Parts Of Complex Dielectric Permittivity Research Articles

Comparison between optical and electrophysical data on hole concentration in zinc doped p-GaAs

Optical and electrophysical properties of Cz-grown zinc doped p-GaAs samples have been investigated. Middle-infrared reflection spectra of ten p-GaAs samples have been obtained. Galvanomagnetic Van der Pau measurements have been made on these samples also, and the values of resistivity and Hall coefficient have been calculated. All experiments have been carried out at room temperature.Reflection spectra have been processed by Kramers–Kronig relations. The spectral dependences of real and imaginary parts of complex dielectric permittivity have been obtained and loss function has been calculated. The value of characteristic wave number corresponding to high-frequency plasmon-phonon mode has been determined by loss function maximum position.The theoretical calculations have been made, and the dependence has been obtained which gave the possibility to determine heavy hole concentration value at T = 295K by the value of characteristic wave number. Then by comparison of optical and Hall data the values of light hole mobility to heavy hole mobility ratio have been determined. This mobility ratio has been shown to be equal to (1.9–2.8) which is considerably less, than predicted theoretical value based on assumption that both light and heavy holes are scattered by optical phonons. It has been suggested that scattering mechanisms of light and heavy holes might be quite different.

Effect of low-dose-rate ionizing radiation on the complex dielectric permittivity of CdZnTe crystals

For the first time, the change in the real and imaginary parts of Cd1-xZnxTe crystals complex dielectric permittivity when exposed to ionizing radiation with a small exposure dose rate (about hundreds of μR/h) has been studied. Significant changes in the values of both parts of complex dielectric permittivity have been revealed. Regularities of specified changes have been established and explained taking into account a different radiation effect on free and bound charges. The basis of effect is the changes in the charge carrier localized states of point defect associates. Their appearance is due to a high concentration and a variety of intrinsic structural defects in the studied crystals as a consequence of the deviation of the crystal composition from the stoichiometric one.

Morphological, structural, optical, broadband frequency range dielectric and electrical properties of PVDF/PMMA/BaTiO3 nanocomposites for futuristic microelectronic and optoelectronic technologies

Polymer blend nanocomposite (PBNC) films consisted of fluoropolymer poly(vinylidene fluoride) (PVDF) and plexiglass polymer poly(methyl methacrylate) (PMMA) blend host matrix (fixed composition blend of PVDF/PMMA = 80/20 wt/wt%) with barium titanate (BaTiO3) ceramic nanofiller of varying concentrations (x = 0, 2.5, 5, 10, and 15 wt%) were prepared via a state-of-the-art solution-cast method. Scanning electron microscope (SEM) images evidenced high homogeneity of these PBNC films and a huge alteration in the spherulite morphology of the PVDF with the increase in dispersed BaTiO3 concentration in the polymer blend matrix. The X-ray diffraction (XRD) patterns identified the presence of electro-active polar β- and γ-phases of the PVDF crystallites in all the composite materials which are supported by the results of Fourier transform infrared (FTIR) spectra. The differential scanning calorimeter (DSC) thermograms explained the high melting temperature of these overlapped PVDF polymorphs and the degree of crystallinity altered anomalously with the variation of nanofiller concentration. The absorbance of ultraviolet-visible (UV-Vis) radiations enhanced while the direct energy band gap of the 80PVDF/20PMMA blend matrix and also the semiconducting BaTiO3 was found to decrease with the increased concentration of nanomaterial in the host polymer matrix. The ambient temperature broadband dielectric spectra covering the frequency range from 20 Hz to 1 GHz explain that the real part of complex dielectric permittivity reduced with a huge dispersion at higher radio frequencies where the dielectric loss tangent and electric modulus spectra exhibited an intense chain segmental relaxation process. The electrical conductivity of these PBNC films increased with frequency augmented and illustrated a small variation for different concentration composites. The experimental results demonstrated that these PVDF/PMMA/BaTiO3 films could be potential candidates for frequency tunable nanodielectric, electromagnetic interference shielders, a flexible dielectric substrate, thermal insulators, and bandgap regulated materials for futuristic microelectronic, capacitive energy storage, and optoelectronic technologies.

