Frequency Dependent Dielectric Behavior Research Articles

A Theoretical Approach to Study the Frequency Dependent Dielectric behavior of Breast Cancer Cells using AlN buffer-based AlGaN/GaN HEMT

Abstract This article investigates the applicability of open gated high electron mobility transistor (HEMT) as a biosensing platform for Breast cancer detection. The present study reports the detection of healthy (MDA-10) and malignant cells (MDA-MB-231) associated with breast cancer using high-quality AlN buffer AlGaN/GaN HEMT with dual cavity structure formed by etching out the gate metal from source and drain sides under the gate region. The AlN buffer AlGaN/GaN HEMT provides better 2DEG confinement and large conduction band offset than GaN buffer. The proposed design is analyzed at frequencies of 900 MHz and 10 GHz, as breast cells have distinct dielectric properties at different microwave frequencies. The variation in dielectric constant of the cavity region corresponding to biomolecular species will change the device’s electrical characteristics and hence can be used to detect breast cancer cells. In this work, the device sensing parameters considered for analysis are shift in threshold voltage and drain current sensitivity. The device performance has also been analyzed by optimizing cavity thickness and length to select the best design for the sensing. The effect of non-ideal conditions such as steric hindrance and probing is also studied by emulating these real time effects in simulation. The device shows a maximum drain current sensitivity of 29.94% for 20 nm of cavity thickness and 1µm of the cavity length. The results depict that the proposed device design exhibits a highly sensitive response and can be promising alternate for future biosensing applications.

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.

Synthesis and performance assessment of silica dispersed nano-composite polymer gel electrolyte for high-performance solid-state supercapacitors

Nano-composite polymer gel electrolyte (NCPGE) films are prepared by incorporating liquid electrolyte (EC-PC-TEABF4) into polyvinyldinefloroide co-hexafluoropropylene (PVDF-HFP) polymer with dispersed SiO2 nano-particles using solution cast technique. The NCPGE is optimized for the highest ionic conductivity by varying wt% of SiO2 nanoparticles in PGE [(1:4){PVDF-HFP + EC-PC-TEABF4}]. Highest conductivity of 8.2 × 10−3 Scm−1 is found for optimized composition [(1:4){PVDF-HFP + EC-PC-TEABF4} + SiO2 (15 wt%)] of NCPGE. Structural and morphological studies have been done using XRD, FTIR, and SEM. Frequency dependent dielectric behaviour is understood using dielectric constant and modulus analysis in a wide range of frequencies. The ionic transference number is 0.96 and an electrochemical potential window of ∼ 3.5 V has been obtained. Fabrication of electric double layer capacitor (EDLC) is done by sandwiching NCPGE between activated carbon (AC) electrodes. The electrochemical performance of fabricated supercapacitor is evaluated by impedance spectroscopy, cyclic voltammetry, and galvanostatic charge–discharge techniques. Results show significant improvement in the quality of synthesized electrolyte.

Optimization of dielectric phenomenon in 0.8[(1-x)SrCoO2.29 + xCr2FeO4] + 0.2PZT tri-phase composites

Composite materials are emerging and have potential to revolutionize the modern technology. In this work, a series of tri-phase composite materials having the chemical formula; 0.8[(1-x) SrCoO2.29+xCr2FeO4] + 0.2PZT, is synthesized to explore their energy storage capability. In this series, SrCoO2.29 and Cr2FeO4 ceramics are synthesized by using a sol-gel auto-combustion process while PZT is prepared by the solid-state method. The XRD analysis confirmed the formation of cubic crystal structure of the SrCoO2.29 and Cr2FeO4 and the rhombohedral phase of PZT. The SEM images exhibited an increase in average grain size with the incorporation and increasing contents of Cr2FeO4. The presence of all constituting elements with the exact stoichiometric ratio is validated through EDX analysis. Wide-range frequency-dependent dielectric behavior showed a dramatic fall in dielectric constant with increasing frequency. A same frequency dependent behaviour of ε'' and tanδ is witnessed as that of ε'. The investigation of electric modulus reveals that in the low-frequency region it possesses a trivial value which became significantly large with the increase of frequency. The presence of a relaxation peak in the plot of the imaginary part of the electric modulus plays a decisive role to distinguish the small and large range hopping mechanism. The complex impedance analysis revealed different electroactivity of composite material in the different frequency domains which made them viable for advanced energy storage devices working in the vast frequency range.

