共查询到20条相似文献,搜索用时 31 毫秒
1.
The high frequency ionic conductivity of RbAg4I5 single crystals was measured in the range from 0.1 MHz to 8 GHz using a microwave reflection method. In the whole temperature region studied (30°C to 135°C) the bulk conductivity was found to be frequency independent and to coincide with the latest published values for the static conductivity. This result is in contradiction with values reported formerly in literature but agrees very well with recent measurements on the structurally similar solid electrolyte AgI. 相似文献
2.
P. Lunkenheimer G. Knebel A. Pimenov G. A. Emel’chenko A. Loidl 《Zeitschrift für Physik B Condensed Matter》1995,99(4):507-516
The complex conductivity of La2CuO4+δ has been investigated for frequencies 20 Hz≤ν≤4 GHz and temperatures 1.5K≤T≤450 K. Two single crystals with δ≈0 and δ≈0.02 were investigated, using dc (four-probe), reflectometric and contact-free techniques. At high temperatures the dc conductivity is thermally activated with low values of the activation energy. For low temperatures Mott's variable range hopping dominates. The real and imaginary parts of the ac conductivity follow a power-law dependence σ~v s, typical for charge transport by hopping processes. A careful analysis of the temperature dependence of the ac conductivity and of the frequency exponents has been performed. It is not possible to explain all aspects of the ac conductivity in La2CuO4+δ by standart hopping models. However, the observed minimum in the temperature dependence of the frequency exponents strongly suggests tunneling of large polarons as dominant transport process. 相似文献
3.
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
4.
ac Conductivity measurements are carried out across the metal to insulator transition in NiAl0.7Cr0.7Fe0.6O4. The low frequency data is analyzed using Summerfield scaling theory for hopping conductivity. The exponent of the scaling
behavior has significantly different values in the conducting and insulating regimes. The hopping frequency and the zero frequency
conductivity are found to increase with temperature, slowly in the metallic regime and rapidly in the insulating regime. 相似文献
5.
F.E. SalmanN. Shash H. Abou El-HadedM.K. El-Mansy 《Journal of Physics and Chemistry of Solids》2002,63(11):1957-1966
AC conductivity and dielectric studies on vanadium phosphate glasses doped with lithium have been carried out in the frequency range 0.2-100 kHz and temperature range 290-493 K. The frequency dependence of the conductivity at higher frequencies in glasses obeys a power relationship, σac=Aωs. The obtained values of the power s lie in the range 0.5≤s≤1 for both undoped and doped with low lithium content which confirms the electron hopping between V4+ and V5+ ions. For doped glasses with high lithium content, the values of s≤0.5 which confirm the domination of ionic conductivity. The study of frequency dependence of both dielectric constant and dielectric loss showed a decrease with increasing frequency while they increase with increasing temperature. The results have been explained on the basis of frequency assistance of electron hopping besides the ionic polarization of the glasses. The bulk conductivity increases with increasing temperature whereas decreases with increasing lithium content which means a reduction of the V5+. 相似文献
6.
Studies of dielectric relaxation and ac conductivity have been made on three samples of sodium tungsten phosphate glasses over a temperature range of 77–420 K. Complex relative permitivity data have been analyzed using dielectric modulus approach. Conductivity relaxation frequency increases with the increase of temperature. Activation energy for conductivity relaxation has also been evaluated. Measured ac conductivity (σm(ω)) has been found to be higher than σdc at low temperatures whereas at high temperature σm(ω) becomes equal to σdc at all frequencies. The ac conductivity obeys the relation σac(ω)=Aω S over a considerable range of low temperatures. Values of exponent S are nearly equal to unity at about 78 K and the values decrease non-linearly with the increase of temperature. Values of the number density of states at Fermi level (N(E F)) have been evaluated at 80 K assuming values of electron wave function decay constant α to be 0.5 (Å)?1. Values of N(E F) have the order 1020 which are well within the range suggested for localized states. Present values of N(E F) are smaller than those for tungsten phosphate glasses. 相似文献
7.
A novel set of glasses of the type (B2O3)0.10-(P2O5)0.40-(CuO)0.50−x-(MoO3)x, 0.05≤x≥0.50, have been investigated for dielectric properties in the frequency range 100 Hz-100 kHz and temperature range 300-575 K. From the total conductivity derived from the dielectric spectrum the frequency exponent, s, and dc and ac components of the conductivity were determined. The temperature dependence of dc and ac conductivities at different frequencies was analyzed using Mott's small polaron hopping model, and the high temperature activation energies have been estimated and discussed. The observed initial decrease in conductivity (ac and dc) and increase in activation energy with the addition of MoO3 have been understood to be due to the hindrance offered by the Mo+ ions to the electronic motions. The observed peak-like behavior in conductivity (dip-like behavior in activation energy) in the composition range 0.20-0.50 mol fractions of MoO3 may be due to mixed transition effect occurring in the present glasses. The temperature dependence of frequency exponent, s, has been analyzed using different theoretical models. It is for the first time that the mixed transition metal ion (TMI) doped borophosphate glasses have been investigated for dielectric properties and conductivity over wide temperature and frequency ranges and the data have been subjected to a thorough analysis. 相似文献
8.
