Characterization and transport properties of intercalated polypyrrole-vanadium pentoxide xerogel nanocomposite

Layered vanadium pentoxide (V₂O₅) xerogel is used as host material for the synthesis of conducting polypyrrole intercalated nanocomposites. Powder X-ray diffraction spectra show the increase of interlayer space of V₂O₅ xerogel indicating the formation of polypyrrole in the interlayer space of the host. Thermal stability of intercalated polypyrrole is superior compared to bulk polypyrrole. Dc conductivity of the xerogel follows Arrhenius type temperature dependence while the nanocomposites exhibit Mott's three-dimensional variable range hopping. Optical band gap decreases with intercalation of polypyrrole.     

Effect of vanadium pentoxide on the electrical, dielectric, and optical properties of poly(vinyl alcohol)/vanadium pentoxide nanocomposites

In this study, the effect of vanadium pentoxide (V₂O₅) on the electrical, dielectric, and optical properties of poly(vinyl alcohol) (PVA)/V₂O₅ nanocomposites was examined. The PVA/V₂O₅ nanocomposites were prepared by solution mixing, followed by film casting. The as-prepared films were characterized by X-ray diffraction, thermogravimetric analysis, as well as impedance spectroscopy. The obtained results indicated that, with increasing V₂O₅ content, the PVA composite exhibits considerable vestige of crystallization and the PVA peaks become broader. The electrical conductivity, σ _dc, increases as the temperature and the dopant level of V₂O₅ increase. The frequency dependence of alternating current conductivity was governed by a critical frequency, ω _p. The values of ω _p are found to be thermally activated. The loss tangent (tan δ) shows a peak with the frequency, which indicates a dielectric relaxation in these composites with relaxation time decreases with both temperature and V₂O₅ content increase. Optical absorption edge and direct and indirect energies for all mentioned samples were determined and discussed.     

Dielectric relaxation in vanadium phosphate glasses

An asymmetric distribution of relaxation times has been inferred from an increase in the Cole-Cole distribution parameter α with increasing values of ωτ in 62% v₂O₅–38% P₂O₂ glass. The conventional Debye type relaxation loss peaks in the frequency range 10²–10⁵ Hz are observed in this sample above 85°K. The extrapolated values of dielectric constant and relaxation time below 100°K seem unexpectedly large while the high temperature extrapolated values of ?' are close to ?_∞ as expected. Probably the conventional dielectric loss peaks are observed only above a critical temperature at which the carriers gain sufficient energy to be excited to the conduction band edge. Below this temperature hopping of carriers within kT of the Fermi level may dominate and conventional Debye type dielectric loss peaks may lose their significance as envisaged in the models of frequency dependent ac conductivity.     

Grain size effects on dynamics of Li-ions in Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> glass-ceramic nanocomposites

Li₃V₂(PO₄)₃ glass-ceramic nanocomposites, based on 37.5Li₂O-25V₂O₅-37.5P₂O₅ mol% glass, were successfully prepared via heat treatment (HT) process. The structure and morphology were investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM). XRD patterns exhibit the formation of Li₃V₂(PO₄)₃ NASICON type with monoclinic structure. The grain sizes were found to be in the range 32–56 nm. The effect of grain size on the dynamics of Li⁺ ions in these glass-ceramic nanocomposites has been studied in the frequency range of 20 Hz–1 MHz and in the temperature range of 333–373 K and analyzed by using both the conductivity and modulus formalisms. The frequency exponent obtained from the power law decreases with the increase of temperature, suggesting a weaker correlation among the Li⁺ ions. Scaling of the conductivity spectra has also been performed in order to obtain insight into the relaxation mechanisms. The imaginary modulus spectra are broader than the Debye peak-width, but are asymmetric and distorted toward the high frequency region of the maxima. The electric modulus data have been fitted to the non-exponential Kohlrausch–Williams–Watts (KWW) function and the value of the stretched exponent β is fairly low, suggesting a higher ionic conductivity in the glass and its glass-ceramic nanocomposites. The advantages of these glass-ceramic nanocomposites as cathode materials in Li-ion batteries are shortened diffusion paths for Li⁺ ions/electrons and higher surface area of contact between cathode and electrolyte.     

Transport properties of lead phosphate glass doped by cobalt,vanadium and chromium oxides

The electrical transport properties were investigated of a glass system of basic composition 50?mol. % Pb₃O₄–50?mol. % P₂O₅ containing CoO, Cr₂O₃ or V₂O₅ dopanys. The ac conductivity and the thermoelectric power were measured as a function of temperature. Properties such as dielectric constant, loss factor tangent and electrical conductivity are reported in the frequency range 200?Hz–100?kHz and temperature range 300–450?K. The variation in electrical conductivity with temperature was found to depend on the types of transition metal ions involved. The temperature dependence of the frequency exponent, s, was analyzed using different theoretical models. The variation of the thermoelectric power with temperature indicated the presence of more than one conduction mechanism for the investigated samples. This result was confirmed with the results of the dielectric properties at different frequencies. The introduction of cobalt ions in glass formers improves the electrical properties of non-crystalline ionic conductors.     

