non-Debye Type Dielectric Relaxation Research Articles

Electrical transport and dielectric relaxation mechanism in Zn0.5Cd0.5Fe2O4 spinel ferrite: A temperature- and frequency-dependent complex impedance study

In the present study, the frequency-dependent dielectric relaxation and electrical conduction mechanisms in sol-gel-derived Zn0.5Cd0.5Fe2O4 (ZCFO) spinel ferrite were studied in the temperature range of 343–438 K. The formation of the ZCFO spinel ferrite phase with space group Fd3m was confirmed by X-ray diffraction analysis. The dielectric relaxation and electrical conduction mechanisms were studied using complex impedance spectroscopy (CIS). In the Nyquist plots, depressed semicircles were fitted with an equivalent circuit model with configuration (RGBQGB) (RGQG), signifying the contributions from grain boundaries and grains to the charge transport mechanism in the sample. The frequency-dependent AC conductivity was found to follow Jonscher's power law, and the frequency exponent term depicted the overlapping large polaron hopping (OLPH) model as the dominant transport mechanism. The activation energies for conductivity, electric modulus and impedance were calculated to identify the nature of the charge carriers governing the relaxation and conduction mechanisms in the prepared sample. Complex modulus studies confirmed the non-Debye type of dielectric relaxation, whereas tangent loss and dielectric constant analyses confirmed the thermally activated hopping mechanism of charge carriers in Zn0.5Cd0.5Fe2O4 spinel ferrite.

Evidence of self-biased magnetoelectric coupling in eco-friendly (Na0.41K0.09Bi0.5TiO3-Ba0.85Ca0.15Zr0.1Ti0.9O3)-(CoFe2O4) particulate composites

The magnetoelectric (ME) properties of eco-friendly 1-x(0.94Na0.41K0.09Bi0.5TiO3-0.06Ba0.85Ca0.15Zr0.1Ti0.9O3)-x (CoFe2O4) (NKBCZT-CFO) with x = 0, 0.1, 0.2, 0.3 and 0.4 particulate composites were investigated. The X-ray diffraction studies provided evidence for the simultaneous existence of constituent phases (ferroelectric and ferromagnetic) in the composite. The structural and surface morphology analysis of the composite affirmed the homogeneous and densely packed distribution of CFO grains within the NKBCZT matrix. The composite's multiferroic behavior at room temperature was confirmed through the characterization of P vs E and M vs H hysteresis loops. The observed values of remnant polarization (Pr) and coercive field (Ec) are 26.7 μC/cm2 and 35.5 kV/cm, respectively, for 10 mol% of CFO. The increase in CFO content resulted in a decrease in the ferroelectric properties, possibly due to the conductive behaviour exhibited by CFO, and correlated with leakage current measurement. For the composite containing 40 mol% of CFO, the estimated values of remanent (Mr), saturation (Ms) magnetization, coercive field (Hc), and magnetic moment (µB) are 2.35 emu/g, 21.85 emu/g, 104.2 Oe, and 0.86 µB, respectively. The non-Debye type dielectric relaxation processes have been observed in the composites, and the electron hopping mechanism resulted in a higher dielectric constant (εʹ). Enhancement in relaxor nature had been observed through Vogel-Fulcher analysis with CFO content. The evidence of ME coupling was revealed through the direct ME voltage coefficient (αME) and magnetocapacitance (MC) measurement. The observed maximum value of MC measured at 1 kHz for the 20 mol% CFO is ∼5.6 %. Self-biased ME coupling (non-zero αME at HDC = 0 Oe) was observed in 20 and 30 mol% of CFO composite. The highest measured value of αME for 20 and 30 mol% CFO is 3.63 mV/cm.Oe and 4.09 mV/cm.Oe at HDC = 0 Oe respectively. The strong ME interaction and significant value of self-biased ME αME suggest that these composites can be explored for magnetic sensor and ME memory device applications.

