Frequency Dependent Electrical Modulus Research Articles

The effects of frequency change on dielectric characteristics in dye-based organic layers

In order to examine the dielectric properties of the Au/B1/p-Si, Au/B2/p-Si, Au/B3/p-Si and Au/B4/p-Si structures, BODIPY dye-based organic layers was coated as a thin film between the metal-semiconductor as the interface. Electrical conductivity, real and imaginary parts of the electrical module, dielectric loss and dielectric constant parameters were calculated in the frequency range of 100–1000 kHz at room temperature. The effect of frequency on dielectric constant and dielectric loss values was not regular in forward bias for Au/B1/p-Si and Au/B2/p-Si at low frequency, but was consistent with frequency for Au/B3/p-Si and Au/B4/p-Si. Dielectric parameters generally behaved as functions of voltage and frequency. The changes in the frequency-dependent electrical modulus were attributed to the relaxation process, polarization, and surface conditions.

Dielectric and physical properties of aqueous solutions of 1,3-dimethylurea at 298.15 K

The complex dielectric function ε*(ω) = ε'(ω)-jε“(ω) is studied for aqueous solutions of 1,3-dimethylurea (1,3-DMU) at constant temperature 298.15 K across the frequency range 20 Hz to 2 MHz. Dielectric properties are measured using Agilent E 4980 precision LCR meter with a four terminal liquid test fixture (Agilent-16452). From measured dielectric data, the frequency dependent electric modulus M*(ω), electrical conductivity σ*(ω) and complex impedance spectra Z*(ω) were obtained. Effects of concentration variation of 1,3-DMU in distilled water on dielectric and electrical properties are discussed to gain information about the self-aggregative nature of 1,3-dimethylurea and dissociation process in aqueous solutions. Density, viscosity, and refractive index of all the solutions are measured and reported.

Comparative study of the effect of different interlayer thicknesses on frequency dependent electric modulus and conductivity in Au/n-Si structures

Frequency dependent capacitance (C) and conductance (G/ω) data for Au/n-Si structures fabricated at room temperature without interlayers and with 5 nm and 10 nm aluminium-oxide (Al2O3) interlayer thicknesses are investigated. The Al2O3 interlayers were deposited by atomic layer deposition. Data on the complex electric modulus (M*) and alternating current electrical conductivity (σac) values are acquired for the three structures in the 3 kHz-3 MHz frequency range between (-3 V) – (+5 V) bias interval and compared. It was observed that the C and G/ω values decreased with the increase in frequency and interlayer thickness and that the frequency increases as a result of polarization which also increases M*, especially in 5 nm and 10 nm interlayered structures. Frequency and interlayer thickness increment have a positive impact by increasing σac, while conductivity has been shown to be highly sensitive to the presence of an interlayer and to its thickness.

Effect of La/Cr co-doping on dielectric dispersion of phase pure BiFeO3 nanoparticles for high frequency applications

Abstract Energy storage materials play a vital role in modern technology. A single device can perform multifunctions if fabricated using a multifunctional material like BiFeO3. For this purpose, a series of La and Cr doped BiFeO3 was synthesized using sol‒gel auto-combustion technique. A single phase rhombohedral distorted perovskite crystal structure related to bismuth ferrite with space group R3c (161) was confirmed from the X-ray diffraction patterns. Doping of La/Cr at Bi/Fe lattice sites in BiFeO3 did not affect the crystal symmetry of the parent compound. Morphological analysis exhibited homogeneous micro structures showing uniform distribution of multi-shaped grains with decreasing porosity and grain sizes with increasing Cr contents. These materials exhibited the conventional ferrite-like dielectric response, which gradually decreased with increasing frequency and lastly became constant in the high frequency regime. Impedance spectroscopy revealed the contribution of grains, grain boundaries and interfaces in electrical response of the samples. Frequency dependent electric modulus analysis confirmed the non-Debye type relaxation.

Structural, electrical and ferroelectric properties of lithium niobate-bismuth ferrite solid solutions

In this present communication, a polycrystalline lead-free system with composition Bi0.60Li0.40Fe0.60Nb0.40O3 (BLFNO termed further) is synthesized using a cheap conventional ceramic processing route. It featured with resistive, capacitive and dielectric properties of the synthesized composition. Room temperature XRD (X-ray diffraction) technique used to determine the single phase formation, structure and lattice parameters. The SEM micrograph reveals the non-uniform distribution of grains with highly dense grain growth. The complex impedance and modulus technique help to analyze the electrical properties of the sample. The frequency and temperature dependent electrical characteristics occurring in the sample were carried out in a wide temperature (25–500 °C) and frequency (1 kHz-1MHz) range. The Nyquist plot depicts the contribution of both grain and grain boundary effect in the prepared composition. The temperature dependent AC conductivity shows the activation energy for conduction. The frequency dependent electrical modulus and impedance analysis suggest non–Debye type relaxation behavior in the sample.

