Dependent Dielectric Constant Research Articles

Radiation response of zirconium silicate P-MOS capacitor

The chemical bonding of zirconium silicate films were examined by FTIR. The capacitance-voltage (C-V) measurements before and after irradiation were performed at high frequency. Furthermore, significant changes were observed depending on the radiation dose of the oxide traps and the intensity of the interface state. The sensitivity of this MOS capacitor is 4.3, 31.3 and 15.6 times less sensitive compared to the same thickness as Sm2O3, Al2O3 and Gd2O3. Therefore, it can be used as radiation-resistant material in nuclear reactors and space applications due to its stable electrical characteristics compared to other defined dielectrics. Interface states, (Nit) Barrier potential (Φb) and oxide traps (Not) have also been investigated depending on the radiation effects. Φb is one of these important electrical properties. Φb values decreased with increasing in radiation dose. Besides, radiation and frequency dependent dielectric constant (ε′), dielectric loss (ε″) and dielectric loss tangent (tanδ) and conductivity (σac) of zirconium silicate were investigated. It is concluded that high-k zirconium Silicate is suitable for electronics applications in radiation harsh environment.

Phenomenological theory of phase transitions in the MPB region of (1−x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 single crystals

ABSTRACTA higher-order Landau–Ginzburg–Devonshire theory is proposed to describe phenomenologically the complex phase transitions in the MPB region of the relaxor ferroelectric (1−x)Pb(Mg1/3Nb2/3)O3-xPbTiO3(PMN-PT) single crystals. Using the singularity theory, a structurally stable 10th-order potential with four varying expansion coefficients (a1, a11, a2 and a12) depending on temperature and composition is found out. By studying on two- and three-dimensional sections of a four-dimensional phase diagram a1-a11-a2-a12 in the space of phenomenological parameters, the range of coefficient parameters by which the structural stability of the potential model can be guaranteed is determined. The theoretical temperature-composition phase diagram is constructed and it is shown that this is in good agreement with both recent experimental data and first-principle calculation for the symmetry change. Moreover, temperature dependence of dielectric constants for various compositions is studied.

Study of the optical, dielectric and magnetic properties of the Bi0.75La0.25FeO3 sample

Bi0.75La0.25FeO3 sample has been fabricated by a novel hydrothermal-assisted co-precipitation method. The X-Ray diffraction (XRD) and Fourier transform infrared (FTIR) studies confirmed that the sample was crystallized in orthorhombic (Pbnm) and rhombohedral (R3c) phases. Using differential thermal analysis (DTA), it is observed that the sample exhibits a Neel temperature (TN= 581 K) and Curie temperature (TC=1017K). UV-visible absorption spectrum of the sample exhibits two doubly degenerate d-d transitions and three charge transfer transitions. The temperature dependence of dielectric constant of the sample at different frequencies (0.12 to 100 kHz) exhibits two anomaly peaks at 497 and 707 K. An asymmetric shift in the coercive field of the hysteresis loop (M-H) indicates the presence of exchange bias effect in the sample.

Theoretical model for size, dimension and shape effect on electrical behavior of semiconductor nanomaterials

The present study is an effort to develop a simple analytical model without any adjustable parameter for observing the collective effect of size, dimension and shape on electrical susceptibility and dielectric constant of nanomaterials. The size dependence of electrical susceptibility and dielectric constant has been observed for some pure as well as binary semiconductor nanomaterials, in three different dimensions (i.e., nanoparticles, nanowires and nanofilms). It has been observed that the electrical susceptibility and dielectric constant both show reduction with the decrement in size, due to the increased surface-to-volume ratio and lower coordination number. The present study reveals that the difference between the values of electrical susceptibility of nanoparticles and nanowires (5–50%) is less in comparison with nanofilms (10–90%). This difference diminishes on moving toward the higher size range. The decrement in the value of dielectric constant with size is found, maximum for nanoparticles (10–80%) followed by nanowires (10–70%) and minimum in nanofilms (5–60%). The outcomes for the size-dependent dielectric constant have been compared with the available experimental and other theoretical data and found consistency in calculated results with experimental data. The model has been extended to investigate the cross-sectional shape effect along with size on the electrical susceptibility and dielectric constant of nanowires due to large applications by incorporating shape factor. Four different cross-sectional shapes: spherical, square, rectangular and hexagonal nanowires, have been taken for the present study. The calculated results of dielectric constant have been compared with the available experimental data, and close agreement was found. It has been observed that the electrical susceptibility and dielectric constant have the highest value for spherical cross-sectional-shaped nanowires and the lowest for rectangular cross-sectional-shaped nanowires. Deviation graphs show that the values of electrical susceptibility and dielectric constant for rectangular, square and hexagonal cross-sectional-shaped nanowires deviate from spherical nanowires as 2–14%, 2–4% and 1–2%, respectively. The present study confirms the importance of shape effect along with size and dimension for electrical properties of semiconductor nanomaterials.

