Complex Impedance Spectroscopic Analysis Research Articles

Effect of Ce Doping on the Structural, Dielectric, Ferroelectric, and Optical Characteristics of Bi3LaTi3O12 Ceramic

Herein, cerium‐modified bismuth lanthanum titanate (Bi3LaTi3−xCexO12) with composition x = 0, 0.1, 0.2, and 0.3, prepared using solid‐state reaction route is reported. The initial phase from room temperature X‐ray diffraction and Rietveld refinement analysis confirms the orthorhombic symmetry of the compound. Scanning electron micrograph shows an increase in grain size of the compounds from 0.61 to 0.80 μm with cerium doping. Temperature‐dependent dielectric study reveals diffused type of phase transition (DPT) around 257 °C for Bi3LaTi3O12. DPT becomes more evident with cerium substitution, and is distinctly observed for Bi3LaTi2.8Ce0.2O12. Complex impedance spectroscopic analysis indicates negative temperature coefficient of resistance behavior and non‐Debye type of relaxation in the compound. The room temperature P–E hysteresis loop confirms the ferroelectric property in the studied compounds. Moreover, with cerium substitution, energy storage efficiency increases from 62.7% to 77.1%. UV–visible spectroscopic analysis of the compounds shows reduction in the energy bandgap from 3.02 to 2.87 eV (for direct transition) and from 2.88 to 1.37 eV (for indirect transition) with incorporation of cerium at Ti site. Consequently, high energy storage density and low optical bandgap energy observed indicate the material's amenity for energy harvesting and optoelectronic device applications.

Investigation of structural and ionic conductivity in the new organic-inorganic bromide:[(C3H7)4P]2Cd2Br6

The organic-inorganic compounds with alkylphosphonium groups were employed in many fields of applications as reported in various studies. Furthermore, these materials had shown diverse transitions depending on the preparation process. In this paper, a novel organic-inorganic hybrid [(C3H7)4P]2Cd2Br6, has been synthesized and characterized by single crystal X-ray diffraction, differential scanning calorimetry and complex impedance spectroscopy measurement. The crystal structure refinement shows that the crystallization of the [(C3H7)4P]2Cd2Br6 compound was achieved in the Triclinic system (P-1: space group, Ci: Schoenflies's nomenclature) with the following unit cell dimensions: a ​= ​13.662 (3) Å, b ​= ​16.146 (4)Å, c ​= ​16.857(4) Å, α ​= ​114.867 (6)°, β ​= ​91.650 (8)°, γ ​= ​114.357 (7)°and Z ​= ​3.The differential scanning calorimetry (DSC) analysis shows an endothermic peak at 364 ​K upon heating which attributed to a structural phase transition. The study of the AC conductivity and the dielectric properties confirm the existence of the phase transition. Complex impedance spectroscopic analysis indicated both, the presence of bulk contribution and non-Debye type in the material. The bulk resistance decreases with increasing temperature indicating a typical semiconductor behavior. The thermal evolution of the conductivity is found to obey the Arrhenius law with activation energies, 0.55 ​eV in region I and 0.78 ​eV in region II.

Sepiolite grafted polypyrrole: Influence of degree of grafting on structural, thermal, and impedance properties of nanohybrid

AbstractConductive pyrrole monomer was grafted on vinyl modified sepiolite by surface initiated emulsion graft polymerization. Effect of process variables such as monomer, initiator, and surfactant on degree of grafting (%) were investigated. Maximum 745% degree of grafting was obtained at optimized grafting conditions. Structural changes in sepiolite by grafting of polypyrrole chains was confirmed by Fourier transform infrared spectroscopy and X‐ray diffraction techniques. Surface morphology of the grafted nanohybrid was investigated by scanning electron microscopy (SEM). Thermal studies were carried out to acquire information concerning thermal stability of the synthesized materials and it was found increasing with the increase in grafting (%) of polypyrrole in sepiolite grafted polypyrrole (MS‐g‐PPy). Complex impedance spectroscopic analysis was carried out to study the effects of grafting of PPy on the ac electrical properties of synthesized nanohybrid composite at ambient temperature in the frequency range of 0.5–107 Hz. The value of electrical conductivity was affected by degree of grafting (%) and maximum value of 0.85 × 10−4 S/cm was achieved. Both dielectric loss factor and permittivity increase with the decrease of frequency exhibiting strong interfacial polarization at low frequency.

