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1.
Cadmium telluride (CdTe) nanomaterials have been synthesized by soft chemical route using mercapto ethanol as a capping agent. Crystallization temperature of the sample is investigated using differential scanning calorimeter. X-ray diffraction and transmission electron microscope measurements show that the prepared sample belongs to cubic structure with the average particle size of 20 nm. Impedance spectroscopy is applied to investigate the dielectric relaxation of the sample in a temperature range from 313 to 593 K and in a frequency range from 42 Hz to 1.1 MHz. The complex impedance plane plot has been analyzed by an equivalent circuit consisting of two serially connected R-CPE units, each containing a resistance (R) and a constant phase element (CPE). Dielectric relaxation peaks are observed in the imaginary parts of the spectra. The frequency dependence of real and imaginary parts of dielectric permittivity is analyzed using modified Cole–Cole equation. The temperature dependence relaxation time is found to obey the Arrhenius law having activation energy ~0.704 eV. The frequency dependent conductivity spectra are found to follow the power law. The frequency dependence ac conductivity is analyzed by power law. 相似文献
2.
《Current Applied Physics》2009,9(4):826-832
We have reported the structural and electrical properties of nano particles of Al doped Ni0.2Cd0.3Fe2.5O4 ferrite using X-ray diffraction, dielectric spectroscopy and impedance spectroscopy at room temperature. XRD analysis confirms that the system exhibits polycrystalline single phase cubic spinel structure. The average particle size estimated using Scherrer formula for Lorentzian peak (3 1 1), has been found 5(±) nm. The results obtained show that real (ε′), imaginary (ε″) part of the dielectric constant, loss tangent (tan δ), and ac conductivity (σac) shows normal behaviour with frequency. The dielectric properties and ac conductivity in the samples have been explained on the basis of space charge polarization according to Maxwell–Wagner two-layer model and the Koop’s phenomenological theory. The impedance analysis shows that the value of grain boundary impedance increases with Al doping. The complex impedance spectra of nano particles of Al doped Ni–Cd ferrite have been analyzed and explained using the Cole–Cole expression. 相似文献
3.
CdS nanoparticles have been synthesized by a chemical reaction route using thiophenol as a capping agent. The frequency-dependent
dielectric dispersion of cadmium sulphide (CdS) is investigated in the temperature range of 303-413 K and in a frequency range
of 50 Hz-1 MHz by impedance spectroscopy. An analysis of the complex permittivity (ɛ′ and ɛ″) and loss tangent (tan δ) with frequency is performed by assuming a distribution of relaxation times. The scaling behaviour of dielectric loss spectra
suggests that the relaxation describes the same mechanism at various temperatures. The frequency-dependent electrical data
are analysed in the framework of conductivity and modulus formalisms. The frequency-dependent conductivity spectra obey the
power law. 相似文献
4.
M. Soosen Samuel Jiji Koshy Anoop Chandran K.C. George 《Physica B: Condensed Matter》2011,406(15-16):3023-3029
Highly optical, good crystalline and randomly aligned ZnO nanorods were synthesized by the hydrothermal method. The dielectric properties of ZnO nanorods were attributed to the interfacial polarization at low frequencies (below 10 kHz) and orientational polarization at higher frequencies. The observed ω(n?1) dependence of dielectric loss was discussed on the basis of the Universal model of dielectric response. Dielectric loss peak was composed of the Debye like loss peak at higher frequencies and interfacial loss peak at lower frequencies. Charge transport through the grain and grain boundary region was investigated by impedance spectroscopy. At higher temperatures the conductivity of the nanorod was mainly through the grain interior and the overall impedance was contributed by the grain boundary region. The activation energy of nanorod was calculated as 0.078 eV, which is slightly higher than the reported bulk value. 相似文献
5.
C. Tsonos I. Stavrakas C. Anastasiadis A. Kyriazopoulos A. Kanapitsas D. Triantis 《Journal of Physics and Chemistry of Solids》2009,70(3-4):576-583
The present work deals with the electrical properties of typical cement mortars during the hardening process, cured at low relative humidity. Measurements were made by using dielectric spectroscopy (DS) over a broad frequency range of 10 Hz–1 MHz and isothermal depolarization current (IDC) techniques, for several weeks after sample preparation. This work presents a coherent study of the various formalisms employed in dielectric spectroscopy. Each of these formalisms contributes to the development of the complete relaxation mechanisms that are responsible for the frequency spectrum. After the first week of hardening, when the DC conductivity effects were absent, two distinct dielectric relaxation mechanisms were observed in the frequency spectrum of the complex permittivity ε* and tan δ functions. The mechanism positioned at low-frequency region (few kHz) is observed for the first time, as we know from the literature, on cement mortars. The relaxation times of both mechanisms were found to increase gradually, while the strength of the relaxation mechanisms varied also as a function of the hardening time. Fitting analysis in complex impedance Z* and electric modulus M* formalisms revealed also the existence of two short-range relaxation mechanisms of conductivity. We suggest that the low-frequency relaxation is related to the closed capillary pores and the high-frequency relaxation to the C-S-H gel pores. An increase of the mean dimension, of both types of pores, estimated from our data analysis with hardening time. 相似文献
6.
