Real Part Of Dielectric Constant Research Articles

Optically tuned dielectric property of barium titanate thin film by THz spectroscopy

The dielectric property of ferroelectric barium titanate (BaTiO3) thin film with optical field was investigated by terahertz time-domain spectroscopy at room temperature. Experimental results showed that dielectric constant of BTO film was increased with the optical pump powers, and tunability of the real part of dielectric constant could be reached to74%. The reason of realizing high modulation depth could be explained as photorefractive and photothermal effects. Furthermore, the variation of refractive index displayed a monotonically increase with the optical powers.

Electronic and Optical Properties of γ- and -Alumina by First Principle Calculations

The electronic and optical parameters of {\gamma}-Al2O3 and {\theta}-Al2O3 have been studied by using the first principle within the framework of density function theory (DFT). The computational approach is based on full-potential linearized augmented plane wave method (FP-LAPW) within the generalized gradient approximation (GGA), local density approximation (LDA), and modified Becke-Johnson potential (mBJ). The results show that these compounds have a direct gap ({\Gamma}-{\Gamma}) of about 5.375 eV and 4.716 eV for {\gamma}-Al2O3 and {\theta}-Al2O3, respectively. Several optical parameters of these materials are also investigated. The values of the real part of dielectric constant are found to be 3.259 and 3.694 for {\gamma}-Al2O3 and {\theta}-Al2O3, respectively, which are close to the experimental one (3.416). The refractive index is 1.806 and 1.922 for {\gamma}-Al2O3 and {\theta}-Al2O3 respectively, and shows a good agreement with the experimental result which is 1.86. GGA findings are consistent with the experimental results and are better than the other approximations. There are no salient differences between GGA and LDA results. The results advocate using this material as a transparent conducting layer in solar cell structure, which can be operated in a wide energy range.

Effect of Vanadium Doping on Microstructure and Dielectric Behavior of CaCu<sub>3</sub>Ti<sub>4</sub>O<sub>12</sub> Ceramics

In this work, effect of vanadium doping of CaCu₃Ti₄O₁₂ (CCTO) on microstructure and complex dielectric constant over wide frequency (100 Hz-1 MHz) and temperature (0°C – 160°C) ranges has been studied. The vanadium doping of CCTO system results in an increase of grain size, the grains being surrounded by melted-like grain boundaries. Real parts of dielectric constant of all samples are similar at low frequency (<1 kHz). In doped samples, above 1 kHz, a relaxation appears which is evidenced by a drop of real part of permittivity and a peak of its imaginary part. This relaxation phenomenon is very significant at relatively low doping rates and then decreases again as vanadium content increases. AC conductivity behavior of vanadium-doped CCTO can be divided in three regions depending on conduction processes. The calculated activation energies were close to 0.46 eV.

High dependency of dielectric properties on copper ions content in the Na2O–P2O5–ZnO glass matrix

The work in the current study is mainly oriented to investigate the dielectric and some optical properties of (80 − x)[(Na2O)–(P2O5)]–20(ZnO)–x(CuO) glasses, with x-values ranging from 0.0 to 0.5 (x = 0, 1, 2, 3, 4 and 5 mol%). The frequency and composition dependences of the dielectric parameters are discussed and analyzed for insight into the dielectric properties of these glasses in an applied ac electric field of frequencies extending from 1.05 to 100 kHz. The max and min values of real part of dielectric constant (RPDC) and imaginary part of dielectric constant (IPDC) were estimated. The range of values of RPDC between 118.01 and 575.10 for RPDCMax, and 106.85–515.08 for RPDCMin were estimated. The range of values of IPDC between 9.28 and 57.08 for IPDCMax, and 2.85–18.92 for IPDCMin were estimated. The high dependencies of this type of glasses were obtained.

