Electrical conductivity and dielectric properties of sulfamic acid doped polyaniline

The temperature and frequency dependence of dielectric constant (ε′) and dielectric loss (ε″) is studied for different samples of polyaniline (PANI), doped with different concentration of sulfamic acid in the frequency range (10–100 kHz) and temperature range (300–400 K). The dc conductivity has also been measured to see the effect of sulfamic acid and the conduction mechanism has been explained by the propagation of polaron through a conjugated polymer chain due to shifting of double bonds (alternation), which gives rise to electrical conduction.     

Conductivity and thermal studies of blend polymer electrolytes based on PVAc–PMMA

The polymer electrolytes comprising blend of poly(vinyl acetate) (PVAc) and poly(methylmethacrylate) (PMMA) as a host polymer and LiClO₄ as a dopant are prepared by solution casting technique. The amorphous nature of the polymer–salt complex has been confirmed by XRD analysis. The DSC thermograms show two T_g's for PVAc–PMMA blend. A decrease in T_g with the LiClO₄ content reveals the increase of segmental motion. Conductance spectra results are found to obey the Jonscher's power law and the maximum dc conductivity value is found to be 1.76 × 10^− 3 S cm^− 1 at 303 K for the blend polymer complex with 20 wt.% LiClO₄, which is suitable for the Li rechargeable batteries. The conductivity–temperature plots are found to follow an Arrhenius nature. The dc conductivity is found to increase with increase of salt concentration in the blend polymer complexes.     

Novel molybdenum disulfide nanosheets–decorated polyaniline: Preparation,characterization and enhanced electrocatalytic activity for hydrogen evolution reaction

Novel molybdenum disulfide nanosheets–decorated polyaniline (MoS₂/PANI) was synthesized and investigated as an efficient catalyst for hydrogen evolution reaction (HER). Compared with MoS₂, MoS₂/PANI nanocomposites exhibited higher catalytic activity and lower Tafel slope for HER in H₂SO₄ solution. The amount of 19 wt% PANI for coupling with MoS₂ resulted in a high current density of 80 mA cm⁻² at 400 mV (vs. RHE). In addition, the optimal MoS₂/PANI nanocomposite showed impressive long-term stability even after 500 cycles. The enhanced catalytic activity of MoS₂/PANI nanocomposites was primarily ascribed to the effective electron transport channels of PANI and the increase of electrochemically accessible surface area in composite materials, which was advantageous to facilitate the charge transfer at catalyst/electrolyte interface.     

The dc and ac properties of potassium trioxalatoferrate (III) trihydrate

The complex potassium trioxalatoferrate (III) trihydrate {K₃(Fe(C₂O₄)₃ · 3H₂O)} was synthesised and characterised by energy dispersion X-ray fluorescence (XRF) and X-ray diffraction (XRD). The electrical and dielectric properties of the complex pellet were studied by ac- and dc-techniques in room temperature and in a temperature range of 293–373 K. The data of the ac conductivity as a function of frequency in a frequency range of 1–100 kHz follow the correlated barrier hopping CBH model and the parameters of the model were determined and connecting them with the optical properties. The temperature dependence of dc conductivity shows that the semiconducting behaviour of conduction phenomenon in the complex is realised by hopping mechanism between localised states and the minimum hopping distance was determined. High relative permittivity of about 30 at 100 kHz was obtained for the complex, which can find technological applications like alternative for the SiO₂ insulator in MOS devices.     

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.     

