Dc Conductivity Values Research Articles

Epitaxial films of the proton-conducting Ca-doped LaNbO4 material and a study of their charge transport properties

Ca-doped LaNbO4 (LCNO) material has shown outstanding stability in harsh environments in combination with moderate proton-conductivity in polycrystalline samples at intermediate temperatures below 800°C under a wet atmosphere. However, in polycrystalline materials the role of grain boundaries is believed to play a predominant role in protonic conductivity, which may make more difficult the study of the intrinsic properties of the material. For that reason the present study focuses on the preparation of epitaxial films by pulsed laser deposition on NdGaO3 (110) single crystal substrates. Under certain deposition conditions the films grow epitaxially with a monoclinic structure (fergusonite) and b-axis orientation. A polymorph change between the monoclinic and tetragonal structure has been observed at 250°C. The film charge transport properties are analyzed under different atmospheres, dry and wet O2 and H2 as well as under deuterated conditions by using D2 and D2O in order to check for the characteristic isotopic effect of the proton transport. Although a certain proton conductivity was observed under reducing wet atmospheres unexpected large DC conductivity values (of about 5.5S/cm for the 80nm thin LCNO film at 800°C in dry O2) have been observed for all films and ambient conditions.

Synthesis, characterization, spectral and electrical properties of peripherally tetratriazole-substituted phthalocyanines and its metal complexes

The substituted [1,2,4]triazole 3 was obtained from the reaction between compound 1 and compound 2. Novel substituted phthalonitrile 5 was prepared by the substitution of the nitro group of 4-nitrophthalonitrile 4 with triazole moiety 3. The synthesis of metal-free, zinc, nickel, cobalt and copper phthalocyanines with four substituted [1,2,4]triazole groups on peripheral position were performed from cyclotetramerization of novel substituted dinitrile compound 5. Metal-free phthalocyanine 6 and its Zn-, Ni-, Co- and Cu- complexes 7–10 were prepared in DMAE at reflux temperature. All new compounds were characterized by a combination of elemental analyses, IR, 1H/13C NMR, MS and UV–vis spectroscopy. Aggregation behaviors of NiPc 8 and CuPc 10 were also investigated. While NiPc 8 was aggregated in acetone, DMF, DMSO, THF, ethylacetate and toluene and non-aggregated in dichloromethane and pyridine at 10 × 10−6 mol dm−3 concentration, CuPc 10 showed monomeric behavior in dichloromethane, DMSO, DMF, pyridine, THF and showed aggregation in acetone, ethylacetate and toluene at 14 × 10−6 mol dm−3 concentration. On the other hand, substituted NiPc 8 and CuPc 10 did not show aggregation behavior between 4 × 10−6–14 × 10−6 mol dm−3 concentration range in chloroform. Dc and ac conductivity and Impedance Spectroscopy (IS) studies were also done on thin films of compounds 6, 7, 8, 9 and 10 as a function of temperature (295–523 K) and frequency (40–105 Hz) under vacuum (∼2 × 10−3 mbar) in dark. The compounds 7, 8, 9 and 10 showed nearly same dc conductivity values in the measured temperature range. Variation of dc conductivity of 6, 7, 8, 9 and 10 with temperature exhibited the semiconducting behavior. Variation of ac conductivity of the films with frequency represented by the function σac = Aωs. The results indicated that charge transport mechanism of the films can be explained by hopping and small polaron tunneling model for 6, 7, 8, 9 and 10 depending on temperature and frequency region. Results of the impedance spectra measurements showed that, at high temperatures, depressed semicircles with different radius indicate deviation from Debye dispersion relation.

Holographic p-wave superconductors in quasi-topological gravity

We construct a holographic p-wave superconductor model in the framework of quasi-topological gravity in the probe limit. The relation between the critical temperature and the coupling parameters of higher curvature terms is investigated. The numerical results for conductivity are presented as well. It turns out that our data fit the Drude model very well in the low-frequency limit, and the values of dc conductivity as well as the relaxation time are obtained numerically.

