Decrease In Bulk Resistance Research Articles

Effect of Sodium Ion Addition on Copper Selenide/Chitosan Film Towards Electrical and Shielding Efficiency Improvement

The operation of electronic devices can be disrupted by unwanted electromagnetic signals, affecting its operation. Deploying electromagnetic shielding is a viable solution to minimize the impact of electromagnetic interference (EMI). The conventional methods of electromagnetic shielding use metal gaskets to safeguard sensitive electronic components, which have drawbacks of cost and weight. Hence, electromagnetic shielding polymer can be an alternative to replace metal gaskets. This work investigates the effect of sodium ion (Na) addition to copper selenide/chitosan (CuSe/Ch) film for electromagnetic shielding applications. The shielding polymers were produced using solution casting methods, while the CuSe was synthesized using the chemical coprecipitation method. Impedance spectroscopy and two port waveguide methods were used to characterize the prepared polymer's electrical properties and shielding efficiency. The results indicate that Na incorporation in the CuSe/Ch film resulted in a 47 % decrease in bulk resistivity and increased DC conductivity from 6.07 × 10-6 S/cm to 3.69 × 10˗5 S/cm. The AC conductivity of films containing Na demonstrates a similar level of conductivity at lower frequencies, followed by a sharp increase at higher frequencies, indicating a more substantial influence of Na at higher frequencies. Higher absorption shielding efficiency (SEA) and lower reflection shielding efficiency (SER) were achieved by introducing Na into the CuSe chitosan film. The Na/CuSe/Ch film shows higher total shielding efficiency at an average of 20 dB, equivalent to 99 % of the EM power shield.

Structural, dielectric and complex impedance analysis of Pb-free BaTiO3-Bi(Mg0.5Ce0.5)O3 ceramics

(1–x)BaTiO3–xBi(Mg0.5Ce0.5)O3 (0.00 ≤ x ≤ 0.10) ceramics were prepared via a solid-state sintering route to investigate their structural, dielectric, impedance and energy storage properties. Phase analysis revealed tetragonal to pseudo-cubic phase transition in compositions with x ≥ 0.06. Doping of BaTiO3 with Bi(Mg0.5Ce0.5)O3 decreased the average grain size from ≥ 10 µm to submicron level which decreased the electrical conductivity and increased the electrical breakdown strength up to 250 kV cm−1. The observed decrease in bulk resistance with an increase in temperature demonstrated a typical negative temperature coefficient of resistance-type behavior for these ceramics. The x = 0.08 composition exhibited a high energy storage density (∼1.84 J cm−3) with a recoverable energy density (∼1.26 J cm−3) and an electrical breakdown strength ∼250 kV cm−1. The obtained results demonstrate that this ceramic can be considered to be a good candidate for application in advanced pulsed power capacitors.

The effects of SiO2 addition on the phase, microstructure, dielectric, and energy storage properties of BaTiO3-based ceramics

0.94BaTiO3–0.06Bi(Mg0.5Ce0.5)O3 + xwt.% SiO2 ceramics with 0 ≤ x ≤ 2 were synthesized via a solid-state reaction route. The secondary phase (Ba2TiSi2O8) was obtained in the XRD result of the sample 0.94BT –0.06BMC + 2 wt.% SiO2. At x = 1, this ceramic displayed a high εr (∼1843), small Δεr/εr25°C values (≤±15 %) in the temperature range 25 to 150 ℃, and low tanδ (≤0.03) in the temperature range 25 to 350 ℃. A decent energy storage density (Ws = 2.089 J cm−3), recoverable energy density (Wrec = 1.035 J cm−3), and high dielectric breakdown strength (BDS = 285 kV cm−1) were achieved for the sample 0.94BT –0.06BMC + 1 wt.% SiO2. The decrease in bulk resistance with an increase in temperature exhibited negative temperature coefficient of resistance (NTCR) behavior. The fine grain morphology of the ceramic with the composition 0.94BT –0.06BMC + 1 wt.% SiO2 improves the Ea (2.08 eV) and BDS (285 kV cm−1).