Impedance spectroscopic studies of an organic semiconductor device incorporating a thin film of highly doped ZnPc with MoO3

We use experimental results of low signal impedance spectroscopy to investigate the conduction mechanism in organic semiconductor, zinc phthalocyanine (ZnPc). The first 10 nm, of a total of 150 nm thermally deposited ZnPc, was doped with molybdenum oxide (MoO₃) by co-evaporation to obtain a 20% doping concentration. The ac electrical parameters were measured at room temperature in the dc bias and frequency ranges of 0–5 V and 100 Hz–0.1 MHz, respectively. The variation of bulk resistance with applied bias presents a clear indication of space charge limited conduction in the fabricated device. The experimental results show a strong frequency dependence of capacitance and loss tangent at low frequencies and high applied bias, while at higher frequencies and low applied bias a weak dependence is observed. Moreover, the ac conductivity shows a strong dependence on frequency and is found to vary as ω^s with the index s≤1.15 suggesting a dominant hopping mechanism of conduction.     

Preparation of poly(vinyl phosphate-b-styrene) copolymers and its blend with PPO as proton exchange membrane for DMFC applications

Poly(vinyl phosphate-b-styrene) (poly(VPP-b-St)) block copolymers were prepared via consecutive telomerization of vinyl acetate (VAc), atom transfer radical polymerization (ATRP) with styrene, saponification, and phosphorylation with phosphorus oxychloride. The resulting block copolymers were characterized by FT-IR and pH titration. Then, the block copolymers were blended with poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) to prepare direct methanol fuel cell (DMFC) membrane. The performance of poly(VPP-b-St)/PPO blend membranes was measured in terms of proton conductivity, methanol permeability, thermal and hydrolytic stability. The proton conductivities were in the range of 10^− 4 to 10^− 2 S/cm (60 °C, RH = 95%); the methanol permeabilities were in the range of 4.14 × 10^− 8 to 9.62 × 10^− 8 cm²/s (25 °C), and quite lower than that of Nafion® 117. Also, the thermal stability of the blend membranes was characterized by TGA, and was stable up to 400 °C; the blend membranes had better hydrolytic stability.     

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″).     

Preparation and characterization of conductive nanostructured particles based on polyaniline and cellulose nanofibers

Conducting polyaniline (PANI) and cellulose coated PANI (PANI-NC) nanostructures with sizes of about 80–100 nm, doped with hydrochloric acid were synthesized by a sonochemical method. Both type of particles resulted electrically conductive (direct current conductivity of 0.059 and 0.075 S/cm for PANI and PANI-NC structures, respectively) and could be dispersed easily in water, leading to green colored suspensions that remain stable for more than 4 h. The morphology, crystallinity, electrical conductivity (σ) and thermal stability of the obtained PANI based structures were investigated and compared. Furthermore, UV–Vis spectroscopy and rheology of water suspensions were used to explain the measured properties. Although the concentration of cellulose fibers used to synthesize the PANI-NC structures was very low, important differences respect to the neat PANI fibers regarding the microstructure, electrical conductivity and suspension behavior were found.     

Hydrophilic polyaniline nanofibrous architecture using electrosynthesis method for supercapacitor application

An electrosynthesis process of hydrophilic polyaniline nanofiber electrode for electrochemical supercapacitor is described. The TGA–DTA study showed polyaniline thermally stable up to 323 K. Polyaniline nanofibers exhibit amorphous nature as confirmed from XRD study. Smooth interconnected fibers having diameter between 120–125 nm and length typically ranges between 400–500 nm observed from SEM and TEM analysis. Contact angle measurement indicated hydrophilic nature of polyaniline fibers. Optical study revealed the presence of direct band gap with energy 2.52 eV. The Hall effect measurement showed room temperature resistivity ∼3 × 10⁻⁴ Ω cm and Hall mobility 549.35 cm⁻²V⁻¹ s⁻¹_. The supercapacitive performance of nanofibrous polyaniline film tested in 1 M H₂SO₄ electrolyte and showed highest specific capacitance of 861 F g⁻¹ at the voltage scan rate of 10 mV/s.     

