Impedance Formalism Research Articles

Enhanced Spectroscopic Insight into Acceptor-Modified Barium Strontium Titanate Thin Films Deposited via the Sol-Gel Method.

In the present paper, composite thin films of barium strontium titanate (BaxSr1-xTiO3) with an acceptor modifier (magnesium oxide-MgO) were deposited on metal substrates (stainless steel type) using the sol-gel method. The composite thin films feature BaxSr1-xTiO3 ferroelectric solid solution as the matrix and MgO linear dielectric as the reinforcement, with MgO concentrations ranging from 1 to 5 mol%. Following thermal treatment at 650 °C, the films were analyzed for their impedance response. Experimental impedance spectra were modeled using the Kohlrausch-Williams-Watts function, revealing stretching parameters (β) in the range of approximately 0.78 to 0.89 and 0.56 to 0.90 for impedance and electric modulus formalisms, respectively. Notably, films modified with 3 mol% MgO exhibited the least stretched relaxation function. Employing the electric equivalent circuit method for data analysis, the "circle fit" analysis demonstrated an increase in capacitance from 2.97 × 10-12 F to 5.78 × 10-10 F with the incorporation of 3 mol% MgO into BST-based thin films. Further analysis based on Voigt, Maxwell, and ladder circuits revealed trends in resistance and capacitance components with varying MgO contents, suggesting non-Debye-type relaxation phenomena across all tested samples.

Investigation of structural, temperature and frequency dependent dielectric behavior of Zn2SnO4@amorphous SiO2 core shell nanocomposites

Herein, the detailed investigation of frequency and temperature dependent dielectric behavior of Zn2SnO4@SiO2 core shell nanocomposites (CSNs) is reported. Powder XRD analysis and FTIR spectral analysis were employed to comprehend the structure. The chemical and valence states are analyzed using XPS which confirms the existence of Zn, Sn, and SiO2, each with their distinctive Zn 2p, Sn 3d, and Si 2p valence states. The core shell formation is confirmed from their distinct color contrast in the TEM micrographs. The electrical response was investigated using impedance spectroscopy in the frequency range 1Hz-1 MHz at various temperatures. Positive temperature coefficient of resistance type behavior was established from impedance and modulus formalism. The total conductivity values were well fitted by the universal Jonscher law σtotal = σdc+ Aωn, and the temperature dependence of dc conductivity was discussed.

Dielectric relaxation and conductivity phenomena in ferroelectric ceramics at high temperatures

The issues related to microstructure and its effects on functional properties of electroceramics become increasingly prominent with the progressive downscaling of electronics. In this study, temperature-dependent dielectric and impedance data of BaTiO3 (BT), Sr-doped BT (BST) and layer-structured BaBi4Ti4O15 (BBTO) ceramics are systematically investigated to reveal the effects of doping and perovskite layering on the dielectric relaxation and conduction processes at high temperatures. By using complex impedance spectroscopy, it is demonstrated that the ceramics are electrically heterogeneous structures displaying a non-ideal Debye-like behavior at high temperatures. Using a suitable equivalent circuit model, the impedance diagrams at different temperatures are simulated and the refined values of macroscopic resistance and capacitance are used for the identification and characterization of particular microstructural regions (grains, grain boundaries, interfaces, etc.). The approach of combining the impedance, electric modulus and permittivity formalisms is demonstrated to be effective in explaining the peculiarities of the electrical charge transport mechanism and relaxation in the grains, grain boundaries and interface layers of the ceramics.

Impedance Spectroscopy of Binary Mixtures of Dimethyl Silicone Fluid and Methyl Iso Butyl Ketone

A precision LCR metre was used to measure the parallel resistance (RP) and parallel capacitance (CP) of a capacitive cell filled with samples of binary mixes of methyl isobutyl ketone (MIBK) and dimethyl silicone fluid (DMSF), over the frequency range of 100 Hz to 2 MHz, at a temperature of 303.15 K. Using RP and CP, complex impedance Z*(ω) was computed. A four-element equivalent circuit model was used to fit the complex impedance data. The fitting provided the values of various circuit elements representing various electrical processes occurring in the capacitive measurement cell under the influence of an applied ac field. The Bode plot presentation of the complex impedance data confirmed the values of various circuit elements determined using the fitting process. Complex impedance formalism supports the observation of the electronic double-layer capacitance (EDLC) phenomena and ionic conduction relaxation phenomena.