Frequency-Dependent Electric Modulus Spectroscopy of (Co3O4)x/(CuTl)-1223 Nanoparticles–Superconductor Composites

The (CuTl)0.5Ba2Ca2Cu3O10−δ {CuTl-1223} superconducting phase was synthesized by a well-established solid-state reaction route and the semiconducting antiferromagnetic cobalt oxide (Co3O4) nanoparticles were prepared by a chemical sol–gel method. The final (Co3O4)x/(CuTl)-1223; (x = 0–2.0 wt.%) nanoparticles–superconductor composites were obtained by adding Co3O4 nanoparticles in CuTl-1223 phase of the CuTl-based superconducting family. A temperature range of 77–298 K was chosen for frequency-dependent electric modulus spectroscopy measurements of (Co3O4)x/(CuTl)-1223 composites to interpret the dynamical aspects of electrical transport phenomena, such as ac-conductivity, carrier hopping rate, etc. The influence of grains as well as the grain boundaries on the ac-conduction properties was witnessed from the complex electric modulus spectra of these composite samples. The grain boundaries showed higher capacitance compared with the grains. This behavior of capacitance was decreased for grain boundaries and increased for grains with higher values of operating temperature in all the superconducting composite samples. The shifting of peaks towards a lower frequency regime in imaginary parts of the electric modulus spectra with increasing Co3O4 nanoparticle contents showed the presence of non-Debye-type relaxation within the material. The effects of these semiconducting antiferromagnetic Co3O4 nanoparticles on the ac-conduction mechanism of the host CuTl-1223 phase were studied, particularly in the perspective of the capacitive resistance contribution via electric modulus spectroscopy measurements.

The dielectric and electrical properties of bismuth oxide nanoparticles within organic network: the effect of temperature and the role of polarons

In this communication, we report the dielectric property of organic molecule functionalized bismuth oxide nanoparticles under different temperature and frequency condition. A large value of dielectric constant and a non-Debye type of relaxation phenomena has been witnessed due to the polaron induced polarization of the system. The frequency dependent electrical modulus of the material is discussed in the light of localized and non-localized relaxation process of the polaron. The AC-conductivity behaviour is modeled based on two different mechanisms, (a) polaron tunneling (at lower frequency) and (b) polaron hopping (at higher frequency). The organic-inorganic hybrid system also exhibited a unipolar resistive switching performance with a stable ON/OFF current ratio (∼102) when used as an active material for a suitable device under a DC-bias.

Influence on loading terbium manganate on optical, thermal and electrical properties of polyvinyl alcohol nanocomposite films

In this article, optical, thermal and electrical properties of different wt% of TbMnO3 (TMO) nanoparticles (NPs) loaded poly(vinyl alcohol) (PVA) films are reported in detail. The films are structurally characterised by X-ray diffraction spectroscopy and field emission scanning electron microscopy (FESEM). Optical parameters such as optical band gap energy $$\left( {{E_g}} \right)$$ , Urbach energy $$\left( {{E_U}} \right)$$ are calculated. Red shift in the absorption band of the nanocomposite films indicates the complex formation between the nanofiller and the matrix. Thermal strength increases in TMO-PVA films than the pure PVA film. A reduction in the glass transition temperature $$\left( {{T_G}} \right)$$ of the nanocomposite films is noticed with the insertion of TMO NPs in the PVA matrix. DC conductivity of the samples is explained by Mott’s variable range hopping model, Greave’s model, small polaron hopping model, non-adiabatic hopping model to explain the conduction mechanism. Modified Cole–Cole model explains the frequency variation of dielectric spectra. The relaxation peak position shifts towards lower frequency region with the inclusion of TMO filler in the PVA matrix indicating the decrease in mobility of the dipolar functional groups in the polymer chain. Modified Kohlrausch–Williams–Watts model is applied to explain the frequency dependent electric modulus spectra. AC conductivity of the films is explained by Jonscher’s power law. Correlated barrier hopping model is applied here. The presence of large current of the films at zero voltage may be due to the presence of ferroelectricity in the nanocomposite systems. Oxygen related defect states exist in the polymeric system which exhibit trapping of the charge carriers.

