Imaginary Part Of Dielectric Constant Research Articles

Effect of UV Exposure on Some Optical Properties of As-Se Based Chalcogenide Glasses

Bulk As40Se60 glass was prepared by melt quenching technique. Amorphous films of As40Se60 were prepared by thermal evaporation technique then exposed in UV light for 10 minutes. Virgin and exposed thin films were analyzed using transmission spectra to determine thickness (d), refractive index (n), extinction coefficient (k), optical absorption coefficient (α), optical band gap (Eg) and real and imaginary parts of dielectric constants (ϵ′ and ϵ″). Results show 10 minutes UV exposure cause photodarkening (red shift in the optical band gap) and photorefraction (increase in refractive index) in As40Se60 thin film, which can be utilized for various photonic applications.

Impedance Spectroscopy and FTIR Studies of PEG ‐ Based Polymer Electrolytes

Ionic conductivity of poly(ethylene glycol) (PEG) ‐ ammonium chloride (NH4Cl) based polymer electrolytes can be enhanced by incorporating ceramic filler TiO2 into PEG‐NH4Cl matrix. The electrolyte samples were prepared by solution casting technique. FTIR studies indicates that the complex formation between the polymer, salt and ceramic filler. The ionic conductivity was measured using impedance spectroscopy technique. It was observed that the conductivity of the electrolyte varies with TiO2 concentration and temperature. The highest room temperature conductivity of the electrolyte of 7.72×10−6 S cm-1 was obtained at 15% by weight of TiO2 and that without TiO2 filler was found to be 9.58×10−7 S cm−1. The conductivity has been improved by 8 times when the TiO2 filler was introduced into the PEG–NH4Cl electrolyte system. The conductance spectra shows two distinct regions: a dc plateau and a dispersive region. The temperature dependence of the conductivity of the polymer electrolytes seems to obey the VTF relation. The conductivity values of the polymer electrolytes were reported and the results were discussed. The imaginary part of dielectric constant (εi) decreases with increase in frequency in the low frequency region whereas frequency independent behavior is observed in the high frequency region.

Synthesis and optical characterization of nanocrystalline CdTe thin films

From several years the study of binary compounds has been intensified in order to find new materials for solar photocells. The development of thin film solar cells is an active area of research at this time. Much attention has been paid to the development of low cost, high efficiency thin film solar cells. CdTe is one of the suitable candidates for the production of thin film solar cells due to its ideal band gap, high absorption coefficient. The present work deals with thickness dependent study of CdTe thin films. Nanocrystalline CdTe bulk powder was synthesized by wet chemical route at pH≈11.2 using cadmium chloride and potassium telluride as starting materials. The product sample was characterized by transmission electron microscope, X-ray diffraction and scanning electron microscope. The structural characteristics studied by X-ray diffraction showed that the films are polycrystalline in nature. CdTe thin films with thickness 40, 60, 80 and 100 nm were prepared on glass substrates by using thermal evaporation onto glass substrate under a vacuum of 10 −6 Torr. The optical constants (absorption coefficient, optical band gap, refractive index, extinction coefficient, real and imaginary part of dielectric constant) of CdTe thin films was studied as a function of photon energy in the wavelength region 400–2000 nm. Analysis of the optical absorption data shows that the rule of direct transitions predominates. It has been found that the absorption coefficient, refractive index ( n) and extinction coefficient ( k) decreases while the values of optical band gap increase with an increase in thickness from 40 to 100 nm, which can be explained qualitatively by a thickness dependence of the grain size through decrease in grain boundary barrier height with grain size.

The Effect of Thickness on Some Optical Properties of Sb2S3 Thin Films Prepared by Chemical Bath Deposition

Sb2S3 thin films have been prepared by chemical bath deposition on a glas sub Absorbance and transmittance spectra were recorded in the wavelength range (30-900) nm. The effects of thickness on absorption coefficient, reflectance, refractive index, extinction coefficient, real and imaginary parts of dielectric constant were estimated. It was found that the reflectivity, absorption coefficient , extinction coefficient, real part of dielectric constant and refractive index, all these parameters decrease as the thickness increased, while the imaginary part of the dielectric constant increase as the thickness increased.

