Thermal,dielectric and conductivity studies on PVA/Ionic liquid [EMIM][EtSO4] based polymer electrolytes

Polymer electrolyte films of (PVA+15 wt% LiClO₄)+x wt% Ionic liquid (IL) 1-ethyl-3-methylimidazolium ethylsulfate [EMIM][EtSO₄] (x=0, 5, 10, 15) were prepared by solution cast technique. These films were characterized using TGA, DSC, XRD and ac impedance spectroscopic techniques. XRD result shows that amorphosity increases as the amount of the IL in PVA+salt (LiClO₄) is increased. DSC results confirm the same (except (PVA+15 wt% LiClO₄)+10 wt% IL). The dielectric and conductivity measurements were carried out on these films as a function of frequency and temperature. The addition of IL significantly improved the ionic conductivity of polymer electrolytes. Relaxation frequency vs. temperature plot for (PVA+15 wt% LiClO₄)+x wt% IL were found to follow an Arrhenius nature. The dielectric behavior was analyzed using real and imaginary parts of dielectric constant, dielectric loss tangent (tan δ) and electric modulus (M′ and M″).     

Influence of lithium potassium zirconate nanoparticles on the electrical properties and structural characteristics of poly(vinyl alcohol) films

We investigated the influence of lithium potassium zirconate (LiKZrO₃) nanoparticles on the electrical properties and structural characteristics of poly(vinyl alcohol) (PVA) films. PVA/LiKZrO₃ nanocomposite films were prepared by casting of aqueous solutions with varying LiKZrO₃ content (0.5, 1.0, and 2.0 wt.%). The dielectric constant (ε′), dielectric loss (ε″), AC conductivity (σ_ac), dielectric loss tangent (tan δ), and electric modulus (M′ and M″) of the nanocomposite films were measured over a range of frequencies at ambient temperature. The results show increases in σ_ac and M′ with frequency, whereas ε′, ε″, and tan δ decreased with increasing frequency. The films were also characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and X-ray diffraction (XRD) techniques. DSC and XRD revealed the nature of LiKZrO₃ nanoparticle interaction with the PVA matrix. TGA analysis revealed an increase in thermal stability of the nanocomposites with increasing nanoparticle concentration. Scanning electron microscopy confirmed uniform dispersion of LiKZrO₃ nanoparticles in the PVA matrix.     

Magnetic and dielectric properties of nanophase manganese-substituted lithium ferrite

Nanocrystalline manganese-substituted lithium ferrites viz. Li_0.5Fe_2.5−xMn_xO₄ (2.5≤x≥0) were prepared by sol-gel autocombustion method. X-ray diffraction analysis confirmed that as the concentration of manganese increases the cubic phase changes to the tetragonal phase. The variation of saturation magnetization was studied as a function of manganese content. All the compositions indicate that they are ferrimagnetic in nature. The dielectric constant, dielectric loss tangent and ac conductivity of all samples were measured at room temperature as a function of frequency. These parameters decrease with increase in frequency for all of the samples. The substitution of manganese plays an important role in changing the structural and magnetic properties of these ferrites. The compositional variation of dielectric constant and d.c. resistivity shows an inverse trend of variation with each other.     

Conduction mechanism and the dielectric relaxation process of a-Se75Te25−xGax (x=0, 5, 10 and 15 at wt%) chalcogenide glasses