Realization of structural and optical properties of CdZnO composite coated films for photovoltaic cell applications

CdZnO composite coated films were deposited on glass substrate by screen printing method at the sintering temperature of 450°C and 550°C. The morphological and structural details of composite films were characterized by Scanning Electron microscope (SEM), Powder X-Ray Diffraction (XRD) and Fourier Transform Infrared (FTIR) techniques. Similarly, optical properties were analyzed by UV–vis and Photoluminescence (PL) spectroscopy. XRD patterns revealed increase in crystallite size with increasing sintering temperature. SEM images clearly show agglomeration and increase in the grain size of the nanoparticles in high temperature sintered film. Similarly, FTIR spectra exhibit a slight shift in peak positions and increase in intensity of peaks with increase in sintering temperature. The optical absorption measurements have been used to evaluate the values of refractive index, extinction coefficients of these direct- energy band gap semiconductor films with energy band gaps distributed in the range of ∼2.81eV at 450°C and ∼2.70eV at 550°C. The imaginary and real parts of dielectric constants are also calculated, while PL spectra showed band emission shifting towards the higher side (red shift) with increase in sintering temperature. These studies revealed that on increasing sintering temperature the crystallinity of the film improves with reduction in lattice deformations in such composite films.

Determination of density of states, conduction mechanisms and dielectric properties of nickel disulfide nanoparticles

Temperature and frequency dependent ac electrical measurements were used to explore density of states, conduction mechanisms and dielectric properties of nickel disulfide (NiS2) nanoparticles. The NiS2 nanoparticles were prepared by conventional one step solid state reaction method at 250 °C. X-ray diffraction (XRD) confirmed cubic phase of prepared nanoparticles. Scanning electron microscope (SEM) images revealed presence of irregular shaped nanoparticles as small as 50 nm. The ac electrical measurements were carried out from 300 K to 413 K. Two depressed semicircular arcs from 20 Hz to 2 MHz showed presence of bulk and grain boundary phases in NiS2 nanoparticles at all temperatures. Small polaron hopping conduction from 300 K to 393 K and correlated barrier hopping conduction mechanism at temperatures higher than 393 K was observed. High value of density of states (of the order of 1024 eV−1cm−3) was calculated from ac conductivity. At low frequencies high values (of the order of 104-107) of real part of dielectric constant (ε′) were observed at different temperatures. These observations suggest that NiS2 nanoparticles may find applications in electronic devices.

Dielectric and optical properties of CuO containing sodium zinc phosphate glasses

Dielectric and optical properties of 45 P2O5-34 ZnO-(20?x)Na2O-1 Al2O3-xCuO glasses (0?x?5) were investigated. The frequency and composition dependencies of the dielectric parameters were analysed and discussed. The values of real part of dielectric constant (RPDC) lie between 748 to 1169 for RPDCMax, and 654 to 1031 for RPDCMin. The range of values of imaginary part of dielectric constant (IPDC) extends from 39.4 to 57.5 for IPDCMax and from 27.3 to 40.1 for IPDCMin. It was observed that each of these parameters begins to decrease with increasing CuO content, but further addition of CuO causes their rise. Thus, small amount of CuO causes a decrease in both RPDC and IPDC until CuO content reaches 2mol%, thereafter, they nearly return to their original values at 5mol% of CuO. Similar behaviour was observed for AC conductivity. Transmittances of the investigated glasses were also measured and used to estimate their optical absorption coefficients and optical band gaps. The optical energy gap is ~4 eV for the samples with up to 4mol% CuO, while it is somewhat higher (~5 eV) for the glass with 5mol% CuO.

