AC Electrical Properties Research Articles

AC and DC electrical properties of graphene nanoplatelets reinforced epoxy syntactic foam**This work was carried out at Southern University, Mechanical Engineering Department, Baton Rouge, LA 70802, United States of America.

Benefits of employing graphene nanopletlates (GNPLs) in composite structures include mechanical as well as multifunctional properties. Understanding the impedance behavior of GNPLs reinforced syntactic foams may open new applications for syntactic foam composites. In this work, GNPLs reinforced syntactic foams were fabricated and tested for DC and AC electrical properties. Four sets of syntactic foam samples containing 0, 0.1, 0.3, and 0.5 vol% of GNPLs were fabricated and tested. Significant increase in conductivity of syntactic foams due to the addition of GNPLs was noted. AC impedance measurements indicated that the GNPLs syntactic foams become frequency dependent as the volume fraction of GNPLs increases. With addition of GNPLs, the characteristic of the syntactic foams are also observed to transition from dominant capacitive to dominant resistive behavior.

Structural and AC electrical properties study of solid metal urea complexes

The complexation of solid urea with (Co[Formula: see text]), (Cu[Formula: see text]) or (Ni[Formula: see text]) ions has been studied by using dielectric spectroscopy technique over a wide frequency range at different temperatures. Samples' structure were investigated by XRD, FTIR and FT-Raman spectroscopy. FTIR and Raman analysis indicated that the urea coordinates with the metal atoms through the same oxygen–metal bond (O–M). Furthermore, XRD analysis showed that the samples have polycrystalline structure with single phase. The permittivity of complexes was found at much higher values than that of the ligand (pure urea), showing structure dependency. Furthermore, two relaxation peaks were observed in the dielectric loss spectra corresponding to the orientation polarization of urea molecule, and some parts of urea molecule may be NH2 groups. Both relaxation peaks correspond to thermally activated because they were shifted to higher frequency with the temperature increase. The peak position for the low frequency relaxation peak was observed at the same relaxation time ([Formula: see text][Formula: see text]s), corresponding to the coordination mode through the same O–M bond. Novelty of this work is the successful finding of the relationship between the crystalline phase, coordination mode and the dynamic molecular behavior of solid urea and its complexes using the dielectric spectroscopy technique.

Electronic conduction mechanism and optical spectroscopy of Indigo carmine as novel organic semiconductors

Indigo carmine (IC) is an organic material dye that can be used as an organic semiconductor. The IC powder pellet was characterized by X-ray diffraction (XRD), Fourier transforms infrared spectroscopy, AC\DC electric conductivity and optical diffused reflectance spectroscopy. The XRD measurements revealed that the IC powder is crystallized in triclinic system structure with the space group P1 and both the optimized lattice and refinement cell parameters have calculated before and after refinement for the first time by using the program Crysfire and Checkcell software. The Kubelka–Munk model was used to determine the band gap energies of the IC powder pellet. Based on this model, the IC powder pellet presents two band gaps equal to 1.982 and 1.689 eV in the studied photon energy ranges. The first optical band gap (1.982 eV) is related to the basic HOMO–LUMO transition, and the other optical transition gap (1.689) is related to the trap inside the HOMO–LUMO gap i.e. onset/inset gap. The multi-band gap of IC powder can enhance the light absorption and can make this material suitable for organic solar cell devices. The dielectric parameters are analyzed and investigated. The DC electrical conductivity upon reciprocal (1000/T) of IC powder was determined by using the two-probe electrical conductivity measuring instrument. The AC electrical conductivity and dielectric properties can support the charge-hopping carriers of barriers of various heights. IC is a promising organic semiconductor material for various aspects in the field of organic technology.

Zn doped NiFe2O4- Pb (Zr0.58Ti0.42)O3 multiferroic nanocomposites: Magnetoelectric coupling, dielectric and electrical transport

