BaxSr1-xTiO3 sol-gel thin films with x--0.5, 0.7 and 0.8 have been fabricated as AI/BST/Pt capacitor. The AC conductivity and dielectric properties over a frequency rang of 10 Hz and I MHz have been studied in order t...BaxSr1-xTiO3 sol-gel thin films with x--0.5, 0.7 and 0.8 have been fabricated as AI/BST/Pt capacitor. The AC conductivity and dielectric properties over a frequency rang of 10 Hz and I MHz have been studied in order to explore the ion dynamics and relaxation mechanisms in the films. The frequency dependent conductivity plots show three regions of conduction processes. Dielectric results show that ε＇ at low frequencies increases as Sr content decreases, whereas at high frequencies, it shows opposite variation, which is attributed to the dipole dynamics. The electric modulus plots reveal the relaxation peaks which are not observed in the ε＂ plots and the contribution of the grains, grain boundaries and electrode to the relaxation mechanisms.展开更多
The ac conductivity of the bulk amorphous chalcogenide system (As2Te3)100-xGex (where x=0,5,10,15 and 25 at. pct) was investigated at variable frequencies ranging from 50 Hz to 100 kHz and at different temperatures ra...The ac conductivity of the bulk amorphous chalcogenide system (As2Te3)100-xGex (where x=0,5,10,15 and 25 at. pct) was investigated at variable frequencies ranging from 50 Hz to 100 kHz and at different temperatures ranging from 3O to 160℃. lt was found that at a fixed temperature, where n <1 and decreases with temperature. The complex impedence Z was measured over the same frequency and temperature ranges. All samples give a semicircle arc originating at the origin point. This indicates that each composition can be described only by one resistance R and one capacity C, both parallelly combined. The centre below the real axis indicates the relaxation behaviour of the system. The activation energies for conduction were calculated.展开更多
Lead free(K_(0.5)Na_(0.5))NbO_(3)(KNN)ceramics were prepared by conventional solid state reaction route.For single perovskite phase formation,calcination temperature was optimized at 850℃for 6h,whereas for dense morp...Lead free(K_(0.5)Na_(0.5))NbO_(3)(KNN)ceramics were prepared by conventional solid state reaction route.For single perovskite phase formation,calcination temperature was optimized at 850℃for 6h,whereas for dense morphology the sintering of the ceramic was carried out at 1120℃for 4h.X-ray diffraction XRD analysis confirmed the formation of single phase with orthorhombic structure at room temperature.Impedance analysis and AC conductivity studies of the KNN sample was carried out in the temperature range of 703-773 K.Impedance study showed the increase in conducting behavior at higher temperature.The temperature dependence of AC conductivity indicated that the conduction process is due to doubly ionized oxygen vacancies in the higher temperature region.展开更多
The compositional dependence of ac conductivity(δac),real(δ′)and imaginary(δ′′)parts of complex electric conductivity(δ*)was investigated as a function of temperature(T)and frequency(f) for Mn_(0.7+x)Zn_(0.3)Si...The compositional dependence of ac conductivity(δac),real(δ′)and imaginary(δ′′)parts of complex electric conductivity(δ*)was investigated as a function of temperature(T)and frequency(f) for Mn_(0.7+x)Zn_(0.3)Si_(x)Fe_(2-2x)O_(4),x=0.0,0.1,0.2 and 0.3 spinel ferrite system.The compositional dependence of lattice constant values suggested that the most of the substituted Si4+-ions reside at grain boundaries and only a few Si-ions are inside grains.The variation ofδ_(ac)(x,f,T)is explained on the basis of segregation and diffusion of Si4+ions at grain boundaries and grains,respectively,and the electrode effect.Thermal variation of ac conductivity at fixed frequency suggested two different mechanisms which could be responsible for conduction in the system.It is found that δ*is not the preferred presentation for dielectric data and the scaling process of real part of conductivity by normalized frequency and the scaled frequency were found unsuccessful.The fitting results of ac conductivity data with path percolation approximation were found suitable in low-frequency regime while in high-frequency regime,effective medium approximation(EMA)was found successful.展开更多
Monophasic and polycrystalline double perovskite Eu_(2)CoMnO_(6)has been synthesized,and its structural characterization,fre-quency and temperature-dependent dielectric relaxation have been studied.Observed thermally ...Monophasic and polycrystalline double perovskite Eu_(2)CoMnO_(6)has been synthesized,and its structural characterization,fre-quency and temperature-dependent dielectric relaxation have been studied.Observed thermally activated dielectric relaxation was explained using the empirical Havriliak-Negami(HN)dielectric relaxation function with an estimated activation energy E~0.22 eV and attempt frequency f0~2.46×10^(9)Hz.The frequency-dependent AC conductivity data,over a wide range of tempera-ture(100-325 K),followed the empirical universal power law behavior(~f n,n is the constant exponent)showing two different frequency exponents,respectively,in the high-and low-temperature regions.The high-temperature(>275 K)conductivity data followed the continuous time random walk(CTRW)approximation model proposed by Dyre.However,this model failed to repro-duce the observed conductivity spectra in the low-temperature side(<200 K).Interestingly,both the high-and low-temperatures’conductivity data can be scaled to the master curve with suitably chosen scaling parameters.展开更多
The polyaniline/copper oxide(PANI/CuO)nanocomposite was prepared by mixing solutions of polyaniline and copper oxide nanoparticles in dimethyl sulfoxide(DMSO).The synthesized polymer nanocomposites were characterized ...The polyaniline/copper oxide(PANI/CuO)nanocomposite was prepared by mixing solutions of polyaniline and copper oxide nanoparticles in dimethyl sulfoxide(DMSO).The synthesized polymer nanocomposites were characterized by X-ray powder diffraction(XRD),scanning electron microscope(SEM)and UV-visible spectroscopy.The characteristic peaks in XRD and UV-visible spectra confirmed the presence of CuO in the polymer structure.SEM images indicated morphological changes in the composite matrix as compared to the pristine PANI.The DC conductivity measurements were performed using two-probe method for various temperatures.AC conductivity and dielectric response of the composites were investigated in the frequency range of 10^(2)-10^(6)Hz using LCR meter.Dielectric permittivityε′(w)and dielectric loss factorε″(w)were investigated.It was observed thatε′(w)andε″(w)decrease with increase in frequency at all temperatures.At a particular frequency it is observed that bothε′(w)andε″(w)increase with increase in temperature.It was also observed that AC conductivity increased with increase in frequency and temperature.展开更多