Geoelectrical constraints on radar probing of shallow water-saturated zones within karstified carbonates in semi-arid environments

Abstract Shallow carbonates are of utmost importance as potential sources of groundwater in karstified semi-arid terrains. Ground-Penetrating Radar (GPR) is being increasingly used as a prominent mapping tool in such environments. However, its potential in exploring and identifying shallow water-saturated zones (WSZs) in carbonates is constrained by the geoelectrical properties of carbonate soils as a function of moisture content. We report results of a case study that includes laboratory geoelectrical characterization and their comparison to in situ GPR attenuation measurements performed on Cretaceous Edwards Formation rudist mounds in central Texas, which we hypothesize as analogs for water-bearing formations in semi-arid karstified carbonate terrains. Dielectric measurements on field-collected rock samples carried out in the laboratory under controlled conditions of moisture saturation suggest that real and imaginary parts of dielectric constants of rocks with higher porosity and/or permeability have steeper dependence on pore moisture content; they produce better dielectric contrasts but allow shallower penetration. Our analyses suggest that within carbonates, dielectric contrasts improve with decrease in sounding frequency and/or increase in moisture content; and the relationship between dielectric permittivity and moisture content may be represented by 3rd order polynomial equations. GPR surveys using a wide-band 400 MHz antenna reveal subsurface mound morphologies with heights of ∼ 1–2 m and basal diameters of ∼ 8–10 m resembling outcrop analogs. Each mound appears to be composed of smaller amalgamated lithounits that seem geoelectrically similar. Amplitudes decays of the backscattered radar signal correlate to moisture distribution. Measuring the differences in signal attenuation allows differentiation between saturated and non-saturated zones. Velocity analyses of GPR profiles enable estimation of moisture distribution in the vicinity of the mounds. Optimal delineation and production of high-resolution GPR data up to a depth of ∼ 10 m were observed for a sounding frequency of ∼ 250 MHz with moisture content of ∼ 5% by weight. Below this moisture level, the dielectric contrast is insufficient to uniquely identify water-saturated zones from the surrounding geoelectrical context, and above it, the radar signal is substantially attenuated leading to a total inefficiency of the method.

Ab initio study of structural, electronic and optical properties of Ca1−xSrxS compounds

Full-potential linearized augmented plane wave method (FP-LAPW) within density functional theory has been used to calculate structural, electronic and optical properties of Ca1� xSrxS, an alkali earth chalcogenide, with varying compositional parameter x in the range 0oxo1. Whereas the structural properties are discussed in terms of charge transfer between the two cations, calculated electronic band structure and density of states have been analyzed in terms of contribution from the S p, Ca d and Sr d states. Furthermore, we have calculated some optical properties such as real and imaginary parts of dielectric constant, e(o), and the calculated results have been discussed in comparison with the existing experimental data and other theoretical calculations.

Dielectric relaxation in complex perovskite oxide In(Ni 1/2Zr 1/2)O 3

The dielectric study of indium nickel zirconate, In(Ni 1/2Zr 1/2)O 3 (INZ) synthesized by solid state reaction technique is performed in a frequency range from 500 Hz to 1 MHz and in a temperature range from 303 to 493 K. The X-ray diffraction analysis shows that the compound is monoclinic. A relaxation is observed in the entire temperature range as a gradual decrease in ɛ′( ω) and as a broad peak in ɛ″( ω) in the frequency dependent real and imaginary parts of dielectric constant, respectively. The frequency dependent electrical data are analyzed in the framework of conductivity and electric modulus formalisms. The frequencies corresponding to the maxima of the imaginary electric modulus at various temperatures are found to obey an Arrhenius law with activation energy of 0.66 eV. The Cole–Cole model is used to study the dielectric relaxation of INZ. The scaling behaviour of imaginary part of electric modulus suggests that the relaxation describes the same mechanism at various temperatures. The frequency dependent conductivity spectra follow the universal power law.