Unveiling frequency-dependent dielectric behavior of cellulose-based polymer electrolyte at various temperature and salt concentration

Dielectric behavior of cellulose-based polymer electrolyte was studied at various temperature and salt concentration. A polymer electrolyte membrane based on cellulose acetate (CA) as the polymer host and LiClO4 as the dopant salt was fabricated using the solution casting technique. The dopant salt concentration was varied as 0.3, 0.5, 0.67, and 1M. Dielectric relaxation spectroscopy characterization were performed using potentiostat at frequency ranging from 0.1 Hz to 1 MHz. Measurements were performed by sandwiching the membrane between stainless steel plates. The ionic conductivity was then calculated based on the Cole–Cole plot obtained from the impedance measurement. It was found that sample 1 M had the highest ionic conductivity at high frequencies. However, the frequency-dependent conductance plot showed that the ionic conductivity of the 1 M sample significantly decreased at low frequencies, i.e. from 3.41×10-5 S/cm at 1 MHz to 1.9×10-8 S/cm at 0.1 Hz. Other samples did not experience this phenomenon, including those with a Celgard© commercial membrane to represent commercial Li-ion batteries. This is caused by excess charge accumulation, leading to a high concentration of immobile charge carriers, which reduces the available free volume surrounding the polymer chain. This resulted in a significant decrease in ionic conductivity at low frequencies. Temperature variation was also performed on the conductivity measurement at 30-70 °C. Temperature variation showed more predictable behavior, where increasing the temperature activated charge carriers and enhanced ionic conductivity, from 1.81×10-5 S/cm at room temperature to 9.04×10-5 at 70°C. Sweeping across the frequency range results in a consistent sequence of ionic conductivities among the samples at various temperatures. This work is beneficial for evaluating a biomass-based polymer electrolyte complex in a Li-ion battery environment. Feasibility studies can be performed at various concentrations and temperatures to determine the optimal level of dopant salt input across a broad frequency range.

Tuning of structural, electrical and transport behaviour of cobalt nanoferrite by dysprosium ions substitution

Present study explores the structural, electrical and transport properties of dysprosium cation (Dy3+) substitution on (Fe+3) site in cobalt nonoferrites [CoFe2-xDyxO4 (Dy(x) = 0.00, 0.05, 0.10 & 0.15)] prepared by sol-gel chemical route. X-ray diffraction pattern confirms the pure cubic spinel structure for all samples. The average crystallite size was found in the range of 49 to 72 nm with no linear variation with incresing doping concentration of (Dy3+) ions. The values of lattice parametres is found to be changed from 8.34 to 8.39 Å for pristine cobalt nanoferrite (CoFe2O4) and sample having highest doping concentration i.e. Dy(x) = 0.15 respectively. The porosity observed to be decrease linearly with increasing (Dy3+) ion concentration. The electrical properties have been investigated by analyzing dielectric behaviour in the frequency range of 75 kHz- 5 MHz and temperature range of 100K– 400K. The frequency dependent dielectric behaviour at different temperatures is explained in terms of Maxwell–Wagner and Koop’s phenomenological models. Ferrite with Dy(x) = 0.15 have achieved highest dielectric constant in the range of 441 to 5234 which was measured at 100K (5 MHz) and 400K (75 kHz) respectively. The electrical resistivity of each of the ferrite sample reduces with rising temperature representing the semiconductor behaviour of all ferrites which is due to the thermally triggered charge carriers hopping between (Fe2+) and (Fe3+) ions and associated with higher drift mobility. The increase in drift mobility at room temperature with increasing (Dy3+) ion concentration is considered to be a sign of improved transport behaviour. The high value of dielectric constant and low dielectric loss of all these ferrites make them suitable for the memory storage devices.