Bulk resistance and internal contacts of carbon fiber paper determined via X-ray computed tomography

Owing to the challenge of irregular morphology, the impact of compressed carbon fiber paper (CFP) on fuel cell performance and durability is intricate. As a carbon-carbon composite, the internal contact state of CFP directly determines its mechanical and physical properties. In this paper, fiber distribution and intersection of uncompressed CFP are achieved by X-ray computed tomography. Then we established an analytical model of bulk resistance based on the electron transfer path and provided a function to describe the internal contact state with strain. The results imply that the increasing number of electron paths and the variation of the contact state are the main factors for the decrease in bulk resistance under compression. The turning points in the contact state curve divide the range of pressure into fiber contact, elastic-plastic deformation and fiber fracture region, which can be used to assess the mechanical properties of CFP and determine the optimal pressure for fuel cell assembly.

Effect of ZnO Nanofiller on Structural and Electrochemical Performance Improvement of Solid Polymer Electrolytes Based on Polyvinyl Alcohol-Cellulose Acetate-Potassium Carbonate Composites.

In this study, a solution casting method was used to prepare solid polymer electrolytes (SPEs) based on a polymer blend comprising polyvinyl alcohol (PVA), cellulose acetate (CA), and potassium carbonate (K2CO3) as a conducting salt, and zinc oxide nanoparticles (ZnO-NPs) as a nanofiller. The prepared electrolytes were physicochemically and electrochemically characterized, and their semi-crystalline nature was established using XRD and FESEM. The addition of ZnO to the polymer–salt combination resulted in a substantial increase in ionic conductivity, which was investigated using impedance analysis. The size of the semicircles in the Cole–Cole plots shrank as the amount of nanofiller increased, showing a decrease in bulk resistance that might be ascribed to an increase in ions due to the strong action of the ZnO-NPs. The sample with 10 wt % ZnO-NPs was found to produce the highest ionic conductivity, potential window, and lowest activation energy (Ea) of 3.70 × 10–3 Scm–1, 3.24 V, and 6.08 × 10–4 eV, respectively. The temperature–frequency dependence of conductivity was found to approximately follow the Arrhenius model, which established that the electrolytes in this study are thermally activated. Hence, it can be concluded that, based on the improved conductivity observed, SPEs based on a PVA-CA-K2CO3/ZnO-NPs composite could be applicable in all-solid-state energy storage devices.

Influence of ionic liquid on the dielectric relaxation behavior of SWCNT reinforced poly(vinyl alcohol) based nanocomposites

Polymer nanocomposites based on single-walled carbon nanotubes (SWCNT) and poly(vinyl alcohol) have been successfully prepared using a solvent casting approach. The dispersion pattern of SWCNT in the PVA matrix has been analyzed by a high-resolution transmission electron microscope (HRTEM). The mechanical and thermal stability of the films were assessed. The effect of SWCNT loading and imidazolium-based ionic liquid on the dielectric relaxation behavior of the PVA-based nanocomposites has been explored in the frequency range of 1 to 106 Hz at room temperature. The dielectric properties such as dielectric permittivity (εʹ), real and imaginary impedance (Zʹ and Zʹʹ), AC conductivity (σac) as well as Nyquist plot of the fabricated nanocomposites were explored in the presence and absence of ionic liquid (IL). The dielectric permittivity and AC conductivity increased with an increase in SWCNT loading and presence of IL due to the enhanced interfacial polarization of the SWCNT at the interface and proper dispersion of SWCNT throughout the polymer matrix. The decrease in impedance (Zʹ and Zʹʹ) with the increase in SWCNT loading is due to the enhanced proximity between the conductive channels. The reduction in semicircular area under the Nyquist plot in presence of IL and increasing SWCNT loading indicated the capacitive nature of fabricated nanocomposites and a decrease in bulk resistivity.