We have investigated the room temperature magnetoelectric coupling, temperature dependent impedance and dielectric properties of xZn0.3Ni0.7Fe2O4 – (1-x) Pb (Zr0.58Ti0.42)O3 (x = 0.2, 0.3, 0.4 and 0.5) nanocomposites. The nanocomposites have been prepared through low temperature chemical pyrophoric reaction process followed by solid state reaction route. The magnetoelectric coupling has been measured as a function of applied magnetic field at different frequencies and different angles between applied magnetic field and measured electric field. The observed magnetoelectric coupling may be due to the field dependent magnetostriction of the piezomagnetic phase of the composite. Noticeably, the magnetoelectric coupling is strongly depended on the frequencies, angles and volume fraction of the piezomagnetic phase of the nanocomposites. Polarization – Electric field loop shows the room temperature ferroelectric nature of nanocomposites. The ac electrical properties of the nanocomposites have been studied employing impedance spectroscopy technique. The temperature dependent impedance studies reveal the grain boundaries plays the dominating role. Thermally tunable dielectric properties of nanocomposites exhibit the Maxwell – Wagner interfacial polarization in the system. Electromechanical resonance response is observed at the higher frequency region. The ac conductivity of the nanocomposites has been investigated at different temperatures and fitted by Jonscher's power law. The conduction mechanism is mainly due to the small and large polaronic hopping in the system.

Light tuning DC and AC electrical properties of ZnO-rGO based hybrid nanocomposite film

We have investigated the electrical and optoelectrical properties of a zinc oxide (ZnO):reduced graphene oxide (rGO) nanocomposite film prepared through the sol gel process on a glass substrate under dark and illumination conditions of light. The bandgap of the composite film is decreased from the pure ZnO nanofilm due to the formation of a Zn-O-C bond in the composite film. The linear behavior in the Current-Voltage curve is attributed to Ohmic contact between ZnO and rGO grains. The photocurrent of the composite film is found to increase with an increase in light intensity having two different slopes, indicating an enhancement of the mobility of carriers and dissociation rate of excitons. The observed decrement of the impedance value with the intensity of light may be due to the flow of charge carriers and the presence of the light dependent relaxation process in the system. Nyquist plots have been fitted using a parallel combination of grain boundary resistances and grain boundary capacitance at different intensities of light. The relaxation frequency is observed to shift towards the high frequency regime. Carrier transit time has been calculated from relaxation frequency showing opposite behavior with the intensity of light. These results indicate the higher generations of photogenerated carriers at the interface between rGO and ZnO grains and an enhancement of the charge transport process due to the increment of the mobility of charge carriers in the system.

Thermal and ac electrical properties of N-methylanthranilic acid below room temperature

In this study, we investigated the thermal and alternating current (ac) electrical properties of N-methylanthranilic acid. Based on data obtained by differential scanning calorimetry, we detected two endothermic transitions at ≈ 213 K and ≈265.41 K. The weakening of hydrogen bonds as the temperature increased appeared to be the main cause of these phase transitions. We also recorded the melting point at about 475.5 K. Both the ac conductivity (σac) and complex dielectric constant (ε∗=ε'−jε'') were studied as functions of temperature over the frequency range from 1 kHz to 100 kHz. We observed significant variations in the thermal and electrical properties before and after the transition temperature at 265.41 K. The conduction mechanism responsible for the ac electrical properties before this transition was due to overlapping large polarons. These novel results are expected to have impacts on the application of organic semiconductors and dielectrics.

Electrical and gas sensing properties of novel cobalt(II), copper(II), manganese(III) phthalocyanines carrying ethyl 7-oxy-4,8-dimethylcoumarin-3-propanoate moieties

The synthesis of metallophthalocyanines (M [Formula: see text] Co, Cu, Mn) bearing four ethyl 7-oxy-4,8-dimethylcoumarin-3-propanoate moieties was performed. These novel compounds were characterized by elemental analysis, [Formula: see text]H-NMR spectroscopy, FT-IR, UV-vis and mass spectral data. DC and AC electrical properties of the films of metallophthalocyanines were investigated in the temperature range of 295–523 K. AC measurements were performed in the frequency range of 40–10[Formula: see text] Hz. Activation energy values of the films took place between 0.55 eV–0.93 eV. Impedance spectroscopy measurements revealed that bulk resistance decreases with increasing temperature, indicating semiconductor properties. DC conductivity results also supported this result. Their gas sensing properties were also investigated for the vapors of Volatile Organic Compounds (VOCs), [Formula: see text]-butyl acetate (200–3200 ppm) and ammonia (7000–56000 ppm) between temperatures 25–100°C. Sensitivity and response times of the films for the tested vapors were reported. The results were found to be reversible and sensitive to the vapors of [Formula: see text]-butyl acetate and ammonia. It was found that Mn(OAc)Pc showed better sensitivity than CoPc and CuPc for [Formula: see text]-butyl acetate vapors at all measured vapor concentrations and temperatures. Mn(OAc)Pc also showed better sensitivity than CoPc and CuPc for ammonia vapors at 22°C.