Se₇₅Te_25−xGa_x (x=0, 5, 10 and 15 at wt%) chalcogenide compositions were prepared by the well known melt quenching technique. Thin films with different thicknesses in the range (185–630 nm) of the obtained compositions were deposited by thermal evaporation technique. X-ray diffraction patterns indicate that the amorphous nature of the obtained films. The ac conductivity and the dielectric properties of the studied films have been investigated in the frequency range (10²–10⁵ Hz) and in the temperature range (293–333 K). The ac conductivity was found to obey the power low ω^s where s≤1 independent of film thickness. The temperature dependence of both ac conductivity and the exponent s can be well interpreted by the correlated barrier hopping (CBH) model. The experimental results of the dielectric constant ε₁ and dielectric loss ε₂ are frequency and temperature dependent. The maximum barrier height W_m calculated from the results of the dielectric loss according to the Guintini equation, and agrees with that proposed by the theory of hopping of charge carriers over a potential barrier as suggested by Elliott for chalcogenide glasses. The density of localized state was estimated for the studied film compositions. The variation of the studied properties with Ga content was also investigated. The correlation between the ac conduction and the dielectric properties were verified.     

Thermal,vibrational, and dielectric studies on PVP/LiBF4+ionic liquid [EMIM][BF4]-based polymer electrolyte films

Free-standing polymer electrolyte membranes based on poly(vinyl) pyrrolidone (PVP)/salt(LiBF₄) having different amounts of ionic liquid (IL) [EMIM][BF₄] were prepared and characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infrared (FT-IR) spectroscopy, and alternating current (AC) impedance spectroscopic techniques. The DSC results show a shift in T_m of PVP with salt/or IL content. TGA and DTGA (first derivative of TGA) results give evidence of the presence of uncomplexed PVP, PVP/salt, and PVP/IL complexes. Signatures of these entities are also present in the dielectric spectra. Complexation of PVP with salt and IL has been confirmed by FT-IR analysis. Electrical conductivity as a function of temperature has been studied for PVP/LiBF₄/IL [EMIM][BF₄]. Role of IL in changing phase transition, conductivity, and dielectric relaxation frequency has been discussed.     

Studies on frequency and gate voltage effects on the dielectric properties of Au/n-Si (110) structure with PVA–nickel acetate composite film interfacial layer

The admittance technique was used in order to investigate the frequency dependence of dielectric constant (????), dielectric loss (????), dielectric loss tangent (tan??), the ac electrical conductivity (?? _ac), and the electric modulus of PVA (Ni-doped) structure. Experimental results revealed that the values of ???? , ????, (tan??), ?? _ac and the electric modulus show fairly large frequency and gate bias dispersion due to the interface charges and polarization. The ?? _ac is found to increase with both increasing frequency and voltage. It can be concluded that the interface charges and interfacial polarization have strong influence on the dielectric properties of metal?Cpolymer?Csemiconductor (MIS) structures especially at low frequencies and in depletion and accumulation regions. The results of this study indicate that the ???? values of Au/PVA/n-Si with Nickel-doped PVA interfacial layer are quite higher compared to those with pure and other dopant/mixture??s of PVA.     

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.     

Structural and electrical properties of nanostructured cerium phosphate

Cerium phosphate nanomaterials with different morphologies and sizes were synthesized via a hydrothermal process at 150 °C using cetyl-trimethyl-ammonium-bromide and ethylene-diamine-tetra acid as surfactants. The obtained samples were characterized by X-ray diffraction and a scanning electron microscope. A possible growth mechanism was proposed to reveal the formation process. The structural properties and the electrical conductivities of CePO₄ nanomaterials were studied. The activation energies were obtained from Arrhenius plots where E _a?=?1.06 eV. The ac conductivity at different temperatures for CePO₄ nanomaterials showed frequency independence in the lower frequency range. The dielectric measurements were carried out as a function of frequency and temperature. Variation of the dielectric properties and the ac conductivity with frequency revealed that the dispersion is due to a Maxwell-Wagner type of interfacial polarization in general.     