《Solid State Ionics》2006,177(13-14):1107-1110
The dispersion curves of the dielectric response of NH4HSO4 show that the corrected imaginary part of permittivity, εʺ, and its real part ε′ versus frequency reveal a dielectric relaxation around 9.1 × 105 Hz at 31 °C, which shifts to higher frequencies (∼ 106 Hz) as the temperatures increases. The relaxation frequency shows an activated relaxation process over the temperature range 31–83 °C with activation energy Ea = 0.14 eV, which is close to that derived from the dc conductivity. We suggest that the observed dielectric relaxation could be produced by the H+ jump and SO4− reorientation that cause distortion and change the local lattice polarizability inducing dipoles like HSO4−. 相似文献
7.
《Current Applied Physics》2007,7(2):215-219
The temperature and frequency dependence of dielectric constant (ε′) and dielectric loss (ε″) is studied for different samples of polyaniline (PANI), doped with different concentration of sulfamic acid in the frequency range (10–100 kHz) and temperature range (300–400 K). The dc conductivity has also been measured to see the effect of sulfamic acid and the conduction mechanism has been explained by the propagation of polaron through a conjugated polymer chain due to shifting of double bonds (alternation), which gives rise to electrical conduction. 相似文献
8.
《Current Applied Physics》2010,10(4):1013-1016
The LiCoVO4 compound is synthesized by solution-based chemical method. X-ray diffraction analysis exhibits a single phase nature of the compound with cubic structure. The dielectric constant (εr), tangent loss (tanδ) and a.c. conductivity (σac) have been studied as a function of frequency and temperature using complex impedance spectroscopy (CIS) technique. The variation of (εr and tanδ) with frequency at studied temperatures shows a dispersive behavior at low frequencies. Frequency dependence of σac at different temperatures obeys Jonscher’s universal power law governed by the relation: σac = σdc + Aωn, where n is the frequency exponent in the range of 0 ⩽ n ⩽ 1 and A is a constant that depends upon temperature. 相似文献
9.
Polymer nanocomposite electrolytes (PNCEs) of poly(ethylene oxide) and sodium perchlorate monohydrate complexes with montmorillonite
(MMT) clay up to 20 wt.% MMT concentration of poly(ethylene oxide) (PEO) are synthesized by melt compounding technique at
melting temperature of PEO (∼70 °C) and NaClO4 monohydrate (∼140 °C). Complex dielectric function, electric modulus, alternating current (ac) electrical conductivity, and
impedance properties of these PNCEs films are investigated in the frequency range 20 Hz to 1 MHz at ambient temperature. The
direct current conductivity of these materials was determined by fitting the frequency-dependent ac conductivity spectra to
the Jonscher power law. The PNCEs films synthesized at melting temperature of NaClO4 monohydrate have conductivity values lower than that of synthesized at PEO melting temperature. The complex impedance plane
plots of these PNCEs films have a semicircular arc in upper frequency region corresponding to the bulk material properties
and are followed by a spike in the lower frequency range owing to the electrode polarization phenomena. Relaxation times of
electrode polarization and ionic conduction relaxation processes are determined from the frequency values corresponding to
peaks in loss tangent and electric modulus loss spectra, respectively. A correlation is observed between the ionic conductivity
and dielectric relaxation processes in the investigated PNCEs materials of varying MMT clay concentration. The scaled ac conductivity
spectra of these PNCEs materials also obey the ac universality law. 相似文献
10.
A novel PVA/CuI nanocomposite polymer electrolyte layer synthesized via the reduction of CuCl2 by NaI in an aqueous PVA solution. The as-prepared films were characterized by X-ray diffraction, scanning electron microscope, as well as impedance spectroscopy. The obtained results indicated the formation of hexagonal CuI nano particles of ≈55 nm sizes embedded in the PVA matrix. In addition, the study of dielectric parameters and conductivity of PVA/CuI nanocomposite in wide range of temperature and frequency are given and discussed. The frequency dependence of ac-conductivity suggests power law with an exponent 0.026 < s < 0.73 which predicts hopping of charge carriers. The bulk conductivity showed activation with temperature, significant values of activation energy are deduced and discussed. An average value of the energy gap width, 2.05 eV obtained using optical absorption in UV–visible spectra for PVA/CuI nanocomposite polymer electrolyte. 相似文献
11.