Current–voltage hysteresis and dielectric properties of PVA coated MWCNT film

In this work, we have prepared polyvinyl alcohol (PVA) coated multiwall carbon nanotube (MWCNT) film by an in situ chemical oxidative preparation technique. The thermogravimetric analysis clearly explains the thermal degradation of pure polymer and polymer nanocomposite film. We have studied the AC electrical transport properties and current–voltage (I–V) characteristic of PVA–MWCNT composites within the temperature range 300 ≤ T ≤ 423 K and frequency range 150 Hz ≤ f ≤ 2 MHz. It is observed that the dielectric constant of the composite film increases significantly. The frequency variation of AC conductivity follows the power law ( $$ \omega^{S} $$ ) and a sharp transition from small polaron tunneling to correlated barrier hopping model is found. The imaginary part of electric modulus shows non-Debye type asymmetric behaviour. The impedance spectroscopy shows the negative temperature coefficient of resistance of the composite film. Nyquist plot of the composite film at different temperatures is established from impedance measurement. The current–voltage characteristic (under ± 20 V) shows hysteresis behaviour and field dependent resistance. We simulate the experimentally observed current density–electric field data with the established theory.

Multiple electrical phase transitions in Al substituted barium hexaferrite

Barium hexaferrite is known to be a very good ferromagnetic material. However, it shows very good dielectric properties, i.e., the dielectric constant is comparable to that of the ferroelectric material. However, its crystal symmetry does not allow it to be a ferroelectric material. Hence, the electrical properties have revived the considerable research interest on these materials, not only for academic interest, but also for technological applications. There are a few reports on temperature dependent dielectric behavior of these materials. However, the exact cause of dielectric as well as electrical conductivity is yet to be established. Hence, Al (very good conducting material) substituted barium hexaferrite (BaFe12−xAlxO19, x = 0.0–4.0) has been prepared by following the modified sol-gel method to understand the ac and DC electrical properties of these materials. The crystal structure and parameters have been studied by employing the XRD and FTIR techniques. There are two transition temperatures, which have been observed in the temperature dependent ac dielectric and DC resistivity measurement. The response of dielectric behaviors to temperature is similar to that of the ferroelectric material; however, the dielectric polarization is due to the polaron hopping, which is evident from the DC resistivity analysis. Hence, the present observations lead to understand the electrical properties of barium hexaferrite. The frequency dependent dielectric dispersion can be understood by the modified Debye model. More interestingly, the dielectric constant decreases and DC resistivity increases with the increase in the Al concentration, which has the correlation between bond length modifications in the crystal due to substitution.

Hydrothermal synthesis, structural, electrical and magnetic studies of cathode material Li2FeZrO4 for lithium ion batteries

In this present work, Li2FeZrO4 has been synthesized by hydrothermal method. The material is characterized using XRD, TGA, FTIR, UV–Vis, VSM and impedance spectroscopy. The powder XRD patterns of Li2FeZrO4 sintered at 800 °C shows that these crystallites are stable in room temperature with tetragonal structure of space group p141 and the average crystallites size is found to be 38 nm. Due to its structural stability, ac electrical properties in terms of complex Impedance Z*(ω), complex permittivity e*(ω), complex conductivity σ*(ω) and complex electric modulus M*(ω) of the sample have been evaluated as a function of frequency at different temperatures. The shape of the impedance spectra reveals the non-Debye nature of the relaxation processes of the present material. The relaxation process consists of two different polarization processes i.e., hopping charge polarization (“pinned dipole”) and dielectric dipolar like polarization (“free dipole”) mechanism. The dc conductivity activation energy E σ has been calculated for the material along with the activation energy for hopping conduction and dielectric relaxation. Magnetic properties have been investigated by vibrating sample magnetometer (VSM) for the sample at various temperatures.

Prediction of filler/matrix interphase effects on AC and DC electrical properties of carbon reinforced polymer composites

This study predicts the effect of the conducting filler/insulating matrix interphase on the electrical properties of two series of percolated systems, differing from the type of carbon black particles mixed in an amine‐cured epoxy matrix, diglycidylic ether of bisphenol F. To take into account the interactions between the conducting filler and the matrix, as well as filler–filler overlapping, we introduce three parameters, characteristic of the interphase zone, such as concentration, conductivity and volume, on the generalized effective medium (GEM) model for DC and AC electrical conductivities. These interphase parameters, characterizing the boundary of the shaded zone between the macromolecular chain and the conducting particles, depend on the filler type and concentration. One output of GEM‐modified model is that it provides a mean to estimate the volume, concentration and intrinsic conductivity of the interphase in a composite by fitting the experimental data over a broad range of frequency. POLYM. COMPOS., 40:346–352, 2019. © 2017 Society of Plastics Engineers