Impedance, Electrical Equivalent Circuit (EEC) Modeling, Structural (FTIR and XRD), Dielectric, and Electric Modulus Study of MC-Based Ion-Conducting Solid Polymer Electrolytes.

The polymer electrolyte system of methylcellulose (MC) doped with various sodium bromide (NaBr) salt concentrations is prepared in this study using the solution cast technique. FTIR and XRD were used to identify the structural changes in solid films. Sharp crystalline peaks appeared at the XRD pattern at 40 and 50 wt.% of NaBr salt. The electrical impedance spectroscopy (EIS) study illustrates that the loading of NaBr increases the electrolyte conductivity at room temperature. The DC conductivity of 6.71 × 10−6 S/cm is obtained for the highest conducting electrolyte. The EIS data are fitted with the electrical equivalent circuit (EEC) to determine the impedance parameters of each film. The EEC modeling helps determine the circuit elements, which is decisive from the engineering perspective. The DC conductivity tendency is further established by dielectric analysis. The EIS spectra analysis shows a decrease in bulk resistance, demonstrating free ion carriers and conductivity boost. The dielectric property and relaxation time confirmed the non-Debye behavior of the electrolyte system. An incomplete semicircle further confirms this behavior model in the Argand plot. The distribution of relaxation times is related to the presence of conducting ions in an amorphous structure. Dielectric properties are improved with the addition of NaBr salt. A high value of a dielectric constant is seen at the low frequency region.

The effect of thermal treatment on ac/dc conductivity and current fluctuations of PVDF/NMP/[EMIM][TFSI] solid polymer electrolyte

The experimental study deals with the investigation of the effect of diverse crystallinity of imidazolium ionic-liquid-based SPE on conductivity and current fluctuations. The experimental study was carried out on samples consisting of [EMIM][TFSI] as ionic liquid, PVDF as a polymer matrix and NMP as a solvent. After the deposition, the particular sample was kept at an appropriate temperature for a specific time in order to achieve different crystalline forms of the polymer in the solvent, since the solvent evaporation rate controls crystallization. The ac/dc conductivities of SPEs were investigated across a range of temperatures using broadband dielectric spectroscopy in terms of electrical conductivity. In SPE samples of the higher solvent evaporation rate, the real parts of conductivity spectra exhibit a sharper transition during sample cooling and an increase of overall conductivity, which is implied by a growing fraction of the amorphous phase in the polymer matrix in which the ionic liquid is immobilized. The conductivity master curves illustrate that the changing of SPEs morphology is reflected in the low frequency regions governed by the electrode polarization effect. The dc conductivity of SPEs exhibits Vogel–Fulcher–Tammann temperature dependence and increases with the intensity of thermal treatment. Spectral densities of current fluctuations showed that flicker noise, thermal noise and shot noise seems to be major noise sources in all samples. The increase of electrolyte conductivity causes a decrease in bulk resistance and partially a decrease in charge transfer resistance, while also resulting in an increase in shot noise. However, the change of electrode material results in a more significant change of spectral density of current fluctuations than the modification of the preparation condition of the solid polymer electrolyte. Thus, the contact noise is considered to contribute to overall current fluctuations across the samples.

Single-walled carbon nanotube filled thermoplastic polyurethane nanocomposites: Influence of ionic liquid on dielectric properties