OPTICAL PROPERTIES OF LASER-COLOURING MARKED STAINLESS STEEL

Laser colour-marking method often displace conventional marking techniques. Complicated technology of laser-induced periodic surface structure creation on stainless steel samples allows changing their surface morphology and optical properties, which were studied in this work by atomic force microscopy (AFM), laser scanning microscopy, reflectance spectroscopy and ellipsometry. Reflectance spectra of the samples demonstrate reflectance maxima correlate with the visible colours of the samples and with the extrema in the non-monotonic spectral dependences of the derivative of real part of complex dielectric permittivity extracted from the ellipsometric data. Thus, the most intensive light scattering takes place when the real part of complex dielectric permittivity falls down quickly with changing wavelength. We did not observe any “azimuth anisotropy” in our optical measurements at constant incidence angle: the spectra were the same independently of the light incidence plane orientation (parallel or perpendicular to the previous laser light spot scanning direction). We suppose that this selective resonance-like light scattering is due to the sample surface inhomogeneity, which is the result of previous laser treatment. This assumption agrees with estimations based on laser microscope and AFM images as well as with predictions of Mie theory. Thus, the colours of the samples under study are due to the light scattering by randomly distributed surface species with different sizes.

Development of a Resonant Microwave Sensor for Sediment Density Characterization.

In this study, a sensor based on the development of a planar antenna immersed in sediments dedicated to water content monitoring in this type of material is proposed and experimentally validated. It is produced by a conventional Printed Circuit Board (PCB) manufacturing process on a double-sided metalized FR4 substrate. The sensitivity of the sensor is ensured by the variation of the real part of the complex dielectric permittivity of sediments with water content at around 1 GHz. As shown, in this frequency range, electrode polarization and Maxwell–Wagner polarization effects become negligible, leading to only a bulk water polarization sensitivity. The sensor operates in the reflection mode by monitoring the variation of the resonant frequency as a function of the sediment density through the S11 reflection measurements. An experimental sensitivity of was achieved. Despite the simplification of data interpretation at the considered frequency, the influence of ionic species such as NaCl in sediments on the real part of the relative complex dielectric permittivity is highlighted. This demonstrates the importance of considering a second parameter such as the S11 level at low frequency or the electrical conductivity to extract the density from the frequency measurements.

Role of ionic contribution in dielectric behaviour of a nematic liquid crystal with variable cell thickness

In this research article, we have investigated the dielectric properties of a nematic liquid crystal (NLC), namely 4 cyano-4′- pentylbiphenyl (which is commonly known as 5CB), in sample cells of variable thickness. The dielectric behaviour has been studied through a LCR meter in the frequency ranging from 20 Hz to 1 MHz. It was observed that the real part of complex dielectric permittivity (ε') decreases and the peak value of the energy dissipated per unit cycle (ε′′) increases on increasing the cell thickness. It has also been noticed that the relaxation frequency of LC material under investigation shifts towards the lower side with the increment in the sample cell thickness. The observed dielectric behaviour has been attributed to the contribution of the ionic species available in the NLC used. The mobilized ions have a significant contribution in influencing the dielectric studies of 5CB in thin cells. Further, all the above mentioned physical attributes of 5CB will play an important role in fabricating a device which is not only cost effective but also has higher transmittance and negligible power consumption.

Charge Transport in Layer Gallium Monosulfide in Direct and Alternate Electric Fields

It was established that the variable-range-hopping mechanism of dc-conductivity takes place in the GaS single crystal at low temperatures. The parameters of localized states in the forbidden gap of studieGaS samples have been evaluated. Dielectric properties (loss tangent, real (e') and imaginary (e'') parts of complex dielectric permittivity and ac-conductivity across the layers of the GaS layered single crystals have been studied in the frequency range f = 5 × 104 to 3.5 × 107 Hz. The results demonstrate that the dielectric dispersion in the GaS single crystal has a relaxation nature. Over the studied frequency range, the ac-conductivity of the GaS crystal varies as f0.8, characteristic of hopping conduction through localized states near the Fermi level. The Fermi-level density of states, the spread of their energies, and the mean hop distance and time have been estimated.