Powder synthesis and electrical,dielectric spectroscopic characterization of rare earth disilicates (D-Er2Si2O7): Transistor scaling-22 nm or beyond

Rare earth disilicates are now a day's being analyzed as a dielectric layer for transistor scaling for the advanced 22 nm regime or beyond. So to explore these materials, the polymorphic powdered Er₂Si₂O₇ (D phase) is synthesized by solid state double sintering method to study its characteristics. Structural characterization has been performed by X-ray diffraction. SEM and EDX results shows the rods like morphology of particles and composition. The dc electrical properties are evaluated by two probe method as a function of temperature. The dielectric spectroscopic measurements of D-Er₂Si₂O₇ are performed in the temperature range 300–420 K and frequency range 1 kHz to 1 MHz. The dc electrical transport phenomenon is analyzed using Mott’s variable-range hopping approach. The ac conductivity σ_ac(ω) is obtained through the dielectric spectroscopic measurements.     

Super-protonic phase transition and fast ionic conductivity of Li+ in [Li0.2(NH4)0.8]2TeCl6

The differential scanning calorimetry diagram of [Li_0.2(NH₄)_0.8]₂TeCl₆ showed one anomaly at 526 K accompanied with a shoulder at 505 K.The conductivity plot exhibits two anomalies at 496 and 526 K, which characterize the beginning and the end of the crossing to superionic conductor state. The low temperature conduction is ensured essentially by Li⁺. A sudden jump confirms the presence of a superionic protonic transition related to the fast motion of Li⁺ and H⁺ ions. Above 526 K, the high temperature phase is characterized by high electrical conductivity (10^− 3 Ω^− 1 m^− 1) and low activation energy (E_a < 0.3 eV).The dielectric constant evolution as a function of frequency and temperature revealed the same anomaly.Transport properties in this material appear to be due to Li⁺ and H⁺ ions' hopping mechanism.     

Dielectric relaxation in NH4HSO4 above room temperature

The dispersion curves of the dielectric response of NH₄HSO₄ show that the corrected imaginary part of permittivity, εʺ, and its real part ε′ versus frequency reveal a dielectric relaxation around 9.1 × 10⁵ Hz at 31 °C, which shifts to higher frequencies (∼ 10⁶ Hz) as the temperatures increases. The relaxation frequency shows an activated relaxation process over the temperature range 31–83 °C with activation energy E_a = 0.14 eV, which is close to that derived from the dc conductivity. We suggest that the observed dielectric relaxation could be produced by the H⁺ jump and SO₄⁻ reorientation that cause distortion and change the local lattice polarizability inducing dipoles like HSO₄⁻.     

Structural and optical properties of La-doped BaSnO3 thin films grown by PLD

In this study the structural and optical properties of lanthanum-doped BaSnO₃ powder samples and thin films deposited on fused silica were investigaed using laser ablation. Under an oxygen pressure of 5×10⁻⁴ mbar, phase pure BaSnO₃ films with a lattice constant of 0.417 nm and grain size of 21 nm were prepared at 630 °C. The band gap of BaSnO3 powder sample and thin films was calculated to be 3.36 eV and 3.67 eV, respectively. There was a progressive increase in conductivity for thin films of BaSnO₃ doped with 0~7 at% of La. The highest conductivity, 9 Scm⁻¹, was obtained for 7 at% La-doped BaSnO₃. Carrier concentration, obtained from Burstein-Moss (B-M) shift, nearly matches the measured values except for 3 at% and 10 at% La-doped BaSnO₃ thin films.     