Electrically conductive nanocomposites based on thermoplastic polyurethane (TPU) and single walled carbon nanotube (SWCNT) have been successfully prepared by solution casting technique. Prior to mixing, SWCNT is first dispersed in DMF and ionic liquid 1-Allyl-3-methyl imidazolium chloride (AMIC). The SWCNT phase is uniformly dispersed in the ionic liquid (IL) containing systems as observed in HRTEM and FESEM photomicrographs. The dielectric properties like dielectric permittivity (ε'), AC conductivity (σac), real and imaginary parts of impedance (Z' and Z'') of TPU/SWCNT nanocomposites have been analysed in the frequency range of 1–106 Hz. A comparison study of the dielectric properties of the systems with and without IL are thoroughly investigated. Increasing trend of ε' with increasing the SWCNT loading is mostly due to the increase in polarizable dipoles and adequate interfacial polarization of the charge carriers in the field direction. Frequent hopping and tunnelling mechanism with increasing the SWCNT loading is mainly responsible for the hike in σac. The increase in close proximity between the conductive channels with increase in conductive SWCNT loading and incorporation of IL reflects from the decrease in Zʹ and Z ʹʹ of the systems. The semi-circular nature of the Nyquist plot informs about the dielectric and capacitive characteristics of the developed nanocomposites and the decrease in area under the Nyquist plot significantly explains about the decrease in bulk resistivity.

The Study of the Degree of Crystallinity, Electrical Equivalent Circuit, and Dielectric Properties of Polyvinyl Alcohol (PVA)-Based Biopolymer Electrolytes.

This report presents a facile and efficient methodology for the fabrication of plasticized polyvinyl alcohol (PVA):chitosan (CS) polymer electrolytes using a solution cast technique. Regarding characterizations of electrical properties and structural behavior, the electrochemical impedance spectroscopy (EIS) and X-ray diffraction (XRD) are used, respectively. Crystalline peaks appear in the XRD pattern of the PVA:CS:NH4I while no peaks can be seen in the XRD pattern of plasticized systems. The degree of crystallinity is calculated for all the samples from the deconvoluted area of crystalline and amorphous phases. Considering the EIS measurements, the most conductive plasticized system shows a relatively high conductivity of (1.37 × 10−4) S/cm, which is eligible for applications in energy storage devices. The analysis of the EIS spectra reveals a decrease in bulk resistance which indicates an increase in free ion carriers. The electrical equivalent circuit (EEC) model is used in the analysis of EIS plots. Dielectric properties are modified with the addition of glycerol as a plasticizer. It is proved that the addition of glycerol as a plasticizer lowers ion association. It also shows, at the low-frequency region, a large value of a dielectric constant which is correlated with electrode polarization (EP). The distribution of relaxation times is associated with conducting ions.

Dielectric Relaxation Behavior of Silver Nanoparticles and Graphene Oxide Embedded Poly(vinyl alcohol) Nanocomposite Film: An Effect of Ionic Liquid and Temperature.

This paper presents the dielectric characteristics of nanocomposite films of poly(vinyl alcohol) (PVA) embedded with silver (Ag) nanoparticles and graphene oxide(GO). The nanocomposite films were fabricated by using the solvent casting approach. The morphological analysis was carried out through scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The dielectric relaxation behavior of nanocomposite films was analyzed in the frequency range of 101 to 106 Hz, by varying GO loading. The temperature effect was investigated over the temperature range of 40 to 150 °C. The effect of ionic liquid (IL) was also explored by comparing the dielectric behavior of films fabricated without using ionic liquid. The conductive filler loading variation showed a significant effect on dielectric permittivity(ε′), complex impedance (Z*) and electric conductivity (σac). The obtained results revealed that the dielectric permittivity (ε′) increased by incorporating Ag nanoparticles and increasing GO loading in PVA matrix. An incremental trend in dielectric permittivity was observed on increasing the temperature, which is attributed to tunneling and hopping mechanism. With an increase in nanofiller loading, the real part of impedance (Z′) and imaginary part of impedance (Z″) were found to decrease. Further, the semicircular nature of Nyquist plot indicated the decrease in bulk resistivity on increasing GO loading, temperature and incorporating ionic liquid. On the basis of above findings, the obtained GO-Ag-PVA nanocomposite films can find promising applications in charge storage devices.