Investigation of Dielectric and Energy Storage Performance of (1-x)BaTiO3-xBi(Zn2/3Nb1/3)O3 Ceramic for Possible MLCC Application

The dielectric and energy-storage performance of (1-x)BaTiO3(BT)-xBi(Zn2/3Nb1/3)O3(BZN) [0 ≤ x ≤ 0.15] materials are presented in this manuscript for potential multilayer ceramic capacitor application. The solid-state reaction method is adapted for the preparation of the ceramics. X-ray diffraction patterns of the ceramics reveal the formation of pure perovskite pseudo-cubic structure with space group P m −3 m. Temperature and frequency-dependent dielectric behavior are analyzed to understand the change in dielectric performance with the rise in BZN concentration. The degree of diffuseness in the phase transition has been analyzed by using the modified Curie-Weiss Law. The temperature Coefficient of Capacitance (TCC) has been calculated to analyze the thermal stability of the material. The P-E hysteresis loop measurement has been carried out at different applied fields and found that 0.15 mol% of BT-BZN can withstand maximum electric field exposure without undergoing any electrical breakdown. The energy storage efficiency is calculated for all the compositions and maximum efficiency is obtained for x = 0.15. The frequency-dependent P-E hysteresis is carried out and frequency stability of polarization is obtained for 0.85BT-0.15 BZN ceramic.

Influence of Ba-doping on the structural and physical properties of Sr2−xBaxFeVO6 double perovskites

The influence of A-site Ba-doping on the structural, dielectric, magnetic, and optical properties of double perovskite (BaxSr2−x)FeVO6 (BSFV(x): x = 0.0–2.0) ceramics prepared by solid-state reaction method, is reported. X-ray diffraction patterns and Rietveld refinements revealed that the BSFV(x) samples with x = 0.0–1.0 crystallized in a cubic crystal structure with an Fm3̅m symmetry whereas the samples with x = 1.5 and 2.0 crystallized in a hexagonal crystal structure with R3c symmetry. Their unit cell volumes increased progressively with the Ba-doping content due to the steric effect generated by the progressive increase of the average ionic radius at A-site, 〈rA〉. SEM images revealed the BSFV(x) samples were highly dense with ceramic grains of polyhedral morphology. Their average grain sizes increased from 2.0(2) μm (x = 0.0) to 5.0(3) μm (x = 2.0). X-ray energy dispersive spectroscopy data gave out the chemical compositions of these samples, which were close to the nominal stoichiometric values. FTIR spectra verified the vibrating modes of the [FeO6] and [VO6] octahedrons in the present samples. XPS spectra confirmed dual chemical valence states of Fe element (Fe2+ and Fe3+) and a triple oxidation states of V element (V3+, V4+ and V5+) as well as two species of oxygens in the BSFV(x) samples. The BSFV ceramics exhibited a strongly frequency-dependent dielectric behavior and a diffuse phase transition, which were resulted from the dielectric response of oxygen vacancies and the electron hopping between the variable cations at B-site as well as the B-site cationic random occupancy. Magnetic Curie temperature (TC) and effective magnetic moment (μeff) decreased as increasing the Ba-doping content due to the weakening of superexchange magnetic interactions between the Fe and V ions. The optical band gaps (Eg) of the BSFV(x) samples extracted from UV-Visible spectra, were in the range of 1.94 – 2.42 eV, exhibiting a blue shift towards semiconductor range as increasing the Ba-doping content. The overlapping between the O-2p and Fe/V-3d orbitals contributes to the Eg in the BSFV samples.

