Increase In Dc Conductivity Research Articles

Electrical Conductivity and Optical Properties of Polyaniline Intercalated Graphite Oxide Nanocomposites

Layered graphite oxide is used as host material for the synthesis of conducting polymer intercalated nanocomposites. Powder X-ray diffraction, Fourier transform infrared, and UV-VIS absorption spectra indicate the formation of polyaniline within the interlamellar spaces of graphite oxide. The red shift of UV-VIS absorption associated with graphite oxide is found. The direct current (dc) conductivity increases by about three orders of magnitude compare with pristine graphite oxide. The temperature dependence dc conductivity of the nanocomposite follows Mott's three-dimensional variable range hopping. The alternating current (ac) conductivity suggests correlated barrier hopping of conduction process. The conductivity relaxation time varies in the range of 10(-5)-10(-7) Sec.

Electronic relaxation in zinc iron phosphate glasses

The electrical and dielectric properties of 10ZnO–30Fe2O3–60P2O5 (mol%) glasses, melted at different temperatures were measured by impedance spectroscopy in the frequency range from 0.01Hz to 3MHz and over the temperature range from 303 to 473K. It was shown that the dc conductivity strongly depends on the Fe(II)/[Fe(II)+Fe(III)] ratio. With increasing Fe(II) ion content from 17% to 37% in these glasses, the dc conductivity increases. Procedure of scaling conductivity data measured at various temperatures into a single master curve is given. The conductivity of the present glasses is made of conduction and conduction-related polarization of the polaron hopping between Fe(II) and Fe(III), both governed by the same relaxation time, τ. The high frequency dispersion in electrical conductivity arises from the distribution in τ caused by the disordered glass structure. The evolution of the complex permittivity as a function of frequency and temperature was investigated. At low frequency the dispersion was investigated in terms of dielectric loss. The thermal activated relaxation mechanism dominates the observed relaxation behavior. The relationship between relaxation parameters and electrical conductivity indicates the electronic conductivity controlled by polaron hopping between iron ions.

Study of the effective parameters on mechanical and electrical properties of carbon black filled PP/PA6 microfibrillar composites

In this study the electrical and mechanical properties of microfibrillar polypropylene (PP)/polyamide6 (PA6) blend filled with super conductive carbon black (CB) have been investigated. In situ microfibrillar PP/PA6 composites filled with CB are produced using a single screw extruder equipped with a spinneret. Glycidyl methacrylate (GMA) grafted polypropylene (PP-g-GMA) is used as the compatibilizer. To investigate the effects of extensional flow on the microstructure, electrical and mechanical properties, three adaptors with various convergence angles were designed, prepared and applied between the extruder and the spinneret. To optimize the effects of processing and material parameters on the electrical and mechanical properties, the Taguchi method of experimental design is used. Material and processing factors which are studied include: concentration of PA6, compatibilizer level, CB concentration, drawing speed of melt spinning line, adaptor angle, order of mixing and temperature profile along the extruder. The results show an increase in DC conductivity of up to 10 11 times in comparison with pure PA6, by increasing the concentration of CB, drawing speed, adaptor angle and optimizing other parameters. By optimizing processing and material factors studied here, strength of microfibrillar structured composites is increased of up to 80% in comparison to pure PP.

Electrical transport properties of poly[2-methoxy-5-(2′-ethyl hexyloxy)-1,4-phenylene vinylene] thin films doped with acridine orange dye

The electrical properties of poly[2-methoxy-5-(2′-ethyl hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) films were studied at different concentrations of acridine orange (AO) dye in the temperature range (293–416 K). MEH-PPV was dissolved in n-butyl acetate and was doped with different concentrations of AO dye solution. The MEH-PPV films were prepared by spin-coating technique with the speed of 1000 rpm. For conductivity measurements, Cu electrode contacts in planar configuration were made on the top surface of the film by RF sputtering. The DC conductivity and steady-state photoconductivity measurements were performed on these spin-coated thin films. It was observed that the doping of AO dye reduces the electrical resistivity as well as activation energies and enhances DC conductivity and photoconductivity. An increase in DC conductivity can be explained in terms of hopping conduction in the wide range of localised states. Photoconductivity measurements are useful in determining the nature of optical charge generation and transport in conjugated polymers. The value of T 0 (measurement of disorderness) is in good agreement with the XRD spectra, which depicts the amorphous nature of the pure MEH-PPV film. Photocurrent dependence on incident radiation has also been observed which follows the power law ( I ph∝ F γ ). This dependence shows that the recombination with in the localised state is predominant.