Transport and dielectric properties of V2O5-MnO-TeO2 glasses

The frequency (1-10 kHz) and temperature (80-350 K) dependences of the ac conductivity and dielectric constant of the V₂O₅-MnO-TeO₂ system, containing two transition-metal ions, have been measured. The dc conductivity _dc measured in the high-temperature range (200-450 K) decreases with addition of the oxide MnO. This is considered to be due to the formation of bonds such as V--O--Mn and Mn--O--Mn in the glass. The conductivity arises mainly from polaron hopping between V^4+M and V⁵⁺ ions. It is found that a mechanism of adiabatic small-polaron hopping is the most appropriate conduction model for these glasses. This is in sharp contrast with the behaviour of the Mn-free V₂O₅-TeO₂ glass, in which non-adiabatic hopping takes place. High-temperature conductivity data satisfy Mott's small-polaron hopping model and also a model proposed by Schnakenberg in 1968. A power-law behaviour ( _ac = Aω^s , with s < 1) is well exhibited by the ac conductivity σ_ac data of these glasses. Analysis of dielectric data indicates a Debye-type relaxation behaviour with a distribution of relaxation times. The MnO-concentration-dependent σ_ac data follow an overlapping large-polaron tunnelling model over the entire range of temperatures studied. The estimated model parameters are reasonable and consistent with changes in composition.     

Dielectric dispersion in PbO-Sb2O3-As2O3:V2O5 glasses

Dielectric properties, viz. dielectric constant ε′, loss tan δ and a.c conductivity σ_ac (over a wide range of frequency and temperature) and dielectric breakdown strength of PbO-Sb₂O₃-As₂O₃ glasses doped with V₂O₅ (ranging from 0 to 0.5 mol%) are studied. Analysis of these results, based on optical absorption and ESR spectra, indicates that the insulating strength of the glasses is comparatively high when the concentration of V₂O₅ is about 0.3 mol% in the glass matrix.     

Synthesis of solid solutions of Mn and Bi substituted V2O5 and substitutional effect in structural and optoelectronic behavior

V₂O₅ is an attractive material with enormous technological applications such as cathode material in lithium batteries and electrochromic displays. Mn and Bi substitution in vanadium pentoxide (V₂O₅) was done by conventional solid state reaction technique with different composition. The chemical composition, structural and optical properties were investigated employing different techniques, such as XRD, SEM and UV-Vis Spectra. XRD studies exhibit the predominant (0 0 1) peak of orthorhombic phase. SEM image shows the uniformity of the material synthesized. Variable transmittance is exhibited by samples doped with different percentages of dopants. The dielectric property studies and ac conductivity measurements were carried out by Hioki LCR Hi-Tester.     

Impact of MoO3 concentration,frequency and temperature on the dielectric properties of zinc phosphate glasses

Phosphate glasses with the chemical composition of 47P₂O₅–24ZnO-(29-x)Na₂O-xMoO₃, x = 0, 2, 4, 6, 8 and 10, have been prepared using the melt quenching technique. Dielectric properties of these phosphate glasses are carried out in the frequency range from 1 to 100 kHz at different temperatures. Dielectric parameters such as dielectric constant ε′, dielectric loss ε′′ and ac conductivity of the investigated glasses have been evaluated. The dependences of these dielectric parameters on frequency, composition and temperature have been discussed. It is found that dielectric constant decreases with increasing frequency due to the reduction of space-charge polarization and dipole polarization. The dependence of ac conductivity on the MoO₃ content indicates a competition between electronic and ionic conduction. The temperature dependence of the dielectric parameters reveals a rising trend of the dielectric parameters with temperature. This rising trend is indicated due to the increase of the amplitude of the thermal vibration of the charge carriers which facilitates the electron hopping and drifting of the mobile ions. The linear trend of the ln(σ_ac)-1000/T plot indicates that ac conductivity of the investigated glasses is thermally-activated transport process and follows the Arrhenius equation. The activation energy and its composition dependence have been reported.     