Investigation of room temperature multiferroic properties in sol-gel derived gadolinium, cobalt doped BiFeO3 nanoceramics

Detailed studies of structural, dielectric, magnetic, ferroelectric, and optical properties of a chemically sol-gel synthesized series of Bi1 − xGdxFe1 − yCoyO3 (x = 0, 0.1 and y= 0, 0.1) nanoceramics are presented. These nanoceramics attract attention as promising candidates for application as room temperature multiferroics in spintronics devices, exhibiting an optimistic set of properties. The average particle sizes of all the samples are calculated, and it was found to be ∼45 nm from the Scanning Electron Microscopy image. The dielectric behavior of the prepared nanoceramics was investigated over a wide frequency (100 Hz–103 kHz) and a temperature (35–350 °C) range. Interestingly, a low temperature dielectric anomaly is observed at around 170 °C for Bi0.9Gd0.1Fe0.9Co0.1O3 due to the magnetoelectric coupling. A noticeably large value of dielectric constant (∼990) and a low tan δ loss have also been observed for this nanoceramic at room temperature. The complex impedance spectroscopic analysis was also performed by plotting Nyquist plots, and the corresponding activation energies are evaluated from the Arrhenius fittings. Magnetization measurements of the samples reveal the presence of weak ferromagnetism due to surface spins as well as a noticeable improvement in the magnetic properties with Gd and Co doping. Ferroelectric properties have also been observed to be slightly improved because of doping, though it becomes somewhat lossy for Gd and Co doped samples. All the promising improved properties directly depend on the subsequent increase in the bandgap from 2.29 eV to 2.45 eV, with doping in the parent BiFeO3 compound confirmed from UV–Vis spectroscopy.

Distribution of relaxation time in solution-processed polycrystalline CZTS thin films: Study of impedance spectroscopy

Here we report the complex impedance spectroscopic analysis of polycrystalline CZTS thin films synthesized by sol-gel spin coating technique without any post deposition sulphurization. The films are characterized by microstructural, compositional, optical and electrical studies to confirm the formation of kesterite phase of CZTS comprises of well distributed compact grains with the optical band gap 1.44 eV. Room temperature electrical characterizations of the CZTS thin films by four-probe and Hall effect technique revealed the p-type conductivity of the films with resistivity ~ 1.45 × 10−2 Ω cm, mobility ~ 3.7 × 103 cm2 V−1 s−1 and carrier concentration ~ 1.82 × 1017 cm−3. The distribution of relaxation time (DRT) function with improved frequency resolution is reconstructed from the impedance spectra of CZTS film recorded in the frequency range 50 Hz to 5 MHz at room temperature to identify the number of electrical processes in the polycrystalline film. The Nyquist plot is fitted into electrical model consist of three parallel combinations of resistor (R) and capacitor (C) in series as three major peaks in DRT function indicates the presence of different relaxation processes with major contributions from core grains along with smaller contributions from grain boundary and interfaces. The room temperature frequency dependence of dielectric constant, loss tangent and ac conductivity is also studied for the CZTS films.