Sub‐THz complex dielectric constants of smectite clay thin samples with Na+/Ca++ ions

AbstractWe implement a technique to characterize the electromagnetic properties at frequencies 100 to 165 GHz (3 cm−1 to 4.95 cm−1) of oriented smectite samples using an open cavity resonator connected to a submillimeter wave VNA (Vector Network Analyzer). We measured dielectric constants perpendicular to the bedding plane on oriented Na+ ion and Ca++ ion stabilized smectite samples deposited on a glass slide at ambient laboratory conditions (room temperature and room light). The clay layer is much thinner (∼30 μm) than the glass substrate (∼2.18 mm). The real part of dielectric constant, ϵre, is essentially constant over this frequency range but is larger in Na+ ion than in Ca++ ion infused clay. The total electrical conductivity (associated with the imaginary part of dielectric constant, ϵim) of both samples increases monotonically at lower frequencies (&lt;110 GHz) but shows rapid increase for Na+ ions in the regime &gt; 110 GHz. The dispersion of the samples display a dependence on the ionic strength in the clay interlayers, i.e., ζ potential in the Stern layers.

Controlling of spectral and optical parameters of the F8T2 liquid–crystalline polymer (LCP) by molarity for optoelectronic devices

In here, spectral and optical properties of the F8T2 polymer for different molarities were investigated by solution technique for optoelectronic applications. The interesting and useful results were obtained for optoelectronic applications. The absorption band of F8T2 polymer exhibits a vibronic structure with two peaks at 288 and 453nm due to π–π* electronic transition. The electronic spectra of the F8T2 can be characterized visible (Q) band and Soret (B) band. The significant spectral parameters such as absorption coefficient, molar extinction coefficient, mass extinction coefficients, electric dipole line strength and oscillator strength of the F8T2 polymer were calculated. The direct allowed band gap (Egd) and indirect allowed band gap (Egid) values (2.230 and 2.251eV, respectively) of the F8T2 polymer for 1.200μM are the highest values, while the Egd and Egid values (1.723 and 2.033eV, respectively) of the F8T2 for 9.460μM are the lowest values. The Egd values of the F8T2 polymer are lower than the Egid values. The real part of dielectric constant of the F8T2 polymer is composed normal and anomalous dispersion regions. F8T2 polymer can be used in the fabrication of many optoelectronic devices due to good soluble, spectral and optical properties.

Effect of multi wall carbon nanotube on electrical properties 4-[4-((S)-Citronellyloxy)benzoyloxy]benzoic acid liquid crystal host

Dielectric properties, conductivity mechanisms and current–voltage characteristics of Multi Wall Carbon Nanotube (MWCNT) doped and pure Liquid Crystal (LC) material was investigated using impedance spectroscopy method in the frequency range of 100 Hz to 15 MHz. Liquid crystalline material, 4-[4-((S)-Citronellyloxy)benzoyloxy]benzoic acid (CBBA) as a host material and MWCNT was used as doping material in this study. In order to observe the effects of doping MWCNT into LC on dielectric properties, an MWCNT material was doped into CBBA structure with 1 wt%. Real part of dielectric constants (ɛ′), imaginary part of dielectric constant (ɛ′′), i.e. dielectric loss, dissipation factor/dielectric loss tangent (tanδ) were obtained for the pure and doped LC samples. In addition, dielectric strength (Δɛds), negative dielectric anisotropy (Δɛda), absorption coefficients (α) and relaxation times (τ) were calculated from the empirical data. I–V characteristics of pure LC and doped LC structures were carried out at micro-current levels by current–voltage measurements.

Influence of microwave annealing on optical and electrical properties of plasma-induced defect structures in Si substrate