Spectroscopic Ellipsometry Study on Surface Roughness and Optical Property of AZO Films Prepared by Direct-Current Magnetron Reactive Sputtering Method

All as-deposited AZO films by direct current magnetron reactive sputtering (DC-MS) exhibit ZnO characteristic (002) and (103) diffraction peaks. Especially, AZO films prepared at 200° C show a strongest (002) c-axis preferential orientation due to the minimum stress along the (002) orientation. The results show that larger stress easily induces a rougher surface. The film real and imaginary parts of dielectric constants show a sharp changes near the optical absorption edge due to the interband direct transition. The film blue and red shifts of the optical absorption edge can be explained in terms of the change of free-electron concentration in as-deposited AZO films.

Microstructure and magnetic properties of microwave sintered M-type barium ferrite for application in LTCC devices

M-type barium ferrite material has been widely applied in microwave gyromagnetic devices, but its high sintering temperature restrains its application in chip microwave gyromagnetic devices. In our experiment, single phase barium ferrite has been fabricated at low temperature by microwave sintered (MS) method, the sintering time and temperature were significantly reduced from 22 h and 100 °C for the conventional sintering (CS) process to 2 h and 840 °C for MS process, respectively. Experiments show that MS treated barium ferrite materials possess excellent properties with a saturation magnetization of 53.6 emu/g and coercive force 623.8 Oe. In the frequency range of 1 MHz–1.8 GHz, the real and imaginary part of permeability is between 1.8–3.0 and 0–0.55, and the real and imaginary part of dielectric constant is between 2.4–2.7 and 0–0.15; respectively. Our results indicate that the microwave sintering method is a potential important technique in LTCC technology.

Effect of composition and forming parameter on evaporated Ag–As–Te thin films

The effect of increasing Ag content on the conduction phenomena of Ag x As 50− x Te 50 with 3 ≤ x ≤ 20 glass system of thickness ≈150 nm is investigated. The optical constants (refractive index ( n), extinction coefficient ( K), real and imaginary part of dielectric constant) have been analyzed. The values of ( n) decreases with incident photon energy, the results are interpreted in terms of the change in concentration of localized states due to the shift in Fermi level. A correlation between the electrical, optical constants and cohesive energy has been estimated. In addition, the analysis of the results suggests that the effect of Ag content increasing electronic conduction of the system.

Dielectric anomaly in Li-doped zinc oxide thin films grown by sol–gel route

Sol–gel route was employed to grow polycrystalline thin films of Li-doped ZnO thin films (Zn1-xLixO, x=0.15). Polycrystalline films were obtained at a growth temperature of 400–500 °C. Ferroelectricity in Zn0.85Li0.15O was verified by examining the temperature variation of the real and imaginary parts of dielectric constant, and from the C–V measurements. The phase transition temperature was found to be 330 K. The room-temperature dielectric constant and dissipation factor were 15.5 and 0.09 respectively, at a frequency of 100 kHz. The films exhibited well-defined hysteresis loop, and the values of spontaneous polarization (Ps) and coercive field were 0.15 μC/cm2 and 20 kV/cm, respectively, confirming the presence of ferroelectricity.

Applications of the expanded basis method to study the behavior of light in polaritonic photonic crystal slab with losses

We apply the expanded basis method (EBM) to investigate the behavior of light in polaritonic photonic crystal (PC) slabs with losses. The influence of losses on transmissivity is studied. It is found that the transmissivity is significantly lowered with the increase of losses, in particular, it is abruptly decreased in the vicinity of transverse-optical-phonon frequency. The electromagnetic (EM) dissipation is mainly dominated by the imaginary part of dielectric constant of PC. The larger the imaginary part of the dielectric constant, the more the EM energy depletion is. The variation of EM dissipation with the number of period layers in the PC slab is approximately linear or oscillatory increase with the number of period layers.