Structural and dielectric properties of Ba3V2O8 ceramics

Polycrystalline sample of Ba₃V₂O₈ was prepared by a high-temperature solid-state reaction technique. Preliminary X-ray diffraction (XRD) analysis confirms the formation of single-phase compound of hexagonal (rhombohedral) crystal structure at room temperature. Microstructural analysis by scanning electron microscope (SEM) shows that the compound has well defined grains, which are distributed uniformly throughout the surface of the sample. The dielectric properties of the compound studied in a wide frequency range (10²–10⁶ Hz) at different temperatures (25–400 °C), exhibits that they are temperature dependent. Detailed analysis of impedance spectra showed that the electric properties of the material are strongly dependent on frequency and temperature. The activation energy, calculated from the temperature dependence of ac conductivity (dielectric data), was found to be 0.23 eV at 50 kHz in the higher temperature region.     

Dielectric relaxation and ac conductivity behavior of carboxyl functionalized multiwalled carbon nanotubes/poly (vinyl alcohol) composites

We study the dielectric relaxation and ac conductivity behavior of MWCNT-COOH/Polyvinyl alcohol nanocomposite films in the temperature (T) range 303–423 K and in the frequency (f) range 0.1 Hz–1 MHz. The dielectric constant increases with an increase in temperature and also with an increase in MWCNT-COOH loading into the polymer matrix, as a result of interfacial polarization. The permittivity data were found to fit well with the modified Cole-Cole equation. Temperature dependent values of the relaxation times, free charge carrier conductivity and space charge carrier conductivity were extracted from the equation. An observed increment in the ac conductivity for the nanocomposites was analysed by a Jonscher power law which suggests that the correlated barrier hopping is the dominant charge transport mechanism for the nanocomposite films. The electric modulus study revealed deviations from ideal Debye-type behavior which are explained by considering a generalized susceptibility function. XRD and DSC results show an increase in the degree of crystallinity.     

Dielectric properties for the ordered-perovskite cuprate Sr2Cu(Re0.69Ca0.31)O6

Dielectric properties are reported on polycrystalline cubic ordered-perovskite cuprate Sr₂Cu(Re_0.69Ca_0.31)O₆ in the frequency range 10 Hz-100 kHz at temperature from 300 to 500 K. Both the dielectric permittivity and dielectric loss factor are found to be frequency and temperature dependent. The enhanced value of the low frequency dielectric permittivity is associated to ionic polarization and interfacial phenomena. The material is found to possess significantly high dielectric permittivity. The calculated ac conductivity suggests semiconducting behaviour for the Sr₂Cu(Re_0.69Ca_0.31)O₆.     

Transport and dielectric properties of thin polycrystalline CoO films

Transport and dielectric properties of polycrystalline CoO films were studied as functions of the applied field, frequency and temperature. TheI–V plots showed that the Poole-Frenkel field emission mechanism is responsible for conduction at fields>10⁵ V/cm. The ac conductivity σ(ω), the imaginary part of the dielectric constantε ₂, and tan δ plots as functions of frequency revealed three dispersion regions. The σ(ω) andε ₂ frequency dependence indicates a non-adiabatic hopping of charge carriers at low frequencies and adiabatic hopping at high frequencies. The activation energy of a dielectric oscillator is 0.15 eV. Work supported by the Office of Naval Research.     

Influence of iron ions on dielectric properties of the PbO–Bi2O3–B2O3 glass system

PbO–Bi₂O₃–B₂O₃ glasses containing small concentrations of Fe₂O₃ (0–1 mol%) were subject to dielectric studies (dielectric constant ε′; loss tan δ; and ac conductivity σ _ac) over a wide range of frequency and temperature. From spectroscopic (infrared, optical absorption and ESR spectra) and magnetic susceptibility studies, variations in these properties with dopant ion concentration were analyzed in terms of different oxidation states and iron ion environment in the glass network.     

Ion conductivity and dielectric relaxation behavior in FIC silver based phospho-molybdate glasses

Electrical conductivity and dielectric relaxation studies of silver ion-conducting glasses have been prepared using xAg₂SO₄-15Ag₂O-(90-x)(90P₂O₅-10MoO₃) glass system over a temperature range of 298–353 K and frequencies of 10 Hz to 10 MHz. DC conductivities exhibit Arrhenius behavior over the entire temperature range with a single activation barrier. The ac conductivity behavior of these glasses has been analyzed using single power law; conductivity increases linearly in logarithmic scale with Ag₂SO₄ concentration. The power law exponent (s) decreases, while stretched exponent (β) is insensitive to increase of temperature. Scaling behavior has also been carried out using the reduced plots of conductivity and frequency, which suggest that ion transport mechanism remains unaffected at all temperatures and compositions.     

