermal oxidation for 4 h in air at 900 °C.

Graphene oxide-filled conducting polyaniline composites as methanol-sensing materials

Polyaniline/graphene oxide (PANI/GO) composites were prepared by polymerization of aniline monomer in the presence of GO under acidic conditions. The synthesized samples were characterized by Fourier transform infra red spectroscopy, ultraviolet–visible absorption, Raman spectroscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and thermogravimetric analysis. The direct current electrical conductivity of the composite was calculated by a four-probe technique. It is found that the conductivity dramatically increased to 241 S m−1 for PANI/GO (5 wt%) composite at 110 °C compared to pure PANI (7.5 S m−1). The composite material was investigated as a methanol vapour sensor and compared with pure PANI. The methanol-sensing characteristics of the prepared composite was monitored by measuring the change in electrical resistivity on exposure to methanol vapour at different concentrations. The resistivity of PANI increases on exposure to methanol vapour because of strong hydrogen bonding between methanol with the polymer chain. A density functional theory study was carried out to verify the proposed concept of hydrogen bonding between the polymer chains and methanol. The presence of GO in PANI/GO composite increases the sensitivity towards methanol as compared with the pure PANI.

Infrared spectra, optical constants and semiconductor behavior of 5-(2-phenylhydrazono)-3,3-dimethylcyclohexanone thin films

The 5-(2-phenylhydrazono)-3,3-dimethylcyclohexanone (PHDMC) is synthesized by reacting 5,5-dimethylcyclohexane-1,3-dione with 2-phenylhydrazine. Synthesized PHDMC is polycrystalline with monoclinic space group, P21/a. Miller’s indices values for each diffraction peak in the X-ray diffraction spectrum are calculated. Thin films of PHDMC with different thickness values (0.83–1.247μm) are prepared by thermal evaporation technique and they exhibit amorphous structure. Different vibrational modes, observed in infrared spectra of the powder and thin films, were assigned to the molecular bonding structure of PHDMC compound. The optical properties of PHDMC thin films are investigated by measuring the optical transmittance and reflectance at the normal incidence of the light in the spectral range 200–2500nm. The refractive and absorption indices of the films are found to be independent of the film thickness range mentioned above. The refractive index is analyzed and the dispersion parameters are extracted. Analysis of the absorption coefficient spectra showed that the films have two major indirect allowed electronic transitions; the corresponding optical band gaps are estimated as 2.1 and 3.2eV in the framework of electronic band-to-band transition theory. The direct current electrical conductivity measurements showed the semiconductor property of the films.

Dye-sensitized Solar Cells with New One-Dimensional Halide-Bridged Cu(I)–Ni(II) Heterometal Coordination Polymers Containing Hexamethylene Dithiocarbamate Ligand

One-dimensional (1D) halide-bridged Cu(I)–Ni(II) heterometal coordination polymers containing a hexamethylene dithiocarbamate (Hm-dtc) ligand have been synthesized and crystallographically characterized. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of the coordination polymers were estimated using UV-Vis-NIR and photoelectron spectroscopies, and it was revealed that these coordination polymers have appropriate HOMO levels for use as dye sensitizers. Direct-current electrical conductivity measurements and impedance measurements indicated that these 1D Cu(I)–Ni(II) heterometal coordination polymers were insulators (σ300K &lt; 10−12 S cm−1). In addition, the coordination polymers were used as sensitizing materials in dye-sensitized solar cells (DSSCs). DSSCs with 1D Cu(I)–Ni(II) heterometal coordination polymers showed lower performances than those with 1D halide-bridged Cu(I)–Cu(II) mixed-valence coordination polymers.

Low temperature dc electrical conduction in reduced lithium niobate single crystals

The direct current (dc) electrical conductivity of unreduced and reduced lithium niobate (LiNbO3) single crystals has been measured at room temperature (∼300K). The dc conductivity and activation energy show strong dependence on the degree of oxygen reduction in LiNbO3 single crystals. The dc conductivity exhibits a peak as a function of increasing degree of oxygen reduction. These results have been analysed assuming small polaron hopping conduction between Nb4+ and Nb5+ ion sites. The temperature dependence of dc conductivity of reduced LiNbO3 single crystal, exhibiting the highest dc conductivity, has been examined in the temperature range 77–373K. The observed dc conductivity data has been analyzed and explained in terms of Mott’s variable range hopping (VRH) conduction model involving a single phonon hopping process.

Switching Phenomena of Amorphous Ga5Ge15Te80 Chalcogenide Thin Films for Phase-Change Memories

a-Ga5Ge15Te80 chalcogenide thin films have been prepared using the e-beam evaporation technique. The amorphous structure of the deposited films has been confirmed using x-ray diffraction and transmission electron microscopy techniques. The direct-current (DC) electrical conductivity and switching phenomena were studied for different Ga5Ge15Te80 film thicknesses at different temperatures. The determined activation energy ΔEσ was found to be independent of the film thickness (268 nm to 562 nm) in the measured temperature range (300 K to 380 K). I–V characteristic curves of the amorphous Ga5Ge15Te80 films show a memory switching behavior. The mean value of the threshold voltage \( \bar{V}_{\rm{th}} \) increases linearly with increasing film thickness, and decreases exponentially with increasing temperature. The values of switching activation energy e were calculated for different film thicknesses. The obtained results were explained on the basis of a thermal model for initiating the switching process, which indicates the possibility of using the composition for phase-change memory.

Electrochemical impedance study of the lignin-derived conducting polymer

Electrochemical impedance spectroscopy was applied to the study of conducting lignin-derived polymers to be used in all-solid-state potentiometric chemical sensors. Conducting polymers were produced by step-growth polymerization of modified eucalyptus kraft lignin with isocyanate and doped by multi-wall carbon nanotubes (MWCNTs). Lignin possesses ion-exchange properties due to the presence of a variety of functional groups, which makes it an attractive active substance for chemical sensing. Co-polymerization allows fixing lignin inside polymer matrix ensuring high stability of the resulting material. Doping of the lignin-based polyurethane with multi-wall carbon nanotubes (MWCNTs) was adopted as a mean to obtain electrically conductive system with low mass of filler. The direct current (DC) electrical conductivity and the dielectric properties of the conducting polymers have been evaluated at MWCNTs contents from 0 to 0.72% (wt.) at the frequencies between 40Hz and 100MHz in the temperature range −100 to 100°C. The percolation model theory was used to describe DC and the low frequency behaviour, where the electrical conductivity and the dielectric constant were expressed by scaling laws near the threshold conduction. The lignin-based polyurethane presented low critical concentration of MWCNTs around 0.18wt.%. The dielectric analysis was carried out using the modulus formalism and the dielectric relaxation behaviour was modelled using the Cole–Cole expression.