Investigation of AC conductivity and dielectric relaxation of lithium modified zinc borate semiconducting glasses for energy storage applications

Conductivity spectra of (80-x)B2O3.20ZnO.xLi2O (x = 10, 20, 30 and 40) glass series were studied in frequencies ranging from 0.1 Hz to 106 Hz and temperature ranging from 313 K to 573 K. The experimental data of ac conductivity is fitted using the Almond West model, and the parameters such as direct current conductivity (σdc), frequency exponent (s) and crossover frequency (ωH) have been extracted. Overlapping Large Polaron Tunneling is found to be applicable in studied glasses. Activation energy estimated from conductivity (0.89–1.39 eV), electric modulus (0.88–1.32 eV), and impedance (0.89–1.27 eV) analysis are in good agreement. Activation energy corresponding to ionic conduction in x = 30 and 40 mol% is found to be 1.09 and 1.10 eV respectively. Highest conductivity ∼2.5 × 10−5 Scm−1 is obtained for 40B2O3.20ZnO.40Li2O glass composition at 573 K. Impedance formalism indicates that electric conduction occurs via Li+ and electrons/polarons. It makes the studied glasses suitable for energy storage devices.

Reinvestigation of conducting properties of Ca-doped barium titanate

Relaxation processes of Ba1−xCaxTiO3 ceramics with x = 0.05, 0.10 and 0.23 Ca contents were studied by combining the dielectric modulus and complex impedance experiments. Use of both methods permits an exploration of relaxation processes in both time and frequency domains, including relaxation distribution function at low and high frequency relaxation regions (grain and grain boundary). From an analysis using the complex impedance formalism, the predominant time distribution relaxation function turns out to be a Cole-Cole type, whereas from the dielectric modulus formalism it is described by non-Debye relaxation functions. While activation energies derived from the dielectric modulus formalism are characteristic of doubly-ionized oxygen vacancies (0.85–1.00 eV), they are from the complex impedance approach expressed as a typical electronic conduction (1.2–1.5 eV). It was identified that the impedance formalism describes well the relaxation in the low frequency regime with similar activation energy derived from the Jonscher power law (1.1–1.4 eV). The present study highlights the potential of using both impedance and dielectric modulus formalisms to identify and quantify non-Debye relaxation process and conducting properties in mixed electronic-ionic conductors.

Effect of seasonal variation in dielectric properties of groundwater from Vadodara region

Groundwater samples were collected during different months from the same site from Vadodara district of Gujarat state. The complex permittivity of the water samples were precisely determined over the frequency span 20 Hz to 2 MHz. Complex permittivity spectral data were converted into complex impedance formalism. Obtained results were analysed to get information of seasonal variation in groundwater quality. Dielectric constant for all samples is found to decrease linearly and rapidly with increase in frequency up to about 4 kHz, after which it decreases slowly and achieves static value approximately 78, near 2 MHz for all water samples. Dielectric loss for the water sample collected in monsoon season (August) is the highest, which shows the presence of ions dissolved from the soil in rain water. DC resistance values, determined from the complex impedance plane plot (Z′’ vs. Z″), suggested an increase in the conductivity of the water samples collected near the end of monsoon season, due to the dissolved minerals and salts from soil. The calculated values of ε′’/ε′’ DW and ε″/ε″DW ratio for the water sample of August’18 show a relatively large increase during the post-monsoon month of August’18, above 2 kHz, as compared to other months.