Antiferromagnetic and dielectric behavior in polycrystalline GdFe0.5Cr0.5O3 thin film

Single phase materials with both spontaneous electric polarization and magnetization are rare, despite remarkable efforts in developing magnetoelectric multiferroics. In this work, a single-phase polycrystalline GdFe0.5Cr0.5O3 (GFCO) thin film was spin-coated onto a platinized silicon substrate. X-ray diffraction data suggest that the film exhibits an orthorhombic perovskite structure with a Pbnm space group. No other impurity phases were detected. Magnetization measurements reveal the Néel temperature of the GFCO film to be ∼220 K and illustrate a weak ferromagnetic component at 5 K, which could be due to spin canting. Frequency dependent ferroelectric–paraelectric transition was observed around 480 K, indicating the diffuse relaxor-like behavior. The electric field dependent polarization measurements show a lossy behavior below 200 K. The electric field dependent dielectric constant (tunability) measured at 1 MHz in a wide temperature range reveals that the tunability maximizes near the observed dielectric maxima, which further confirms the ferroelectric to paraelectric transition in the present film.

Photostability and electrical and magnetic properties of cobalt oxide nanoparticles through biological mechanism of endophytic fungus Aspergillus nidulans

The study elaborates magnetic and electrical properties of greenly synthesized cobalt oxide (Co3O4) nanoparticles through endophytic fungus Aspergillus nidulans isolated from medicinal plant Nothapodytes foetida, which examines the ability of the nanoparticles to be magnetized and electrified, being one of the yardsticks for energy application. On increasing the precursor concentration from 2 to 10 mM, there is a shift in paramagnetic to weak ferromagnetic behavior of nanoparticles with the increase in saturation magnetization (Ms) from 0.161 to 7.75 emu/g. Frequency dependence of dielectric constant is found to increase with an increase in frequency, and the aforementioned nanoparticles can be used as a dielectric up to 1,50,000 Hz as dissipation factor is lesser than one. Besides, photostability study has indicated that the particles are stable for at least 45 days. Through liquid chromatography–mass spectrometry (LC–MS) analysis, phytochelatins are identified to be involved in the biosynthesis of nanoparticles.

Structural, Optical, and Multiferroic Properties of Yttrium (Y3+)-Substituted BiFeO3 Nanostructures

Nanoparticles of Bi1-xYxFeO3 (x = 0.0, 0.1, 0.15, 0.2) were synthesized by sol-gel pursued auto-combustion route. X-ray diffraction (XRD) pattern was recorded for analysis of the phase formation of pristine BiFeO3 (BFO) and Y3+-substituted samples. A systematic decrease in crystallite size with increasing concentration of Y3+ was observed by XRD and W-H plot. FESEM micrograph demonstrated clearly that the average grain size is decreased with increasing Y3+ ion concentration. Compositional analysis was carried out by EDS. Optical properties of the developed nanoparticles were examined by diffuse reflectance spectroscopy; it is observed that optical band gap decreases with increase in Y3+ ion concentration. Vibrating sample magnetometer (VSM) analysis revealed weak ferromagnetic behavior for pristine BFO. The ferromagnetic behavior has been enhanced with increasing concentration of Y3+ ions in BFO. Temperature dependence of dielectric constant shows an anomaly near the antiferromagnetic transition temperature in the developed materials that revealed the existence of magnetoelectric coupling in all the samples. Improved ferroelectric property has been observed by virtue of enhancement in the polarization of all substituted samples. Variation of electric field–guided strain with applied electric field has shown asymmetric behavior for samples x ≤ 0.15 and symmetric loop has been observed for x = 0.2 with the highest peak to peak strain value which makes it active material for electronic and magnetic devices.