Ion irradiation induced electrochemical stability enhancement of conducting polymer electrodes in supercapacitors

We have explored the effects of 120 MeV Si9+ ion beam irradiation on the electrical, structural and capacitance properties of HClO4 doped polyaniline conducting polymer electrodes. The swift heavy ion (SHI) irradiated conducting polymer films exhibited upto 70% increase in crystallinity and dc conductivity with improved surface morphology. The supercapacitors fabricated with ion irradiated polyaniline electrodes showed enhancement of electrochemical stability and slight decrease in internal resistance, which could be attributed to the removal or stabilization of the volatile surface groups and decrease in surface roughness upon ion irradiation. Fluence dependent small increase in coulombic efficiency is observed in the supercapacitors with SHI irradiated polymer electrodes because of the increase in dc conductivity of the polymer electrodes upon irradiation.

Dielectric properties of pyrochlore (Bi1.5Zn0.5)(Nb0.5M1.5)O7 (M=Ti, Sn, Zr, and Ce) dielectrics

Pyrochlore type systems with generic formula (Bi1.5Zn0.5)(Nb0.5M1.5)O7 (M=Ti, Sn, Zr, and Ce) have been synthesized to investigate the influence of M on the dielectric properties. It was found that the incorporation of Sn or Ce resulted in a reasonably reduced dielectric constant. The incorporation of Zr and Ce has led to an appreciable increase in dc conductivity in high temperature. The dc conductivity diminishes as the size of M grows. Dielectric constants, temperature coefficient, and dc conductivity of series ceramics were studied and the relationships among composition, crystal structure, and properties were discussed.

Influence of temperature and frequency on the electrical conductivity and the dielectric properties of nickel phthalocyanine

Abstract The temperature and frequency dependence of the AC conductivity σac(ω), the dielectric constant e′(ω) and the dielectric loss e″(ω) were studied on pellet samples of nickel phthalocyanine (NiPc) with evaporated ohmic Au electrodes in the frequency range from 20 kHz to 10 MHz and within the temperature range from 303 to 600 K. The DC conductivity σdc has also been measured in the considered range of temperature. Two temperatures – induced changes in the thermal activation energy ΔE have been observed. For T ⩽ 435 K, ΔE1 = 0.322 eV; for 435 K ⩽ T ⩽ 525 K, ΔE2 = 0.497 eV; for T ⩾ 525 K, ΔE3 = 0.703 eV. These variations in the activation energy were attributed to a partial phase transformation from α- to β-NiPc phase and as a change from extrinsic to intrinsic conduction mechanism. The AC conductivity σac(ω) showed temperature independence and it has been found to vary with angular frequency as ωs with the index s ⩽ 1 suggesting a hopping conduction mechanism at low temperatures and high frequency. At higher temperatures and lower frequencies a free-band conduction mechanism was observed. Both the dielectric constant e′(ω) and the dielectric loss e″(ω) increased with temperature and decreased with frequency in the investigated ranges. Such characteristics, reveal that the tested organic NiPc exists in the form of molecular dipoles which remain frozen at low temperature, whereas at higher temperatures, when the dipoles attaining rotational freedom, the dielectric constant was found to decrease with increasing frequency and increase with increasing temperature. The increase in the dielectric loss e″(ω) with increasing temperature at low frequencies can be understood in terms of an increase in DC conductivity.

Effect of silver on dielectric properties of the Se–Te system

The DC conductivity and dielectric parameters of the system of a-Se 96− x Te 4Ag x ( x = 0 , 4, 8, 12 and 16) glasses have been investigated. The frequency and temperature dependence of the dielectric constants ( ε ′ ) and the dielectric loss ( ε ″ ) have been studied in the frequency range from 120 Hz to 100 kHz and the temperature range 300–390 K. Dielectric dispersion is observed when Ag is incorporated into the a-Se–Te system in the entire temperature range. These results are explained on the basis of DC conduction loss and dipolar-type dielectric dispersion. It is also observed that the DC conductivity increases and the activation energy decreases upon increasing Ag content in the system.