Magnetoelectric coupling and AC electrical properties of xLa0.7Sr0.3MnO3 – (1-x) HoMnO3 (x = 0.1, 0.3 and 0.5) lead free multiferroic nanocomposites

We have investigated magnetoelectric effect and ac electrical properties of xLa0.7Sr0.3MnO3 (LSMO) - (1-x) HoMnO3 (HMO) (x = 0.1, 0.3 and 0.5) multiferroic nanocomposites prepared through low temperature pyrophoric reaction method. The series of nanocomposites have been found to exhibit room temperature ferroelectric and ferromagnetic behaviour. The magnetoelectric response has been detected in this series of lead free nanocomposites at room temperature. The ac electrical properties of this series of composite have been studied employing impedance spectroscopy technique. The value of impedance has been found to be decreased with increase in magnetic field. This observation has been attributed to the depinning of LSMO domain walls at the grain boundaries pinning centres and thereby enhancing the spin dependent transport mechanism in the composites. Moreover, impedance has been observed to decrease with increase in both frequency and temperature due to the charge carrier or polarons of the system acquiring sufficient amount of thermal energy to overcome the high resistive barrier. Nyquist plots at different temperatures have been fitted using parallel combinations of grain boundaries resistance and grain boundaries capacitance for LSMO and HMO grains, where grain boundaries resistances are found to decrease with increase in temperatures. Furthermore, we have estimated activation energy of those composites at a same temperature range using Arrhenius relation.

XZn0.3Ni0.7Fe2O4–(1 − x)HoMnO3 (x = 0.1, 0.3 and 0.5) nanocomposites: magnetoelectric, magnetodielectric and AC electrical response

We have investigated room temperature magnetoelectric coupling, magnetic fields and temperatures dependent ac electrical properties of chemically synthesized xZn0.3Ni0.7Fe2O4–(1 − x)HoMnO3 (x = 0.1, 0.3 and 0.5) nanocomposites. The magnetoelectric voltage is measured in both longitudinal and transverse direction. The value of magnetodielectric effect and magnetoimpedance is found to ~18 and ~20% for magnetostriction property of the magnetostictive material of the samples. Nyquist plots have been fitted using parallel combinations of resistances-constant phase element circuits showing dominant role of grain boundaries and interface of two types of grains of the samples. We have estimated activation energy of those composite using Arrhenius relation from relaxation frequencies and further verified from dielectric measurement. AC conductivity curves follow a Jonscher’s double power law attributing the conduction mechanism for the small and large polaronic hopping in the system.

AC and DC electrical conductivity, dielectric and magnetic properties of Co0.65Zn0.35Fe2−x Mo x O4 (x = 0.0, 0.1 and 0.2) ferrites

Cobalt–Zinc ferrites are an important material for designing multiferroic composite. The Mo (4d-transition metal) doped Cobalt–Zinc ferrites are synthesized using ceramic (solid-state reaction) method. Investigation of detailed ac and dc electrical conductivity, dielectric and magnetic properties of Co0.65Zn0.35Fe2−x Mo x O4 (x = 0.0, 0.1 and 0.2) spinel ferrites have been reported here. The recorded XRD pattern confirms the formation of inverse spinel structure of the material. The dielectric dispersion has been studied in detail and the existence of non-Debye type relaxation behavior has been confirmed. The dielectric tangent loss is found to be very small at high frequency. The ac conductivity follows the correlated barrier hopping like model. Also the conduction process can be best explained on the basis of Verwey-de Boer mechanism. Magnetic phase transition of the material is estimated from magnetization vs. temperature plots.

Studies on AC Electrical Conductivity, Dielectric Properties and Ion Transport in PVA polymeric Electrolytes

Studies on AC Electrical Conductivity, Dielectric Properties and Ion Transport in PVA polymeric Electrolytes

Study of complex impedance spectroscopic properties of the α-NaCuPO4 compound

In the present study, α-NaCuPO4 compound was prepared by solid-state reaction method and characterized by X-ray powder diffraction and infrared spectroscopy. The AC electrical conductivity and dielectric relaxation properties of this compound have been investigated by means of impedance spectroscopy measurements over a wide range of frequencies and temperatures 209 Hz–1 MHz and 598–708 K, respectively. Both impedance and modulus analysis exhibit the grain and grain boundary contribution in the electrical response of the sample. It was found that the data of the AC measurements follow the overlapping large polaron tunneling model and the model’s parameters were determined.