Structural, morphological, optical, electrical and dielectric features based on nanoceramic Li4Ti5O12 filler reinforced PEO/PVP blend for optoelectronic and energy storage devices

Polymer nanocomposite films had been fabricated by the solution casting process using the organic matrix of polyethylene oxide/polyvinylpyrrolidone (PEO/PVP: 50/50 wt%) blend and various filling levels of lithium titanium oxide nanoparticles (Li4Ti5O12 NPs). The TEM and XRD techniques indicated the phase purity of the cubic Li4Ti5O12 NPs with a crystallite size of about 69 nm. The FTIR spectra revealed that the complexation/miscibility between the PEO/PVP blend components were existed through the formation hydrogen bonding between the main functional groups of these polymers and also the loaded NPs fundamentally behaved as geometrical incarceration for the structure of PEO/PVP matrix, due to the formation of polymer-nanoparticles interactions. The SEM images indicated observable variations in the size of PEO spherulites, formed aggregations and pores of host matrix on 1 wt% Li4Ti5O12 NPs and additional 3 and 5 wt%. The optical features of nanocomposites such as optical energy band gap and refractive index were evaluated through the UV/vis. absorbance spectra, where the redshift for the main absorption edge of the filled films implied that Li4Ti5O12 NPs had been successfully embedded into the PEO/PVP matrix. The maximum refractive index and the lowest optical bandgap energy were obtained for the nanocomposite sample (5 wt%). The AC electrical conductivity σac and the dielectric response of the prepared samples were studied, where the loaded NPs increased the values of σac, dielectric loss, and dielectric constant of the PEO/PVP blend and the dielectric constant of the nanocomposite films decreased with increasing the applied frequency. The electrical modulus formalism (M*) and impedance formalism (Z*) were used to analyze the impedance data. The enhancements in the optical and electrical characteristics make these nanocomposite materials appropriate for many uses such as integral thin film capacitors, flexible nanodielectrics for organoelectronic devices, high power Li-ion batteries, optical band gap tuner and many optoelectronic devices.

Investigation of conduction mechanism and UV light response of vertically grown ZnO nanorods on an interdigitated electrode substrate.

Vertically aligned zinc oxide nanorod (ZnO-NR) growth was achieved through a wet chemical route over a comb-shaped working area of an interdigitated Ag-Pd alloy signal electrode. Field-emission scanning electron microscopy images confirmed the formation of homogeneous ZnO-NRs grown uniformly over the working area. X-ray diffraction revealed single-phase formation of ZnO-NRs, further confirmed by energy-dispersive X-ray spectroscopy analysis. Temperature-dependent impedance and modulus formalisms showed semiconductor-type behavior of ZnO-NRs. Two electro-active regions i.e., grain and grain boundary, were investigated which have activation energy ∼0.11 eV and ∼0.17 eV, respectively. The conduction mechanism was investigated in both regions using temperature-dependent AC conductivity analysis. In the low-frequency dispersion region, the dominant conduction is due to small polarons, which is attributed to the grain boundary response. At the same time, the correlated barrier hopping mechanism is a possible conduction mechanism in the high dispersion region attributed to the bulk/grain response. Moreover, substantial photoconductivity under UV light illumination was achieved which can be attributed to the high surface-to-volume ratio of zinc oxide nanorods as they provide high density of trap states which causes an increase in the carrier injection and movement leading to persistent photoconductivity. This photoconductivity was also facilitated by the frequency sweep applied to the sample which suggests the investigated ZnO nanorods based IDE devices can be useful for the application of efficient UV detectors. Experimental values of field lowering coefficient (βexp) matched well with the theoretical value of βS which suggests that the possible operating conduction mechanism in ZnO nanorods is Schottky type. I-V characteristics showed that the significantly high photoconductivity of ZnO-NRs as a result of UV light illumination is owing to the increase in number of free charge carriers as a result of generation of electron-hole pairs by absorption of UV light photons.

Comparative Study on the Nonlinear Theory and PIC Simulation of Confocal Gyro-TWAs

The large-signal theory, including the BEAMLETS model and averaged coupling impedance formalism, of confocal gyrotron traveling-wave amplifiers (gyro-TWAs) with diffractive loss has been derived. As an example, a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${W}$ </tex-math></inline-formula> -band gyro-TWA with uniform confocal circuits and curved-profile magnetic field is theoretically studied and then well validated by three-dimensional particle-in-cell (3-D-PIC) simulation in detail. The results predicted by our code achieve excellent agreement with the PIC simulation over 92–104 GHz regarding the electron efficiency and radio frequency (RF) wave efficiency profile along the circuit position and saturation amplification performance, with a saturation input power difference of less than 20%.