This paper presents a model to describe alternating current （AC） conductivity of DNA sequences, in which DNA is considered as a one-dimensional （1D） disordered system, and electrons transport via hopping between l...This paper presents a model to describe alternating current （AC） conductivity of DNA sequences, in which DNA is considered as a one-dimensional （1D） disordered system, and electrons transport via hopping between localized states. It finds that AC conductivity in DNA sequences increases as the frequency of the external electric field rises, and it takes the form of σac（ω） - ω2 ln^2（1/ω）. Also AC conductivity of DNA sequences increases with the increase of temperature, this phenomenon presents characteristics of weak temperature-dependence. Meanwhile, the AC conductivity in an offdiagonally correlated case is much larger than that in the uncorrelated case of the Anderson limit in low temperatures, which indicates that the off-diagonal correlations in DNA sequences have a great effect on the AC conductivity, while at high temperature the off-diagonal correlations no longer play a vital role in electric transport. In addition, the proportion of nucleotide pairs p also plays an important role in AC electron transport of DNA sequences. For p 〈 0.5, the conductivity of DNA sequence decreases with the increase of p, while for p ≥ 0.5, the conductivity increases with the increase of p.展开更多
This work explores the dielectric and electrochemical properties of solid biopolymer blend electrolytes(SBEs)based on a combination of alginate and polyvinyl alcohol(PVA),doped with varying concentrations of ammonium ...This work explores the dielectric and electrochemical properties of solid biopolymer blend electrolytes(SBEs)based on a combination of alginate and polyvinyl alcohol(PVA),doped with varying concentrations of ammonium iodide(NH4I).The SBEs were synthesized using the solution casting method,and their ac conductivity exhibited an optimal value of 1.01×10^(-5) S·cm^(-1) at 25 wt.%NH4I.Detailed dielectric and modulus spectroscopy analyses revealed distinctive trends in relation to NH4I concentration,suggesting complex dielectric relaxation behavior.The universal power law(UPL)analysis identified the Small Polaron Hopping(SPH)mechanism as the dominant conduction process in the optimal sample.These results demonstrate that NH4I-doped alginate-PVA SBEs possess favorable electrochemical properties,positioning them as potential candidates for energy storage and ionic transport devices.展开更多
Alternating current（AC） conductivity and dielectric properties of thermally evaporated Au/Pt OEP/Au thin films are investigated each as a function of temperature（303 K–473 K） and frequency（50 Hz–5 MHz）.The fre...Alternating current（AC） conductivity and dielectric properties of thermally evaporated Au/Pt OEP/Au thin films are investigated each as a function of temperature（303 K–473 K） and frequency（50 Hz–5 MHz）.The frequency dependence of AC conductivity follows the Jonscher universal dynamic law.The AC-activation energies are determined at different frequencies.It is found that the correlated barrier hopping（CBH） model is the dominant conduction mechanism.The variation of the frequency exponent s with temperature is analyzed in terms of the CBH model.Coulombic barrier height Wm,hopping distance Rω,and the density of localized states N（EF） are valued at different frequencies.Dielectric constant ε1（ω,T） and dielectric loss ε2（ω,T） are discussed in terms of the dielectric polarization process.The dielectric modulus shows the non-Debye relaxation in the material.The extracted relaxation time by using the imaginary part of modulus（M’’）is found to follow the Arrhenius law.展开更多
CuO nanoparticles were synthesized by aqueous precipitation method and CuO doped PVA nanocomposites (1 wt, 2 wt, 3 wt, 4 wt and 5 wt) were prepared by solution casting method. The pellets of CuO nanoparticles and film...CuO nanoparticles were synthesized by aqueous precipitation method and CuO doped PVA nanocomposites (1 wt, 2 wt, 3 wt, 4 wt and 5 wt) were prepared by solution casting method. The pellets of CuO nanoparticles and films of CuO doped PVA nanocomposites were used for electrical studies in the frequency range of 50 Hz to 5 MHz and in the temperature range of 303 to 338 K. The dielectric constant decreases while the AC electrical conductivity increases with increasing frequency and also with increase in temperature. XRD study confirms the crystalline nature of CuO nanoparticles and the average crystallite size is found to be around 8 nm. The peak widths in XRD pattern of PVA-CuO nanocomposites are broadened by incremental addition of CuO nanomaterials which implies an increase in the amorphous character of PVA-CuO nanocomposites that result in greater ionic diffusivity and high ionic conductivity. It is clear from UV-Vis spectral analysis that, increase in CuO concentration decreases the optical band gap from 4.978 eV to 3.03 eV. The FTIR (3700 - 650 cm<sup>-1</sup>) spectra of nanocomposite films are observed with changes by the addition of CuO nanomaterials.展开更多