Effect of alkaline-earth ions on the dynamics of alkali ions in bismuthate glasses

The effect of alkaline earth ions on the dynamics of ${\mathrm{Li}}^{+}$ ions in bismuthate glasses has been studied in the temperature range $353--503\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and in the frequency range $10\phantom{\rule{0.3em}{0ex}}\mathrm{Hz}--2\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$. The dc conductivity increases and activation energy decreases with the increase of a particular alkaline earth content for the glasses with a fixed alkali content. The increased modification of the network due to the increase in alkaline earth content in the compositions is responsible for the increasing conductivity. Also the compositions with smaller alkaline earth ions were found to exhibit higher conductivity. Although the conductivity increases with the decrease of ionic radii of alkaline earth ions, the activation energy shows a maximum for the Sr ion. The electric modulus and the conductivity formalisms have been employed to study the relaxation dynamics of charge carriers in these glasses. The alkali ions were observed to change their dynamics with the change of the alkaline earth ions. The same anomalous trend for activation energy for the conductivity relaxation frequency and the hopping frequency was also observed for glasses containing SrO. It was also observed that the mobile lithium ion concentrations are independent of nature of alkaline earth ions in these glasses.

Compositional dependence of the physical properties of Ge 1Se 9− xTe x amorphous system

The compositional dependence of electrical conductivity, optical absorption and refractive index of thin films of the Ge 1Se 9− x Te x amorphous system in the range 0 ≤ x ≤ 4 is investigated. The obtained results were correlated with the character of the chemical bond for the prepared compositions through a study of parameters such as average heat of atomization and average coordination number. The activation energy for electrical conduction decreases with Te content and consequently there is an increase in DC conductivity with Te content. A shift in the absorption edge towards the lower energy side of spectrum was observed due to the increase of Te content and a consequent decrease in the optical energy gap. The effect of γ-radiation up to a dose of 10 Mrad on the optical and electrical properties was also studied.

Dielectric behavior and impedance spectroscopy of bismuth iron phosphate glasses

The electrical and dielectrical properties of Bi2O3–Fe2O3–P2O5 glasses were measured by impedance spectroscopy in the frequency range from 0.01Hz to 4MHz and over the temperature range from 303 to 473K. It was shown that the dc conductivity strongly depends on the Fe2O3 content and Fe(II)/Fetot ratio. With increasing Fe(II) ion content from 17% to 34% in the bismuth-free 39.4Fe2O3–59.6P2O5 and 9.8Bi2O3–31.7Fe2O3–58.5P2O5 glasses, the dc conductivity increases. On the other hand, the decrease in dc conductivity for the glasses with 18.9mol% Bi2O3 is attributed to the decrease in Fe2O3 content from 31.7 to 23.5mol%, which indicates that the conductivity for these glasses depends on Fe2O3 content. The conductivity for these glasses is independent of the Bi2O3 content and arises mainly from polaron hopping between Fe(II) and Fe(III) ions suggesting an electronic conduction. The evolution of the complex permittivity as a function of frequency and temperature was investigated. At low frequency the dispersion was investigated in terms of dielectric loss. The thermal activated relaxation mechanism dominates the observed relaxation behavior. The relationship between relaxation parameters and electrical conductivity indicates the electronic conductivity controlled by polaron hopping between iron ions. The Raman spectra show that the addition of up to 18.9mol% of Bi2O3 does not produce any changes in the glass structure which consists predominantly of pyrophosphate units.

Study of 160 MeV Ni 12+ ion irradiation effects on electrodeposited polypyrrole films

Conducting polymer polypyrrole thin films doped with LiCF 3SO 3, [CH 3(CH 2) 3] 4NBF 4 and [CH 3(CH 2) 3] 4NPF 6 have been electrodeposited potentiodynamically on ITO coated glass substrate. The polymer films are irradiated with 160 MeV Ni 12+ ions at three different fluences of 5 × 10 10, 5 × 10 11 and 3 × 10 12 ions cm −2. An increase in dc conductivity of polypyrrole films from ∼100 S/cm to ∼170 S/cm after irradiation with highest fluence is observed in four-probe measurement. X-ray diffractogram shows increase in the crystallinity of the polypyrrole films upon SHI irradiation, which goes on increasing with the increase in fluence. Absorption intensity increase in the higher wavelength region is observed in the UV–Vis spectra. The SEM studies show that the cauliflower like flaky microstructure of the surface of polypyrrole films turns globular upon SHI irradiation at fluence 5 × 10 11 ions cm −2 and becomes smooth and dense at the highest fluence used. The cyclic voltammetry studies exhibit that the redox properties of the polypyrrole films do not change much on SHI irradiation.