Dielectric relaxation in a cadmium chloride-doped polymeric blend

The temperature- and frequency-dependent relaxation processes in films of a polymeric blend comprising a polyvinyl alcohol (PVA)/polyvinyl acetate (PVAc) co-polymer blended with polyvinyl pyrrolidone (PVP) in equal proportion by weight, and doped with an inorganic metallic salt, cadmium chloride $$(\hbox {CdCl}_{2})$$ , at 0.0 wt% and 10.2 wt% doping levels (DLs), have been studied using dielectric relaxation spectroscopy (DRS). The frequency response of dielectric parameters for these samples has been studied with variation in temperature, from 303 up to 373 K, at different fixed frequencies (from 12 Hz up to 200 kHz). Study of Cole–Cole plots reveals a decrease in bulk resistivity of the samples with increase in temperature, which is attributed to thermally induced increase in the mobility of polymer chains. A 10-fold increase in bulk conductivity is observed for doped films with a DL of 10.2 wt%, when compared with the bulk conductivity of the un-doped (0.0 wt% DL) sample. The temperature dependence of dielectric parameters at different frequencies has been studied and the activation energy has been calculated. The relaxation time is found to be of the order of a few milliseconds, which implies that electrical conduction in $$\hbox {CdCl}_{2}$$ -doped PVA/PVAc–PVP blend films is predominantly due to the migration of ions. The variation of AC conductivity with frequency is in agreement with Jonscher’s universal power law. AC conductivity of the sample is found to increase significantly with an increase in temperature of the sample. Frequency-dependent dielectric properties of $$\hbox {CdCl}_{2}$$ -doped PVA/PVAc–PVP blend films, for various DLs, are also studied at room temperature.

Effect of temperature and electron beam irradiation on the dielectric properties and electromagnetic interference shielding effectiveness of ethylene acrylic elastomer/millable polyurethane/SWCNT nanocomposites

The blend nanocomposites based on single-walled carbon nanotubes (SWCNT), ethylene acrylic elastomers (AEM) and millable polyurethane (MPU) have been successfully prepared with 0.5 to 5 parts by weight/volume per hundred parts of rubber(phr) of SWCNT loading loading. The sheets prepared by using hydraulic press have been exposed to electron beam (EB) to induce cross-linked networks. The characteristic shifting of CO vibration in the FTIR spectra confirms the formation of hydrogen bonding between the two phases. The SWCNT filler dispersion in blend phase has been analyzed by high-resolution transmission electron microscope (HRTEM). The effect of SWCNT and EB dose on cross-link density, swelling, gel fraction and dielectric properties have been studied. The cross-linked density increases with an increase in radiation doses and SWCNT loading, which is confirmed from Flory-Rehner analysis. The swelling percent of the EB cross-linked nanocomposites decreases with increase in EB dose and SWCNT loading. However, the gel fraction increases with increase in EB dose and SWCNT loading. The dielectric relaxation behavior of the EB-treated nanocomposites has been analyzed in a wide range of frequency (1–106 Hz), temperature (25–120 °C), EB dose (50–400 kGy) and SWCNT loading (0.5–5.0 phr). The increase in temperature and SWCNT loading, the dielectric permittivity (ε′) increases, however with EB dose ε′ exhibits a decreasing behavior. This can be explained on the basis of interfacial polarization of the SWCNT phase in the interface. The blend nanocomposites show an increasing trend of AC conductivity (σac) with the increase in SWCNT loading, EB dose, and temperature which is due to the hopping and tunneling mechanism. The blend nanocomposites show the percolation behavior in the range of 1.46 phr SWCNT with respect to σac value. The real and imaginary parts of the impedance (Z′ and Z′′) have been found to decrease with increase in SWCNT loading. Semicircular nature of the Nyquist plot explains the decrease in bulk resistivity of the systems with SWCNT loading and temperature. The electromagnetic interference shielding effectiveness (EMI SE) of the fabricated conductive nanocomposites has been studied in the frequency range of 2 × 109–8 × 109 Hz and reflection occurring at the surface (SER), absorption of the electromagnetic radiation (SEA) and the total shielding effectiveness (EMI SE) of the external electromagnetic radiation by the developed nanocomposites have been measured. The effect of SWCNT loading, radiation dose and frequency on SER, SEA and EMI SE have been analyzed and SEA and EMI SE are increased with an increase in both SWCNT and radiation dose.