Fast and wide-band response infrared detector using porous PZT pyroelectric thick film

Porous lead zirconate titanate (PbZr_0.3Ti_0.7O₃, PZT30/70) thick films and detectors for pyroelectric applications have been fabricated on alumina substrates by screen-printing technology. Low temperature sintering of PZT thick films have been achieved at 850 °C by using Li₂CO₃ and Bi₂O₃ sintering aids. The microstructure of PZT thick film has been investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The dielectric properties were measured using HP 4284 at 1 kHz under 25 °C. The permittivity and loss tangent of the thick films were 94 and 0.017, respectively. Curie temperature of PZT thick film was 425 °C as revealed by dielectric constant temperature measurement. The pyroelectric coefficient was determined to be 0.9 × 10⁻⁸ Ccm⁻² K⁻¹ by dynamic current measurement. Infrared detector sensitive element of dual capacitance was fabricated by laser directly write technology. Detectivity of the detectors were measured using mechanically chopped blackbody radiation. Detectivity ranging from 1.23 × 10⁸ to 1.75 × 10⁸ (cm Hz^1/2 W⁻¹) was derived at frequency range from 175.5 Hz to 1367 Hz, and D^*’s −3 dB cut-off frequency bandwidth was 1.2 kHz. The results indicate that the infrared detectors based on porous thick films have great potential applications in fast and wide-band frequency response conditions.     

Organic dopant added polyvinylidene fluoride based solid polymer electrolytes for dye-sensitized solar cells

The effect of phenothiazine (PTZ) as dopant on PVDF/KI/I₂ electrolyte was studied for the fabrication of efficient dye-sensitized solar cell (DSSC). The different weight percentage (wt%) ratios (0, 20, 30, 40 and 50%) of PTZ doped PVDF/KI/I₂ electrolyte films were prepared by solution casting method using DMF as a solvent. The following techniques such as Fourier transform infrared (FT-IR), differential scanning calorimetry (DSC), X-ray diffractometer (XRD) and AC-impedance analysis have been employed to characterize the prepared polymer electrolyte films. The FT-IR studies revealed the complex formation between PVDF/KI/I₂ and PTZ. The crystalline and amorphous nature of polymer electrolytes were confirmed by DSC and XRD analysis respectively. The ionic conductivities of polymer electrolyte films were calculated from the AC-impedance analysis. The undoped PVDF/KI/I₂ electrolyte exhibited the ionic conductivity of 4.68×10⁻⁶ S cm⁻¹ and this value was increased to 7.43×10⁻⁵ S cm⁻¹ when PTZ was added to PVDF/KI/I₂ electrolyte. On comparison with different wt% ratios, the maximum ionic conductivity was observed for 20% PTZ-PVDF/KI/I₂ electrolyte. A DSSC assembled with the optimized wt % of PTZ doped PVDF/KI/I₂ electrolyte exhibited a power conversion efficiency of 2.92%, than the undoped PVDF/KI/I₂ electrolyte (1.41%) at similar conditions. Hence, the 20% PTZ-PVDF/KI/I₂ electrolyte was found to be optimal for DSSC applications.     

Mesopore size dependence of the ionic diffusivity in alumina based composite lithium ionic conductors

Ordered-mesoporous Al₂O₃ was synthesized by a sol–gel method using neutral copolymer surfactants as structure-directing agents. The pore size was controlled over the 3–15 nm range by the use of various surfactants. Composites composed of the synthesized mesoporous Al₂O₃ and a lithium ion conductor (LiI) were prepared. The maximum dc electrical conductivity, 2.6 × 10^− 4 S cm^− 1 at 298 K, was observed for 50 LiI·50 Al₂O₃ composite with 4.2 nm average mesopore size, which was considerably higher than the previously reported LiI-alumina composites. A systematic dependence of conductivity upon pore size was observed, in which conductivity increased with decreasing pore size, except for samples with a pore size of 2.8 nm. The lithium ion diffusion coefficient determined by the ⁷Li pulsed field gradient nuclear magnetic resonance (PFG-NMR) showed excellent agreement with the measured conductivity calculated by the Nernst-Einstein equation. On the other hand, lithium migration activation energies obtained by quasielastic neutron scattering (QENS) and ⁷Li NMR spin-lattice relaxation time (T₁) were considerably smaller than those obtained from electrical conductivity and PFG-NMR. This could be explained by the ion migration mechanism in heterogeneous composites and a possible enhancement of conductivity in mesoscopically confined spaces.     