The authors investigate the effects of microwave annealing (MWA) on the recovery of plasma process-induced ion-bombardment damage in Si substrates. For damage creation, Ar discharges by a capacitively coupled plasma etcher are used. For damage repairing, the MWA or a rapid thermal annealing (RTA) are conducted. The authors employ spectroscopic ellipsometry (SE), photoreflectance spectroscopy (PRS), and capacitance-voltage (C-V) measurement to analyze the damaged structures. Recovery of the damage is discussed by comparing the obtained parameters before and after the annealing processes. In the SE analysis, the change in the real part of dielectric constant (Δεr) is investigated. The Δεr spectral peak around 3.4 eV decreases with an increase in the annealing temperature (Ta) for both MWA and RTA, indicating the decrease in the density of defects created in the Si substrate. In the PRS analysis, the spectral peak intensity is found to decrease by the plasma exposure, and then to increase with Ta, which implies the recovery of the Si crystalline structure by MWA as well as by RTA. In the C-V measurement, the voltage shift (ΔVb) in the respective C-V curves is used as a measure of the number of defects present in the surface and interface damaged regions. The ΔVb in the negative bias direction is observed after the plasma exposure for all damaged structures, while after annealing the ΔVb in the positive bias direction is confirmed, suggesting the recovery of the damage in the surface and interface regions. Moreover, it is experimentally found that MWA induces larger |ΔVb| than RTA. These findings indicate the decrease in carrier trap sites in the surface and interface regions of damaged structures, and that MWA is more effective in repairing such damage than RTA. The authors propose a model explaining these mechanisms where defect-induced dipole moments that interact with the incident microwave are considered. The present results draw a new damage-recovery picture by MWA, in particular, for plasma-induced damage in surface and interface regions of Si substrates.

Dielectric behaviour of Zn substituted Cu nano-ferrites

Herein, the dielectric properties such as permittivity (real part ε′ and imaginary part ε′′) and dielectric loss tangent (tanδ) are reported for Zn substituted Cu ferrites (Cu1−xZnxFe2O4; 0≤x≤1) composite using the sol–gel auto-combustion method. The variations of real and imaginary part of dielectric constant, tanδ and AC conductivity (σac) are studied at room temperature in the frequency range of 100Hz–120MHz. The real part of dielectric constant decrease with increasing frequency and the imaginary part (ε′′) varies with frequency showing the characteristic peak for each sample. The relation of tanδ with frequency shows relaxation spectra. Further, the σac tended to increase with increase in frequency. The variation in dielectric constant may be explained on the basis of space charge polarization, according to Maxwell and Wagner two-layer model. The dielectric constant and tanδ as a function of temperature are also studied with different temperatures ranging from 323K to 583K.

Annealed SnO2 thin films: Structural, electrical and their magnetic properties

SnO2 thin films of ~150nm thicknesses were deposited on quartz substrate by pulse laser deposition technique and annealed at 600–900°C for 1h with a variation of 100°C per sample. The X-ray diffraction patterns show that as deposited SnO2 thin film was completely amorphous while annealed SnO2 thin films were randomly oriented, polycrystalline in nature and correspond to the rutile phase. The average crystallite size estimated using Scherrer and Williamson–Hall equations was found to increase with annealing temperature. In addition to the three fundamental Raman peaks at 473cm−1, 627cm−1 and 766cm−1 corresponding to the tetragonal rutile phase of SnO2, two IR active Raman bands and one Raman forbidden mode were also observed at 500cm−1, 690cm−1 and 544cm−1 respectively. The dc resistivity measurements in the temperature range of 297–400K show semiconducting behavior of all the annealed thin films. Room temperature dielectric properties of all the samples show dispersion which is explained in the light of Koop's theory based on Maxwell–Wagner two layer models. The dielectric parameters: real part of dielectric constant, dielectric loss and ac conductivity show their maximum value for SnO2 film sample annealed at 600°C. The dielectric loss shows anomalous behavior and exhibits relaxation peaks (Debye peaks) at lower and middle frequencies. Complex impedance plots (Nyquist plots) for annealed SnO2 thin films show two well-resolved semicircles corresponding to two different electrical transport mechanisms which stand for grain and grain boundary. It is observed that the contribution of grains in the conduction process starts dominating over the grain boundary with the increase in annealing temperature. From a magnetic hysteresis loop, it is clear that all the single phase SnO2 thin films annealed at different temperatures are ferromagnetic at room temperature and the value of saturation magnetization shows its maximum for the film annealed at 600°C.