Effect of sintering temperature on structural, magnetic, dielectric and optical properties of Ni–Mn–Zn ferrites

Spinel ferrite [Formula: see text][Formula: see text][Formula: see text]Fe2O4 was prepared by a conventional ceramic process followed by sintering at three different temperatures (1050[Formula: see text] C, 1100[Formula: see text] C and 1150[Formula: see text] C). X-ray diffraction (XRD) investigations stated the single-phase cubic spinel structure and the FTIR spectra revealed two prominent bands within the wavenumber region from 600 cm[Formula: see text] to 400 cm[Formula: see text]. Surface morphology showed highly crystalline grain development with sizes ranging from 0.27 [Formula: see text]m to 0.88 [Formula: see text]m. The magnetic hysteresis curve at ambient temperature revealed a significant effect of sintering temperature on both coercivity ([Formula: see text] and saturation magnetization ([Formula: see text]. Temperature caused a decrease in DC electrical resistivity, while the electron transport increased, suggesting the semiconducting nature of all samples and that they well followed the Arrhenius law from which their activation energies were determined. The values of Curie temperature ([Formula: see text] and activation energy were influenced by the sintering temperature. Frequency-dependent dielectric behavior (100 Hz–1 MHz) was also analyzed, which may be interpreted by the Maxwell–Wagner-type polarization. The UV–vis–NIR reflectance curve was analyzed to calculate the bandgap of ferrites, which showed a decreasing trend with increasing sintering temperature.

Relaxation processes and conduction behaviour in PVDF-TrFE and KNN-based composites

Polymer-ceramic composites have gained considerable attention in flexible electronic devices due to their uncommon features such as high dielectric constant, low conductivity, and good mechanical flexibility. The electrical and mechanical responses of various components (ceramic grain & grain boundary, polymer chains, and interface) need to be elucidated to rationally design high-performance polymer-ceramic composites. This paper provides a detailed analysis of dynamic mechanical and frequency-dependent dielectric behaviour with temperature to discern the various mechanisms responsible for the relaxations in the polyvinylidene fluoride-trifluoro ethylene/K0·5Na0·5NbO3–CaZn1/3Ta2/3O3 (PVDF-TrFE/KNN-1CZT) composite fabricated using solution casting technique. The FTIR spectra and x-ray diffraction patterns indicate the existence of the polar β-phase, confirming the ferroelectric nature of polymer films. The ferroelectric-paraelectric phase transition (TC ∼ 130 °C) of polymer film obtained from the DSC & DMA data was corroborated by the dielectric study. The introduction of ceramic fillers in polymer induces an additional relaxation in the 10 kHz to 1 MHz frequency range, owing to the ceramic-polymer interface formation, which is responsible for increment in the dielectric constant and storage capacity of the composites. The effective dielectric constant of the composite was modelled using the Maxwell-Garnet and Yamada models. The enhanced dielectric constant of composite films (εr ∼ 28) with the addition of dielectric filler qualifies these materials for flexible high-performance capacitive devices. Further, this study enables a better understanding of the various relaxation processes in the composite with dielectric fillers.

Effect of synthesis methods on dielectric performance of ZnO nanoparticles

ABSTRACT Zinc oxide (ZnO) nanoparticles are widely studied for the application of dye-sensitised solar cells (DSSCs). The control of nanoscale morphology and microstructural properties of ZnO is critical for DSSCs performance. The current study provides an insight about the effect of synthesis methods (i.e. co-precipitation and sol–gel) on structural, optical and electrical properties of ZnO nanoparticles. The formation of hexagonal wurtzite phase with space group P63mc was confirmed by Rietveld fitted X-ray diffraction and Raman spectroscopy. The variation in morphology due to different synthesis methods was confirmed by Scanning electron microscopy. Functional groups were identified by Fourier transform infrared spectroscopy. The presence of defects led to the narrowing of band gap of ZnO nanoparticles, and was confirmed by diffuse reflectance spectroscopy. The frequency-dependent dielectric behaviour was explained by means of Maxwell–Wagner–Sillars model. The current study paves the way of potential application of ZnO nanoparticles in DSSCs.