Ion pair correlations due to interference between solvent polarizations induced in water.

Motions of two distinct ions can get correlated because the polarization induced by the ions can propagate through intervening water and can interfere with each other. This important aspect, which is not included in the continuum model based theories, has not been studied adequately. We calculate the effective force between two oppositely charged and similarly charged ions fixed in water as a function of separation distance R. At short separations, R less than 1.5 nm, the effective force vastly differs from the 1/εsR2 dependence advocated by the screened Coulomb's force law (SCFL), where εs is the static dielectric constant of the medium. This breakdown of the SCFL is shown to be due to the persistent interference between the polarizations created by the two charges in a manner similar to the vortex-antivortex pair formation in the XY model Hamiltonian. The distance dependence of dielectric constants, εs(R), extracted from our simulation exhibits interesting features and can be used in future modeling. In addition, we show that the force-force time autocorrelation between two neighboring ions decays differently at short separation and analyze the friction on the ion pair at different separation distances.

A theory of frequency dependence and sustained high dielectric constant in functionalized graphene-polymer nanocomposites

Functionalized graphene/polymer composites are currently under extensive investigation due to their excellent mechanical and functional properties. Within the framework of electrical properties, many experiments have shown that their electrical conductivity and dielectric permittivity are strongly dependent on the frequency of the applied electric field and the volume concentration of graphene fillers. In this paper we first apply Dyre's hopping function and Debye's relaxation function to build the constitutive equations for the graphene fillers, polymer matrix, and the interface regions. In addition, Cauchy's cumulative probabilistic function is also introduced to account for the drastic increase of electron tunneling and the rapid build-up of Maxwell-Wagner-Sillars polarization at the interface. These functions are then integrated into an effective-medium framework in the complex domain to establish a complete theory for the frequency dependence of these two effective properties as a function of graphene loading. The developed theory is highlighted by a direct comparison with the experimental data of reduced graphene oxide/polypropylene (rGO/PP) nanocomposites. The results show that both the theory and experiment display a general increase of conductivity but a decrease of permittivity as frequency increases, and that, with the graphene loading of 0.2 vol%, there is a sustained, high level of dielectric constant beyond 1,000 covering the frequency range up to 104 Hz. This remarkable feature can be of particular significance to energy storage and conversion.

High refractive index properties of oxyfluorosilicate glasses and a unified dielectric model of silicate oxide glasses in the sub-terahertz frequency region

Dielectric properties of oxyfluorosilicate (OFS) glasses have been characterized using Terahertz (THz)-time domain spectroscopy in the sub-THz region as well as optical reflection measurement. OFS glass containing 20 mol% of Nb2O5, which is termed ZNbKLSNd glass, has the highest refractive index of 3.70 in the sub-THz region. The THz and optical refractive indices of various silicate oxide glasses, including OFS glasses, have been confirmed to be correlated by a unified relationship utilizing a parameter defined by the ratio of ionic to electronic polarizability. Additionally, the frequency dependence of the THz dielectric constant has been interpreted by a single oscillator model for all silicate oxide glasses including OFS glasses. On the basis of the present unified dielectric model, the very high refractive index of ZNbKLSNd glass has been attributed to the lowering of oscillator resonance wavelength originated from the incorporation of Nb2O5intermediate network former.

Electric Double Layers with Surface Charge Regulation Using Density Functional Theory.

Surprisingly, the local structure of electrolyte solutions in electric double layers is primarily determined by the solvent. This is initially unexpected as the solvent is usually a neutral species and not a subject to dominant Coulombic interactions. Part of the solvent dominance in determining the local structure is simply due to the much larger number of solvent molecules in a typical electrolyte solution.The dominant local packing of solvent then creates a space left for the charged species. Our classical density functional theory work demonstrates that the solvent structural effect strongly couples to the surface chemistry, which governs the charge and potential. In this article we address some outstanding questions relating double layer modeling. Firstly, we address the role of ion-ion correlations that go beyond mean field correlations. Secondly we consider the effects of a density dependent dielectric constant which is crucial in the description of a electrolyte-vapor interface.