Fibers reinforced composite materials offer a combination of strength and modulus that are either comparable to or better than many traditional metallic materials.The research on natural fiber based composite material...Fibers reinforced composite materials offer a combination of strength and modulus that are either comparable to or better than many traditional metallic materials.The research on natural fiber based composite materials fit well into this ecological image.This paper reports the conduction mechanism and ac conductivity,activation energy behavior of Polypropylene and banana fiber reinforced thermoplastic composites.Polypropylene[-CH_(2)-CH_(2)-CH_(2)-]n and different fiber content(wt.%)of polypropylene-banana fibers(natural fiber)composites were fabricated using a hot-press molding system.The optimum fabrication parameters were established(initial pressure,temp.etc.).These composite test samples were fabricated so the short fibers were randomly oriented in the matrix.The detail investigation of the a.c.conductivity and conduction mechanism of polymer composites would provide information about the relaxation processes,activation energy etc.which are dependent on frequency,temperature and time.The activation energy involved in the above processes can also be estimated from this study.The measurements were performed over a wide range of frequency of 60 Hz to 3 MHz and temperature range from 30℃(303°K)to 110℃(383°K).Experimental results of the ac properties of pure polypropylene and polypropylene-natural banana fiber composites were compared.It has been established that the fabricated composition changes its insulating property after adding the natural fibers and gives the better conductivity properties.展开更多
The frequency and temperature dependent electrical conductivity measurements for heat-treated binary glass system with composition of （lO0-x）Bi203-xBaTi03 （x = 20, 30, 40 and 50, in mol%） were carried out. The gla...The frequency and temperature dependent electrical conductivity measurements for heat-treated binary glass system with composition of （lO0-x）Bi203-xBaTi03 （x = 20, 30, 40 and 50, in mol%） were carried out. The glass was prepared by melt quenching technique and their corresponding glass-ceramic nanocomposites were obtained by suitable heat treatment. Nanostructured behavior and electrical properties of these glasses and their corresponding glass-ceramic nanocomposites were studied. X-ray diffraction （XRD） and differential scanning calorimetry confirmed the amorphous nature of the glasses. Moreover, XRD patterns of the samples indicate nanocrystallites embedded in the glass matrix. The Fourier transform infrared spectroscopy （FT-IR） spectral analysis showed that the band positions of glass system are within the wave number range of Bi06, Bi03 and Ti06 structural units. It is observed that the electrical conductivity is enhanced by 102-103 times in the transparent glass-ceramic nanocomposite phase. With further heat treatment, the conductivity decreased considerably in the stage of glass-ceramic nanocomposite phase as compared with the glassy phase sample. Therefore, partially devitrified phase is more suitable as cathode material in secondary batteries compared to its vitreous or fully crystalline counterpart. The conduction mechanism was confirmed to obey the adiabatic small polaron hopping （SPH）. AC conductivity measurements were performed as a function of temperature and frequency, showing a very slow increasing rate at low temperatures and then a fast rate at higher temperatures.展开更多
In the present paper,by applying the Lang-Firsov canonical transformation and the so-called non-crossingapproximation technique,we investigate the joint effects of the electron-phonon interaction and an external alter...In the present paper,by applying the Lang-Firsov canonical transformation and the so-called non-crossingapproximation technique,we investigate the joint effects of the electron-phonon interaction and an external alternatinggate voltage on the transport of a quantum dot system in the Kondo regime.We find that,while the satellite Kondoresonant peaks appear in both the averaged local density of states and the differential conductance,the main Kondopeak at the Fermi energy is greatly suppressed.These results confirm the previous ones derived by other methods,suchas the equation of motion solution.Furthermore,based on the picture of virtual transition between quasi-eigenstates inthe system,we also give a slightly different explanation on these phenomena.展开更多
The main focus of this work is to study the effect of the ionic radius of different rare earth dopant cations RE^(3+)(RE=La,Sm,Dy,and Ho) on structural and various physical properties of sodium bismuth titanate(Na_(0....The main focus of this work is to study the effect of the ionic radius of different rare earth dopant cations RE^(3+)(RE=La,Sm,Dy,and Ho) on structural and various physical properties of sodium bismuth titanate(Na_(0.5)B_(0.5)TiO_(3),NBT) based perovskite nanomaterials.The X-ray diffraction data indicate the successful formation of the rhombohedral phase(space group R3c) of NBT nano perovskite incorporated with various rare earth ions in Bi-site.The lattice parameters were found to increase linearly with the ionic radius of the dopant cation.The ionic radii and atomic mass of rare earth dopants appear to be essential factors in the grain growth of the prepared compositions.The grain growth results in better crystallinity of the sample by reducing the microstrain with the increase of dopant ionic radius.Field emission scanning electron microscopy and energy-dispersive X-ray spectra confirm the prepared compositions' phase purity and stoichiometry.The UV-Vis spectra reveal that La-doped NBT composition exhibits the lowest optical band gap,which unfolds the application of NBT-based perovskite as photoactive material.The ac conductivity and complex impedance spectra unveil that the composition with the largest ionic radius,i.e.,La-doped NBT compound,exhibits the highest dc and bulk conductivity with the lowest activation energy.The frequency-dependent dielectric data follows Havriliak-Negami(HN) formalism and non-Debye type relaxation phenomena.Results also indicate that La-doped NBT composition exhibits the highest dielectric strength value.Thus,this study first elaborates that the increasing ionic radius of the rare earth dopant cation in the Bi-site of NBT perovskite improves its microstructural,optical,and electrical properties.展开更多