Signature of magnetoelectric coupling of xNiFe2O4 – (1-x)HoMnO3 (x = 0.1 and 0.3) multiferroic nanocomposites

The magnetoelectric coupling of xNiFe2O4–(1-x)HoMnO3 (x=0.1 and 0.3) multiferroics nanocomposites prepared through low temperature chemical pyrophoric reaction process has been investigated at room temperature. The signature of magnetoelectric coefficient of these nanocomposites is mainly due to the magnetostriction and magnetodielectric properties of the materials. These nanocomposites show the ferroelectric behaviour at room temperature. AC electrical properties of nanocomposites have been studied with applied magnetic fields and temperatures. Nyquist plots at different magnetic fields and temperatures have been fitted using parallel combinations of resistance-capacitor circuits. Moreover, we have estimated activation energy of those composites using Arrhenius relation, which indicates that same kinds of charge carrier are responsible for relaxation process in grain boundaries and grain of the sample. Furthermore, from the analysis of ac conductivity data as a function of frequency is attributed to the large polaronic hopping in the conduction process in the system.

Polymer complexes. LXVII: electrical conductivity and thermal properties of polymer complexes of quinoline azo dye

A novel series of divalent transition metals (Cu2+, Co2+ and Ni2+) polymer complexes of azo ligand named 5-(2,3-dimethyl-1-phenylpyrazol-5-one azo)-8-hydroxyquinoline (Q) have been synthesized. The azo quinoline ligand (Q) and polymer complexes are characterized by various physicochemical techniques. The thermal properties of the ligand and its isolated polymer complexes are studied using thermogravimetric analysis. The physicochemical investigations elucidate that the azo ligand acts as a neutral bis(bidentate) ligand. The polymer complexes are found to be octahedral geometry. The change in the ac electrical conductivity, loss tangent and dielectric properties are studied upon heating in temperature region 298–550 K and frequency ranging from 0.1 to 100 kHz, moreover, the mechanism of conduction is determined. The electrical conductivity studies indicate that the ligand (Q) and polymer complexes have the semiconducting behavior. The correlated barrier hopping is the dominant conduction mechanism for all samples.

Effect of oxygen vacancies on SrTiO3 electrical properties

SrTiO3-δ (δ = 0.075, 0.125 and 0.25) were prepared in two steps: the preparation of the parent compound SrTiO3 by the solid state reaction method followed by the creation of oxygen vacancies δ, through a thermally activated process. X-ray diffraction analysis shows that all samples crystallize in the cubic structure with Pm3m space group. The grain's size distribution and the samples' surface characteristics were assessed by scanning electron microscopy. Impedance spectroscopy was used to characterize the ac electrical properties of these materials as a function of frequency at various temperatures (240–340 K). The impedance data was well fitted to an (R1CPE1)//(R2CPE2) equivalent electrical circuit model. It was found that the electrical behavior of the ceramics is dominated by the grain-boundary response and increased conductivity values were found for a large amount of oxygen vacancy. The frequency dependence of the conductivity was investigated through the Jonscher's universal power law and the electrical conduction mechanism was found to be strongly dependent on the oxygen vacancies concentration.

Dielectric properties and impedance analysis of polycrystalline Li-Si ferrite prepared by high energy ball milling technique

The effect of Si substitution on the ac electrical conductivity, dielectric and impedance properties of Li0.5+0.5xSixFe2.5−1.5xO4 (0≤x≤0.6) ferrite synthesized by high energy ball milling technique has been reported. The ac measurements were performed over a wide range of frequencies from 100Hz up to 1MHz and as a function of temperature from room temperature up to 960K. Ac electrical conductivity as a function of frequency and temperature exhibited a semiconducting behavior. Small polaron hopping conduction mechanism has been observed in all compositions. For the samples with x=0.0 and 0.1, the correlated barrier hopping mechanism was noticed at first, followed by the small polaron hopping conduction mechanism. The dielectric constant έ and dielectric loss ε″ decrease with increasing frequency and remain constant at higher frequencies, showing the usual dielectric dispersion. The dispersion of the dielectric properties was discussed through Koop’s phenomenological theory. The low dielectric loss tangent at higher frequencies makes the opportunity of these ferrites for high frequency applications. The impedance spectroscopy technique was utilized to investigate the effect of grain and grain boundary on the electrical properties of the present series.