Temperature and frequency dependent response of electrical conduction and dielectric relaxation mechanism in CuCr2O4 tetragonally distorted spinel chromite

Herein, the polycrystalline CuCr2O4 (CCO) electro-ceramic was prepared via the sol-gel self-combustion route. The X-ray powder diffraction analysis at room temperature revealed that the CCO chromite was synthesized in a single phase tetragonally distorted normal spinel structure with I41/amd space group. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) investigated the polycrystalline nature of the compound. The microstructural analysis by field emission scanning electron microscopy (FESEM) explored the surface morphology of micron-sized grains (Gs) distinguished by well-pronounced grain boundaries (GBs) available for electrical response of the material. The color mapping images of elements by energy-dispersive X-ray spectroscopy (EDS) divulged the homogeneous distribution of elements in the compound. The surface chemistry of the compound was studied by X-ray photoelectron spectroscopy (XPS). This information helped in understanding the electronic states of the ions contributing to the electrical networks and mechanisms responsible for the charge transport within the CCO system. The dielectric relaxation and electrical transport properties were analyzed using complex impedance spectroscopy (CIS) over the experimental range of frequency and temperature from 40 Hz to 1 MHz and 243–493 K, respectively. The experimental complex impedance data were analyzed by RGQGRGBQGB equivalent circuit model which resolved the electro-active contributions of bulk and interface of the CCO spinel to its electrical dynamics. The dispersion in AC conductivity was explained by Jonscher's double power law which provided evidence of small polaron hopping (SPH) as a dominant transport mechanism governing electrical conduction in the compound. The temperature-dependent DC conductivity pattern exhibited an Arrhenius-like behavior that followed Mott and Davis's model of SPH. The analysis of complex electrical modulus M*(ω,T) professed the localized and de-localized movements of the charge carriers. The dielectric permittivity response of CCO followed Havriliak-Negami (HN) phenomenology that divulged the existence of non-Debye type dielectric relaxation processes. The interfacial polarization was observed to be accountable for the dispersion in dielectric loss spectra.

Influence of Zn-substitution on structural, magnetic, dielectric, and electric properties of Li–Ni–Cu ferrites

The polycrystalline Li0.15Ni0.6-xZnxCu0.1Fe2.15O4 ferrites are fabricated by the method of conventional solid-state reaction technique. The X-ray diffraction (XRD) confirms that the structure of the composition is a single-phase cubic spinel structure for all samples. The particle size of the compositions is varied from 36 to 52 nm. The lattice parameter and densities are found to increase with enhancing Zn content, as the ionic radius and atomic weight of Zn are greater than Ni. The porosity exhibits a decreasing trend. The average grain size determined using Field Emission Scanning Microscopy (FESEM) increases until x = 0.40, then declines. The Energy-Dispersive Spectroscopy (EDS) examination revealed that the percentage of obtained elements is well matched with the stoichiometric elements. The addition of Zn content acts as an accelerator for enhancing the value of the real part of initial permeability and the highest value is obtained (μiʹ = 276) for the x = 0.40 sample, as well as the highest relative quality factor (RQF) of around 3000. The loss factor for the Zn substituted composition is nine times lower than for the parent composition. The optimum saturation magnetization of around 77.49 emu/g is found for the x = 0.40 sample. The maximum dielectric constant (εʹ = 2.85 × 103) is found for x = 0.10 samples at 10 kHz. Further, from impedance studies, the non-Debye type dielectric relaxation is seen for the Zn-substituted samples. The observed region of the imaginary electric modulus peak signifies the transition of charge carrier mobility from a larger range to a short-range distance. The phenomenon of ac conductivity is attributed to the process of the small polaron hopping mechanism.