《Solid State Communications》2002,121(9-10):531-536
High quality zinc oxide nanoparticles with (002) preferred orientation were prepared by post-thermal annealing zinc implanted silica at 700 °C using two methods. One method was annealing zinc implanted silica at 700 °C for 2 h in oxygen ambient; the other method was sequentially annealing zinc implanted silica at 700 °C in nitrogen and oxygen ambient for 1 h, respectively. X-ray diffraction (XRD), absorption and microphotoluminescence (micro-PL) results indicated that the latter method could create high quality ZnO nanoparticles with (002) preferred orientation and narrow size-distribution. X-ray photoelectron spectra (XPS) showed the formation of ZnO nanoparticles on a silica surface, where the ZnO nanoparticle content increased with increasing oxidation time in an oxygen environment. The processes of the transformation from Zn to ZnO are discussed. 相似文献
12.
《Solid State Ionics》2006,177(26-32):2679-2682
The polymer electrolytes comprising blend of poly(vinyl acetate) (PVAc) and poly(methylmethacrylate) (PMMA) as a host polymer and LiClO4 as a dopant are prepared by solution casting technique. The amorphous nature of the polymer–salt complex has been confirmed by XRD analysis. The DSC thermograms show two Tg's for PVAc–PMMA blend. A decrease in Tg with the LiClO4 content reveals the increase of segmental motion. Conductance spectra results are found to obey the Jonscher's power law and the maximum dc conductivity value is found to be 1.76 × 10− 3 S cm− 1 at 303 K for the blend polymer complex with 20 wt.% LiClO4, which is suitable for the Li rechargeable batteries. The conductivity–temperature plots are found to follow an Arrhenius nature. The dc conductivity is found to increase with increase of salt concentration in the blend polymer complexes. 相似文献
13.
Polymer electrolyte films of (PVA+15 wt% LiClO4)+x wt% Ionic liquid (IL) 1-ethyl-3-methylimidazolium ethylsulfate [EMIM][EtSO4] (x=0, 5, 10, 15) were prepared by solution cast technique. These films were characterized using TGA, DSC, XRD and ac impedance spectroscopic techniques. XRD result shows that amorphosity increases as the amount of the IL in PVA+salt (LiClO4) is increased. DSC results confirm the same (except (PVA+15 wt% LiClO4)+10 wt% IL). The dielectric and conductivity measurements were carried out on these films as a function of frequency and temperature. The addition of IL significantly improved the ionic conductivity of polymer electrolytes. Relaxation frequency vs. temperature plot for (PVA+15 wt% LiClO4)+x wt% IL were found to follow an Arrhenius nature. The dielectric behavior was analyzed using real and imaginary parts of dielectric constant, dielectric loss tangent (tan δ) and electric modulus (M′ and M″). 相似文献
14.
《Current Applied Physics》2009,9(1):165-171
Solid polymer electrolytes based on poly (vinyl alcohol) (PVA) complexed with sodium fluoride (NaF) at different weight percent ratios were prepared using solution cast technique. The structural properties of these electrolyte films were examined by XRD studies. The XRD data revealed that the amorphous domains of PVA polymer matrix increased with increase of NaF salt concentration. The complexation of the salt with the polymer was confirmed by FT-IR studies. Electrical conductivity was measured in the temperature range of 303–373 K and the conductivity was found to increase with the increase of dopant concentration as well as temperature. The dielectric constant (ε′) increased with the increase in temperature and decreased with the increase in frequency. A loss peak was identified at 365 K in the dielectric loss spectra and is attributed to the orientation of polar groups. Measurement of transference number was carried out to investigate the nature of charge transport in these polymer electrolyte films using Wagner’s polarization technique and Watanabe technique. Transport number data showed that the charge transport in these polymer electrolyte systems was predominantly due to ions and in particular due to anions. Using these polymer electrolytes, solid state electrochemical cells were fabricated. Various cell parameters like open circuit voltage (OCV), short circuit current (SCC), power density and energy density were determined. 相似文献
15.
Erbium substituted cobalt ferrite (CoFe2−xErxO4; x=0.0–0.2, referred to CFEO) materials were synthesized by sol-gel auto-combustion method. The effect of erbium (Er3+) substitution on the crystal structure, dielectric, electrical transport and magnetic properties of cobalt ferrite is evaluated. CoFe2−xErxO4 ceramics exhibit the spinel cubic structure without any impurity phase for x≤0.10 whereas formation of the ErFeO3 orthoferrite secondary phase was observed for x≥0.15. All the CFEO samples demonstrate the typical hysteresis (M–H) behavior with a decrease in magnetization as a function of Er content due to weak superexchange interaction. The frequency (f) dependent dielectric constant (ε′) revealed the usual dielectric dispersion. The ε′–f dispersion (f=20 Hz to 1 MHz) fits to the modified Debye's function with more than one ion contributing to the relaxation. The relaxation time and spread factor derived are ∼10−4 s and ∼0.61(±0.04), respectively. Electrical and dielectric studies indicate that ε′ increases and the dc electrical resistivity decreases as a function of Er content (x≤0.15). Complex impedance analyses confirm only the grain interior contribution to the conduction process. Temperature dependent electrical transport and room temperature ac conductivity (σac) analyses indicate the semiconducting nature and small polaron hopping. 相似文献
16.