Room Temperature Structural, Electrical and Dielectric Studies of Ce3+, Pr3+ Doped Hexagonal LaF3 Nanoparticles

Water soluble LaF3: Ce3+, Pr3+ (LFCP) nanocrystals have been synthesized using microwave assisted process. Using de-ionized water (DW) and methanol (M) as solvents nano discs and nano rods with hexagonal geometry were obtained. In agreement with the X-ray diffraction (XRD), Transmission electron microscope (TEM) confirms the average crystalline size of the particles is 20nm which is close to the JCPDS standard card number (32-0483). The functional groups of the synthesized nanoparticles were confirmed by comparative Fourier transform infra red (FTIR) and FT-Raman spectra. Thermo gravimetric analysis (TGA/ DTA) from 100 0C to 900 0C are attributable to the initial removal of water molecules / semi organic ligands shows formation and related internal crystal structure adjustments. The excitation peak was found to be at 254nm which exhibiting blue up conversion fluorescence (459nm). The ionic conductivity at room temperature is found to of order of 10 -6 Scm-1 corresponding to resistivity of order of 105 Ωcm with higher magnitude in DW based nanocrystals. Dielectric constant and dielectric loss show normal dielectric behavior in frequency range of 100Hz - 5MHz with their values falling drastically at low frequencies indicating good optical quality nanocrystals. Dielectric studies involvement of the real part of dielectric constant in the process of polarization.

Electrical Behavior of Probertite by Dielectric Spectroscopy

AbstractIn this work of the material investigation, electrical parameters, which are real part and imaginary part of modulus, dielectric constant, dissipation factor, and conductivity, in the bulk pellet of probertite sample is presented. Electrical properties were investigated via temperature and frequency dependent dielectric spectroscopy. Real and imaginary part of dielectric parameter properties of the probertite were measured at frequencies from 100 to 15M Hz in the temperature range of 25 to 150 °C. Temperature dependence of the real part of the dielectric constant suggests that these compounds exhibit strong electromagnetic absorption and broadband electrical behavior.

Physical properties of RbAu compound

In this paper, we investigated electronic, optic, elastic, dynamic and thermodynamic properties of RbAu compound by density functional theory within the generalized gradient approximation. The calculated static value of real part of dielectric constant is 6.7. The calculated electronic band structure of RbAu shows that RbAu is a semiconductor with an indirect band gap of 0.36 eV. Besides, RbAu obeys mechanical stability and it demonstrates elastic anisotropy. 540K is classical limit for specific heat of RbAu.

Dielectric characteristics and thermal behaviour of terbium fumarate heptahydrate crystals

Dielectric properties, ac conductivity and thermal characteristics of terbium fumarate heptahydrate crystals grown by gel diffusion method have been carried out. The real part of dielectric constant, dielectric loss and ac conductivity of the material have been measured as a function of temperature and frequency of the applied electric field. Dielectric constant, dielectric loss and ac conductivity of the title compound were systematically investigated, showing a hump at about 85 °C, which could be attributed to water molecules in the crystal boundary. The dielectric anomaly exhibited by the material has been correlated with its thermal behaviour. The ac conductivity of the material obeys the Jonscher's power law relation; σ(ω) = σ o + Aω s , with the temperature dependent power exponent s < 1. The ac conductivity of the compound has been found to increase with the increase in frequency. The material is suggested to show protonic conduction. The non-isothermal kinetics was used to evaluate the activation energy for the dehydration step of thermal decomposition of terbium fumarate heptahydrate by using the Coats–Redfern integral method. • Terbium fumarate heptahydrate shows dielectric anomaly due to dehydration. • Dielectric dispersion obeys the well known Universal Power Law(Jonshers power law). • AC conductivity study shows that the material exhibits protonic conductivity.