The comparative investigation on synthesis, characterizations of silver ion-imprinting and non-imprinting cryogels, their impedance spectroscopies and relaxation mechanisms

In the present study, a novel ion-imprinting and non-imprinting cryogel samples have been prepared using ion-imprinting technique and the dielectric properties have been investigated using an impedance spectroscopy method. In the preparation of ion-imprinted cryogel, at the first attempt, N-methacryloly-(l)-cysteine methyl ester was used as the metal complexing monomer. Ag+-imprinted poly(hydroxyethyl methacrylate-N-methacryloly-(l)-cysteine methyl ester) cryogel was produced by bulk polymerization. Poly(2-hydroxyethyl methacrylate) was selected as the basic matrix by considering properties, high chemical and mechanical stability. After removal of template (silver ions), the ion-imprinted cryogel was used for the removal of photo-film-containing materials. The dielectric properties of cryogel samples have also been investigated by impedance spectroscopy within the frequency range of 1 Hz–10 MHz. The real part of the permittivity increases at low frequencies as electrode effects become dominant. It shows a constant value at high frequencies due to dipole polarization. On the other hand, the imaginary part does not show a relaxation peak as the relaxation time of samples is very short. The frequency dependence of electrical modulus has also been investigated. The real part of electrical modulus (M′ (f)) is an indicative of negligible electrode polarization phenomenon in the test material. The behavior of the imaginary part of frequency dependent electrical modulus (M″ (f)) exhibit that the dielectric relaxation process is usually not frequency-activated state. Dielectric relaxation process occurs spontaneously due to the hopping mechanism of charge carriers.

Dielectric, Resistive and Conduction Characteristics of Lead-Free Complex Perovskite Electro-Ceramic: (Bi1/2K1/2)(Zn1/2W1/2)O3

We have investigated the electric field and temperature dependence of dielectric, impedance and conduction characteristics of a lead-free complex distorted perovskite (Bi1/2K1/2)(Zn1/2W1/2)O3 ceramic. The material was synthesized by using a standard high-temperature ceramic technology. Analysis of x-ray diffraction data and patterns collected at room temperature has provided the information on the formation of a distorted perovskite with an orthorhombic crystal system. Dielectric and impedance spectroscopy techniques have been utilized to study the effect of frequency and temperature on the dielectric, impedance and transport (conduction) characteristics of the compound. The mechanism of dielectric relaxation phenomenon in the compound has been analyzed using the dielectric and impedance data collected in a wide range of temperature (100–500°C) and frequency (1 kHz–1 MHz). Analysis of temperature-frequency-dependent Nyquist (impedance) plots has shown an important role of grains (bulk) and grain boundaries in the capacitive and resistive characteristics of the material. Based on the frequency-dependent electrical modulus and impedance data of the compound, the dielectric relaxation of non-Debye type has been suggested. The nature of the temperature- and frequency-dependence of ac conductivity of the compound follows Joncher’s power law. The fabricated compound has some important dielectric characteristics which can potentially be used for electronic devices.

Structural and impedance spectroscopic analysis of Sr/Mn modified BiFeO3 multiferroics

Glycine + urea are used as fuel agents to synthesize polycrystalline nano-particles of as-burnt Bi0.9Sr0.1FeO3 and Bi0.9Sr0.1Fe1−xMnxO3 (x = 0, 0.05, 0.10, 0.15 and 0.20) multiferroic samples using sol–gel auto-combustion method, at relatively low temperature. Structural analysis exhibits the formation of phase pure nano-composites having rhombohedral distorted perovskite structure belonging to space group R3c. Doping of Sr and Mn didn’t disturb the crystal symmetry of the original composite. Field emission scanning electron microscopy revealed that the grains which were initially interlinked with each other became relatively isolated, uniformly distributed and spherical shaped with increasing Mn contents along with increased intergranular porosity. Energy dispersive X-ray spectroscopy confirms the at.% and wt% of all the elements, corresponding to each stoichiometric formula. Dielectric parameters for each sample depict conventional ferrite behavior while hopping of oxygen vacancies contributes a lot in conductivity of the samples. Contribution of grains, grain boundaries and interfaces are evident from impedance spectroscopy. Non-Debye type relaxation is confirmed from the frequency dependent electric modulus and Cole–Cole plots. A solid correlation has been established between electrical properties and microstructure of the samples under investigation.

Dielectric Dispersion and Electric Relaxation Processes Induced by Ionic Conduction in Formamide, 2-Aminoethanol and Their Binary Mixtures

The complex dielectric permittivity, ionic conductivity, electric modulus and impedance spectra of the dipolar molecules formamide (FA), 2-aminoethanol (AE) and their binary mixtures were investigated in the frequency range from 20 Hz to 1 MHz at 303.15 K. Debye-type distributions of the frequency dependent electric modulus and complex impedance were found, corresponding to an ionic conduction relaxation process in the upper frequency regime of the spectra, whereas a spike in the impedance spectra at low frequencies confirms the contribution of an electrode polarization (EP) relaxation process induced by ionic conduction. Due to the high static permittivity of FA, its ionic conductivity was found more than one order of magnitude higher than that of the AE, which is also shown by the comparative values of their EP and ionic conductivity relaxation times. The dependences of dc ionic conductivity values of the binary mixtures on their relaxation times and static permittivity were explored. The concentration dependent static permittivity and the relaxation times led us to infer the formation of a 1:1 H-bonded stable complex between FA and AE molecules with reduction in the number of effective parallel-aligned dipoles.