In the current study,the calcium copper titanate(CCTO)/epoxy,barium titanate(BT)/epoxy and CCTO-BT/epoxy composite samples with variable volume fractions of CCTO and BT are fabricated using hand lay-up and compression...In the current study,the calcium copper titanate(CCTO)/epoxy,barium titanate(BT)/epoxy and CCTO-BT/epoxy composite samples with variable volume fractions of CCTO and BT are fabricated using hand lay-up and compression moulding process. The composite samples are characterized for the frequency dependence on dielectric properties,conductivity,impedance spectroscopy and electrical modulus.X-ray diffraction(XRD)representation of CCTO-BT/epoxy composite samples confirmed the presence of both CCTO and BT ceramic samples separately. The dielectric characteristics of hybrid CCTO-BT/epoxy composite samples with CCTO∶BT ratio of 40∶60, 60∶40,and 50∶50 was found relatively better than those of single ceramic filler reinforced epoxy composites. AC conductivity analysis shows improvement in the results of hybrid filler-filled CCTO-BT/epoxy composites in comparison with single filler-filled epoxy composite.50∶50 CCTO-BT/epoxy composite shows the best AC conductivity value of~ 2.2 ×10^(-5) ohm^(-1)·m^(-1) at a higher frequency of 1MHz. The impedance analysis confirms the higher insulating properties for hybrid 40∶60 and 60∶40 CCTO-BT/epoxy composites with respect to the single and other hybrid ceramic epoxy composites. The analysis suggests the hybrid CCTO-BT/epoxy composites to be adopted as a potential dielectric material for energy storage devices and other electronic applications.展开更多
We construct a doped holographic superconductor in the Gubser–Rocha model,and realize a superconducting dome in the middle of the temperature-doping phase diagram.It is worth noting that unlike in previous research,t...We construct a doped holographic superconductor in the Gubser–Rocha model,and realize a superconducting dome in the middle of the temperature-doping phase diagram.It is worth noting that unlike in previous research,the profile of our dome shrinks inward near to zero temperature.From the numerical observation for the coupling dependence of the phase diagram,we find that the coupling between the two gauge fields plays a crucial role in the formation of the dome.We also analytically calculate the DC conductivity of the normal phase of the system in the momentum dissipation and obtain resistivity which is proportional to the temperature.The AC conductivity is calculated numerically.展开更多
Gadolinium doped Zinc oxide (Zn<sub>1–x</sub>GdxO) nanocrystals with different percentage of Gd content (x = 0, 0.2, 0.4, 0.6, 0.8) have been prepared by the solid state reaction method. The structural, m...Gadolinium doped Zinc oxide (Zn<sub>1–x</sub>GdxO) nanocrystals with different percentage of Gd content (x = 0, 0.2, 0.4, 0.6, 0.8) have been prepared by the solid state reaction method. The structural, mor-phological and chemical studies of the samples were performed by X-ray diffraction (XRD), Scanning electron microscope (SEM) and Energy dispersive X-ray (EDX) analysis. The XRD spectra confirm that all the samples have hexagonal wurtzite structure. Decrease in average crystallite size with an increase in Gd concentration is observed in XRD. SEM images show that the grain size of undoped ZnO is larger than the Gd doped ZnO, specifying the hindrance of grain growth upon Gd doping. The chemical composition of the samples was confirmed using Energy dispersive X-ray (EDX) analysis. The variation of dielectric constant (ε<sub>r</sub>), dielectric loss (tan δ) and AC conductivity as a function of frequency is studied at room temperature in a frequency which ranges from 100 Hz - 4.5 MHz by using LCR Hi TESTER. All the samples exhibit the normal dielectric behavior, i.e. decreases with increase in frequency which has been explained in the light of Maxwell-Wagner model. The dielectric constant and dielectric loss can be varied intensely by tuning Gd concentration in Zn<sub>1–x</sub>Gd<sub>x</sub>O compounds.展开更多
The series of Cr-Zn nano ferrites having the general composition Cr<sub>x</sub>ZnFe<sub>2-x</sub>O<sub>4</sub> (0 ≤ x ≤ 0.5) have been synthesized successfully in the nanocrystall...The series of Cr-Zn nano ferrites having the general composition Cr<sub>x</sub>ZnFe<sub>2-x</sub>O<sub>4</sub> (0 ≤ x ≤ 0.5) have been synthesized successfully in the nanocrystalline form using the sol-gel method. The samples were sintered at 900°C for 3 hours. The effect of chromium substitution on dielectric properties of Zn-ferrites is reported in this paper. The analysis of XRD patterns revealed the formation of single phase cubic spinel structure for all the Cr-Zn ferrite samples. The FTIR spectra show two strong absorption bands in the range of 400 - 600 cm<sup>-1</sup>, which corroborate the spinel structure of the samples. The average grain size was found to be in the nanometer range and of the order of 43 - 63 nm obtained using TEM images. The lattice parameter and crystallite size decrease with increase in Cr concentration (x). The investigation on dielectric constant (ε'), dissipation factor (D) and ac conductivity (σ<sub>ac</sub>) was carried out at a fixed frequency 1 kHz and in the frequency range of 100 Hz to 1 MHz at room temperature using LCR meter. The plots of dielectric constant (ε') versus frequency show the normal dielectric behavior of spinel ferrites. The value of ac conductivity (σ<sub>ac</sub>) increases with increase in frequency for all the compositions. The appearance of the peak for each composition in the dissipation factor versus frequency curve suggests the presence of relaxing dipoles in the Cr-Zn nano ferrite samples. It is also found that the shifting of the relaxation peak towards lower frequency side with an increase in chromium content (x) is due to the strengthening of dipole-dipole interactions. The composition and frequency dependence of the dielectric constant, dielectric loss and ac-conductivity are explained based on the Koop’s two-layer model, Maxwell-Wagner polarization process, and Debye relaxation theory.展开更多
Frequency and temperature dependent dielectric dispersion of 20PbF2？20TeO2？（60？x）B2O3？xEu2O3（x=0 to 2.5, mole fraction, %） glasses prepared by the melt？quenching technique were investigated in the frequency r...Frequency and temperature dependent dielectric dispersion of 20PbF2？20TeO2？（60？x）B2O3？xEu2O3（x=0 to 2.5, mole fraction, %） glasses prepared by the melt？quenching technique were investigated in the frequency range 1 Hz？10 MHz and temperature range 313？773 K. Dielectric relaxation dynamics was analyzed based on the electric modulus behavior. Dielectric losses （tanδ） are found to be negligibly small in the temperature range 313？523 K, proving good thermal stability of the glasses. The present Eu2O3-doped oxyfluroborate glasses showed low dielectric loss at higher frequency and lower temperature, proving their suitability for nonlinear optical materials.展开更多