Optical properties of nanocrystalline FeSi2 and the effects of hydrogenation

Various optical measurements confirm that optical absorption in uniform thin films made from nanocrystalline iron disilicide (nc-FeSi2) with a 3–5nm radius is larger by about 10% than that of single crystalline β-FeSi2. It is also found that the hydrogenation of nc-FeSi2 changes strongly its optical characteristic energies. The nanocrystalline state appears characteristically in the imaginary part of dielectric constants of β-FeSi2 around 2–3eV.

Determination of the optical constants of 2-amino-5-phenyl-1,3,4-thiadiazole by Hartree–Fock and density functional method (B3LYP)

The optical constants (real and imaginary refractive index) and complex dielectric constants of 2-amino-5-phenyl-1,3,4-thiadiazole between 4000 and 400 cm −1 at 25 °C were calculated using the Hartree–Fock and density functional method (B3LYP) and are reported for the first time. The Cauchy parameters obtained from the refractive index spectrum were found to be A=9.870, B=2.85×10 -5 cm 2 and C=8.86×10 −12 cm 4 for experimental results and A=15.369, B=3.19×10 -5 cm 2 and C=1.49×10 −12 cm 4 for HF model and A=9.871, B=1.73×10 -5 cm 2 and C=9.24×10 −13 cm 4 for B3LYP model. The real and imaginary parts of the complex dielectric constant of the compound were calculated. The real part of the dielectric constant is higher than the imaginary part. The variation of the dielectric constant with photon energy indicates that some interactions between photons and electrons in the film are produced in the investigated energy range. These interactions are observed on the shapes of the real and imaginary parts of the dielectric constant and they cause formation of peaks in dielectric spectra. As a result, the optical constants obtained by using HF and DFT (B3LYP) methods show the best agreement with the experimental data.

Optical band gap and optical constants in amorphous Se 96−xTe 4Ag x thin films

The optical constants (absorption coefficient ( α), refractive index ( n), extinction coefficient ( k), real and imaginary part of dielectric constant) have been studied for a-Se 96− x Te 4Ag x (where x = 0 , 4, 8, 12) thin films as a function of photon energy in the wavelength range (500–1000 nm). It has been found that the optical band gap increases while n and k decreases on incorporation of Ag in Se–Te system. The value of α and k increases, while the value of n decreases with incident photon energy. The results are interpreted in terms of the change in concentration of localized states due to the shift in fermi level. A correlation between the optical band gap and electronegativity of the alloys indicates that the optical band gap increases with the decrease of electronegativity.

Impedance spectroscopy studies on Ga‐ion‐modified PLZT ceramics

AbstractPolycrystalline samples of [Pb0.92(La1–zGaz)0.08][Zr0.65Ti0.35]0.98O3 (PLGZT) for z = 0.0, 0.3, 0.6, 0.9, and 1.0 were prepared by a solid‐state reaction technique. The single‐phase formation of the new compounds with tetragonal crystal structures was established by the room‐temperature X‐ray analysis. The occupancy of Ga ion in the La site has been confirmed by FTIR analysis. Complex impedance spectroscopy (CIS) has provided a convincing evidence for the existence of both grain (bulk) and grain boundary effects in the materials, which is also evident from the microstructures, comprise grains separated by well‐defined boundaries. The electrical processes in the sample have been modeled in the form of an electrical equivalent circuit made up of a series combination of two parallel RC circuits attributed to grains and grain boundaries. The real and imaginary parts of dielectric constants have been separated from impedance spectrum results and expressed in terms of loss tangent (tan δ). The ferroelectric transition temperature (Tc) of the materials is evaluated from the plot of real permittivity versus temperature and found to be shifted to higher temperature side with increasing Ga‐ion concentration. A sharp rise in conductivity is observed in the nature of temperature variation of the bulk electrical conductivity (σdc) at higher temperature for all the Ga‐modified PLZT samples. This type of behavior is typical to dielectric ceramics having conductive grain boundary arising out of a relaxation process of the Maxwell–Wagner type. At higher temperature a substantial increase in conductivity ∼10–3 S cm–1 is achieved for complete replacement of the La ion by Ga (z = 1.0). (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Dielectric relaxation study in electron-irradiated ferroelectric poly(vinylidene fluoride-trifluoroethylene) (80/20 mol%) copolymer