Protonic defect induced carrier doping in TTFCOO−NH4+: Tunable doping level by solvent

The origin of carrier doping in TTFCOO−NH4+ has been verified to include protonic defect in salt bridge by means of X-ray photoelectron spectroscopy (XPS), for the first time. The emergence of spin in TTFCOO−NH4+ is tunable over quite a wide range (9–33%) only by selecting a suitable solvent for the salt crystallization. The spin concentration of the solvent-dependent salts weakly correlates with intensity of optical absorption in near-infrared region, values of g-tensor and dc conductivity at rt. The solvents determining doping level of the salt are classified into three categories by self-dissociation ability (pKSH) of solvent, which likely controls inclusion of protonic defect in the salts.

The effect of titania content on the physical properties of polyimide/titania nanohybrid films

AbstractIn this study, a series of PI/TiO2 nanohybrid materials were prepared from polyamic acid of 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride/3,3′‐diaminodiphenyl sulfone, and titania precursor by the sol‐gel method. The titania content in the hybrid system was varied from 0 to 5 wt %. The physical and mechanical properties of the hybrids such as refractive index, optical transmission, and tensile strength were investigated. It was determined that incorporation of titania precursor into the PI matrix improved the refractive indices and tensile modulus of the hybrid films. It was observed that the optical transmittance and tensile strength of the nanohybrids were slightly decreased with the increasing titania content. It was determined that the hybrid films might have enhanced the UV shielding properties compare to the PI films. Furhermore, the hybrid materials showed better thermal stability than the PI. SEM studies demonstrated that titania particles (1 and 3 wt %) were distributed homogeneously through the PI matrix. The effect of the titania content in the PI on DC conductivity and dielectric constant were also analyzed. For the PI film containing 5 wt % titania, activation energy value increased to 1.0 eV from the value of 0.65 eV. DC conductivity value of the films depending on titania content varied between 3.0 × 10−11 and 1.4 × 10−10 S/cm at room temperature. Relative dielectric constants of the films were calculated from capacitance measurements depending on frequency (40–100 kHz) at different temperatures (303–360 K). The values increased with the increasing titania content. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Microstructure, AC impedance and DC electrical conductivity characteristics of NiFe2-xGdxO4 (x = 0, 0.05 and 0.075)

The structure and electrical characteristics of Gd doped Ni ferrite materials, namely NiFe1.95Gd0.05O4 and NiFe1.925Gd0.075O4, are reported to demonstrate their improved electrical properties compared to that of pure NiFe2O4. NiFe1.95Gd0.05O4 and NiFe1.925Gd0.075O4 compounds crystallize in the cubic inverse spinel phase with a very small amount of GdFeO3 additional phase while pure NiFe2O4 crystallize in inverse spinel phase without any impurity phase. The back scattered electron imaging analysis indicate the primary and secondary formation in NiFe1.95Gd0.05O4 and NiFe1.925Gd0.075O4 compounds. Atomic force microscopy measurements indicate that the bulk grains are ∼2-5 micron size while the grain boundaries are thin compared to bulk grains. Impedance spectroscopic analysis at different temperature indicates the different relaxation mechanisms and their variation with temperature, bulk grain and grain-boundary contributions to the electrical conductivity (Rg) and capacitance (Cg) of these materials. The conductivity in pure NiFeO4 is found to be predominantly due to intrinsic bulk contribution (Rg=213 kΩ and Cg=4.5 x 10-8 F). In the case of NiFe1.95Gd0.05O4 and NiFe1.925Gd0.075O4 compounds, grain and grain-boundary contributions to the conductivity are clearly observed. The DC conductivity values (at 300 K) of NiFe2O4, NiFe1.95Gd0.05O4 and NiFe1.925Gd0.075O4 compounds are found to be 1.06 x 10-7 Ω-1 cm-1, 5.73 x 10-8 Ω-1 cm-1 and 1.28 x 10-8 Ω-1 cm-1 respectively.