For this study,we synthesized Aurivillius Bi_(5)Ti_(3)FeO_(15) ceramic using the generic solid-state reaction route and then performed roomtemperature X-ray diffraction to confirm that the compound had a single phase ...For this study,we synthesized Aurivillius Bi_(5)Ti_(3)FeO_(15) ceramic using the generic solid-state reaction route and then performed roomtemperature X-ray diffraction to confirm that the compound had a single phase with no impurities.The surface morphology of the prepared sample was observed to contain microstructural grains approximately 0.2–2μm in size.The dielectric properties of the sample were determined as a function of frequency in a range of approximately 100 Hz to 1 MHz at various temperatures(303 K≤T≤773 K).Nyquist plots of the impedance data were found to exhibit a semi-circular arc in the high-temperature region,which is explained by the equivalent electrical circuit(R_(1)C_(1))(R_(2)QC_(2)),where R_(1) and R_(2) represent the resistances associated with the grains and grain boundaries,respectively,C_(1) and C_(2) are the respective capacitances,and Q is the constant phase element(CPE),which accounts for non-Debye type of behavior.Our results indicate that both the resistance and capacitance of the grain boundaries are more prominent than those of the grains.The alternating current(ac)conductivity data were analyzed based on the Jonscher universal power law,which indicated that the conduction process is dominated by the hopping mechanism.The calculated activation energies of the relaxation and conduction processes were very similar(0.32 to 0.53 eV),from which we conclude that the same type of charge carriers are involved in both processes.展开更多
文摘BaxSr1-xTiO3 sol-gel thin films with x--0.5, 0.7 and 0.8 have been fabricated as AI/BST/Pt capacitor. The AC conductivity and dielectric properties over a frequency rang of 10 Hz and I MHz have been studied in order to explore the ion dynamics and relaxation mechanisms in the films. The frequency dependent conductivity plots show three regions of conduction processes. Dielectric results show that ε＇ at low frequencies increases as Sr content decreases, whereas at high frequencies, it shows opposite variation, which is attributed to the dipole dynamics. The electric modulus plots reveal the relaxation peaks which are not observed in the ε＂ plots and the contribution of the grains, grain boundaries and electrode to the relaxation mechanisms.
文摘The ac conductivity of the bulk amorphous chalcogenide system (As2Te3)100-xGex (where x=0,5,10,15 and 25 at. pct) was investigated at variable frequencies ranging from 50 Hz to 100 kHz and at different temperatures ranging from 3O to 160℃. lt was found that at a fixed temperature, where n <1 and decreases with temperature. The complex impedence Z was measured over the same frequency and temperature ranges. All samples give a semicircle arc originating at the origin point. This indicates that each composition can be described only by one resistance R and one capacity C, both parallelly combined. The centre below the real axis indicates the relaxation behaviour of the system. The activation energies for conduction were calculated.
文摘Lead free(K_(0.5)Na_(0.5))NbO_(3)(KNN)ceramics were prepared by conventional solid state reaction route.For single perovskite phase formation,calcination temperature was optimized at 850℃for 6h,whereas for dense morphology the sintering of the ceramic was carried out at 1120℃for 4h.X-ray diffraction XRD analysis confirmed the formation of single phase with orthorhombic structure at room temperature.Impedance analysis and AC conductivity studies of the KNN sample was carried out in the temperature range of 703-773 K.Impedance study showed the increase in conducting behavior at higher temperature.The temperature dependence of AC conductivity indicated that the conduction process is due to doubly ionized oxygen vacancies in the higher temperature region.
基金New Delhi for supporting the work under Major Research Project scheme and Dr.D.S.Kothari Post Doctoral Fellowship,respectively(2015-2018).
文摘The compositional dependence of ac conductivity(δac),real(δ′)and imaginary(δ′′)parts of complex electric conductivity(δ*)was investigated as a function of temperature(T)and frequency(f) for Mn_(0.7+x)Zn_(0.3)Si_(x)Fe_(2-2x)O_(4),x=0.0,0.1,0.2 and 0.3 spinel ferrite system.The compositional dependence of lattice constant values suggested that the most of the substituted Si4+-ions reside at grain boundaries and only a few Si-ions are inside grains.The variation ofδ_(ac)(x,f,T)is explained on the basis of segregation and diffusion of Si4+ions at grain boundaries and grains,respectively,and the electrode effect.Thermal variation of ac conductivity at fixed frequency suggested two different mechanisms which could be responsible for conduction in the system.It is found that δ*is not the preferred presentation for dielectric data and the scaling process of real part of conductivity by normalized frequency and the scaled frequency were found unsuccessful.The fitting results of ac conductivity data with path percolation approximation were found suitable in low-frequency regime while in high-frequency regime,effective medium approximation(EMA)was found successful.
文摘Monophasic and polycrystalline double perovskite Eu_(2)CoMnO_(6)has been synthesized,and its structural characterization,fre-quency and temperature-dependent dielectric relaxation have been studied.Observed thermally activated dielectric relaxation was explained using the empirical Havriliak-Negami(HN)dielectric relaxation function with an estimated activation energy E~0.22 eV and attempt frequency f0~2.46×10^(9)Hz.The frequency-dependent AC conductivity data,over a wide range of tempera-ture(100-325 K),followed the empirical universal power law behavior(~f n,n is the constant exponent)showing two different frequency exponents,respectively,in the high-and low-temperature regions.The high-temperature(>275 K)conductivity data followed the continuous time random walk(CTRW)approximation model proposed by Dyre.However,this model failed to repro-duce the observed conductivity spectra in the low-temperature side(<200 K).Interestingly,both the high-and low-temperatures’conductivity data can be scaled to the master curve with suitably chosen scaling parameters.
基金supported by SERO-UGC(India),No.MRP5883/15,under the Minor Research Project Scheme.