Effect of calcination temperature on optical, magnetic and dielectric properties of Sol-Gel synthesized Ni0.2Mg0.8-xZnxFe2O4 (x = 0.0–0.8)

The Ni0.2Mg0.8-xZnxFe2O4 (x = 0.0, 0.2, 0.4, 0.6 & 0.8) nanomaterials were prepared via sol-gel technique. These samples were calcined at three different temperatures (T) such as 400, 450 and 500 °C/5 h. Furthermore, the X-ray diffraction (XRD) patterns of all the calcined samples revealed the single phase cubic spinel structure. The lattice constants (a = b = c) were noticed to be increasing with increase of ‘x’. The grain shape, size and distribution of x = 0.0–0.8 contents were analyzed using field emission electron microscope (FESEM). The x = 0.2 content provided higher optical band gap energy (Eg) value than the remaining contents. Furthermore, the magnetization versus magnetic field (M − H) curves indicated the superparamagnetic nature of x = 0.0–0.8 contents. The high saturation magnetization (Ms) was noticed for x = 0.4 and 0.6 contents. In addition, the distribution of cations like Ni+2, Mg+2, Zn+2, Fe+3 and Fe+2 was performed between the tetrahedral (A) and octahedral (B) sites. The frequency dependence of dielectric constant (ε′), dielectric loss (ε") and ac-electrical conductivity (σac) was investigated as a function of composition. Moreover, the temperature variation of ε′ showed the decreasing trend of dielectric transition temperature (Te) with increase of ‘x’. The high ε′ of 163.1 (at 1 MHz) was noticed at x = 0.2 content calcined at 500 °C. Using the power law fit applied to the log σac-log ω plots, the dc-electrical conductivity (σdc) and exponent (n) parameters were calculated.

Enhanced transport properties in Ce doped cobalt ferrites nanoparticles for resistive RAM applications

Abstracts Polycrystalline Cerium doped Cobalt ferrite with general formula CoFe x − 2 Ce x O 2 (X = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5) was synthesized by Co-precipitation method. The effect of Cerium substitution on the structural, dielectric, electrical and switching properties of spinel cobalt ferrite nanoparticles was studied. Formation of the spinel structure was confirmed by X-ray Diffraction (XRD) analysis. With increase in cerium content, secondary phase (CeO2) was also identified. The frequency dependent dielectric constant, AC electrical conductivity, dielectric loss, dielectric loss tangent and impedance was investigated in the frequency range of 20Hz–3MHz. Dielectric constant, AC conductivity and dielectric loss decreased with the addition of Cerium contents. From impedance study, the role of grains and grain boundaries with in prepared spinel ferrite nanoparticles was investigated. The values the activation energies and drift mobility are calculated from the DC electrical resistivity measurements. DC resistivity and hence, activation energy increases with increasing Cerium contents. Resistive switching properties were studied using current–voltage (I–V) measurements. All I–V curves in the current study exhibit a hysteresis loop-type behavior. Hysteresis loop-type trend confirm that resistive switching effect exist in Cerium doped Cobalt ferrites nanoparticles. Our study suggest that Cerium doped Cobalt ferrites have high potential for resistance switching memory devices like Resistive Random-Access Memory (ReRAM). Resistive switching mechanism in Cerium doped cobalt ferrites nanoparticles is also explained by available theoretical model.

Methods of estimations of the band gap for kesterite Cu2ZnSnS(Se)4

This paper presents a study related to methods of estimation of the band gap for kesterite-type Cu2ZnSnS(Se)4 based on their electronic structure and optical properties driven by the first-principles calculations within the hybrid functional. The estimations have been performed by four different methods. The first one is based on the band structure estimated as the difference of the energy corresponding to the conduction band and valence band edges. The rest three methods are based on the spectral distribution of the absorption coefficient α(ħω) driven from the first-principles calculations: (i) Tauc plot, (ii) first derivative of α(ħω) on photon energy ħω in the energy range around the fundamental absorption edge, and (iii) linear combination of the methods (i) and (ii). We show that the band gap estimated by different methods can deviate each from other drastically and the large difference is not only relayed to defects, impurities and other lattice imperfections. We show also, that the influence of lattice anisotropy on optical properties of CZTS and CZTSe is negligible. We have pointed out importance of the dependence of dielectric constant on surface texture. The equation describing dependence of dielectric constant on the experimentally observed surface texture is derived.