Charge transport mechanism in intercalated polypyrrole aluminum‐pillared montmorillonite clay nanocomposites

AbstractNanocomposites based on intercalated conducting polypyrrole (PPy) into the galleries of inorganic aluminum‐pillared Montmorillonite (Al‐PMMT) clay with varying concentrations of Al‐PMMT were prepared by in situ chemical polymerization. The intercalation was confirmed by X‐ray diffraction pattern. Charge transport mechanism in these composites was investigated by temperature dependent direct current conductivity measurements. An increase in DC conductivity value on addition of (Al‐PMMT) clay in the composites at all temperatures and a transition from three‐dimensional (3D) Mott's variable range hopping (VRH) process in pristine PPy to one‐dimensional (1D) Mott's VRH process in the intercalated polymer composites has been observed. This transition in charge transport mechanism of PPy from 3D VRH to 1D VRH on intercalation has been interpreted in terms of straightening and linearization of polymer chains and decrease in inter‐chain interactions in the intercalated PPy. Enhancement in mechanical properties and increase in thermal stability of the nanocomposites was also observed with the increase in weight percentage of Al‐PMMT in PPy‐Al‐PMMT composites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Electrical and optical properties of pure and Pb2+ ion doped PVA − PEG polymer composite electrolyte films

Pb2+ ion conducting polymer composite electrolyte films, based on polyvinyl alcohol and polyethylene glycol doped with Pb(NO3)2 salt, were prepared using the solution cast technique. X-ray diffraction patterns of polymer composite with salt reveal the decrease in the degree of crystallinity with increasing concentration of the salt. The dielectric plots show an increase in dielectric permittivity at low frequency side with increasing salt concentration as well as temperature. The frequency dependence of ac conductivity obeys the Jonscher power law, and the maximum dc conductivity value is found to be 2.264×10−7 S/m at 303 K for the polymer composite with 30 mol% Pb(NO3)2. The activation energy for the ion in polymer electrolyte has been calculated from the modulus plots, and is in good agreement with the activation energy calculated from the temperature-dependent dc conductivity plot. The modulus plots indicate the non-Debye nature of the sample. For pure and doped films at room temperature, the impedance plots exhibit only one semicircle, indicating the presence of one type of conduction mechanism, whereas for 30 mol% salt doped with electrolyte film at different temperatures, it demonstrated the existence of bulk and electrode–electrolyte interface properties. Optical absorption spectra show a broad peak for all complexes, while compared with pure polymer composite, due to the complex formation of polymer electrolyte with Pb(NO3)2 and their absorption edge, direct band gap and indirect band gap were calculated. It was found that the absorption edge and energy gap values decreased on doping with Pb(NO3)2 dopant.

Fluctuation-Induced Tunneling Conductivity in Nanoporous TiO2 Thin Films

The electronic mechanisms responsible for dark conductivity in nanoporous TiO2 thin films remain only partially understood, although they control the efficiency of charge transport in a wide range of technological applications. Measurements in the 78–335 K temperature range show DC conductivity values spanning over 4 orders of magnitude, with a high-temperature Arrhenius dependence that gradually changes into a temperature-independent plateau at low temperatures. We show evidence that a fluctuation-induced tunneling conductivity (FITC) mechanism is fully consistent with the experimental data. Quantitative agreement is demonstrated for the entire temperature range (T = 78–335 K) with a FITC model parametrized according to atomistic models of nanoporous TiO2 and the characterization of the films by X-ray diffraction and scanning electron microscopy measurements. These findings suggest that dark DC conductivity in nanoporous TiO2 films depends strongly on the properties of the junctions linking the constituent nanoparticles.

Characterization of nanocomposite polymer electrolyte based on P(ECH-EO)

ZrO 2 nanoparticles have been prepared by poly acrylamide gel route. The synthesized nanosized ZrO 2 have been incorporated into plasticized polymer electrolyte (PPE), P(ECH-EO): LiClO 4: γ-BL system to understand the effect of ZrO 2 on the ionic conductivity. The X-ray diffraction pattern of the synthesized ZrO 2 nanoparticles reveals the crystalline phase. The X-ray diffraction patterns of P(ECH-EO) based NCPEM confirm the polymer–salt-nanoparticle complexation. The scanning electron microscope image of NCPEM confirms that the ZrO 2 nanoparticles were distributed uniformly in the polymer matrix. The presence of nano filler has increased the ionic conductivity and the maximum dc conductivity value is found to be 6.24×10 −6 S cm −1 at 303 K for 96(PPE): 4ZrO 2 (mol%).