Insight of the Influence of Cobalt Substitution on the Structural, Microstructural, Optical and Electrical Properties of Tetragonal Barium Titanate Ceramics

The development of lead-free ferroelectric materials is essential for upcoming applications in energy and information storage. We comprehensively report the structural, optical, dielectric and electrical characteristics of BaTi1-x Co x O3 (0.00 ≤ x ≤ 0.10) ceramics prepared using the conventional solid-state route process. The synthesized sample features a single-phase tetragonal structure with P4mm symmetry, as confirmed by the X-ray diffraction investigation. SEM imaging clearly shows that the material was polydispersive. UV–vis diffuse reflectance spectra of the BaTi1-xCoxO3 ceramics has been carried out in order to calculate the optical band gap of each composition. For the prepared samples, Cole-Cole plot of the complex impedance was examined over a wide temperature and frequency range. The compounds displayed non-Debye type dielectric relaxation. The Ferroelectric-Paraelectric phase transition is clearly visible in the T-dependent dielectric spectra for all the samples. After E-poling the ceramics, a well-defined genuine saturated hysteresis loop was established.

Structural, Frequency and Temperature Dependent Dielectric Properties of Zn2+ Substituted Ni-Co Based Spinel Ferrite (ZnxNi0.8−xCo0.2Fe2O4)

Zinc substituted nickel-cobalt ferrites, i.e., ZnxNi0.8−xCo0.2Fe2O4 (x = 0.0, 0.05, 0.10 and 0.20) with average crystallite size 100 nm were synthesized by citrate-gel auto-combustion method to investigate effects of Zn2+ substitution on the structural and dielectric properties. Both X-ray diffraction (XRD) and IR spectroscopy studies confirms the formation of pure cubic spinel structure. Variation of lattice parameter infers Vegard’s law linear dependence with the addition of Zn2+ concentration. The temperature-dependent behavior of dielectric and modulus spectra has been studied within the frequency range 100 Hz-100 kHz for different temperatures between 100 K and 400 K. It was concluded that the dielectric responses of ZnxNi0.8−xCo0.2Fe2O4 are found to be frequency dependent and thermally activated. Also, In the Zn doped ferrites variations of dielectric loss (tan δ) and the imaginary part of electric modulus (M") show the presence of the non-Debye type of dielectric relaxation. Rise in Zinc concentration leads to a decrease in dielectric constant (ε r) due to the declining of Fe3+–O–M2+ conducting network (M is Co or Ni). Here, we report a low loss tangent factor of the order of for the sample Ni0.6Zn0.2Co0.2Fe2O4 make this composition suitable for high frequency-applications at room temperature. The activation energy is calculated from electric modulus formalism and DC electrical conductivity and found to increase with further substitution of Zn2+ concentration.

Study of LaCoO3 Across Insulator–Metallic Phase Transition

The standard solid-state reaction method was used to prepare perovskite LaCoO3 crystal successfully. The crystal structure was confirmed by means of powder X-ray diffraction. An investigation of the electrical properties shows an interesting temperature dependence. The real and imaginary parts of the dielectric constant show maximum at 533 K and minimum at 548 K. This indicates an Insulating-Metallic phase transition. It was found that the activation energy \(\Delta E_{a}\) in the semiconducting region was about 0.80 eV. The grain resistance shows an inverse dependence on temperature justify negative temperature coefficient of resistance exhibit. The crystal exhibits non-Debye type dielectric relaxation.

Characterization of Pb(Fe1/2Nb1/2)O3 ceramic as a potential candidate for photovoltaic and magnetoelectric applications

An impurity-free Pb(Fe1/2Nb1/2)O3 (PFN) ceramic was prepared using a conventional solid-state reaction method with precisely controlled sintering temperature. The PFN ceramic exhibits monoclinic symmetry and shows a dense morphology with equiaxed grains of about 1–2 μm. It exhibits a diffused phase transition at approximately 381 K. From the data of dielectric loss tangent and the imaginary parts of impedance and electrical modulus, a non-Debye type dielectric relaxation was investigated, and it was found that the short-range hopping of oxygen vacancies contributes to the dielectric relaxation and the relaxation time distribution is temperature independent. The PFN ceramic exhibits slim ferroelectric hysteresis loops and a linear magnetic hysteresis loop, indicating that the PFN ceramic is paramagnetic; the band gap is estimated to be 2.04 eV. Photoconductivity and photovoltaic responses with a nonzero open-circuit voltage and short-circuit photocurrent were detected. Moreover, magnetoconductivity was measured. This work implies that the PFN ceramic is a potential candidate for magnetoelectric and photovoltaic applications.