Complex impedance formalism: An alternative approach for exploration of relaxation dynamics in conductive materials

A new method, the complex impedance formalism, is presented to disclose the relaxation process of conducting materials. This method is an extrapolation of the dielectric modulus formalism in the Bode representation of the impedance. As in the dielectric modulus formalism, the relaxation process can be approached in both the frequency and time domains for non-Debye relaxation type. The complex impedance formalism is tested by analysis of the relaxation process of the solid BaTiO3 material at high temperatures. A combination of complex impedance and dielectric modulus formalism provides us with a better understanding concerning individual relaxation regions. The complex impedance formalism allows the hidden relaxation process at low frequency regime to be accessible, whereas the dielectric modulus formalism discloses the relaxation process at high frequency in mixed electronic-ionic conductors.

Tetragonal structure and dielectric behaviour of rare-earth substituted La0.8Co0.16-xEu0.04GdxTiO3 (x = 0.04–0.16) nanorods

La0.8Co0.16-xEu0.04GdxTiO3 (LCEGT) (x = 0.04–0.16) nanorods were synthesized via low temperature hydrothermal process. The X-ray diffraction studies revealed that the formation of tetragonal structure along with the secondary phases of α-Eu2TiO3. The lattice parameters, unit cell volume were observed to be decreased with the increase of Gd3+ from 0.04 to 0.16, and X-ray density increased from 11.01 to 11.67 g/c.c. with the Gd3+ composition. FESEM and TEM images confirmed the formation of mixed morphology consisting of nanorods and nanospheres in all samples. The dielectric analysis studied in-between frequencies 10 kHz–8 MHz discovered that the dielectric constant decreases from 4653 to 306 with the increase of Gd3+ composition from 0.04 to 0.12. The dielectric loss at 1 MHz was observed to be decreased from 223 to 28 with the increase of Gd3+ in the sample. The ac-conductivity increases from 0.0015 to 0.0223 S/cm with the increase of frequency from 10 kHz to 8 MHz for the Gd3+ = 0.04 sample. The impedance and dielectric modulus formalism were studied as a function of composition and frequency. The conduction process is through the grains in place of grain boundaries and non-Debye type of relaxations revealed from Cole-Cole plots. The studied properties of LCEGT nanorods indicate that the material is suitable for dielectric absorber and charge stored capacitor applications.

Epoxy-based/BaTiO3 nanodielectrics: Relaxation dynamics, charge transport and energy storage

Epoxy/BaTiO3 nanocomposites developed at low nanofiller concentrations with their dielectric relaxations, charge transport dynamics and capacitive energy storage were investigated via dielectric spectroscopy and dc charge-discharge experiments. Two relaxation processes were observed, namely the α- and β-relaxations, attributed to the dynamic Tg process and local motions, respectively. Another process located at low frequencies and high temperatures was identified as interfacial polarization. The charge transport properties were examined via the ac conductivity and impedance formalisms, indicating a beneficial effect with the increase of the nanofiller content. The dc conductivity was calculated from the ac spectra and exhibited Arrhenius temperature dependence. The theoretical energy density was found to increase up to 3.5 times comparing to the neat epoxy resin, highlighting the reinforcing dielectric/capacitive effect of the BaTiO3 nanoparticles on the epoxy resin. Comparisons between the theoretical energy densities and experimentally determined values were also discussed in detail.

Thermal Analysis, Dielectric Response and Electrical Conductivity of Silicon Phthalocyanine Dichloride (SiPcCl2) Thin Films

This research is a detailed examination of the effect of post-annealing on the structure and electrical conductivity of silicon phthalocyanine dichloride (SiPcCl2) thin films. Differential thermal analysis (DTA) is used to determine the temperature limit of thermal stability for a sample of silicon phthalocyanine dichloride (SiPcCl2). The results of differential thermal analysis (DTA) proved that silicon phthalocyanine dichloride (SiPcCl2) is thermally stable up to 415 K. The dielectric behavior and the electrical conductivity of silicon phthalocyanine dichloride (SiPcCl2) thin films were investigated under a temperature effect from 303 K to 383 K and a frequency from 200 Hz to 20 MHz. The frequency and temperature dependence of dielectric loss and dielectric constant values were explained in terms of dielectric polarization theory. The alternative current (AC) conductivity response toward the frequency change obeys Jonscher’s power law. The correlated barrier hopping (CBH) model is utilized and adapted to fit the conduction mechanism in the high- and low-frequency regions. Both the complex electric modulus and the impedance formalisms are used to illustrate the dielectric characteristics of the silicon phthalocyanine dichloride (SiPcCl2). The potential height value of the hopping barrier, Wm, and activation energy value, Eac, for dielectric relaxation were determined.