Proton-conducting polymer electrolyte based on PVA-PAN blend doped with ammonium thiocyanate

Blending of polymers is one of the most useful methods for modulating the conductivity of solid polymer electrolytes. Blend polymer electrolytes have been prepared with polyvinyl alcohol (PVA)-polyacrylonitrile (PAN) blend doped with ammonium thiocyanate with different concentrations by solution casting technique, using dimethyl formamide (DMF) as the solvent. The prepared electrolytes are characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), nuclear magnetic resonance (NMR), ultraviolet (UV), and ac impedance measurement techniques. The increase in amorphous nature of the blend polymer electrolyte by the addition of salt is confirmed by XRD analysis. The complex formation between the polymers and the salt has been confirmed by FTIR analysis. The thermal behavior has been examined using DSC and TGA. The maximum conductivity has been found to be 2.4?×?10^?3 S cm^?1 for 92.5PVA/7.5PAN/25 % NH₄SCN sample at room temperature. The temperature dependence of conductivity has been studied with the help of Arrhenius plot, and the activation energies are calculated. The proton conductivity is confirmed by dc polarization measurement technique. ¹H NMR studies reveal the presence of protons in the sample. A proton battery is constructed with the highest conducting sample, and its open circuit voltage is measured to be 1.2 V     

Growth and characterization of pure and potassium iodide-doped zinc tris-thiourea sulphate (ZTS) single crystals

Single crystals of pure and potassium iodide (KI)-doped zinc tris-thiourea sulphate (ZTS) were grown from aqueous solutions by the slow evaporation method. The grown crystals were transparent. The lattice parameters of the grown crystals were determined by the single-crystal X-ray diffraction technique. The grown crystals were also characterized by recording the powder X-ray diffraction pattern and by identifying the diffracting planes. The FT-IR spectrum was recorded in the range 400-4500 cm⁻¹. Second harmonic generation (SHG) was confirmed by the Kurtz powder method. The thermo gravimetric analysis (TGA) and differential thermal analysis (DTA) studies reveal that the materials have good thermal stability. Atomic absorption studies confirm the presence of dopant in ZTS crystals. The electrical measurements were made in the frequency range 10²-10⁶ Hz and in the temperature range 40-130 °C along a-, b- and c-directions of the grown crystals. The present study shows that the electrical parameters viz. dc conductivity, dielectric constant, dielectric loss factor and ac conductivity increase with increase in temperature. Activation energy values were also determined for the ac conduction process in grown crystals. The dc conductivity, dielectric constant, dielectric loss factor and ac conductivity of KI-doped ZTS crystal were found to be more than those of pure ZTS crystals.     

Magnetic and dielectric studies of nanocrystalline zinc substituted Cu-Mn ferrites

Ferrites with the general formula Cu_1−xZn_xFeMnO₄ (where 0≤x≤1) were prepared through a citrate gel auto-combustion route. Structural characterizations carried out by X-ray diffraction reveal that the lattice constant increases with increase in zinc content. Transmission electron microscopic measurements confirm the nanoscale nature of the particles. Room temperature saturation magnetization was measured as a function of zinc concentration. The saturation magnetization increases up to x=0.25 and then decreases as zinc concentration increases. Dielectric permittivity, dielectric loss tangent, ac conductivity and complex dielectric impedance were studied in the frequency range 20 Hz-1 MHz. The results indicated a usual dielectric dispersion due to the Maxwell-Wagner type of interfacial polarization. Dielectric loss showed similar behavior as dielectric permittivity. The ac conductivity increased linearly with frequency. Complex impedance spectroscopic studies confirmed that conduction in the samples is via grain boundaries. In general, substitution of zinc plays an important role in changing the structural, electrical and magnetic properties of these ferrites.     

Effect of Zn substitution on the electrical properties of Bi2Co0.1V0.9O5.35 synthesized by sol-gel method

Samples of Bi₂V_0.9Co_0.1-xZn_xO_5.35, 0.02 ≤ x ≤ 0.08 with layered Aurivillius structure were synthesized successfully by sol-gel citrate method. Structural and electrical characterization of compositions has been investigated by X-ray diffraction, thermogravimetric analysis–differential scanning calorimetric (TGA–DSC) analysis and AC impedance spectroscopy. The tetragonal γ phase has been observed for all investigated samples. The AC impedance response of samples has been measured in the frequency range of 20 Hz to 1 MHz. The impedance for pellets decreases as thermal energy increases. The contribution of grain to the conduction process is more than that of grain boundary. The ionic conductivity and dielectric permittivity are found to be composition-dependent and increase with increasing Zn concentration. The maximum electrical conductivity observed for the composition x = 0.08 is σ = 4.51 × 10^?4 S cm^?1 at 300 °C.     