Influence of Zinc Oxide Nanoparticles on the Optical, Dielectric and Electromagnetic Interference Shielding Performance of Polystyrene Films

In the present work, Zinc oxide (ZnO) nanoparticles are synthesized using solvothermal technique. Polystyrene-ZnO (PS/ZnO) nanocomposite films are synthesized by solution casting procedure. PS/ZnO films are analyzed by XRD, FTIR and UV-Vis spectroscopic techniques. The addition of ZnO into the PS film is found to decrease the optical band gap (OBG) from 4.07 eV to 1.86 eV. Frequency dependence of dielectric constant (ε′), loss tangent (tanδ), ac conductivity (σac) and electromagnetic (EM) interference shielding effectiveness (SE) studies have been undertaken on the pure PS and PS/ZnO films. Insertion of ZnO into pure PS polymer matrix is found to enhance ε′, tanδ, σac, and SE considerably. The ε′ and tanδ were reduced with an enhancement in the frequency. σac of PS/ZnO nanocomposites was enhanced with rise in frequency and electrical conduction process in PS/ZnO film is in agreement with an electron-hopping model. EM interference SE is reduced with rise in the frequency. PS/ZnO films were proven as a favorable functional substance for the absorbing of EM waves at lower frequencies.

Pressure dependence of ferroelectric quantum critical fluctuations

The effect of ferroelectric fluctuations on the temperature dependent dielectric constant of SrTiO$_3\,$(STO) has been long studied. Those fluctuations have been shown in recent years to be quantum critical and STO demonstrated to form the archetypal quantum critical paraelectric. The effect of those same fluctuations on the pressure and temperature dependence of the ferroelectric soft phonon mode as the system is tuned away from criticality are reported for the first time in this paper. We show that the mean field approximation is confirmed experimentally. Furthermore, using a self-consistent model of the quantum critical excitations including coupling to the volume strain and without adjustable parameters, we determine logarithmic corrections that would be observable only very close to the quantum critical point. Thus, the mean-field character of the pressure dependence is much more robust to the fluctuations than is the temperature dependence. We predict stronger corrections for lower dimensionalities however. The same calculation confirms that the Lydanne-Sachs-Teller relation is valid over the whole pressure and temperature range considered. Therefore, the measured dielectric constant can be used to extract the frequency of the soft mode down to 1.5 K and up to 20 kbar of applied pressure. The soft mode is observed to stiffen further, raising the low-temperature energy gap and returning towards the expected shallow temperature dependence of an optical mode. This behavior is consistent with the existence of a quantum critical point on the pressure-temperature phase diagram of STO, which applied pressure tunes the system away from. This work represents the first experimental measurement of the stiffening of a soft phonon mode as a system is tuned away from criticality, a potentially universal phenomenon across a variety of phase transitions and systems in condensed matter physics.

Altered polar character of nanoconfined liquid water

Dielectric properties of nanoconfined water are investigated by theory and computer simulations. The authors observe a dependence of the effective static dielectric constant of water with the confinement while the total dipole moment relaxation appears largely independent of it. These anomalous properties are explained in terms of a destructive interference of inwardly propagating surface induced long range correlations.