High remnant polarization, high dielectric constant and impedance performance of Nb/In Co-doped Bi0.49La0.01Na0.49Li0.01TiO3-δ ceramics

The new ferroelectric oxides, Bi0.49La0.01Na0.49Li0.01Ti0.99(Nb1-xInx)0.01O3-δ (hereafter abbreviated as BLNLTN1-xIx), with x = 0.5–0.65 were fabricated using conventional solid state reaction method. The effects of Niobium (Nb) and Indium (In) as B-site substitutions on phase, microstructure, dielectric, ferroelectric, complex impedance and complex electric modulus properties were systemically analyzed. Hysteresis graphs indicated that BLNLTN0.5I0.5 comparatively have the highest remnant polarization (Pr) of about 49.83 µC/cm2. Moreover, the dielectric studies of BLNLTN0.5I0.5 showed the highest relative dielectric constant (εr) i.e. 4599.3 in comparison to all other compositions. In addition, it also indicated very small loss of <0.045 at 1kHz over a broad range of temperature i.e. room temperature (RT) to 380°C. By comparing BLNLTN0.5I0.5 with BNT, Pr and εr were increased 13.46% and 26.3%, respectively whereas coercive electric field (Ec) and tanδ were decreased 41.06% and 1.96%, respectively. The impedance analysis for BLNLTN0.5I0.5 revealed a gradual decrease in bulk resistance (Rb) with the increase in temperature. Also, it showed negative temperature coefficient of resistance (NTCR) property at 500–800°C and a polydispersive non-debye type relaxation at 800°C. The complex electric modulus analysis proved that effect is mainly due to the bulk grains. Their basic analysis i.e. XRD and SEM studies showed a single phase perovskite structure, spherical grain shape and decreasing average grain size trend with increasing x content. The overall analysis has confirmed the significance of Nb/In co-doping in Bi0.49La0.01Na0.49Li0.01TiO3-δ and showed it as a capable dielectric material for fabricating high-temperature ceramic capacitors.

Impedance Spectroscopy Study of Hydrothermally Synthesized Nano-semiconducting Bornite (Cu5FeS4)

Chalcogenide compound Bornite (Cu5FeS4) was prepared by hydrothermal synthesis method. Here, Citric acid (CA) was introduced in the hydrothermal reaction as a chelating agent to get the phase purity in the Bornite product. The room temperature Powder X-Ray Diffraction (PXRD) confirms the phase purity with cubic crystal structure. The Field Emission Scanning Electron Microscope (FESEM) image confirms the formation of flower shaped micro architecture consisting nano-flakes of the synthesized Bornite material and the optical band gap energy (=1.87 eV) was estimated from UV-VIS absorption spectra. Room temperature (303 K) Complex Impedance Spectroscopy (CIS) study for different forward dc bias voltages (0V-0.8V) on the thin film of synthesized material was performed. CIS analysis demonstrates the relaxation phenomenon and decrease in bulk resistance with increasing forward dc bias voltages reveals the involvement of bulk resistance in electrical conduction mechanism. Moreover the dependency of ac/dc conductivity on the forward dc bias voltage was analyzed on the basis of hopping mechanism for electrical transport processes.