Impact of V substitution on the physical properties of Ni–Zn–Co ferrites: structural, magnetic, dielectric and electrical properties

We have investigated the Vanadium- (V) substituted Ni–Zn–Co ferrites where the samples are prepared using the solid-state reaction technique. The impact of V5+ substitution on the structural, magnetic, dielectric and electrical properties of Ni–Zn–Co ferrites has been studied. The XRD analysis confirms the formation of a single-phase cubic spinel structure. The lattice constants have been calculated both theoretically and experimentally along with other structural parameters such as bulk density, x-ray density and porosity. The FESEM images are studied for analyzing the surface morphology. FTIR measurement confirms spinel structure formation. The saturation magnetization (M s), coercive field (H c) and Bohr magnet on (μ B) are calculated from the obtained M-H loops. The temperature-dependent permeability is studied to obtain the Curie temperature. The frequency and the composition dependence of permeability are also analyzed. Frequency dependent dielectric behavior and ac resistivity are also investigated. An inverse relationship is observed between the composition dependent dielectric constant and ac resistivity. The obtained results such as the electrical resistivity, dielectric constants and magnetic properties suggest the appropriateness of the studied ferrites in microwave device applications.

Polymer Composites with Improved Dielectric Properties: A Review

Materials exhibiting high dielectric constant (k) values find applications in capacitors, gate dielectrics, dielectric elastomers, energy storage device, while materials with low dielectric constant are required in electronic packaging and other such applications. Traditionally, high k value materials are associated with high dielectric losses, frequency-dependent dielectric behavior, and high loading of a filler. Materials with low k possess a low thermal conductivity. This creates the new challenges in the development of dielectric materials in both kinds of applications. Use of high dielectric constant filler materials increases the dielectric constant. In this study,the factors affecting the dielectric constant and the dielectric strength of polymer composites are explored. The present work aims to study the effect of various parameters affecting the dielectric properties of the materials. The factors selected in this study are the type of a polymer, type of a filler material used, size, shape, loading level and surface modification of a filler material, and method of preparation of the polymer composites. The study is focused on the dielectric enhancement of polymer nanocomposites used in the field of energy storage devices. The results show that the core-shell structured approach for high dielectric constant materials incorporated in a polymer matrix improves the dielectric constant of the polymer composite.

Preparation of Ba2FeNbO6 double perovskite ceramics from molten-salt synthesized powders and their dielectric and magnetic properties

Double perovskite Ba2FeNbO6 (BFN) ceramics were prepared from the molten-salt synthesized BFN powders. The BFN powders have a cubic structure with $$ Fm\bar{3}m $$ space group, confirmed by X-ray diffraction patterns. Their average particle sizes increased with the annealing temperature and dwell time whereas decreased with the molten-salt content. X-ray photoemission spectra revealed both Fe2+ and Fe3+ ions present in the BFN powders and oxygen in the forms of lattice oxygen and oxygen vacancies, while niobium was present as Nb5+. The BFN ceramics exhibited significant frequency-dependent dielectric behavior, and two kinds of dielectric relaxor processes were observed. Their activation energies were 0.16 eV and 0.47 eV, respectively. The electron hopping process (between Fe2+ and Fe3+ ions) with the activation energy of 0.16 eV contributes the low-temperature dielectric relaxation process, and an activation energy of 0.47 eV associated with the high-temperature dielectric relaxation is originally from the barrier energy of the thermal motion of the oxygen vacancies. The dielectric relaxation observed at high-temperature region can be explained by Maxwell–Wagner interfacial polarization in the BFN ceramics. M–H plots of the BFN ceramics at different temperatures revealed their antiferromagnetic nature and a weak ferromagnetic behavior at 2 K. The remanent magnetization (Mr) of the BFN ceramics was measured to be 1.75 emu/g at 2 K and coercive field (Hc) as 1.26 kOe. Magnetization splitting was observed at ~ 290 K between the temperature-dependent magnetizations of the BFN ceramics, which were measured under zero field-cooled (ZFC) and field-cooled modes with an external field of 1 kOe. In the ZFC curve, a maximum peak was observed at 14 K, corresponding to the Neel temperature (TN). The TN of the present BFN ceramics shifts toward low temperature as compared with those prepared by conventional solid-state reaction methods. Such a reduction of the Neel temperature is ascribed to the size effect.