Studies of structural and dielectric properties in Co0.9Zn0.1Fe2O4 ceramics

Spinel ferrites have been widely studied due to their remarkable properties such as high saturation magnetisation, large magnetic permeability, and high electrical resistivity. Among the oxides-based magneto strictive spinel ferrite, CoFe2O4 (CFO) possess the highest value of absolute magnetostriction coefficient (–110 ppm). But CFO has the disadvantage of large magnetic anisotropy and high coercivity. Therefore, doping of zinc (Zn) at Co-site of CFO is reported to reduce the magnetic coercivity and increases the resistivity (108Ω) keeping the magnetostriction coefficient with a sizable value. Also, substitution of Zn for Co in CFO reduces magnetic anisotropy. So, in view of this we have prepared Zn modified CFO compound: Co0.9Zn0.1Fe2O4 using sol-gel combustion technique. The room temperature (RT) XRD patterns indicate the formation of single-phase material without appearance of any impurity phases within the detection limit of X-ray diffractometer. The Rietveld refinement on the RT XRD pattern of CZFO sample was carried out using cubic crystal structure with space group Fd-3m. A good agreement between the experimental and the fitted data has been observed. The average crystallite size for the composition was calculated from the XRD patterns using Williamson–Hall method. Scanning electron micrographs displays homogeneous distribution of grains throughout the sample microstructure with the presence of minute amount of pores. The dielectric and electrical properties were studied as function of frequencies at different temperatures. Complex impedance spectroscopic technique study on this sample suggests existence of non-Debye type dielectric relaxation behaviour.

Study of structural, dielectric and AC conductivity properties of SrMoO4

Strontium molybdate (SrMoO4) compound is synthesized using a solid-state reaction route. SrMoO4 was observed to form in tetragonal Scheelite structure with I41/a space group and is confirmed with the help of powder X-ray diffraction studies. The temperature-dependent dielectric constant measured at different frequencies indicated a maximum at around 795 K. The frequency-dependent dielectric maximum reveals the presence of a dielectric relaxation near 795 K. Further, the Nyquist plot analysis shows a depressed semi-circle and manifest the non-Debye type dielectric relaxation in SrMoO4. The SrMoO4 compound possesses a negative temperature coefficient of resistance and is confirmed by fitting the Nyquist plot with a suitable equivalent circuit. The AC conductivity studies ascertain that the observed conduction mechanism in the SrMoO4 as a translational type correlated barrier hopping. The temperature-dependent AC conductivity reveals that the obtained activation energies are comparable with the oxygen vacancies and are responsible for observed dielectric relaxation.

The relaxation processes of dielectric, modulus and impedance in Dy0.55Sr0.45Mn1- xFexO3

The ac electrical properties of orthorhombic ceramics, Dy0.55Sr0.45Mn1-xFexO3 (x = 0, 0.4 and 1.0) in the range of frequency 0.5–107 Hz and temperature 126–299 K have been studied. Across the series, dielectric permittivity and loss increase with increase in Fe concentration. Non-Debye type dielectric relaxation peak was found in x = 0.4 compound among Dy0.55Sr0.45Mn1-xFexO3 materials and consequently activation energy of the dielectric relaxation was calculated. The results of impedance spectroscopy revealed that for higher concentration of Fe in the series, impedance (Z′) is low. The relaxation peaks in impedance, Z″ are observed at different frequency ranges for different Fe concentration in the compounds. From the temperature dependence of these peaks, activation energies are determined. The results of modulus spectra indicated a similar behavior as impedance, but x = 0.4 compound showed a large activation energy among the compounds in the series. Cole-Cole plots displayed negative temperature coefficient of resistance, a normal behavior of semiconductors. These plots also suggested that the dielectric relaxation is of non-Debye type. The scaling behavior in the modulus and impedance suggested that temperature dependence of relaxation processes exists in these materials. These studies and results are significant for materials which exhibit high resistance in low temperature.