Dielectric Properties of Polyethylene/TiO2 Composites

The frequency dependences in the range of 25–106 Hz of dielectric properties (real and imaginary parts of complex dielectric permittivity and electric modulus) of composite materials based on high-density polyethylene and dispersed filler TiO2 are studied. It is shown that the real part of the complex dielectric permittivity e of composites increases with decreasing frequency. The magnitude of the effect increases with an increase in the TiO2 content in the composite of more than 20%. At high frequencies >2 × 103 Hz, the value of e of composites is practically independent of frequency. The frequency dependences of the electric modulus M—the inverse complex dielectric permittivity—are determined. In composites with a TiO2 content of up to 20%, the imaginary part of the electric modulus M' decreases with increasing frequency, and in composites containing from 20 to 50% TiO2, the opposite effect of decreasing M at low frequencies is observed. On the frequency dependences of all dielectric characteristics, there are no peaks indicative of possible mechanisms of dielectric relaxation associated with molecular mobility.

Millimeter waveband dielectric properties of nanocomposite 3d and rare-earth titanates

The transmission and reflection coefficients were measured in frequency range from 17 to 38 GHz for ceramic and nanocomposite titanates. The real and imaginary parts of complex dielectric permittivity were determined from measurements of transmission and reflection coefficients.

Morphological, structural, dielectric and electrical properties of PEO–ZnO nanodielectric films

The morphological, structural, dielectric and electrical properties of aqueous solution-cast prepared poly(ethylene oxide)–zinc oxide (PEO–ZnO) nanocomposite films have been investigated as a function of ZnO nanoparticle concentrations up to 5 wt%. Scanning electron microscopy (SEM) images of these films show that the morphology of pristine PEO aggregated spherulites changes into fluffy, voluminous and highly porous with dispersion of ZnO nanoparticles into the PEO matrix. X-ray diffraction (XRD) study confirms that the crystalline phase of PEO greatly reduces at 1 wt% ZnO, and it again increases gradually with further increase of ZnO concentration. The dielectric relaxation spectroscopy (DRS) over the frequency range 20 Hz–1 MHz reveals that the real part of complex dielectric permittivity at audio frequencies decreases non-linearly whereas it remains almost constant at radio frequencies for these polymeric nanocomposites. Dispersion of nanosize ZnO particles into the PEO matrix reduces the values of dielectric permittivity which also exhibits a correlation with the dispersivity of ZnO nanoparticles. The relaxation peaks observed in the dielectric loss tangent and electric modulus spectra reveal that the electrostatic interactions of nanoscale ZnO particles with the ethylene oxide functional dipolar group of PEO monomer units decrease the local chain segmental dynamics of the polymer. Real part of ac conductivity spectra of these films have been analyzed by power law fit over the audio and radio frequency regions, respectively, and the obtained dc conductivity values for these regions differ by more than two orders of magnitude. The temperature dependent relaxation time and dc conductivity values of the nanodielectric material obey the Arrhenius relation of activation energies and confirm a correlation between dc conductivity and PEO chain segmental motion which is exactly identical to the characteristics of solid polymer electrolytes. Results imply that these nanocomposite materials can serve as low permittivity flexible nanodielectric for radio frequency microelectronic devices and also as electrical insulator for audio frequency operating conventional devices in addition to their suitability in preparation of solid polymer electrolytes.

Determining the form of a relaxator distribution by extrapolation

А new way of determining types of relaxator distribution and their parameters is proposed. It is based on calculating the slopes of high-frequency and low-frequency asymptotes in the frequency dependences of the real and imaginary parts of complex dielectric permittivity and conductivity in dielectrics with polarization relaxation.

Millimeter Waveband Dielectric Properties of Nanocomposite Materials Based on Opal Matrices with Particles of Spinels

The dielectric properties of 3D nanocomposites based on opal matrices containing the particles of compounds with spinel structure have been studied. Microwave measurements have been carried out in the frequency range from 26 to 38 GHz. The frequency dependences of transmission and reflection coefficients are obtained. The values of the real and imaginary parts of complex dielectric permittivity have been retrieved. The X-ray phase analysis of the nanocomposites is performed and their structures are studied.