Electrorheological Characteristics of Poly(diphenylamine)/magnetite Composite-Based Suspension.

Electro-responsive poly(diphenylamine)(PDPA)/Fe3O4 composite particles were prepared by the synthesis of PDPA particles using a chemical oxidative polymerization technique followed by loading nano-sized Fe3O4 particles onto PDPA via a chemical co-precipitation process. The morphological image of the PDPA/Fe3O4 particles was characterized by scanning electron microscope and transmission electron microscope. The crystalline structure was scrutinized by X-ray diffraction. The rheological characteristics of the suspension composed of PDPA/Fe3O4 particles suspended in silicone oil were investigated by a rotation rheometer, demonstrating standard electrorheological (ER) characteristics with a dramatic increase in shear stress and dynamic moduli under the application of an electrical field strength. The shear stress curves under an electrical field could be described using the Bingham model and the yield stress showed a power-law relationship with the electric field strength with an exponent of 1.5, following the conduction model. Furthermore, the frequency-dependent dielectric behaviors of the PDPA/Fe3O4 ER suspension was tested using an inductance (L)-capacitance (C)-resistance (R) (LCR) meter. The dielectric properties were well described using the Cole–Cole equation and were consistent with the results of the ER experiments.

Alkaline-earth metal based coordination polymers assembled from two different V-shaped ligands: Synthesis, structure, and dielectric properties

Four new coordination polymers built of Group(II) metals (Mg, Ca and Ba) and two V-shaped ligands viz. FBA 4,4′-(hexafluoroisopropylidene)bis(benzoic acid) and SBA (4,4′-sulfonyldibenzoic acid) have been crystallized via solvothermal reaction: [Mg3(FBA)2(DMF)2(HCOO)2(H2O)2].2DMF (1), [Ca(FBA)(DMF)] (2) [Ca4(SBA)4(DMF)2].2DMF (3) and [Ba(FBA)(DMA)(H2O)2] (4). Single crystal X-ray analysis established that all the four solids are built of extended metal carboxylate interaction. 1 is a 2D CP with square-shaped channels while 2, 3 and 4 are 3D CPs with rhombic channels. Frequency and temperature dependent dielectric behavior of solids 1–4 showed dielectric constants in the range 8–18 at room temperature. The solids 1 and 3 containing highly polarizable guest molecules (DMF, DMA and H2O) showed relatively higher value of dielectric constants (∼18.0 and ∼13.4 respectively) in comparison to 2 and 4 (∼7.8 and ∼8.0 respectively). Impedance spectroscopy studies (Z′ and Z″) showed that significantly higher dielectric constants in 1–4 arise from intrinsic behavior of the solids. The present work also highlights the influence of polar guest molecules in the structure in altering the dielectric constant.

Ferroelectric and optical modulations of double perovskite Ba2BiVO6

The prevalent solid state route has been endorsed to tailor the eco-friendly polycrystalline ceramic Ba2BiVO6. The qualitative phase analysis through X-Ray Diffraction (XRD) at room temperature affirms the formation of single phase new double perovskite. The surface texture of the investigated sample is carried out through scanning electron microscope (SEM) image. Compositional analysis was shaped through the EDS spectra confirms the absence of any contamination. Vibrational properties of the compound investigated through RAMAN and FTIR spectroscopy and confirms the finger print of atoms in the compound. Optical properties of the material have been carried by UV–Vis and Photo luminescence spectroscopy which confirms the compound can be useful for photo catalytic devices. Temperature and frequency dependent dielectric behavior as well as polarization study confirms the presence of ferroelectricity in the compound. Conduction mechanism as well as leakage property of the material is carried out through respective impedance spectroscopy and ac conductivity study.