Dielectric properties and conductivity in CuO and MoO3 doped borophosphate glasses

A novel set of glasses of the type (B₂O₃)_0.10-(P₂O₅)_0.40-(CuO)_0.50−x-(MoO₃)_x, 0.05≤x≥0.50, have been investigated for dielectric properties in the frequency range 100 Hz-100 kHz and temperature range 300-575 K. From the total conductivity derived from the dielectric spectrum the frequency exponent, s, and dc and ac components of the conductivity were determined. The temperature dependence of dc and ac conductivities at different frequencies was analyzed using Mott's small polaron hopping model, and the high temperature activation energies have been estimated and discussed. The observed initial decrease in conductivity (ac and dc) and increase in activation energy with the addition of MoO₃ have been understood to be due to the hindrance offered by the Mo⁺ ions to the electronic motions. The observed peak-like behavior in conductivity (dip-like behavior in activation energy) in the composition range 0.20-0.50 mol fractions of MoO₃ may be due to mixed transition effect occurring in the present glasses. The temperature dependence of frequency exponent, s, has been analyzed using different theoretical models. It is for the first time that the mixed transition metal ion (TMI) doped borophosphate glasses have been investigated for dielectric properties and conductivity over wide temperature and frequency ranges and the data have been subjected to a thorough analysis.     

Structural and electrical studies of Ba5RTi3V7O30 (R=Ho,Gd, La) compounds

The ferroelectric ceramics Ba₅RTi₃V₇O₃₀ (R=Ho, Gd, La) have been synthesized by solid-state reaction technique. Preliminary X-ray structural analysis confirmed a single-phase formation of the compound in orthorhombic structure. Surface morphology of the compounds was studied by scanning electron microscopy (SEM). Detailed studies of electrical properties (i.e., dielectric constant, loss tangent, ac conductivity) as a function of temperature (RT-773 K) and at four different frequencies (1 kHz, 10 kHz, 100 kHz and 1 MHz) show ferroelectric–paraelectric phase transition of the compounds of diffuse-type. The activation energy has been evaluated from ac conductivity following Arrhenius equation. The conductivity pattern shows that it is strongly frequency dependent and obeys Jonscher's power relation.     

Li2O-P205O-V2O5系统非晶材料电学性质与磁共振研究

本文对Li₂O-P₂O₅-V₂O₅系统非晶态中的几组试样进行了电导率、核磁共振及顺磁共振测试。实验分析表明非晶态的log(σΤ)-1/Τ曲线都是由两个直线段构成。电导率在转变温度以后的“晶化前期”异常增大,这归因于该阶段非晶态结构有序化程度增加所致,利用ESR实验结果对非晶态进行钒离子价态分析表明,该系统非晶态中钒离子仅以V⁴⁺和V⁵⁺状态存在。固定P< 关键词：     

Elastic,impedance spectroscopic and dielectric properties of TiO2 doped nanocrystalline NiCuZn spinel ferrites

ABSTRACT

Nanocrystalline Ni_0.4Cu_0.3Zn_0.3Fe₂O₄ ferrites doped with TiO₂ (0–10?wt %) were prepared by the sol-gel method. Elastic properties of synthesized samples were studied with the help of ultrasonic pulse transmission method. The elastic constants initially increase with an increase in TiO₂ up to 1?wt % and then decline. LCR-Q meter was used to study the dielectric properties within 50?Hz to 5?MHz range of the frequency. The dielectric constant (?′) and dielectric loss tangents were decreased continuously with increased frequency for all the selected samples at room temperature revealing normal dielectric behavior of ferrites. Also, the AC conductivity was increased with an increase in the frequency for all the selected samples. Cole-Cole plots were obtained for all investigated samples and showed single semicircle which indicates that the electrical conduction process appears only due to grain boundaries.     

A new ferroelectric oxide Li2Pb2Pr2W2Ti4Nb4O30: Synthesis and characterization

A new ferroelectric oxide (Li₂Pb₂Pr₂W₂Ti₄Nb₄O₃₀) of tungsten bronze structural family has been synthesized by a solid-state reaction (mixed-oxide) route at high temperature (～1100 °C). X-ray structural analysis with room temperature diffraction data confirms the formation of a single phase compound. The scanning electron microscopic (SEM) texture of the surface of material sample exhibits a uniform grain distribution with a few small voids suggesting the formation of high-density pellet sample. Detailed studies of dielectric constant, tangent loss and polarization with temperature and frequency confirmed the existence of ferroelectric properties in the material with transition temperature much above room temperature. Study of electrical properties (impedance, modulus, conductivity, etc.) of the material exhibits a strong correlation between its micro-structure (i.e., bulk, grain boundary, etc.) and electrical parameters. The nature of variation of dc conductivity with temperature confirms the Arrhenius behavior of the material. The presence of ionic conductivity in the material was observed in its ac conductivity spectrum. Study of frequency dependence of ac conductivity suggests that the material obeys Jonscher's universal power law. The experimental electrical transport properties of the material clearly exhibit the existence of non-exponential-type of conductivity relaxation.