Electrical Properties and DC Conductivity of Phosphoric Acid Doped TGS Single Crystals

Properties of phosphoric acid (H3PO4) doped triglycine sulfate (TGSP) grown from aqueous solutions containing 0.1 to 0.5 moles of H3PO4 have been investigated. Composition analysis indicates a very low incorporation of phosphoric acid in the crystal lattice. Large sized crystals of dimension (70 mm × 40 mm × 25 mm) suitable for IR detector are obtained with 0.2 moles of H3PO4 in solution. The presence of both zwitter and glycinium ions in TGSP is explained through FT-IR analysis. The dielectric dispersion of TGSP crystals in the frequency range from 100 Hz to 100 KHz, and in the temperature range 27 to 65°C has been analyzed. The increased dielectric dispersion in TGSP crystals is found to be related to the increase in dc conductivity, and the increased domain boundary relaxation time. Doped crystals show a broad transition and suppressed value of peak dielectric constant.

Structural and Electrical Properties of the Perovskite Oxide Sr2FeNbO6

The mixed perovskite Sr2FeNbO6 has been shown to have a tetragonal structure with space group I4/m (87), a = 5.6078(1) Å, c = 7.9658(1) Å, V = 250.51(1) Å3 according to electron and X-ray diffraction. The material is redox stable and maintains its structure in a reducing atmosphere. After reducing in 5% H2 at 900 °C for 6 h, Sr2FeNbO6 still exhibits a tetragonal structure with space group I4/m (87), a = 5.6051(1) Å, c = 7.9644(1) Å, V = 250.22(1) Å3, i.e., with a slightly higher degree of tetragonality. A lattice volume contraction of 0.12% was observed during the reduction, which may be attributed to the loss of lattice oxygen. TGA analysis indicates that Sr2FeNbO6 starts to lose oxygen at 300 °C and the total weight loss is about 0.2 wt % from room temperature to 950 °C in 5% H2. The morphology of this material does not significantly change on reduction according to SEM observation. The conductivities of this material in air and 5% H2 were 3.13 × 10-2 and 2.39 S/cm, respectively at 900 °C. The apparent conduction activation energy of Sr2FeNbO6 in air is 0.74 ± 0.02 eV between 400 and 900 °C and in 5% H2 is 0.28 ± 0.02 eV between 140 and 560 °C and 0.58 ± 0.02 eV between 560 and 900 °C, indicating it is a semiconductor in both atmospheres. The increase of dc conductivity of Sr2FeNbO6 at low p(O2) indicates n-type electronic conduction. The dc conductivity of Sr2FeNbO6 at low p(O2) exhibits a p(O2)-1/6 dependence that is interpreted by a simple defect chemistry model.

Synthesis, Characterization, and Conductivity Studies of Poly- o-Methoxyaniline Intercalated into V 2O 5 Xerogel

In this work we study the conductivity properties of poly- o-methoxyaniline/V 2O 5 intercalation compounds obtained through intercalative polymerization of o-methoxyaniline with V 2O 5· nH 2O in hydrogel form and by reacting directly with V 2O 5 film in de-hydrated form (xerogel). These new compounds were characterized using Fourier-transform infrared and ultra-violet/visible spectroscopies, electron paramagnetic resonance, elemental analysis (C, N, H), thermogravimetric analysis, scanning electron microscopy, dc-conductivity and powder X-ray diffraction. For samples formed from V 2O 5 xerogel in film form, an increase in dc-conductivity and a decrease in the thermal activation energy in comparison with pure matrix was observed. The increase in conductivity is attributed to an increase of carrier density in the vanadium oxide lattice and the contribution of polarons from the polymer. On the other hand, for the intercalation compound obtained with V 2O 5· nH 2O in hydrogel form presents a very low room temperature conductivity value. The decrease in conductivity is due to the lack of connectivity of the various parts that compose the material.

Electronic conductivity in Na 2O–FeO–P 2O 5 glasses

dc and ac conductivity were studied in 50P 2O 5–(50− x)FeO– xNa 2O and 50P 2O 5–(50− x)FeO– xCaO (7< x<20; in mol%) glasses. It is shown that the replacement of CaO by Na 2O caused rather small increase in dc and ac conductivity. The conduction in these glasses is predominantly electronic controlled by electron hopping between Fe(II) and Fe(III) sites. Internal friction has been used to study the relaxation phenomena caused by electronic and ionic migration in sodium–iron phosphate glasses. Two peaks attributed to these processes were observed on internal friction spectra in the temperature range of 125–500 K at a frequency of about 1 Hz.