Dielectric relaxation and ac conductivity in magnetoelectric YCrO3 ceramics: A temperature dependent impedance spectroscopy analysis

Here, we report on the temperature and frequency dependent electrical conduction and dielectric behaviour of YCrO3 ceramics. Dielectric studies reveal a peak in the dielectric constant ∼230 K, suggesting presence of spin-charge coupling. Also, an additional broad peak found at ∼450 K is reminiscent of a relaxor like behaviour for YCrO3, attributed to a diffused phase transition. The nature of dc conductivity is of Arrhenius type and shows an abrupt change in the activation energy at ∼230 K and ∼450 K. The activation energy suggests that the polaronic hopping mechanism stabilizes at low temperature while, at higher temperatures, the process is associated with the diffusion of double ionized oxygen vacancies. However, ac conductivity suggests that the overlapping large polaron tunnelling conduction mechanism drives the ac conduction below 300 K and above 300 K, the conduction behaviour is consistent with the correlated barrier hopping conduction mechanism.

Synthesis, structural, dielectric and magnetic properties of spinel structure of Ca2+ substitute in Cobalt ferrites (Co1−xCaxFe2O4)

Non magnetic material Ca2+ as a substitute in Cobalt ferrite (Co1−xCaxFe2O4x = 0.00, 0.05, 0.10 & 0.15) is prepared by self auto combustion method. The synthesized samples were carried out for various characterizations such as X-ray diffraction, Field emission scanning electron microscope (FE-SEM), Dielectric measurement and Magnetic property. X-ray diffraction reveals the values of crystalline size, lattice parameter and x-ray density by using the standard formula. The saturation magnetization (Ms) decreases from 63.92 to 43.17 emu/g for x = 0.00 to 0.15 and the coercivity (Hc) increases gradually from 819.85 to 1312.32 Oe with the increase in Ca2+ concentration. The dielectric properties of synthesized nano materials were carried out at room temperature. The dielectric parameters such as tangent loss, Cole–Cole plot (Impedance, Modulus), and AC Conductivity were determined for various Ca2+ concentration. The frequency dependent dielectric dispersion behaviour of all the samples can be explained by the Maxwell–Wagner two-layer model along with Koop's phenomenological theory. As a result, Ca2+ substituted Cobalt ferrite is enhanced with their dielectric and magnetic property which is suitable for a memory device, recording media application and high frequency device.

Effect of Swift Heavy Ion Irradiation on Dielectric Properties of Manganite Based Thin Films

In this communication, we report the results of the investigations on the structural, microstructural and electrical properties of Y0.95Sr0.05MnO3 (YSMO) thin films with 100 nm thickness grown on (100) single crystalline SrNb0.002Ti0.998O3 (SNTO) substrates using pulsed laser deposition (PLD) technique. YSMO films were irradiated using 100 MeV O+7 swift heavy ions (SHI) with different fluence using 15 UD Tandem Accelerator, IUAC, New Delhi facility. Structural investigations using θ – 2θ X – ray diffraction (XRD) reveal that all the films crystallize in single phasic nature. With increase in ion fluence, structural strain is found to increase upon the irradiation using lower fluence of 1 × 1011 ions/cm2 which can be ascribed to the irradiation induced creation of defects at the interface. Further increase in ion fluence up to 1×1012 ions/cm2 can create more defects resulting in the degradation in lattice structure and hence strain gets enhanced. For the higher ion fluence of 1×1013 ions/cm2, local annealing takes place at the interface which in turn results in the improved structural strain and recrystallization process. To study the surface morphology of the pristine and irradiated films, atomic force microscopy (AFM) measurement was performed. To understand the electrical properties of presently studied YSMO / SNTO pristine and irradiated films, frequency dependent dielectric behavior was studied. It is seen that dielectric constant increases upon irradiation using the fluence of 1 × 1011 ions/cm2 and 1 × 1012 ions/cm2 while gets suppressed for 1 × 1013 ions/cm2 fluence. Variation in dielectric behavior with different ion fluence has been discussed on the basic of lattice strain and universal dielectric response (UDR) model.