Improved dielectric and magnetic properties in modified lithium-ferrites

Single phase polycrystalline lithium ferrites modified with Zn and Mn were synthesized by solid state reaction method. The prepared samples exhibit a markedly increased value in real part of dielectric constant (ε) and a lowest loss tangent (tanδ) for x=0.04 measured in the frequency range 70Hz to 1MHz. The saturation magnetic moment (Ms) varies non-monotonically for different values of x. A maximum value of Ms=76emu/g has been found for x=0.02. Such results in lithium ferrite based ferrites being found rarely.

Effect of Cr3+ substitution on properties of nano-ZnFe2O4

Nano-crystalline ferrite materials with general formula ZnCrxFe2−xO4 (x=0.1, 0.2, 0.3, 0.4 and 0.5) have been synthesized by chemical co precipitation method. The developed materials were characterized for structural, shape/size and electrical properties by using analytical techniques viz. X-ray diffraction (XRD), transmission electron microscopy (TEM), and impedance analyzer respectively. X-ray diffraction pattern confirms the formation of single phase spinel structure of prepared ferrites. The lattice constant of ZnCrxFe2−xO4 (x=0.1, 0.2, 0.3, 0.4 and 0.5) nano-particles decreases with increasing Cr3+ ion content. Nano-size of synthesized ferrite particles were confirmed by electron microscopy. DC-electrical conductivity and activation energy increases with increasing Cr3+ ion content. Dielectric loss (tanδ), real part of dielectric constant (ɛ′), imaginary part of dielectric constant (ɛ″), ac conductivity (σac), real (resistive) part of impedance (Z′) and imaginary part of impedance (Z′′) were analyzed as a function of frequency, composition and temperature using impedance analyzer in the frequency range of (1KHz–5MHz) and temperature range of (300–523K). Dielectric loss (tanδ), dielectric permittivity (ɛ′) and ac conductivity (σac) decreases with increase in Cr3+ substitution which has been explained on the basis of hopping mechanism. Electrical conductivity increases with increasing temperature revealing the semiconducting behavior of prepared ferrites as also observed by the variation in cole–cole plots with temperature. The Nyquist impedance plots of the prepared ferrites clearly reveal the inherent phenomenon involved in conduction mechanism of Cr3+ substituted ZnFe2O4 ferrites.

Synthesis, characterization, surface morphology properties and effects of annealing temperature on optical properties of poly(2-(((5-phenyl-1,3,4-thiadiazole-2-yl)imino)methyl)phenyl methacrylate) (PTMPMA)

In this study, a new 5-phenyl-1,3,4-thiadiazole-containing vinyl monomer and its polymer were synthesized. The characterizations of the ligand, monomer and polymer were carried out using FTIR, UV–Vis, 1H-NMR, elemental analysis and gel permeation chromatography techniques. The roughness average, root-mean-square roughness, surface skewness and surface kurtosis parameters of the poly(PTMPMA) film were found to be 1.98 nm, 2.84 nm, 1.529 and 5.777, respectively. Effects of the annealing temperature on optical properties of the poly(2-(((5-phenyl-1,3,4-thiadiazole-2-yl)imino)methyl)phenyl methacrylate) (PTMPMA) were investigated. The important optical parameters such as refractive index, optical band gap, angle of incidence, imaginary part of optical conductivity and real part of dielectric constants of the poly(PTMPMA) decrease and other important optical parameters such as excitation and dispersion energy, angle of refraction, real part of optical conductivity and imaginary part of dielectric constants of the poly(PTMPMA) increase with increasing annealing temperature. The absorption band edge values of the polymer films were found to be 2.34, 1.85 and 1.74 eV for 298, 523 and 643 K, respectively. The optical band gap values of the polymer films were found to be 3.314, 2.943 and 2.917 eV for 298, 523 and 643 K, respectively. The poly(PTMPMA) can be used as an active polymer layer in production of the electronic devices such as polymer diodes and metal–semiconductor contacts.