High-temperature 0.5BiFeO3–0.5PbFe0.5Nb0.5O3 multiferroic: Microstructure, ferroelectric properties, and Mössbauer effect

Research findings of the microstructure, dielectric, ferroelectric characteristics, and Mössbauer effect of solid solution ceramics with 0.5BiFeO3–0.5PbFe0.5Nb0.5O3 composition in a wide temperature range are presented. The examined ceramic chip surface allows one to draw conclusions about the internal homogeneity of grains and the absence of pores inside them. It was shown that Fe3+ iron cations in the material are valence and they are found only in seven locally different states, which is associated with disorder in the solid solution structure. The Néel temperature is TN ~ 445 K. The anomalous behavior at T < 30 K becomes clear when analyzing the dielectric spectra of 0.5BiFeO3–0.5PbFe0.5Nb0.5O3 ceramics in the range of 10 … 1000 K. It is explained by the appearance of a spin-glass state in the object. The presence of contributions to the dielectric response in ceramics at T > 300 K is revealed. It is claimed that the ferroelectric–relaxor → paraelectric phase transition caused the low-temperature contribution, and the second one is a manifestation of the Maxwell–Wagner polarization and the corresponding non-Debye type dielectric relaxation. The causes of the revealed regularities and the prospects for using the material in the thin films form are discussed.

Conductivity and dielectric properties of lithium-ion biopolymer blend electrolyte based film

In the present work, the effect of lithium salt contents on the ionic conduction of blend biopolymer electrolyte (BBE) comprising chitosan (CS) and methylcellulose (MC) complexed with lithium iodide (LiI) has been explored. The maximum ionic conductivity (6.26 × 10−6 S/cm) was achieved at room temperature upon incorporating 40 wt% of LiI. The frequency-dependent ac conductivity of the BBE follows the Jonscher power law, and the analysis confirmed that the Li-ion conduction mechanism is correlated barrier hopping (CBH) type. The temperature-dependent dc conductivity follows the Arrhenius relation in the investigated temperature ranges. The highest Li-ion conducting sample has minimum activation energy. The dielectric permittivity and dielectric loss decrease regularly with an increase in the frequency of the applied field. The asymmetric and broadening of imaginary modulus peak suggesting a non-Debye type dielectric relaxation.

Investigation on Multiferroic Properties and Conduction Mechanism in Cobalt Doped Bi0.9Nd0.1FeO3 Solid Solutions

Bi0.9Nd0. 1Fe1–x Co x O3 (x = 0.025, 0.050, 0.075 and 0.1) solid solutions have been synthesized by doping of Co3+ at the Fe3+ site using solid-state reaction method. The prepared solid solutions have been investigated for their structural, magnetic, ferroelectric and magneto-dielectric properties and conduction mechanism. The XRD study reveals that all the solid solutions possess a rhombohedral symmetry. The vibrating sample magnetometer study reveals that all the samples possess magnetic orders and the remnant magnetization has been found to be increased from 0.2388 emu/g for x = 0.025 to 0.7112 emu/g for x = 0.1. The non-Debye type dielectric relaxation has been investigated for all the samples. The frequency dependent ac conductivity data follows Jonscher’s Power law. Variation of exponent n versus temperature follows the overlapping large polaron tunneling conduction model. The maximum value of remanent polarization (∼0.152 μC/cm2) was found for x = 0.1. All the samples exhibit positive magneto-dielectric response in the low-frequency region with the highest magneto-capacitance value of 13.54% at 500 Hz for sample x = 0.1.