Inclusion of polyaniline in electrodeposited bismuth sulphide thin films: Synthesis and characterization

Structural, electrical and optical properties of polyaniline (PAni) doped Bi₂S₃ composite thin films prepared by electrodeposition method are reported. X-ray diffraction pattern indicates its polycrystalline nature and crystallite size increases with increase in the concentration of PAni. FTIR studies reveal that the dopant PAni has affected the absorption phenomenon in the IR region of the Bi₂S₃ thin films. The optical band gap energy is found to be 1.91 eV for as-deposited Bi₂S₃ thin film and it decreases with increase in the concentration of PAni. The morphology of the doped films changes due to the addition of PAni. Electrical studies indicate that the conductivity increases with increase in the concentration of PAni. The conduction results from a hopping due to localized states in the temperature range 300–358 K. Above 358 K, the conduction process is explained by the traps at grain boundaries of partially depleted grains.     

Oxygen nonstoichiometry and transport properties of strontium substituted lanthanum cobaltite

Oxygen nonstoichiometry, structure and transport properties of the two compositions (La_0.6Sr_0.4)_0.99CoO_3−δ (LSC40) and La_0.85Sr_0.15CoO_3−δ (LSC15) were measured. It was found that the oxygen nonstoichiometry as a function of the temperature and oxygen partial pressure could be described using the itinerant electron model. The electrical conductivity, σ, of the materials is high (σ > 500 S cm^− 1) in the measured temperature range (650–1000 °C) and oxygen partial pressure range (0.209–10^− 4 atm). At 900 °C the electrical conductivity is 1365 and 1491 S cm^− 1 in air for LSC40 and LSC15, respectively. A linear correlation between the electrical conductivity and the oxygen vacancy concentration was found for both samples. The mobility of the electron-holes was inversely proportional with the absolute temperature indicating a metallic type conductivity for LSC40. Using electrical conductivity relaxation the chemical diffusion coefficient of oxygen was determined. It was found that accurate values of the chemical diffusion coefficient could only be obtained using a sample with a porous surface coating. The porous surface coating increased the surface exchange reaction thereby unmasking the chemical diffusion coefficient. The ionic conductivity deduced from electrical conductivity relaxation was determined to be 0.45 S cm^− 1 and 0.01 S cm^− 1 at 1000 and 650 °C, respectively. The activation energy for the ionic conductivity at a constant vacancy concentration (δ = 0.125) was found to be 0.90 eV.     

Structural and electrical properties of ZnO-doped 8 mol% yttria-stabilized zirconia

8 mol% Yttria-stabilized zirconia (8YSZ) powder was prepared by coprecipitation. ZnO (0.5, 1.0, 2.0, 5.0, 10.0 wt.%) was added to the YSZ powder through a mechanical mixing method. The densification , microstructure and electrical properties of the YSZ ceramics sintered at 1300 °C for 2 h, were investigated. It was found that the small addition of ZnO was effective in reducing the sintering temperature and promoting the densification rate of the ceramics. The 5.0 wt.% ZnO-doped YSZ has ∼ 96% relative density, as compared to ∼ 89% relative density for the undoped sample. The total conductivity of 8YSZ was evidently increased by doping small amount of ZnO. For the 0.5 wt.% doped sample, the total conductivity of 2.89 × 10^− 2 Ω^− 1 cm^− 1 and an increase of 120% in conductivity were observed at 800 °C, as compared to that of the undoped one. We also found that the grain boundary (GB) conductivity could be improved by small addition of ZnO. At intermediate temperature (∼ 300 °C), the maximum enhancement of GB conductivity was observed with 5.0 wt% ZnO dopant. Finally, the volume percentage of GB in the ceramics was estimated by the brick layer model. The possible mechanism related to the improved GB conduction of the YSZ due to the ZnO additions was discussed.