Dielectric loss,conductivity relaxation process and magnetic properties of Mg substituted Ni–Cu ferrites

The dielectric properties, dc and ac electrical resistivities of Mg substituted Ni–Cu ferrites with general formula Ni_0.5Cu_0.5−xMg_xFe₂O₄ (0.0≤x≤0.5) have been investigated as a function of frequency, temperature and composition. ac resistivity of all the samples decreases with increase in the frequency exhibiting normal ferrimagnetic behavior. The frequency dependence of dielectric loss tangent showed a maximum in between 10 Hz and 1 kHz in all the ferrites. The conductivity relaxation of the charge carriers was examined using the electrical modulus formulism, and the results indicate the presence of the non-Debye type of relaxation in the prepared ferrites. Similar values of activation energies for dc conduction and for conductivity relaxation reveal that the mechanism of electrical conduction and dielectric polarization is the same in these ferrites. A single ‘master curve’ for normalized plots of all the modulus isotherms observed for a given composition indicates that the distribution of relaxation time is temperature independent. The saturation magnetization and coercivity as calculated from the hysteresis loop measurement show striking dependence on composition.     

Study of the structural, dielectric and magnetic properties of Bi2O3 and PbO addition on BiFeO3 ceramic matrix

In this paper we studied the effects of Bi₂O₃ and PbO addition on BiFeO₃ (BFO) ceramic matrix. The structural, dielectric and magnetic properties of fifteen BFO samples were discussed in view of possible applications in RF and microwave devices. The present work also reports the preparation of the samples. Polyvinyl alcohol (PVA) and tetraethyl orthosilicate (TEOS) were also added as a binder in the fabrication procedure. The samples have been studied by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and magnetic hysteresis measurements. Further, a study based on impedance spectroscopy also has been done. Dielectric permittivity (ε′) and dielectric loss (tan δ) were measured at room temperature in the frequency range 100 Hz-10 MHz, as well as a.c. conductivity. The -Im[Z(f)] versus Re[Z(f)] plot has been obtained. The samples were investigated in view of possible applications like miniaturized filters, diplexers and dielectric resonator antennas (DRA). In the RF and MW frequency region, the application of magneto-dielectric and multiferroic perovskite composite materials is desirable for the miniaturization of components.     

Dielectric behavior of nano-structured and bulk Li Ni Zn ferrite samples

The ac conductivity and dielectric properties of spinel ferrite nanoparticles of Li_0.1(Ni_1−xZn_x)_0.8Fe_2.1O₄ (x=0.0–1.0) prepared by the chemical co-precipitation method were investigated as functions of frequency and temperature by using a complex impedance technique. Parts of the precipitated powders were pressed into a disk-shape and were sintered at 1473 K for 2 h to increase the particle size to the bulk scale (dimensions >100 nm). The ac conductivity of the samples increases with increasing temperature, ensuring the semiconducting behavior of both nano and bulk samples, in agreement with the Koops model to describe heterogeneous structures. The significant decrease in ac conductivity σ′_ac, dielectric constant, and dielectric loss of the as-prepared nanosamples compared to their bulk counterparts is correlated to the small size of the grain compared to the grain boundary size. This might be useful for many applications requiring the reduction of eddy current effects.     