Structural evolution, dielectric relaxation and modulus spectroscopic studies in Dy substituted NBT-BT ferroelectric ceramics

We report the effect of partial substitution of Dy3+ rare earth ion in NBT-BT lead free ceramics on its structural, microstructural, ferroelectric and dielectric phase transitions. The Rietveld refined X-ray diffraction analysis revealed a coexistence of dual phase with major monoclinic (Cc) along with minor tetragonal (P4mm) in all Dy-NBT-BT ceramics. The T-dependent dielectric broad band spectroscopic study revealed that Dy-substituted NBT-BT ceramics exhibits two diffuse dielectric anomalies renowned as Ferro (FE) to anti Ferro (AFE) i.e., depolarization phase transition ( $$T_{d}$$ ) and Antiferro (AFE) to paraelectric (PE) i.e., curie phase transition ( $$T_{C}$$ ), below 150 °C and well above 300 °C temperature regions respectively. The complex frequency dependent dielectric and modulus spectroscopy analysis supports the Non-Debye type dielectric relaxation process was dominated for all the measured ceramics. T-dependent AC-conductivity study revealed, thermally activated charge carries and single ionized oxygen vacancies are found to contribute conduction process at different temperature regions. Room temperature polarization hysteresis (P–E) loops analysis exposed a slim asymmetric shape with Dy substitution increasing that indicates conversion of hard to soft ferroelectric character. Remnant polarisation ( $$P_{r}$$ ) and coercive field ( $$E_{c}$$ ) decreases with dopant concentration shows the tetragonality dominance with Dy substitution. Furthermore, an optimum recoverable energy density 1.477 J/cm3 was obtained in NBT-BT at Dy = 0.03 compositions that designate the materials could be useful for future high energy storage density applications.

The electrical modulus, conductivity and dielectric properties of Mn3TeO6 multiferroic compound

In this communication, the complex oxide Mn3TeO6 (MTO) compound was synthesized by solid-state reaction (SSR) method with high processing temperature. Mn3TeO6 compound was characterized by using the XRD technique at room temperature. The material was found in single phasic nature, and compositional purity was confirmed by using EDAX analysis. FE-SEM analysis was carried out to study the morphological properties of the prepared Mn3TeO6 (MTO) compound. Frequency-dependent electrical properties have been studied by using Complex Impedance Spectroscopy (CIS) characterization technique. Complex permittivity analysis (Dielectric constant ε′ and Dielectric loss ε’’) of the Mn3TeO6 (MTO) compound has been studied. The dielectric constant of the compound is found to increase with temperature (303 K–393 K). Dielectric behavior has been successfully explained by theoretically fitting the cole cole model and comparing results with experimental values. Cole cole plot from permittivity analysis indicates non-Debye type dielectric relaxation mechanism present in the studied compound. This has been discussed in detail on the basis of complex modulus study for the Mn3TeO6 compound. Electrical conductivity analysis has been carried out by theoretically fitting of observed data with power law. The conductivity parameter with s < 1 suggests CBH (Correlated Barrier Hopping) mechanism responsible for conduction. As increase in temperature, conductivity was found to be increased. Fitting parameters obtained from the theoretical aspect have been discussed in the present context.

Dielectric relaxation behavior and overlapping large polaron tunneling conduction mechanism in NiO–PbO μ-cauliflower composites

The NiO–PbO μ-cauliflower composites was synthesized via glycine assisted self-ignition techniques with an objective to investigate its temperature evolving distinct dielectric relaxor behavior and alternating current conduction mechanism, for exploring its application as high energy storage devices. The x-ray diffraction and Raman spectroscopy was utilized to characterize exquisite phase formation of the composites. The temperature dependent dielectric properties was performed in a broad range from 100 Hz to 1 MHz and it exhibits a diffuse phase transition in high temperature region. The Non-Debye type dielectric relaxation with grain and grain boundary contribution of different activation energy was confirmed by Nyquist plot (Z′−Z′′) of impedance spectra. Broad dielectric relaxation plateau was observed in the low temperature and high frequency region and electronic hopping motion with interfacial polarization is the underlying mechanism of it, instead of dipolar relaxation and internal barrier effect. The real ac conductivity was fitted by well-known Almond-west equation and the temperature dependent frequency exponent (S) confirmed double overlapping large polaron tunneling model (OLPT) model of electrical conduction mechanism from room temperature (298 K) to 533 K. The ac activation energies varries from 0.39 eV to 0.21 eV with high frequency dispersion and variable range hoppping (VRH) model is introduced to correlate the dc conductivity.