Structural, electric and dielectric properties of Ni0.5Zn0.5FeCoO4 ferrite prepared by sol-gel

Ni0.5Zn0.5FeCoO4 spinel ferrite was elaborated using sol-gel technique. X-ray diffraction patterns indicate that sample has a cubic spinel type structure with Fd-3m space group. The change in Raman modes and relative intensity were observed due to ball milling and consequently to the decrease of particle size and cationic redistribution. The Raman spectra show peaks appearing at 450 and 490 cm−1 corresponding to T2g (2) and T2g (3), respectively. It may be noted that both of these modes shift toward the higher wavenumber with the substitution of Zn by Ni in Ni0.5Zn0.5FeCoO4 ferrite. Mössbauer spectroscopy analysis shows one tetrahedral A-site and two octahedral B-sites. Due to Zn doping, the hyperfine magnetic fields are much smaller than for CoFe2O4 and NiFe2O4 ferrites. The Jonscher’s power low was used to describe the ac-conductivity measurements. Frequency dependence of dielectric constant (ε″) and tangent loss (tan) display a dispersive behavior at low frequencies that can be explained by the Maxwell Wagner model and Koop's theory. Electric modulus formalism has used to study the relaxation dynamics of charge carriers. The complex impedance spectra (Nyquist plots) show well-defined semicircles which are strongly dependent on the temperature.

Evidence of proton beam irradiation compared to isotope effect

In this study, we obtained experimental results similar to the isotope substitution effect by using the proton irradiation of K(H0.47D0.53)2PO4 (DKDP) ferroelectric single crystals. Temperature dependence of dielectric constants showed that the ferroelectric phase to paraelectric phase transition temperature increased from 175 K to 195 K of approximately 20 K after the proton beam irradiation. It was observed that the vibration mode P(OD)2 was changed from 893 to 884 cm−1 in Raman spectroscopy. In 1H Magic Angle Spinning (MAS) Nuclear Magnetic Resonance (NMR) experiments, the isotropic chemical shift after proton irradiation decreased from 14.46 to 14.32 ppm, which is indicative of the change of the O–H…O the equilibrium distance of hydrogen bonds estimated as 1.60066 Å and 1.62228 Å before and after the proton irradiation, respectively. It was observed that the Full width at half maximum (FWHM) line width also decreased from 563 to 244 Hz in 1H MAS spectral line shape, which is indicative of obeying the displacive phase transition model.

Stirring-mediated anomalous dielectric behaviour of electrodeposited and in situ oxidized FeAl2O4 thin films

Spinel ferrites, due to high permeability and stability, possess remarkable features that make them a favourable candidate for spintronic applications. Electrodeposition method is used for the synthesis of iron aluminium oxide (FAO) thin films. A series of samples are prepared by keeping deposition time constant at 10 min, and in situ oxidation time varied as 5 min, 10 min, 15 min and 20 min by anodic electrodeposition. These electrodeposited FAO thin films are annealed at 500 Oe applied magnetic field at 300 °C in vacuum. At 5-min oxidation time, mixed structural phases, i.e. FeAl2O4 and Al2O3, are observed, whereas phase-pure FeAl2O4 is observed at 10-min oxidation time. A further increase in oxidation time to 15 min and 20 min results in reappearance of mixed phases. Phase-pure FeAl2O4 thin film at oxidation time of 10 min exhibits bond angle of ~ 158.59° with + ive tilt ~ 4.59°. A decrease in bond angle (i.e. ~ 139.20°) with − ive tilt ~ − 14.8° is observed with an increase in oxidation time to 20 min. SEM micrographs show the formation of octahedral and dodecahedral grains for 10-min oxidation time with grain size in the range of 2–3 μm. FTIR and Raman analysis confirms the formation of FeAl2O4 thin film at 10-min oxidation time with the appearance of bands at 610.94 cm−1 and 753 cm−1, respectively. Magnetic hysteresis curves show a ferromagnetic behaviour of iron aluminium oxide thin films. Thin film prepared using 10-min oxidation time shows a relatively higher value of saturation magnetization Ms (17.89 emu/cm3). Anomalous dielectric behaviour is observed for FeAl2O4 thin films due to the resonance phenomena at higher frequencies. Dielectric constant of ~ 37.96 at log f = 5.0 is observed for 10-min oxidation time. Temperature-dependent dielectric study is also carried out in the temperature range of 30–210 °C. Fitting of Cole–Cole plots through ZView software shows a strong dependence of dielectric constant on grain boundary resistance. This is to be emphasized that detailed study on the dielectric and impedance properties of electrodeposited iron aluminium oxide thin films is rare to be found. Having knowledge of room temperature and temperature-dependent dielectric properties of iron aluminium oxide thin films will help in extending the field of application to the microelectronic industry.