Space group symmetries of the phases of(Pb0.94Sr0.06)(ZrxTi1−x)O3across the antiferrodistortive phase transition in the composition range0.620≲x≲0.940

The existing controversies about the space group symmetries of Pb(ZrxTi1-x)O3 (PZT) above and below antiferrodistortive (AFD) phase transition temperature (TAFD) in the Zr4+- rich (0.620<x<0.940) compositions are addressed using the results of dielectric, synchrotron x-ray powder diffraction (SXRPD) and neutron powder diffraction (NPD) studies. These compositions undergo an AFD phase transition above room temperature due to tilting of oxygen octahedral leading to a superlattice phase of PZT. We have substituted 6% Sr2+ at Pb2+-site to enhance the tilt angle and thereby the intensity of the superlattice peaks. The real and imaginary parts of complex dielectric permittivity have been used to locate the paraelectric to ferroelectric and ferroelectric to AFD phase transitions. Rietveld analysis of SXRPD and NPD profiles unambiguously reject the rhombohedral phases in R3c and R3m space groups below and above TAFD, respectively, with or without a coexisting monoclinic phase in Cm space group, and confirm that the true symmetries are monoclinic in Cc and Cm space groups below and above TAFD, respectively. Based on these and previous findings a phase diagram of PSZT for 0.40<x<0.90 showing stability fields of monoclinic Cc and monoclinic Cm, tetragonal P4mm and cubic Pm3m phases has also been presented.

Microwave Dielectric Properties of Ceramic and Nanocomposite Titanates of Transition Metal

Ceramic and nanocomosite samples of the titanates of transition metals have been synthesized and their microwave dielectric properties have been investigated. Frequency and magnetic field dependences of the transmission and reflection coefficients in centimeter and millimeter wavebands were measured. It is established for most of studied ceramic titanates that transmission coefficient increases and reflection coefficient decreases when frequency increases. An absorption maximum has been found for ceramic sample made of Co0.9Fe0.1TiO3. The real and imaginary parts of complex dielectric permittivity were determined from measurements of transmission and reflection coefficients. On the whole, real part of dielectric permittivity of nanocomposite titanates based on an opal matrix is less than for ceramic titanates.

Complex Dielectric Permittivity of Sandy Loam as a Function of Salinity and Biomass at Microwaves

Real and Imaginary parts of Complex Dielectric Permittivity (ε’ and ε” ) of Sandy Loam soil have been measured in the frequency range 150 MHz – 2.4 GHz using a Vector Network Analyzer at varied Moisture contents, Salinity and Biomass. The Emissivity of the soil for normal incidence was also calculated from measured values of Complex Permittivity. The measured permittivity data show strong dependence on moisture content. Salinity causes higher permittivity and dielectric loss. Biomass appears to enhance the permittivity data due to increase in porosity of the soil. The emissivity of the soil was observed to decrease with increasing soil moisture and soil salinity, but it increases with biomass.

Characteristics of dielectric properties and conduction mechanism of TlInS2:Cu single crystals

Single crystals of TlInS2:Cu were grown by the modified Bridgman method. The dielectric behavior of TlInS2:Cu was investigated using the impedance spectroscopy technique. The real (ε1), imaginary (ε2) parts of complex dielectric permittivity and ac conductivity were measured in the frequency range (42–2×105) Hz with a variation of temperature in the range from 291K to 483K. The impedance data were presented in Nyquist diagrams for different temperatures. The frequency dependence of σtot (ω) follows the Jonscher's universal dynamic law with the relation σtot (ω)=σdc+Aωs, (where s is the frequency exponent). The mechanism of the ac charge transport across the layers of TlInS2:Cu single crystals was referred to the hopping over localized states near the Fermi level. The examined system exhibits temperature dependence of σac (ω), which showed a linear increase with the increase in temperature at different frequencies. Some parameters were calculated as: the density of localized states near the Fermi level, NF, the average time of charge carrier hopping between localized states, τ, and the average hopping distance, R.

Measurements of Complex Magnetic Permeability of Nano-Size $\varepsilon$-Al$_{\rm x}$Fe$_{2-{\rm x}}$O$_{3}$ Powder Materials at Microwave and Millimeter Wavelengths