Structural, dielectric and electrical properties of BiFeO3 and BaTiO3 modified Bi(Mg0.5Ti0.5)O3

Bismuth barium magnesium ferric titanate (Bi0.5Ba0.5) (Mg0.125 Ti0.625 Fe0.25)O3 is fabricated through a standard ceramic technology route. By using various experimental techniques, the material has been characterized. Study of crystal structure using XRD (X-ray diffraction) data shows the rhombohedral system. Analysis of dielectric study reveals that the compound has low tangent loss and high dielectric constant at room temperature. At low frequencies and high temperatures, the existence of space charge polarization and the Maxwell–Wagner dielectric mechanism in the material has been realized. The existence of ferroelectricity in the material is confirmed by the PE loop. The impedance plots reveal that the compound shows semiconductor (based on negative temperature of coefficient of temperature) behavior at high temperature ≥ 300 °C. Analysis of Nyquist plots reveals the non-Debye type of dielectric relaxation and the contribution of grains and grain boundaries in the resistive and capacitive nature of the material. From the conductivity analysis, it can be seen that the sample obeys the Josher universal power law, and the Arrhenius type of conductivity. The low-leakage current of compound makes it suitable for the high temperature applications, and hence it shows probable Ohmic-type of conduction mechanism.

Experimental and computational investigation of PVDF–$$\hbox {BaTiO}_{{3}}$$ interface for impact sensing and energy harvesting applications

The interfacial polarization between PVDF and $$\hbox {BaTiO}_{{3}}$$ was studied using density functional theory calculations and atomic charge density analysis. A comparative study of dielectric relaxation, thermodynamic properties and impact analysis of the electrospun polyvinylidene fluoride (PVDF) and a 3 $$\%$$ $$\hbox {BaTiO}_{{3}}$$ –PVDF nanofibrous composite are presented. The frequency-dependent dielectric properties revealed the microstructural feature of the composite material. The impedance analysis and Nyquist plots showed a decrease in the bulk resistance of the composite compared to the pure PVDF. The temperature dependence of the electric modulus shows Arrhenius-type behavior. The electric loss modulus relaxation peak shifts towards the high frequency side which indicates a decrease in relaxation time and faster charge carrier dynamics. The observed non-Debye type dielectric relaxation in electric loss modulus follows a thermally activated process, which can be attributed to the polaron hopping effect. The particle-induced crystallization of the PVDF polymer is supported by thermodynamic properties from differential scanning calorimetric measurements. The observed increase in piezoelectric response from high strain rate impact sensing was attributed to the interfacial interaction between PVDF and $$\hbox {BaTiO}_{{3}}$$ .

Improved conductivity and reduced dielectric loss of Cu- substituted NiFe2O4 for high frequency applications

Abstract To promote suitable materials to be helpful for the electrical devices at high frequency application, we elaborated Cu substituted NiFe2O4 [NiFeCuO4 (NFCO)] by sol-gel reaction route and investigated the effect of Cu2+ on various properties of nanocrystalline NiFe2O4. The formation of pure cubic phase spinel NFCO was confirmed through X-ray diffraction (XRD). Magnetic measurement reveals the ferromagnetic behavior of the material. Exploring of ac conductivity grounded on Jonsher’s power law proves that the conduction is related to the Correlated Barrier Hopping (CBH) model. Our compound exhibits the Relaxor character. Electrical modulus study unveils the presence of the non-Debye type of dielectric relaxation. Activation energies calculated from the conductivity pattern, impedance and Modulus prove to be close, which confirms that the relaxation process and the electrical conductivity may be attributed to the same type of charge carriers. The substitution of Fe by Cu in NiFe2O4 increases the ac conductivity and reduces the dielectric loss compared to NiFe2O4. The semiconductor behavior and the lower values of dielectric loss illustrate that Cu- substituted NiFe2O4 display potential applications for integrated electronic chips, microwave and electrical devices at high frequency.