Evaluation of structure, dielectric and electrical properties of (Li/Ta/Sb) modified (Na, K) NbO3 lead-free ceramics with excess Na concentration

Polycrystalline perovskite structured (Li[Formula: see text] (Na[Formula: see text] K[Formula: see text])[Formula: see text] (Nb[Formula: see text]Ta[Formula: see text] Sb[Formula: see text] O3 ceramics with [Formula: see text], 0.005 and 0.01 mole excess Na concentration were prepared by solid state sintering method. The present study relates the role of excess Na addition with the stoichiometry, density, structure, dielectric and ferroelectric properties of the samples. X-ray diffraction (XRD) pattern exhibits single phase orthorhombic structure. The characteristic Raman modes were observed due to translational modes of cations and vibrational modes of NbO6 octahedra and no structural phase transition were observed. This confirms the formation of single phase perovskite structure and is consistent with XRD results. The dielectric permittivity increases about two times, while dielectric loss decreases by four times for [Formula: see text] composition. The electrical measurements carried by Complex Impedance spectroscopic analysis suggest negative temperature coefficient of resistance (NTCR) behavior.

Broad temperature dependent magnetic and dielectric spectroscopy study of Dy(Fe0.5Cr0.5)O3 multiferroic ceramics

In the present work, we report a comprehensive investigation of dielectric and magnetic phase transition in single phase Dy(Fe0.5Cr0.5)O3 (DFC) bulk ceramics. The Rietveld refinement suggests that DFC exhibit orthorhombic crystal system with Pnma space group. The observed magnetic and structural properties of Dy(Fe0.5Cr0.5)O3 are distinct from both the parent compound DyFeO3 and DyCrO3. Temperature dependent dc-magnetic studies exhibit a complex sequence of three magnetic transitions (TN1 = 261 K, TN2 ∼ 115 K & TN3 ∼ 14 K) below 300 K. The diffuse dielectric peaks were observed in high temperature dielectric studies near at 578 K, indicates diffuse relaxor like dielectric transition. The complex impedance spectroscopic analysis suggests that Non-Debye type dielectric relaxation process is detected.

Structural, electrical, optical and magneto-electric characteristics of chemically synthesized CaCu3Ti4O12 dielectric ceramics

CaCu3Ti4O12 (CCTO) was prepared by a chemical reaction method. The pellets prepared from the calcined powder of the material were sintered at 1100 °C. Analysis of x-ray diffraction pattern, recorded on CCTO powder, confirms the phase formation of CCTO. Studies of dielectric (εr, tanδ) and impedance parameters using dielectric and impedance spectroscopy of the compound have provided information about the electrical properties and the dielectric relaxation mechanism of the material. Detailed studies on the variation of electrical conductivity (dc) with temperature show semi-conducting nature of the material. Study of frequency (of applied electric field) dependence of ac conductivity at different temperatures suggests that the compound follows the Jonscher’s power law. Complex impedance spectroscopic analysis suggests that the semicircles formed in the Nyquist plot are connected to the grains, grain boundary and interface effects. An optical energy band gap of ~1.9 eV is obtained from the UV–visible absorbance spectrum. The magnetic data related to magneto-electric (ME) coefficient, measured by varying dc bias magnetic field, have been obtained at room temperature.

Dielectric relaxation and modulus spectroscopy analysis of (Na0.47 K0.47 Li0.06) NbO3 ceramics

We have investigated the structure, dielectric and electrical properties of lead-free polycrystalline (Na[Formula: see text] K[Formula: see text] Li[Formula: see text]) NbO3 ceramics as a function of temperature and frequency in order to understand the intrinsic contribution of grain/bulk and grain boundary effects toward the dielectric response as well as the electrical conduction mechanism in the samples fabricated by microwave sintering method. X-ray diffraction analysis exhibits perovskite structure with orthorhombic symmetry, which is well supported by the Raman spectroscopic analysis. A minor secondary impurity phase of tungsten bronze structure was observed for samples sintered at 1050[Formula: see text]C, which gets weaker for samples sintered at 1150[Formula: see text]C. Dielectric permittivity was enhanced by 50%, although there was a reduction in the dielectric loss by about 50% at Curie temperature (450[Formula: see text]C) for samples sintered at 1150[Formula: see text]C. Complex impedance spectroscopic analysis indicated non-Debye-type dielectric relaxation present in the samples, and this phenomenon followed thermally activated process related to hopping mechanism. Nyquist plot showed the negative temperature coefficient of resistance, characteristic of the samples.