《Current Applied Physics》2007,7(2):168-171
In the dielectric (Ba,Sr)TiO3 thin films, the correlation between the film thickness and the dielectric properties was investigated. The dielectric properties such as the dielectric constant (ε) and dielectric loss (tan δ) were measured using the capacitor geometry. As the film thickness increased, the dielectric constant also increased due to the reduction of the interfacial dead-layer effect. However, the dielectric loss did not show a monotonous variation with the increasing film thickness. It was found that the dielectric loss correlated well with the non-uniform distribution of local strain, as analyzed by X-ray diffraction, according to the Curie–von Schweidler relaxation law. 相似文献
17.
Glasses of the general formula xLi2O·(20?x)CaO·30P2O5·30V2O5·20Fe2O3 with x=0, 5, 10, 15 and 20 mol% were prepared; IR, density, electrical and dielectric properties have been investigated. Lithia-containing glasses revealed more (P2O7)4?, FeO6, V–O? and PO? groups and mostly have lower densities than those of lithia-free ones. The electrical properties showed random behavior by replacing Li2O for CaO, which has been assigned to the change of the glass structure. The results of activation energy and frequency-dependent conductivity indicate that the conduction proceeds via electronic and ionic mechanisms, the former being dominant. The mechanism responsible for the electronic conduction is mostly thermally activated hopping of electrons from Fe(II) ions to neighboring Fe(III) sites and/or from V4+ to V5+. The dielectric constant (ε′) showed values that depend on the structure of glass according to its content of Li2O. The (ε′) values are ranging between 3 and 41 at room temperature for 1 kHz, yet at high temperatures, glass with 20 mol Li2O exhibits values of 110 and 3600 when measurement was carried out in the range 0.1–1 kHz, and at 5 MHz, respectively. 相似文献
18.
《Current Applied Physics》2009,9(4):717-721
TiO2 thin films were prepared by sol-gel method. The structural investigations performed by means of X-ray diffraction (XRD) technique and scanning electron microscopy (SEM) showed the shape structure at T = 600 °C. The optical constants of the deposited film were obtained from the analysis of the experimentally recorded transmittance spectral data in the wavelength of 200–3000 nm range. The values of some important parameters of the studied films are determined, such as refractive index n and thickness d. In this work, using the transmission spectra, we have calculated the dielectric constant (ε∞) for four layered TiO2 films; a simple relation is suggested to estimate the third-order optical nonlinear susceptibility χ(3). It has been found that the dispersion data obeyed the single oscillator of the Wemple–DiDomenico model, from which the dispersion parameters and high-frequency dielectric constant were determined. The estimations of the corresponding band gap Eg, χ(3) and ε∞ are 2.57 eV, 0.021 · 10−10 esu and 5.20, respectively. 相似文献
19.
The complex permittivity spectra for tert-butyl alcohol (TB) with 2-propanol (2P) were determined over the frequency range of 10 MHz to 20 GHz using the time domain reflectometry (TDR) in the temperature range 25 °C to 55 °C for 11 different concentrations of the system. The static dielectric constant (ε0) and relaxation time (τ) have been determined these spectra using the Debye model. Excess properties and Kirkwood correlation factor of the mixtures have been determined. The excess permittivity is found to be positive in the tert-butyl alcohol rich region and negative in the 2-propanol rich region. However, the excess inverse relaxation time has different trend. The static dielectric constants for the mixtures have also been fitted with the modified Bruggeman model by assuming an additional parameter in the model. It appears that structure of the TB–2P dimer in the TB rich region favors parallel dipole orientation, whereas in the 2P rich region, it favors antiparallel orientation. 相似文献
20.
The dielectric properties of Cu0.5Tl0.5Ba2Ca2?yMgyCu0.5Zn2.5O10?δ (y = 0, 0.5, 1.0, 1.5) superconductor samples were studied at 79 and 290 K by means of capacitance (C) and conductance (G) measurements with the test frequency (f) in the range of 10 KHz to 10 MHz. A negative capacitance (NC) phenomenon has been observed, which is most likely arising due to higher Fermi level of ceramic superconductor samples than metal electrodes. Also the NC may be due to the space charge located at the multiple insulator–superconductor interfaces (grain boundaries) in the materials. The negative dielectric constant (ε′) and loss factor (tan δ) show strong dispersion at low frequencies. The lower thermal agitation at 79 K may enhance the polarizability and hence the dielectric constants (ε′ and ε″). 相似文献