Electric and Dielectric Behavior of Purified Galactomannan Films

This work aimed to extract, purify, and to characterize galactomannan from Adenanthera pavonina L. by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and impedance spectroscopy (IS). Galactomannans (Gal) are polysaccharides, commonly found in the seed endosperm of the Fabaceae family, presenting a chemical structure formed by mannose and galactose, with units connected by glycosidic bonds of D-mannopyranose β(1→4) and by D-galactopyranose α(1→6). Due to their physical-chemical properties and biocompatibility, this biopolymer can be integrated into a vast range of biomedical devices, for example, as biosensors. Galactomannan was extracted from seeds of Adenanthera pavonina L., precipitated in ethyl alcohol, dehydrated, pulverized, and hermetically stored. Galactomannan films purified at 100% were prepared at a concentration of 5% and characterized by FTIR, XRD, and IS. In FTIR, characteristic monosaccharides of Gal were identified as β-D-manopyranose at 814 cm-1 and α-D-galactopyranose at 871 cm-1. From the diffractogram of purified Gal. (GP100), two diffraction peaks are observed at 5.8º and 20º, since the natural interaction of polysaccharides with water, intermediated by ethanol, causes changes related to crystalline-amorphous transitions. IS measurements in the frequency range between 10 Hz and 1 MHz, at room temperature, revealed the existence of a non-Debye relaxation phenomenon, observed using the electrical modulus function formalism (M*) and impedance formalism (Z*), ascribed to the short-range movement of charge carriers. For the purified and crude galactomannan films, we observed that the electrical resistivity is very high, reaching a magnitude of 109 Ω.mm, at the low-frequency region, decreasing to 108 Ω.mm for frequencies higher than 10 kHz. Because of this high impedance characteristic and biocompatibility, purified galactomannan can be easily used as an insulating substrate in biosensors.

Tailoring dielectric properties of cordierite-mullite ceramics through Ceramic Injection Moulding

Cordierite-mullite ceramics have been processed by Ceramic Injection Moulding (CIM) for the first time. The comparison with cordierite-mullite ceramics obtained by conventional ceramic process (CP) proves the effect of processing on the structure, microstructure, thermal and dielectric properties. CIM processing favours formation of larger content of mullite phase, a more homogeneous microstructure and reduced porosity than by conventional processed ceramics. These factors strongly condition the dielectric behaviour, which is analyzed by complex impedance formalism up to 850 °C and 1 MHz. The conduction mechanism is thermally activated and the activation energy is ~2.5 times larger in CP than in CIM ceramics. Thermal expansion coefficient is tuned by processing method, ranging from 3.9·10−6 °C−1 to 4.6·10−6 °C−1. All these findings show the strong influence of processing in cordierite-mullite ceramic composites. This work shows that tailoring composition and CIM parameters allow cordierite-mullite composites to precisely fulfill the requirements for future electronic applications.

Investigation of the conduction mechanism, high dielectric constant, and non-Debye-type relaxor in La0.67Ba0.25Ca0.08MnO3 manganite

The conduction mechanism and electric properties of La0.67Ba0.25Ca0.08MnO3 (LBCM) were analyzed depending on temperature and frequency. The frequency dependence of electrical conduction plot was explained by the jump relaxation model. The electrical conduction process was based on both theoretical conduction models assigned to the Correlated Barrier Hopping and Non-overlapping Small Polaron Tunneling mechanism. The impedance plot studies reveal that the relaxation is a non-Debye poly-dispersive pattern in the LBCM. This compound has excellent dielectric properties such as the dielectric permittivity exceeding 105 at room temperature, i.e., colossal permittivity, and is one of the highest values recorded for ceramic capacitors. Thus, evolution of dielectric permittivity, described in terms of spatial charge polarization based on Koop's phenomenological theory and Maxwell–Wagner's (M– W) model and high dielectric response, has been driven by barrier layers into the grain boundaries and blended structures of Mn3+/Mn4+. The relaxation processes were examined with modulus, impedance formalism, and electrical conductivity. In the thermal analysis, the relaxations mechanism are related oxygen vacancies.