Development of a conductive composite based on polythiophene/Y-zeolite and its response towards sulfide ions

A new potentiometric sensor electrode for sulfide based on conducting polymer films is introduced. A composite of polythiophene (PTP) with Y-zeolite was prepared via chemical oxidative polymerization of thiophene (TP) in presence of a dispersion of Y-zeolite (powder) in CHCl 3 solvent using anhydrous FeCl 3 oxidant. Formation of polythiophene and its subsequent SEM and TEM analysis revealed formation of composite particles with average diameter in the range of 0.3–0.35 μm. DC conductivity value of the PTP-Y-zeolite composite was in the order of 10 − 2 S/cm, which was indeed high compared to that of PTP, produced under identical conditions as above without the presence of Y-zeolite. This composite as active component with graphite powder and binding liquid was mixed and then used for preparation of solid state electrodes. The working temperature range for this electrode is between 20 and 40 °C. The linear dynamic range is 1 × 10 − 7 – 1 × 10 − 4 M and measures total sulfide concentration over a range of pH from 5 to 9. The composite electrode showed high selectivity for sulfide in the presence of many common interfering anions (− log K S, IO 3 − Pot = 6.3, − log K S, BrO 3 − Pot = 5.5, − log K S, S 2 O 3 2 − Pot = 4.8).

Molecular dynamics of poly(ATRIF) homopolymer and poly(AN- co-ATRIF) copolymer investigated by dielectric relaxation spectroscopy

Aiming to develop new dielectric polymers containing CN and F groups with strong dipole moments, a novel copolymer of acrylonitrile (AN) and 2,2,2-trifluoroethyl acrylate (ATRIF) was synthesized in acetonitrile by free radical process as well as the respective homopolymer (poly(ATRIF)). The copolymer’s composition and microstructure were analyzed by FTIR, 1H and 13C NMR spectroscopy and SEC. The molar incorporation of AN determined in the copolymer by NMR was 58 mol%. Thermogravimetric analysis of poly(AN- co-ATRIF) copolymer showed good thermal stability comparatively to the fluorinated homopolymer. Both copolymer, poly(AN- co-ATRIF), and homopolymer, poly(ATRIF), were dielectrically characterized over a frequency range from 10 −1 to 10 6 Hz, and in a temperature range from 223 to 393 K. The dominating relaxation process detected in both materials is the α-relaxation, associated with the dynamic glass transition. A VFTH temperature dependence of the relaxation times ( τ) was found for both materials, as characteristic of cooperative processes, from which the respective glass transition temperatures ( T g( τ = 100 s)) were estimated, which differ ∼40 K, the one of the copolymer being higher (307 K) in accordance to the calorimetric analysis. This effect was attributed to a higher stiffness of the backbone in the copolymer originated by the inclusion of the acrylonitrile groups. Both relaxation functions have the same breath of relaxation times allowing constructing a single master curve, indicating similar non-exponential character. A less fragile behavior was found for the copolymer. This was rationalized in a more straightforward way by the free volume approach instead from a correlation between fragility and intermolecular coupling. It was found that in the copolymer the free volume increases at a lower rate with the temperature increase. It was inferred from the VFTH temperature dependence of the dc conductivity and low values of the decoupling index that ion motion is significantly influenced by the dynamics of the α-process.