A study on leakage current and electrical properties of oleic acid-coated cobalt-doped Mn-Zn ferrite nanocrystalline powders

BackgroundMn-Zn ferrites have drawn a continuously an increasing interest because of their potential applications as multifunctional devices. These materials simultaneously exhibit ferroelectricity and ferromagnetism. The dielectric and leakage current properties of Cobalt substituted Mn-Zn ferrites coated with oleic acid were not reported.MethodsThis paper presents the synthesis, electrical, and leakage properties of nanoparticles of cobalt-doped Mn-Zn ferrite [CoxMnyZnyFe2O4 (x = 0.1, 0.5, and 0.9 and y = 0.45, 0.25, and 0.05)] coated with oleic acid and prepared by chemical co-precipitation method. The crystal structure was determined by X-ray diffraction (XRD), the effect of strain on the electronic structure was analyzed using Williamson-Hall plot. Complex impedance spectroscopic analysis was carried out, and the impedance plots show the resistive and reactive parts of the impedance. Frequency dependence on AC conductivity was investigated for all the compositions, and leakage current properties were also studied.ResultsThe nanoparticles were found to have an average size of 13.62 nm. The average crystallite size (DaveXR) of the precipitated particles found to decrease from 15.22 to 12.65 nm with increasing cobalt substitution. The presence of two semicircular arcs at the lower and higher frequency regions indicates the grain boundary conduction and grain conduction at room temperature. Leakage current density of the order of 10-4 A/cm2 (at field strength of 0.02 kV/cm) was observed for all compositions.ConclusionThe variation of the strain values from negative to positive indicates that the strain changes from compression to tensile. The dielectric permittivity was found to decrease from 104to 103 with increase in frequency. The semicircle in the higher frequency region is attributed to the grain conduction of the materials, and the semicircle in the lower frequency region is due to the grain boundary conduction. Both the grain and grain boundary are found to be active at room temperature. AC conductivity is found to be compositional dependent.

Dielectric and Electrical Properties of BiFeO3–LiTaO3 Systems

Materials of general formula (Bi1−xLix)(Fe1−xTax)O3 (x = 0.0, 0.5) were prepared from polycrystalline BiFeO3 and LiTaO3 by solid-state reaction. Analysis of the basic structural properties of the materials by room-temperature x-ray diffraction revealed the formation of single-phase tetragonal crystals for (Bi0.5Li0.5)(Fe0.5Ta0.5)O3. Scanning electron micrographs confirmed the polycrystalline nature of the materials. The microstructure of the materials comprised uniformly distributed grains of unequal size. Studies of the temperature–frequency dependence of dielectric did not reveal any dielectric anomaly or phase transition in the temperature range studied. The presence of hysteresis loops at room temperature confirmed the known ferroelectricity of BiFeO3 and (Bi0.5Li0.5)(Fe0.5Ta0.5)O3. Complex impedance spectroscopic analysis revealed the materials had negative temperature coefficient of resistance (NTCR)-type behavior. The electrical conductivity and relaxation characteristics of the materials suggested the presence of a thermally activated process, and their values suggested the materials had similar types of conductivity and relaxation species. The frequency dependence of the ac conductivity obeyed Jonscher’s universal power law.

Phase, microstructure and electrical characterization of Ba1−x La x (Zr0.6Ti0.4)1−x/4O3 ceramics