The imaginary part of complex magnetic permeability spectrum confirms the strong ferromagnetic resonance absorptions to appear at 89 GHz for the e-AlxFe2-xO3 nanomagnets prepared by sol-gel techniques for the x value to be 0.66. A strong anomalous dispersion corresponding to 89 GHz resonance is also observed in the real part of magnetic permeability spectrum. The free space quasi-optical spectrometer equipped with a set of tunable backward-wave oscillators as power sources is used in this work to study the transmittance, real and imaginary parts of complex dielectric permittivity and real and imaginary parts of complex magnetic permeability properties of this nano magnet materials. Complex dielectric permittivity and Complex magnetic permeability spectra over six waveguide bands are almost flat in the 8-40 GHz range The vector network analyzer and in-waveguide measurements were employed for the measurements over 8-40 GHz range. The absorption property is suggested to be caused by the natural resonance achieved by the large magnetic anisotropies in this series of aluminum substituted ferrite nanomagnets. The absorption peak shifts to the lower frequencies with increasing value of x -parameter. The average particle size of e-AlxFe2-xO3 nanomagnets lies between 25 to 50 nm. The absorption and dispersion characteristics are repeatable for the same density of the powder material.

Determination of Soil Pore Water Salinity Using an FDR Sensor Working at Various Frequencies up to 500 MHz

This paper presents the application of a frequency-domain reflectometry (FDR) sensor designed for soil salinity assessment of sandy mineral soils in a wide range of soil moisture and bulk electrical conductivity, through the determination of soil complex dielectric permittivity spectra in the frequency range 10–500 MHz. The real part of dielectric permittivity was assessed from the 380–440 MHz, while the bulk electrical conductivity was calculated from the 165–325 MHz range. The FDR technique allows determination of bulk electrical conductivity from the imaginary part of the complex dielectric permittivity, without disregarding the dielectric losses. The soil salinity status was determined using the salinity index, defined as a partial derivative of the soil bulk electrical conductivity with respect to the real part of the soil complex dielectric permittivity. The salinity index method enables determining the soil water electrical conductivity value. For the five sandy mineral soils that have been tested, the relationship between bulk electrical conductivity and the real part of dielectric permittivity is essentially linear. As a result, the salinity index method applied for FDR measurements may be adapted to field use after examination of loam and clayey soils.

The impedance spectroscopic study and dielectric relaxation in A(Ni1/3Ta2/3)O3 [A=Ba, Ca and Sr

We present the results of impedance spectroscopic study with its analytical interpretations in the framework of electric modulus formalism for Barium Nickel Tantalate Ba(Ni1/3Ta2/3)O3 (BNT), Calcium Nickel Tantalate Ca(Ni1/3Ta2/3)O3 (CNT) and Strontium Nickel Tantalate Sr(Ni1/3Ta2/3)O3 (SNT) synthesized by the solid-state reaction technique. The results of powder X-ray diffraction study reveal that BNT and SNT crystallize in cubic structure with lattice parameter a=4.07 Å and 3.98 Å respectively, whereas CNT crystallizes in monoclinic structure having lattice parameters, a=5.71 Å, b=13.45 Å and c=5.47 Å with β=118.3°. The logarithmic angular frequency dependence of the real part of complex dielectric permittivity and loss tangent as a function of temperature indicate significant dielectric relaxation in the samples, which have been explained by the Debye theory. The frequency dependence of the loss peak and the imaginary part of electrical modulus are found to obey the Arrhenius law. The relaxation mechanism of these samples is modeled by the Cole–Cole equation. This confirms that the polarization mechanism in BNT, CNT and SNT is due to the bulk effect arising in semiconductive grains. The scaling behavior of imaginary part of electric modulus M″ suggests that the relaxation describes the same mechanism at various temperatures but relaxation frequency is strongly temperature dependent. The normalized peak positions of tan δ/tan δm and M″/M″m versus log ω for BNT, CNT and SNT do not overlap completely and are very close to each other. These indicate the presence of both long-range and localized relaxation. Due to their high dielectric constant and low loss tangent, these materials may find several technological applications such as in capacitors, resonators, filters and integrated circuits.

Frequency-dependent dielectric properties and electrical conductivity of CdIn2S4 single crystals

The real (ɛ) and imaginary (ɛ″) parts of complex dielectric permittivity and ac conductivity (σac) of CdIn2S4 single crystals (cubic structure) have been measured in the frequency range f = 5 × 104 to 3.5 × 107 Hz. The results demonstrate that the dielectric dispersion in the crystals has a relaxation nature. In the frequency range f = 5 × 104 to 3.5 × 107 Hz, the ac conductivity of single-crystal CdIn2S4 follows the relation σac ∼ f0.8, characteristic of hopping conduction through localized states near the Fermi level.