Conduction behavior in ionic liquids assisted electrodeposited polypyrrole layers

AbstractThe electropolymerization of pyrrole in ionic liquid media was carried out to produce an adherent, uniform, and durable polypyrrole (PPy) films with enhanced electrical properties. A threefold increase in the conductivity value can be attained with the selective choice of polymerizing media and ambient temperature dc conductivity value of 43, 15, and 13 S cm−1 for films grown in 1‐ethyl‐3‐methylimidazolium bis(perfluoroethanesulfonyl)imide, 1‐ethyl‐3‐methylimidazolium triflate and in lithium triflate in acetonitrile respectively. The corresponding localization lengths were found to be 17, 33, and 48 nm indicate that carriers are strongly localized. At low temperature, all three types of PPy films show metallic type behavior. Though transition is observed above 200 K for all the three films, the charge transport mechanism remains unaltered at higher temperatures for the films grown in ionic liquids, while the film grown in lithium triflate in acetonitrile assumes a three‐dimensional variable range hopping conduction behavior. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

Effects of processing conditions on rheological, thermal, and electrical properties of multiwall carbon nanotube/epoxy resin composites

AbstractWe report on the effect of processing conditions on rheology, thermal and electrical properties of nanocomposites containing 0.02–0.3 wt % multiwall carbon nanotubes in an epoxy resin. The influence of the sonication, the surface functionalization during mixing, as well as the application of external magnetic field (EMF) throughout the curing process was examined. Rheological tests combined with optical microscopy visualization are proved as a very useful methodology to determine the optimal processing conditions for the preparation of the nanocomposites. The Raman spectra provide evidence for more pronounced effect on the functionalized with hardener compositions, particularly by curing upon application of EMF. Different chain morphology of CNTs is created depending of the preparation conditions, which induced different effects on the thermal and electrical properties of the nanocomposites. The thermal degradation peak is significantly shifted towards higher temperatures by increasing the nanotube content, this confirming that even the small amount of carbon nanotubes produces a strong barrier effect for the volatile products during the degradation. The ac conductivity measurements revealed lower values of the percolation threshold (pc) in the range of 0.03–0.05 wt %. CNTs for the nanocomposites produced by preliminary dispersing of nanotubes in the epoxy resin, compared to those prepared by preliminary functionalization of the nanotubes in the amine hardener. This is attributed to the higher viscosity and stronger interfacial interactions of the amine hardener/CNT dispersion which restricts the reorganization of the nanotubes. The application of the EMF does not influence the pc value but the dc conductivity values (σdc) of the nanocomposites increased at about one order of magnitude due to the development of the aforementioned chain structure. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011

Concomitant synthesis of polyaniline and highly branched gold nanoparticles in the presence of DNA

The reduction of chloroauric acid using aniline adsorbed on DNA produces highly branched dendritic gold nanoparticles with concomitant formation of polyaniline (PANI) in contrast to the formation of spherical Au nanoparticles in the absence of DNA. The conformation of DNA remains intact in the process as evident from circular dichroism (CD) spectra. The UV–Vis spectrum exhibits a broad absorption peak at 520–900 nm, for a combined effect of the gold surface plasmon and π band to localized polaron band transition of DNA-doped PANI. Both the dendritic Au–PANI–DNA and the spherical Au–PANI systems emit two peaks for excitation with radiation of 300 nm and the intensity ratio of the emission and FRET peak is higher in the dendritic Au–PANI than that in the spherical Au–PANI system. The dc-conductivity values of spherical Au–PANI and dendritic Au–PANI–DNA systems are 1.2 × 10 −10 and 1.7 × 10 −8 S/cm at 30 °C, respectively.

Oxygen-Vacancy-Related Dielectric Relaxation and Electric Conduction in KNbO3 Ceramic

The temperature and frequency dependent dielectric and conductivity properties were measured on as-sintered as well as oxygen annealed KNbO3 ceramics. The results show that in addition to phase transition peaks, well defined relaxation peaks are observed in the temperature range 450–700 K. These peaks could be suppressed by annealing the samples in the oxygen atmosphere. The dc-conductivity and maximum dielectric constant values decreases after oxygen annealing. The results are explained on the basis of defect concentration and their dynamics.