文摘The polyaniline/copper oxide(PANI/CuO)nanocomposite was prepared by mixing solutions of polyaniline and copper oxide nanoparticles in dimethyl sulfoxide(DMSO).The synthesized polymer nanocomposites were characterized by X-ray powder diffraction(XRD),scanning electron microscope(SEM)and UV-visible spectroscopy.The characteristic peaks in XRD and UV-visible spectra confirmed the presence of CuO in the polymer structure.SEM images indicated morphological changes in the composite matrix as compared to the pristine PANI.The DC conductivity measurements were performed using two-probe method for various temperatures.AC conductivity and dielectric response of the composites were investigated in the frequency range of 10^(2)-10^(6)Hz using LCR meter.Dielectric permittivityε′(w)and dielectric loss factorε″(w)were investigated.It was observed thatε′(w)andε″(w)decrease with increase in frequency at all temperatures.At a particular frequency it is observed that bothε′(w)andε″(w)increase with increase in temperature.It was also observed that AC conductivity increased with increase in frequency and temperature.
基金supported by the Doctoral Program Foundation of Institutions of Higher Education,China (Grant No 20070533075)
文摘This paper presents a model to describe alternating current （AC） conductivity of DNA sequences, in which DNA is considered as a one-dimensional （1D） disordered system, and electrons transport via hopping between localized states. It finds that AC conductivity in DNA sequences increases as the frequency of the external electric field rises, and it takes the form of σac（ω） - ω2 ln^2（1/ω）. Also AC conductivity of DNA sequences increases with the increase of temperature, this phenomenon presents characteristics of weak temperature-dependence. Meanwhile, the AC conductivity in an offdiagonally correlated case is much larger than that in the uncorrelated case of the Anderson limit in low temperatures, which indicates that the off-diagonal correlations in DNA sequences have a great effect on the AC conductivity, while at high temperature the off-diagonal correlations no longer play a vital role in electric transport. In addition, the proportion of nucleotide pairs p also plays an important role in AC electron transport of DNA sequences. For p 〈 0.5, the conductivity of DNA sequence decreases with the increase of p, while for p ≥ 0.5, the conductivity increases with the increase of p.
基金University Malaysia Pahang Al-Sultan Abdullah(UMPSA)under the UMPSA Distinguish Grant(RDU233001)Ministry of Higher Education Malaysia(MOHE)under the FRGS fund(FRGS/1/2023/STG05/UMP/02/2).
文摘This work explores the dielectric and electrochemical properties of solid biopolymer blend electrolytes(SBEs)based on a combination of alginate and polyvinyl alcohol(PVA),doped with varying concentrations of ammonium iodide(NH4I).The SBEs were synthesized using the solution casting method,and their ac conductivity exhibited an optimal value of 1.01×10^(-5) S·cm^(-1) at 25 wt.%NH4I.Detailed dielectric and modulus spectroscopy analyses revealed distinctive trends in relation to NH4I concentration,suggesting complex dielectric relaxation behavior.The universal power law(UPL)analysis identified the Small Polaron Hopping(SPH)mechanism as the dominant conduction process in the optimal sample.These results demonstrate that NH4I-doped alginate-PVA SBEs possess favorable electrochemical properties,positioning them as potential candidates for energy storage and ionic transport devices.
文摘Alternating current（AC） conductivity and dielectric properties of thermally evaporated Au/Pt OEP/Au thin films are investigated each as a function of temperature（303 K–473 K） and frequency（50 Hz–5 MHz）.The frequency dependence of AC conductivity follows the Jonscher universal dynamic law.The AC-activation energies are determined at different frequencies.It is found that the correlated barrier hopping（CBH） model is the dominant conduction mechanism.The variation of the frequency exponent s with temperature is analyzed in terms of the CBH model.Coulombic barrier height Wm,hopping distance Rω,and the density of localized states N（EF） are valued at different frequencies.Dielectric constant ε1（ω,T） and dielectric loss ε2（ω,T） are discussed in terms of the dielectric polarization process.The dielectric modulus shows the non-Debye relaxation in the material.The extracted relaxation time by using the imaginary part of modulus（M’’）is found to follow the Arrhenius law.
文摘CuO nanoparticles were synthesized by aqueous precipitation method and CuO doped PVA nanocomposites (1 wt, 2 wt, 3 wt, 4 wt and 5 wt) were prepared by solution casting method. The pellets of CuO nanoparticles and films of CuO doped PVA nanocomposites were used for electrical studies in the frequency range of 50 Hz to 5 MHz and in the temperature range of 303 to 338 K. The dielectric constant decreases while the AC electrical conductivity increases with increasing frequency and also with increase in temperature. XRD study confirms the crystalline nature of CuO nanoparticles and the average crystallite size is found to be around 8 nm. The peak widths in XRD pattern of PVA-CuO nanocomposites are broadened by incremental addition of CuO nanomaterials which implies an increase in the amorphous character of PVA-CuO nanocomposites that result in greater ionic diffusivity and high ionic conductivity. It is clear from UV-Vis spectral analysis that, increase in CuO concentration decreases the optical band gap from 4.978 eV to 3.03 eV. The FTIR (3700 - 650 cm<sup>-1</sup>) spectra of nanocomposite films are observed with changes by the addition of CuO nanomaterials.
文摘Fibers reinforced composite materials offer a combination of strength and modulus that are either comparable to or better than many traditional metallic materials.The research on natural fiber based composite materials fit well into this ecological image.This paper reports the conduction mechanism and ac conductivity,activation energy behavior of Polypropylene and banana fiber reinforced thermoplastic composites.Polypropylene[-CH_(2)-CH_(2)-CH_(2)-]n and different fiber content(wt.%)of polypropylene-banana fibers(natural fiber)composites were fabricated using a hot-press molding system.The optimum fabrication parameters were established(initial pressure,temp.etc.).These composite test samples were fabricated so the short fibers were randomly oriented in the matrix.The detail investigation of the a.c.conductivity and conduction mechanism of polymer composites would provide information about the relaxation processes,activation energy etc.which are dependent on frequency,temperature and time.The activation energy involved in the above processes can also be estimated from this study.The measurements were performed over a wide range of frequency of 60 Hz to 3 MHz and temperature range from 30℃(303°K)to 110℃(383°K).Experimental results of the ac properties of pure polypropylene and polypropylene-natural banana fiber composites were compared.It has been established that the fabricated composition changes its insulating property after adding the natural fibers and gives the better conductivity properties.