Optoelectronic properties of hybrid diodes based on vanadyl-phthalocyanine and zinc oxide

We report an investigation of the optoelectronic properties of a hybrid p-n diode device fabricated using ZnO film prepared by sol-gel technique on which a VOPc organic film is deposited by vacuum evaporation. The charge transport properties of devices having the configurations ITO/ZnO/Al and ITO/ZnO/VOPc/MoO3/Al were investigated at different annealing temperatures (150 °C, 250 °C, 350 °C and 450 °C) by Impedance Spectroscopy (IS). The structural, morphological, optical and electrical properties were also studied at different annealing temperatures. The parameters related to the ITO/ZnO and ZnO/VOPc interfaces such as ideality factor (n), barrier height (qϕB) and rectification ratio (RR) of the diodes were determined from current density-voltage (J-V) characteristics. IS measurements suggest that the large photocurrent generated is due to the decrease in bulk resistance of the device on account of the generation of electron-hole pairs in the organic active layer when exposed to light. The RR and the photocurrent responsivity (Rph) values obtained from the J-V characteristics compare well with those obtained from the IS measurements. It was observed that the absolute value of Rph (470 mA/W) for the p-n diode with ZnO annealed at 350 °C is high compared to that of diodes with different ZnO annealing temperatures. These values also agree well with the values obtained for p-n diodes of other phthalocyanines. Our studies clearly demonstrate that a p-n diode with ZnO film annealed at 350 °C exhibits much better optoelectronic characteristics on account of increased grain size, improved charge injection due to the reduction of barrier height and hence higher (up to 5 orders) charge carrier mobility.

Impedance spectroscopy analysis of Ba 5NdTi 3Nb 7O 30 ferroelectric ceramic

The polycrystalline sample of Ba 5NdTi 3Nb 7O 30, a member of tungsten bronze family, was prepared by solid-state reaction method. X-ray diffraction (XRD) analysis shows the formation of single-phase compound with an orthorhombic structure. Scanning electron micrograph of the material shows uniform grain distribution throughout the sample. Variation of dielectric constant ( ε′ r ) with temperature at different frequencies shows that the compound has a dielectric anomaly of ferroelectric to paraelectric type at 100 °C, and exhibits non-relaxor kind of diffuse phase transition. Studies of electrical properties of Ba 5NdTi 3Nb 7O 30 using the complex impedance spectroscopy (CIS) technique show the decrease in bulk resistance with rise in temperature indicating a typical negative temperature coefficient of resistance (NTCR)-type behaviour. A possible hopping mechanism for electrical transport in the system is evident from the modulus analysis.

Organic Photodetectors Based on Phthalocyanine and Fullerenes: Dielectric Properties

Fabrication and characterization of organic photodetectors based on copper phthalocyanine and fullerenes are presented. We study current-voltage and impedance characteristics of the devices under dark and varied illumination conditions. The current-voltage characteristics in the reverse bias show little or no dark current and large photocurrent. The results show that photocurrent in the devices is associated with a decrease in bulk resistance and an increase in dielectric constant of the active material.

Characterization of electrical properties of Pb-modified BaSnO 3 using impedance spectroscopy

The electrical properties of Pb-modified BaSnO 3 having general formula Ba 1− x Pb x O 3 ( x = 0, 0.05, 0.10, 0.15) were investigated by ac impedance spectroscopy over a wide range of temperature up to 500 °C starting from room temperature in the frequency range 100 Hz–1 MHz. X-ray diffraction (XRD) studies have confirmed the formation of a single-phase compound. Scanning electron micrographs show polycrystalline texture of the material. The surface property indicates considerable change with increased number of voids on Pb doping suggesting an increase of porosity in the material. Complex impedance spectrum indicates a decrease in bulk resistance ( R b) with increase in temperature. Bulk resistance of the material has been observed to be concentration dependent. Conductivity analysis indicates that both ac and dc conductivity of the materials increases with increase in temperature. It shows a typical negative temperature coefficient of resistance (NTCR) behaviour like a semiconductor. The conductivity has been found to decrease initially on Pb doping. A maximum conductivity value of ∼1.01 × 10 −4 Ω m −1 has been observed for 15 wt.% doping of Pb at 500 °C. The electrical modulus analysis provides evidence of single conductivity relaxation of polydispersive nature for both the pure and modified BaSnO 3.