Ba1−x La x (Zr0.6Ti0.4)1−x/4O3 (x = 0.015, 0.025, 0.035, 0.005) ceramics were processed by a conventional mixed-oxide solid state sintering route. All the compositions formed single-phase ceramics within the detection limit of the in-house X-ray diffraction facility when sintered at 1,500 °C for 6 h. The microstructure of all the examined samples comprised densely packed ~1–5 μm irregular shaped grains. The number of relatively smaller grains increased with increasing La content. Raman spectroscopy confirmed the presence of ferroelectric modes in all the investigated samples. Optimum temperature dependent dielectric properties (tanδ ~ 0.005 and er ~ 570 at 100 kHz–1 MHz) were achieved for the x = 0.025 composition at room temperature. For the x = 0.025 composition, tanδ = 0.005, 0.004 and 0.002 were recorded at 100 kHz, 250 kHz and 1 MHz, respectively which indicated a decrease in tanδ with increasing frequency at around room temperature. Complex impedance spectroscopic analysis showed the contribution of bulk and grain boundary in conduction mechanism. The resistance of these ceramics was found to decrease with increasing temperature.

Dielectric And Impedance Spectroscopic Studies Of Multiferroic BiFe1-xNixO3

Multiferroic bismuth ferrites (BFO) and Ni substituted bismuth ferrites (BFNO) were synthesized by standard solid state reaction route. The structural and microstructural studies were carried out. The effect of Ni substitution on dielectric constant and dielectric loss of the samples was studied in a wide range of frequency (100 Hz- 1 MHz) and temperature (27 o C – 420 o C). It has been observed that the dielectric constant increases with increase in Ni doping concentration and attained a maximum value for BFNO(x = 0.075) sample while the dielectric loss has been found to decrease with the doping concentration. This implies a reduction in the conductivity and hence improved the dielectric properties of Ni doped BFO. The anomalous peaks in temperature dependent dielectric studies indicate the increase in antiferromagnetic ordering temperature and possible existence of spin glass states upon Ni substitution in place of Fe. The complex impedance spectroscopic analysis suggests purely the intrinsic nature of the dielectric anomalies. Temperature dependent non-Debye type of dielectric relaxation has also been observed. The Nyquist plots show the negative temperature coefficient of resistance behavior of these compounds. Further it would be interesting to study their magnetic and magnetoelectric properties with the aim of identifying new multifunctional device applications. Copyright © 2014 VBRI press.

Electrical conduction in (Bi0.5Na0.5)0.94Ba0.06TiO3-PVDF 0-3 composites by impedance spectroscopy

The present work describes the use of ac complex impedance and electric modulus spectroscopy techniques to obtain the electrical parameters like electrical conductivity and activation energy of (Bi0.5Na0.5)0.94Ba0.06TiO3 (BNBT06)-PVDF 0-3 composites with (a) 10, (b) 20 and (c) 30 vol. percentage of BNBT06 in the frequency range 100 Hz-5MHz over a temperature range of 35 o C-150°C. SEM micrographs showed almost homogeneous distribution of grains with less porosity for all the compositions and the EDAX patterns confirmed the presence of different constituent elements of the composite samples. Complex impedance spectroscopic analysis indicated the presence of non-Debye type dielectric relaxation in the composites. The bulk resistance showed the NTCR character of the composite materials and the presence of grain-boundary effect along with the bulk contribution, especially in the lower frequency and higher temperature regime, was indicated by the modulus spectroscopic analyses, thus confirming the non-Debye type of multiple relaxations in the system. The ac electrical conductivity data as a function of temperature also endorsed the NTCR character of BNBT06-PVDF 0-3 composites. The ac conductivity based activation energy data allowed insight into the mechanism of the occurring conduction processes in the composite system which are explained on the basis of hopping model of charge carriers. Keywords- Ceramic-polymer 0-3 composites; Grains /grain-boundaries; Hopping conduction; Complex impedance/ modulus spectroscopy; Ac conductivity; Activation energy

Effects of cobalt doping on the microstructure, complex impedance and activation energy in 0.2PZN–0.8PZT ceramics