文摘The frequency and temperature dependent electrical conductivity measurements for heat-treated binary glass system with composition of （lO0-x）Bi203-xBaTi03 （x = 20, 30, 40 and 50, in mol%） were carried out. The glass was prepared by melt quenching technique and their corresponding glass-ceramic nanocomposites were obtained by suitable heat treatment. Nanostructured behavior and electrical properties of these glasses and their corresponding glass-ceramic nanocomposites were studied. X-ray diffraction （XRD） and differential scanning calorimetry confirmed the amorphous nature of the glasses. Moreover, XRD patterns of the samples indicate nanocrystallites embedded in the glass matrix. The Fourier transform infrared spectroscopy （FT-IR） spectral analysis showed that the band positions of glass system are within the wave number range of Bi06, Bi03 and Ti06 structural units. It is observed that the electrical conductivity is enhanced by 102-103 times in the transparent glass-ceramic nanocomposite phase. With further heat treatment, the conductivity decreased considerably in the stage of glass-ceramic nanocomposite phase as compared with the glassy phase sample. Therefore, partially devitrified phase is more suitable as cathode material in secondary batteries compared to its vitreous or fully crystalline counterpart. The conduction mechanism was confirmed to obey the adiabatic small polaron hopping （SPH）. AC conductivity measurements were performed as a function of temperature and frequency, showing a very slow increasing rate at low temperatures and then a fast rate at higher temperatures.
文摘In the present paper,by applying the Lang-Firsov canonical transformation and the so-called non-crossingapproximation technique,we investigate the joint effects of the electron-phonon interaction and an external alternatinggate voltage on the transport of a quantum dot system in the Kondo regime.We find that,while the satellite Kondoresonant peaks appear in both the averaged local density of states and the differential conductance,the main Kondopeak at the Fermi energy is greatly suppressed.These results confirm the previous ones derived by other methods,suchas the equation of motion solution.Furthermore,based on the picture of virtual transition between quasi-eigenstates inthe system,we also give a slightly different explanation on these phenomena.
基金Project supported by the Science and Engineering Research Board(SERB)(Govt.of India)(EMR/2017/000325)。
文摘The main focus of this work is to study the effect of the ionic radius of different rare earth dopant cations RE^(3+)(RE=La,Sm,Dy,and Ho) on structural and various physical properties of sodium bismuth titanate(Na_(0.5)B_(0.5)TiO_(3),NBT) based perovskite nanomaterials.The X-ray diffraction data indicate the successful formation of the rhombohedral phase(space group R3c) of NBT nano perovskite incorporated with various rare earth ions in Bi-site.The lattice parameters were found to increase linearly with the ionic radius of the dopant cation.The ionic radii and atomic mass of rare earth dopants appear to be essential factors in the grain growth of the prepared compositions.The grain growth results in better crystallinity of the sample by reducing the microstrain with the increase of dopant ionic radius.Field emission scanning electron microscopy and energy-dispersive X-ray spectra confirm the prepared compositions' phase purity and stoichiometry.The UV-Vis spectra reveal that La-doped NBT composition exhibits the lowest optical band gap,which unfolds the application of NBT-based perovskite as photoactive material.The ac conductivity and complex impedance spectra unveil that the composition with the largest ionic radius,i.e.,La-doped NBT compound,exhibits the highest dc and bulk conductivity with the lowest activation energy.The frequency-dependent dielectric data follows Havriliak-Negami(HN) formalism and non-Debye type relaxation phenomena.Results also indicate that La-doped NBT composition exhibits the highest dielectric strength value.Thus,this study first elaborates that the increasing ionic radius of the rare earth dopant cation in the Bi-site of NBT perovskite improves its microstructural,optical,and electrical properties.
文摘In the current study,the calcium copper titanate(CCTO)/epoxy,barium titanate(BT)/epoxy and CCTO-BT/epoxy composite samples with variable volume fractions of CCTO and BT are fabricated using hand lay-up and compression moulding process. The composite samples are characterized for the frequency dependence on dielectric properties,conductivity,impedance spectroscopy and electrical modulus.X-ray diffraction(XRD)representation of CCTO-BT/epoxy composite samples confirmed the presence of both CCTO and BT ceramic samples separately. The dielectric characteristics of hybrid CCTO-BT/epoxy composite samples with CCTO∶BT ratio of 40∶60, 60∶40,and 50∶50 was found relatively better than those of single ceramic filler reinforced epoxy composites. AC conductivity analysis shows improvement in the results of hybrid filler-filled CCTO-BT/epoxy composites in comparison with single filler-filled epoxy composite.50∶50 CCTO-BT/epoxy composite shows the best AC conductivity value of~ 2.2 ×10^(-5) ohm^(-1)·m^(-1) at a higher frequency of 1MHz. The impedance analysis confirms the higher insulating properties for hybrid 40∶60 and 60∶40 CCTO-BT/epoxy composites with respect to the single and other hybrid ceramic epoxy composites. The analysis suggests the hybrid CCTO-BT/epoxy composites to be adopted as a potential dielectric material for energy storage devices and other electronic applications.
基金supported by the National Natural Science Foundation of China(Grant Nos.12275166,11875184,12147158 and 11805117)the NFSC-NFR joint program 12311540141.