The relaxor ferroelectric (RFE) behavior in high-energy electron-irradiated poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] 80/20 mol % copolymer system is characterized over a broad frequency and temperature range. The dielectric properties remarkably vary with the irradiated dose in terms of the change from normal ferroelectric (FE) to RFE phase. During the RFE–paraelectric (PE) transition, the dielectric constants, as a function of temperature, can be described by the Vogel–Fulcher (V–F) relation. It has been found that the relationship between the real and imaginary part of dielectric constant in irradiated copolymer can be well fitted with modified Cole–Cole equation and Debye relaxation equation, exhibiting similar features as inorganic RFEs. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2972–2980, 2005

Optical band gap and optical constants in a-Se80Te20−xPbx thin films

Abstract The optical constants (absorption coefficient, refractive index, extention coefficient, real and imaginary part of dielectric constant) have been studied for a-Se80Te20−xPbx (where x = 0, 2, 6, 10) thin films as a function of photon energy in the wave length range (500–1000 nm). It has been found that the optical band gap increases while the refractive index and the extinction coefficient (k) decreases on incorporation of lead in Se–Te system. The value of absorption coefficient (α) and the extinction coefficient (k) increases, while the value of refractive index (n) decreases with incident photon energy. The results are interpreted in terms of the change in concentration of localized states due to the shift in fermi level.

Investigation of Electrical, Dielectric and Electromechanical Properties of Lanthanum Modified Lead Zirconate Titanate Using Impedance Spectroscopy Technique

Complex impedance spectroscopy (CIS) analysis on polycrystalline lanthanum modified lead zirconate titanate (PLZT) has been carried out to investigate its electrical, dielectric and electromechanical properties. CIS has been shown to be an important and very convenient experimental tool to correlate the electrical and dielectric behaviour of ferroelectric ceamics with their microstructure/structure in terms of the relaxations of defect species. The physical structure of the sample pellet has been visualized as comprising of grains separated by grain boundary in accordance with the impedance spectrum observations. The electrical processes in the sample has been modeled in the form of an electrical equivalent circuit made up of a series combination of two parallel RC circuits attributed to grains and grain boundaries. The real and imaginary parts of dielectric constants have been evaluated from impedance spectrum results and expressed in terms of complex permittivity spectrum (Cole-Cole plot). The dielectric phenomenon in PLZT has been observed to be of polydispersive nature with marked deviation from Debye type relaxation process. This result has also been confirmed by complex modulus analysis. Conductivity dispersion has been observed throughout the frequency range in the present investigation up to 400°C beyond which low frequency dispersion and high frequency plateau was found. It has been attributed to Warburg type diffusion phenomenon arising due to ion migration/charge transport at higher temperature.

Crystallization and dielectric properties of 4LiNbO3–SiO2 glass

Crystallization and dielectric behavior of the 4LiNbO 3 –SiO 2 glass have been studied. Differential thermal analysis (DTA) measurements show two exothermic peaks with heating. X-ray measurements identify that the glass crystallizes into LiNbO 3 nanoparticles and Li 6 Si 2 O 7 . Nanoparticles of three-dimensional growth are also identified by atomic force microscopy (AFM) measurements. The activation energy obtained by modified Ozawa equation is 2.7 eV. In electrical measurements, the dielectric response change is interpreted with a connection of viscosity change as the temperature varies. It is found that there is an anomalous relaxation peak in the imaginary part of dielectric constant in the temperature range between 400 and 600 K, caused by a movement of non-bridging oxygen ions.