Dielectric relaxation and the conformer equilibrium in the liquid and glassy states of β-d-fructose

To investigate the ionic and molecular dynamics in the liquid and glassy states of β-d-fructose, its dielectric relaxation spectra (12Hz-500kHz) and dynamic heat capacity (3.33mHz) have been measured from 5K above its melting point through the vitrification range, by allowing sufficient time for attainment of the conformer (or chemical) equilibria. Effects of the change in the conformer population on thermal cycling has been further studied. The dielectric behavior of liquid β-d-fructose is characteristically different from that of other molecular liquids in three ways: (i) the contribution to orientation polarization associated with the fast relaxation process, which persists in the glassy state, is relatively high in the liquid state of β-d-fructose; (ii) this contribution decreases with temperature exceptionally rapidly on cooling; and (iii) the difference in the rates of the two process is exceptionally large. The dynamic heat capacity change through the vitrification region is ∼160J/(molK), and is spread over ∼20K range, and the enthalpy relaxation time is ∼50s at 383K. Transformation of β-pyranose to other conformers and other conformer transformation equilibria change on thermal cycling with the result that the overall relaxation rate increases at T>315K and decreases at T<315K. The relaxation spectrum becomes broader, the dc conductivity increases and the rate of the Johari–Goldstein relaxation whose Arrhenius energy is 42.1kJ/mol increases.

Large paramagnetic effect and related DC conductivity change in semiconducting glasses under high pressure

New electron properties, particularly, magnetic properties are predicted to be induced under high pressures in semiconducting glasses. The rapid increase in the concentration of the positive-U centres, single-spin electrons (holes), with increasing pressure is established, which can give rise to their delocalization, at high pressures in the glasses. The resulting very large para-magnetic effect can drastically change the magnetic properties, and a considerable increase of DC conductivity can also occur. These new properties can be tested experimentally.

Thermal and substituting effects of transition metal ions (Cr 3+ or Mn 4+) on physical properties of (V 2O 5) 0.8-(P 2O 5) 0.2 glass

The effect of introducing transition metal ions of Cr 3+ and M 4+ annealing on the physical properties of (V 2O 5) 0.8-(P 2O 5) 0.2 glass was studied. Three glasses of (V 2O 5) 0.8-(P 2O 5) 0.2, (V 2O 5) 0.7-(P 2O 5) 0.2-(MnO 2) 0.1 and (V 2O 5) 0.7-(P 2O 5) 0.2-(Cr 2O 3) 0.1 have been prepared by melting in an open crucible. The thermal analysis (DTA and TG) of the glasses were recorded. The glass transition ( T g) and the crystallization temperature ( T c) were found to be composition dependent. The X-ray diffraction confirmed the amorphous nature for the virgin samples and the formation of some crystalline phases for annealed samples at 673 K for 24 h. The FTIR spectra of the virgin and annealed samples have been recorded and briefly discussed. The density and the molar volume of the glasses were found to be changed with the composition and the heat treatment of the glasses. The temperature dependence on the dc-electrical conductivity measurements for these glasses is studied over a temperature range from room temperature to 573 K. It was found that the dc-conductivity increases by annealing and decreases by substituting the vanadium by Cr 3+ or Mn 4+. This is explained on the basis of the change occurring in redox pairs ratio during the preparation and the heat treatment of the samples. Electrical conduction was interpreted on the basis of polaron hopping mechanism. The I– V characteristics were measured at room temperature. The I– V behavior shows three regions of conduction, namely, high resistance state (OFF state), turnover point with zero-differential resistance region (∂ V/∂ I = 0) and a differential negative resistance region. The turnover point is dependent on composition. The data in the range up to turnover point are discussed on the basis of an electrothermal process. All results are discussed and correlated on the basis of hopping mechanism between redox pairs.

A study of polarization mechanisms in sodium iron phosphate glasses by partial thermally stimulated depolarization current

The electrical polarization of sodium iron phosphate glasses, containing from 5.3 to 14.9 mol% Na 2O and with a constant Fe/P ratio of 0.67, was investigated by thermally stimulated polarization current (TSPC), and by depolarization current (TSDC) techniques. The partial TSDC measurements showed a group of distributed partial peaks, P 1, whose maximum ranged from 186 to 227 K. A group of higher temperature peaks, P 2, was found in a narrower temperature range from 257 to 264 K, with an additional process, P 2 ′, at about 240 K. The process P 1 was caused by a dipolar relaxation showing a compensation with the compensation point at T c=247 K. The physical meaning of the compensation point could not be related to analogous phenomena in organic polymers. The higher temperature peaks represent space charge relaxations greatly affected by the increase in Na 2O content and influenced by the remaining polarization and conductivity. The most likely cause for the electrical relaxation was an interaction between the Na + ions and the P–O − bonds. Increasing the Na + concentration caused an increase in the TSDC peaks and a slight increase in dc conductivity.