文摘We construct a doped holographic superconductor in the Gubser–Rocha model,and realize a superconducting dome in the middle of the temperature-doping phase diagram.It is worth noting that unlike in previous research,the profile of our dome shrinks inward near to zero temperature.From the numerical observation for the coupling dependence of the phase diagram,we find that the coupling between the two gauge fields plays a crucial role in the formation of the dome.We also analytically calculate the DC conductivity of the normal phase of the system in the momentum dissipation and obtain resistivity which is proportional to the temperature.The AC conductivity is calculated numerically.
文摘Gadolinium doped Zinc oxide (Zn<sub>1–x</sub>GdxO) nanocrystals with different percentage of Gd content (x = 0, 0.2, 0.4, 0.6, 0.8) have been prepared by the solid state reaction method. The structural, mor-phological and chemical studies of the samples were performed by X-ray diffraction (XRD), Scanning electron microscope (SEM) and Energy dispersive X-ray (EDX) analysis. The XRD spectra confirm that all the samples have hexagonal wurtzite structure. Decrease in average crystallite size with an increase in Gd concentration is observed in XRD. SEM images show that the grain size of undoped ZnO is larger than the Gd doped ZnO, specifying the hindrance of grain growth upon Gd doping. The chemical composition of the samples was confirmed using Energy dispersive X-ray (EDX) analysis. The variation of dielectric constant (ε<sub>r</sub>), dielectric loss (tan δ) and AC conductivity as a function of frequency is studied at room temperature in a frequency which ranges from 100 Hz - 4.5 MHz by using LCR Hi TESTER. All the samples exhibit the normal dielectric behavior, i.e. decreases with increase in frequency which has been explained in the light of Maxwell-Wagner model. The dielectric constant and dielectric loss can be varied intensely by tuning Gd concentration in Zn<sub>1–x</sub>Gd<sub>x</sub>O compounds.
文摘The series of Cr-Zn nano ferrites having the general composition Cr<sub>x</sub>ZnFe<sub>2-x</sub>O<sub>4</sub> (0 ≤ x ≤ 0.5) have been synthesized successfully in the nanocrystalline form using the sol-gel method. The samples were sintered at 900°C for 3 hours. The effect of chromium substitution on dielectric properties of Zn-ferrites is reported in this paper. The analysis of XRD patterns revealed the formation of single phase cubic spinel structure for all the Cr-Zn ferrite samples. The FTIR spectra show two strong absorption bands in the range of 400 - 600 cm<sup>-1</sup>, which corroborate the spinel structure of the samples. The average grain size was found to be in the nanometer range and of the order of 43 - 63 nm obtained using TEM images. The lattice parameter and crystallite size decrease with increase in Cr concentration (x). The investigation on dielectric constant (ε'), dissipation factor (D) and ac conductivity (σ<sub>ac</sub>) was carried out at a fixed frequency 1 kHz and in the frequency range of 100 Hz to 1 MHz at room temperature using LCR meter. The plots of dielectric constant (ε') versus frequency show the normal dielectric behavior of spinel ferrites. The value of ac conductivity (σ<sub>ac</sub>) increases with increase in frequency for all the compositions. The appearance of the peak for each composition in the dissipation factor versus frequency curve suggests the presence of relaxing dipoles in the Cr-Zn nano ferrite samples. It is also found that the shifting of the relaxation peak towards lower frequency side with an increase in chromium content (x) is due to the strengthening of dipole-dipole interactions. The composition and frequency dependence of the dielectric constant, dielectric loss and ac-conductivity are explained based on the Koop’s two-layer model, Maxwell-Wagner polarization process, and Debye relaxation theory.
基金supported by a grant-in-aid for a scientific research from the Department of Atomic Energy(DAE)-Board of Research in Nuclear Science[S.No.2012/34/17/BRNS]of the Government of India
文摘Frequency and temperature dependent dielectric dispersion of 20PbF2？20TeO2？（60？x）B2O3？xEu2O3（x=0 to 2.5, mole fraction, %） glasses prepared by the melt？quenching technique were investigated in the frequency range 1 Hz？10 MHz and temperature range 313？773 K. Dielectric relaxation dynamics was analyzed based on the electric modulus behavior. Dielectric losses （tanδ） are found to be negligibly small in the temperature range 313？523 K, proving good thermal stability of the glasses. The present Eu2O3-doped oxyfluroborate glasses showed low dielectric loss at higher frequency and lower temperature, proving their suitability for nonlinear optical materials.
基金Anil Kumar Singh acknowledges the Board of Research in Nuclear Science(BRNS)Mumbai(Sanction No.2012/37P/40/BRNS/2145)+1 种基金the UGC-DAE Consortium for Scientific Research,Mumbai(Sanction No.CRS-M-187,225)the Science and Engineering Research Board(SERB),New Delhi(Sanction No.SR/FTS/PS-187/2011)for funding.
文摘For this study,we synthesized Aurivillius Bi_(5)Ti_(3)FeO_(15) ceramic using the generic solid-state reaction route and then performed roomtemperature X-ray diffraction to confirm that the compound had a single phase with no impurities.The surface morphology of the prepared sample was observed to contain microstructural grains approximately 0.2–2μm in size.The dielectric properties of the sample were determined as a function of frequency in a range of approximately 100 Hz to 1 MHz at various temperatures(303 K≤T≤773 K).Nyquist plots of the impedance data were found to exhibit a semi-circular arc in the high-temperature region,which is explained by the equivalent electrical circuit(R_(1)C_(1))(R_(2)QC_(2)),where R_(1) and R_(2) represent the resistances associated with the grains and grain boundaries,respectively,C_(1) and C_(2) are the respective capacitances,and Q is the constant phase element(CPE),which accounts for non-Debye type of behavior.Our results indicate that both the resistance and capacitance of the grain boundaries are more prominent than those of the grains.The alternating current(ac)conductivity data were analyzed based on the Jonscher universal power law,which indicated that the conduction process is dominated by the hopping mechanism.The calculated activation energies of the relaxation and conduction processes were very similar(0.32 to 0.53 eV),from which we conclude that the same type of charge carriers are involved in both processes.