Effect of positional density on DC conductivity of bamboo fibre

In the present communication, the effect of positional density on the DC electrical conductivity of bamboo fibres was studied. A comparative study was made between the DC conductivity behavior of bamboo fibres taken from upper and lower portions of bamboo. Four samples from each portion going from centre to periphery were taken. Bamboo fibers taken from the upper portion were less dense, hence showing lower values of DC conductivity. In spite of the lower portion of bamboo being more dense, it showed higher values of DC conductivity, which is attributed to moisture content. Bamboo fibres from centre to periphery were taken from the strips cut at 2 mm distance from centre. The DC conductivity increased from centre to periphery. A theoretical model was developed and verified with the experimental results. It was also found that experimentally determined σdc values of bamboo fibres taken from different radial locations from center to periphery were in agreement with those values obtained from the proposed equation.

Role of oxygen vacancies on relaxation and conduction behavior of KNbO3 ceramic

The temperature and frequency dependent dielectric and conductivity properties were measured on as-sintered as well as oxygen annealed KNbO3 ceramics. The results show that in addition to phase transition peaks, well defined relaxation peaks are observed in the temperature range 450–700 K. These peaks could be suppressed by annealing the samples in the oxygen atmosphere. The dc conductivity and maximum dielectric constant values decreases after oxygen annealing. Activation energy, calculated from dielectric relaxation and conductivity data on the samples, suggests that both the processes are due to doubly charged oxygen vacancies formed during sintering process. Dielectric relaxation is attributed to the hopping of oxygen vacancies in the six equivalent sites in perovskite structure. The dielectric and conductivity behaviors are influenced by the density of the samples. The results are explained on the basis of defect concentration and their dynamics.

Particle size distribution, magnetic permeability and dc conductivity of nano-structured and bulk LiNiZn–ferrite samples

Nanoparticles of Li 0.1(Ni 1− x Zn x ) 0.8Fe 2.1O 4 ( x=0–1.0) were prepared by a chemical co-precipitation method. A part of the precipitated powders was sintered at 1473 K for 2 h to obtain bulk samples via increasing the particle sizes. The particle size distribution, dc conductivity and magnetic permeability were investigated for the nano-structured samples and their bulk counterparts. The permeability as a function of temperature revealed the size effect of nano-structure in agreement with the literature. In some of the samples the permeability was almost constant over a considerable range of temperature, which may be useful in practical applications that require stability. Moreover, the nano-size structure caused a significant decrease in dc conductivity values.

RNA−Poly(o-methoxyaniline) Hybrid Templated Growth of Silver Nanoparticles and Nanojacketing: Physical and Electronic Properties

Three nanobiocomposites (PRAg31, PRAg11, and PRAg13; the numbers indicate the weight ratios of poly(o-methoxyaniline) (POMA) and ribonucleic acid (RNA), respectively), produced from the same amount of POMA (P) and silver nitrate (AgNO(3)) with differing proportions of RNA (R) are prepared by aging the aqueous solutions of the mixture for 3 weeks at 30 degrees C. The scanning and transmission electron microscopy (SEM and TEM) indicate Ag nanoparticle formation on the hybrid fiber surface and in the PRAg31 system the hybrid fibrils become coated with metallic Ag, the phenomenon being termed as "nanojacketting". The circular dichroism (CD) spectra indicate a small distortion of RNA conformation from A helix toward B helix. FTIR and UV-vis spectra suggest that POMA (emeraldine base, EB) being doped by Ag(+) become oxidized to its pernigraniline base (PB) form and reduce Ag(+) to metallic Ag. The Ag nanoparticles thus produced become stabilized on the fibril surface by co-ordination through nitrogen atoms of POMA (PB) chains. The much slower red shift of pi band to polaron band transition peak in PRAg31 than that of the other two nanobiocomposites is indicative of difficulty in conformational transitions of POMA chain in the "nanojacketted" hybrid fibrils. The dc-conductivity values of the nanobiocomposites are two orders higher than that of the pure POMA-RNA hybrids. The PRAg31 system exhibits rectification property in the I-V characteristic curves and a probable explanation based on the feasibility of p-n junction formation arising from the transfer of lone pair of electrons of nitrogen of POMA (p-type) to the Ag nanoparticles (n-type) has been offered.