A CoCO3 added Pb((Zn1/3Nb2/3)0.20(Zr0.50Ti0.50)0.80)O3 (0.2PZN–0.8PZT + xCoCO3) system has been prepared and investigated. The tetragonal distortion c/a of specimens increases abruptly with increasing CoCO3 content, but is almost constant for x ≥ 0.2 wt%, confirming that the solubility limit of CoCO3 in 0.2PZN–0.8PZT is about x = 0.2 wt%. Complex impedance spectroscopic analysis, in the temperature range of 250–300 °C from 1 mHz to 10 MHz, provides another evidence that 0.2 wt% is indeed the solubility limit. Both spectroscopic peaks of Z″ and M″ vs frequency are observed in the similar frequency region, indicating the approximated-Debye behavior in the studied systems. Temperature dependent bulk relaxation values are found to obey linear-Arrhenius fit. Based on the activation energy values, it can be concluded that in CoCO3 doping 0.2PZN–0.8PZT, both the single and double ionized oxygen-vacancies contribute to the conduction process.

Effect of propylene carbonate as a plasticizer on (PEO)50AgCF3SO3:SnO2 nanocomposite polymer electrolyte

This work deals with the incorporation of propylene carbonate (PC) as a plasticizer in conjunction with poly (ethylene oxide) (PEO), silver triflate (AgCF3SO3) and nanocrystalline tin oxide (SnO2) for obtaining the nanocomposite polymer electrolyte system (PEO)50AgCF3SO3:2 wt% SnO2 + x wt% PC (x = 10, 20, 30 and 40) by solution casting method. The present electrical conductivity data extracted by means of complex impedance spectroscopic analysis in the frequency range 20 Hz–1 MHz and over the temperature domain 298–373 K have demonstrated that the maximum electrical conductivity value of 5.9 × 10−5 S cm−1 at 298 K would be possessed by the specimen containing 30 wt% PC incorporated into the optimized nanocomposite system (PEO)50AgCF3SO3:2 wt% SnO2. Silver ionic transference number (tAg+) data evaluated using AC/DC polarization technique have indicated that the highest tAg+ value of 0.52 could be realized in the case of the specimen (PEO)50AgCF3SO3:2 wt% SnO2 + 30 wt% PC, whereas the complexation of the plasticizer within the nanocomposite electrolyte has been deduced from the detailed Fourier transform infrared spectroscopic investigation owing to the fact that such results have revealed the appearance of absorption bands corresponding to free triflate ions (CF3SO3−) and PC. Surface morphological features of pure PEO and (PEO)50AgCF3SO3:2 wt% SnO2 + 30 wt% PC nanocomposite systems were analysed through scanning electron microscope. The feasibility of a reduction in the degree of crystallinity of the plasticized system has been indicated by the X-ray diffraction data and confirmed from differential scanning calorimetric results obtained in terms of quantification of crystallinity and reduction in the glass transition temperature due to the addition of the chosen plasticizer into the nanocomposite polymer electrolyte matrix. Interestingly, the all solid-state cell based on the nanocomposite polymer electrolyte, namely, (PEO)50AgCF3SO3:2 wt% SnO2 + 30 wt% PC and silver anode has exhibited an open circuit voltage of 676 mV and short circuit current of 192 μA at room temperature.

Studies of dielectric and electrical properties of a new type of complex tungsten bronze electroceramics

A polycrystalline ceramic with a new type of complex tungsten-bronze type structure, having a general formula K2Ba2Nd2Ti4Nb4W2O30 has been prepared using a high temperature solid-state reaction route after optimizing the calcinations conditions on the basis of thermal analysis results. The material has been characterized by different experimental techniques. The formation of the compound has been confirmed using X-ray diffraction analysis. Dielectric properties (er and tanδ) of the compound as a function of temperature at different frequencies have been carried out. Temperature dependence of dielectric constant indicates the presence of ferroelectric phase transition well above the room temperature. Complex impedance spectroscopic analysis has been carried out as a function of frequency at different temperatures to establish some correlation between the microstructure and electrical properties of the material. The nature of frequency dependence of ac conductivity obeys the Jonscher’s power law. The dc conductivity calculated from the ac conductivity spectrum shows the negative temperature coefficient of resistance behavior like a semiconductor.