Effect of nickel doping on structural, optical and electrical properties of TiO2 nanoparticles by sol-gel method

Nickel-doped anatase TiO₂ nanoparticles have been prepared by sol-gel method. The X-ray powder diffraction study reveals that all the prepared samples have pure anatase phase tetragonal system. The average crystallite size of the prepared sample is 14 nm, when found through transmission electron microscope. A strong frequency dependence of both dielectric constant (?′) and dielectric loss (tan δ) were observed for various dopant levels at room temperature in the frequency range of 42 Hz to 5 MHz. At low frequency, the piling up of mobile charge carriers at the grain boundary produces interfacial polarization giving rise to high dielectric constant. The asymmetric shape of frequency dependence of the dielectric loss for the primary relaxation process is observed for each concentration. From the ac conductivity studies, the reduction in conductivity may arise due to the decreasing particle with the increase in Ni-dopant level.     

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.     

Study of dielectric and impedance properties of Mn ferrites

The paper reports on the effect of Al substitution on the structural and electrical properties of bulk ferrite series of basic composition MnFe_2−2xAl_2xO₄ (0.0≤x≤0.5) synthesized using solid state reaction method. XRD analysis confirms that all the samples exhibit single phase cubic spinel structure excluding presence of any secondary phase. The dielectric constant shows a normal behaviour with frequency, whereas the loss tangent exhibits an anomalous behaviour with frequency for all compositions. Variation of dielectric properties and ac conductivity with frequency reveals that the dispersion is due to Maxwell-Wagner type of interfacial polarization in general and hopping of charge between Fe⁺² and Fe⁺³ as well as between Mn⁺² and Mn⁺³ ions at octahedral sites. The complex impedance plane spectra shows the presence of two semicircles up to x=0.2, and only one semicircle for the higher values of x. The analysis of the data shows that the resistive and capacitive properties of the Mn ferrite are mainly due to processes associated with grain and grain boundaries.     

Influence of the composition of TlGa1 − x Er x Se2 crystals on their dielectric characteristics and parameters of localized states

Frequency dependences of the real (?′) and imaginary (?″) parts of the complex permittivity, the dielectric loss tangent (tanδ), and the ac conductivity (σ_ac) in frequency range f = 5 × 10⁴?3.5 × 10⁷ Hz have been investigated for TlGa_{1 ? x} Er _x Se₂ crystals of various compositions. It has been established that the relaxation dispersion of ?′ and ?″ takes place for the studied crystals. The influence of the erbium content in the crystals on their dielectric coefficients has been studied. The ac conductivity of the TlGa_{1 ? x} Er _x Se₂ single crystals in the high-frequency range obeys the law σ_ac ～ f ^0.8, which is characteristic of the hopping mechanism of charge transfer over the states localized in the vicinity of the Fermi level. Parameters of the states localized in the band gap of TlGa_{1 ? x} Er _x Se₂ and the influence of the composition of the crystals on these parameters have been evaluated.     

Structural,dielectric and ac conductivity properties of Ni-doped HoFeO3 before and after gamma irradiation

A series of samples of HoFe_1?x Ni _x O₃ (x = 0.0, 0.1, 0.3) were prepared using the solid-state reaction technique to understand the structural, dielectric and conductivity properties before and after gamma irradiation of accumulated dose of 625 KGy. The X-ray diffraction confirms that all the samples exist in single-phase orthorhombic structure having space group Pbnm. With increasing dopant Ni, the unit cell volume and lattice parameters undergo small change. X-ray analysis show change in the interplanar spacing and full width at half maximum values after gamma irradiation. The Raman spectra of the samples show modifications after gamma irradiation. It can be easily seen that after gamma irradiation intensity, peak width are completely altered by gamma-absorbed dose. Measurement of dielectric loss and dielectric constant at room temperature was performed before and after gamma irradiation in the frequency range of 20 Hz–1 MHz. It is observed that the value of dielectric constant decreases after irradiation. The ac conductivity is estimated from the dielectric constant and loss tangent. Exposure to gamma radiation results in substantial modification in the physical properties of the Ni-doped Ho-based orthoferrites.