Crystal growth and effect of defects on the dielectric properties of ammonium dihydrogen phosphate (ADP) single crystals

We report the growth of ammonium dihydrogen phosphate, NH4H2PO4 (ADP) single crystals by slow evaporation method and study of their dielectric property. Furthermore, we correlate the effect of the defects present in the single crystals with the dielectric and other related properties. After determination of the solubility limit of ADP salt in water at different temperatures, the seed crystals were nucleated and grown in the supersaturated solution, which was obtained by cooling the higher temperature saturated solution to room temperature. The phase purity of synthesized ADP crystals was studied by powder X-ray diffraction technique, on the finely ground seed crystals. The seed crystals of appropriate size were used for growth of large crystals and also used for dielectric measurements. Two single crystals with different concentrations of defects were used for the investigation of dielectric property at room temperature. The obtained dielectric data are discussed along with their representation in modulus and impedance formalism to understand the dielectric properties of these crystals. Overall, the low frequency Maxwell–Wagner interfacial polarization was found to increase due to the presence of defects in the ADP single crystals.

Electrochemical impedance spectroscopic analysis of aluminum and gallium mixed matrix membranes

Mixed matrix membrane revolutionized the field of electrochemistry with its multiple applications as a solid electrolyte, actuator, sensor, and storage device, because of its better processability, flexibility, and light-weight. The present study is designed to investigate the role of hybrid filler in the electrochemical properties of the mixed matrix membrane. For this purpose, aluminum and gallium hybrids with indole and its derivatives were synthesized using the post-modification method. Then, synthesized hybrids were dispersed evenly into the polysulfone matrix and developed its membrane using the immersion precipitation phase inversion method. The FTIR result of aluminum and gallium hybrids identified the absorption bands of −C=C (1485–1400 cm−1), −CN (1340–1122 cm−1), and –NH (1625–1535 cm−1) with repeating units of Al–O (1178 cm−1) and Ga-O (1132–1117 cm−1). SEM images showed the spherical-shaped aluminum oxide and rod-shaped gallium oxide. XRD pattern corresponded to the cubic and trigonal crystal system of aluminum and gallium oxides. Electrochemical impedance study showed significant improvement in the electrical behavior of aluminum and gallium mixed matrix membranes where aluminum and gallium hybrids as a filler create the continuous network for the easy transportation of the charge carriers. The existence of the peaks at a similar position in both impedance and modulus formalisms suggests relaxations of the same type of charge species at the same type of electroactive region and disclose the real picture of the material.

Study of conduction mechanism, electrical property, and nonlinear electrical behaviors of Ba0.97Bi0.02Ti0.9Zr0.05Nb0.04O3 perovskite

The conduction mechanism, electric properties, and I–V behavior of the polycrystalline Ba0.97Bi0.02Ti0.9Zr0.05Nb0.04O3 (BBTZN) ceramic analyzed as a function of frequency and temperature. The relaxation phenomena were studied with impedance and modulus formalism, while the conductivity mechanism was investigated using electrical conductivity. The thermal evolution of the electrical conduction was adjusted by Jonscher’s Law and explained in terms of the Correlated Barrier Hopping conduction mechanism. The nonlinear current–voltage confirmed the negative temperature coefficient of resistance comportment for our compound. The electrical behavior confirmed that the relaxation processes are of non-Debye type. The study of complex impedance suggests a poly-dispersive non-Debye-type relaxation occurring in the polycrystalline (BBTZN). The dielectric response confirmed the dominance of the Maxwell–Wagner (M–W) model effect in conduction phenomenon. The value of permittivity is highly around 103, and low dielectric loss and low electrical conductivity of around 10–4 S cm−1 for BBTZN were observed. These values make this composition interesting for microelectric applications. In the thermal study, the relaxation processes observed by electrical conductivity, impedance, and modulus are associated with singly and doubly ionized oxygen vacancies for the lower and higher temperature, respectively.