R.H. ChenS.C. Shern 《Journal of Physics and Chemistry of Solids》2002,63(11):2069-2077
Optical observation under the polarizing microscope and DSC measurements on K3H(SeO4)2 single crystal have been carried out in the temperature range 25-200 °C. It reveals a high-temperature structural phase transition at around 110 °C. The crystal system transformed from monoclinic to trigonal. Electrical impedance measurements of K3H(SeO4)2 were performed as a function of both temperature and frequency. The electrical conduction and dielectric relaxation have been studied. The temperature dependence of electrical conductivity indicates that the sample crystal became a fast ionic conductor in the high-temperature phase. The frequency dependence of conductivity follows the Jonscher's universal dynamic law with the relation σ(ω)=σ(0)+Aωn, where ω is the frequency of the AC field, and n is the exponent. The obtained n values decrease from 1.2 to 0.1 from the room temperature phase to fast ionic phase. The high ionic conductivity in the high-temperature phase is explained by the dynamical disordering of protons between the neighboring SeO4 groups, which provide more vacant sites in the crystal. 相似文献
9.
P. Lunkenheimer G. Knebel A. Pimenov G. A. Emel’chenko A. Loidl 《Zeitschrift für Physik B Condensed Matter》1995,99(1):507-516
The complex conductivity of La2CuO4+δ has been investigated for frequencies 20 Hz≤ν≤4 GHz and temperatures 1.5K≤T≤450 K. Two single crystals with δ≈0 and δ≈0.02
were investigated, using dc (four-probe), reflectometric and contact-free techniques. At high temperatures the dc conductivity
is thermally activated with low values of the activation energy. For low temperatures Mott's variable range hopping dominates.
The real and imaginary parts of the ac conductivity follow a power-law dependence σ∼v
s, typical for charge transport by hopping processes. A careful analysis of the temperature dependence of the ac conductivity
and of the frequency exponents has been performed. It is not possible to explain all aspects of the ac conductivity in La2CuO4+δ by standart hopping models. However, the observed minimum in the temperature dependence of the frequency exponents strongly suggests tunneling of large polarons as dominant transport process. 相似文献
10.
A comparative LiZnVO4 and LiMgVO4 conductivity study was done from room temperature to 500 °C and at frequencies from 42 to 1 MHz. The impact of moisture absorption to the materials’ conductivity was investigated. It was shown for LiZnVO4 that moisture absorption is responsible for the decrease of the compound’s conductivity as the material is heated up to 150 °C. The LiZnVO4 bulk activation energy value was calculated to be 1.20 eV. Two grain boundary activation energy values were calculated for the LiZnVO4, 0.59 eV at the lower temperature range and 1.37 eV at the higher temperature range. An explanation for the existence of these two values was given. Both materials’ plots of the loss factor (tanδ) versus frequency at different temperatures were found to display a peak, and the modulus master curves present a scaling behavior that suggests non Debye type conductivity relaxation and ion migration via hopping. 相似文献
11.
The pyrophosphate K2NiP2O7 has been synthesized by the classic ceramic method and characterized by X-ray diffraction, solid-state 31P magic angle spinning (MAS) NMR, and IR and electrical impedance spectroscopy. The solid-state 31P MAS NMR, performed at 121.49 MHz, shows two isotropic resonances at ?17.66 and ?19.94 ppm, revealing the existence of two phosphorus environments in the structure. The electrical conductivity and dielectric properties have been investigated in the frequency and the temperature range of 200 Hz–1 MHz and 603–728 K, respectively. The frequency dependence of the conductivity is interpreted using the augmented Jonscher relation. The close values of activation energies obtained from the analysis of hopping frequency and dc conductivity imply that the transport is through ion hopping mechanism. The charge carrier concentration in the investigated sample has been evaluated using the Almond–West formalism and shown to be independent of temperature. Thermodynamic parameters such as the free energy of activation ΔF, the enthalpy ΔH, and the change in entropy ΔS have been calculated. 相似文献
12.
We present new insights into the Nearly Constant Loss (NCL) effect, which are based on a study of conductivity as a function of temperature and frequency in 0.3Na2O · 0.7B2O3 and 0.5AgI · 0.5AgPO3 glasses. In these systems, the ionic conductivity has been measured over a temperature range from 4 K to 475 K and in a frequency range from a few mHz to a few MHz. The conductivity spectra taken at various temperatures have then been mapped on to a representation of conductivity versus temperature (or inverse temperature) at fixed frequency. Indeed, such plots are often published in studies of the NCL effect. For a given system and a given frequency, an equivalent mapping is achieved by using suitable scaled model conductivity spectra derived from the MIGRATION concept. This enables us to identify, at fixed frequency, the temperature of transition from the ionic conductivity caused by the “ordinary” correlated hopping motion of the mobile ions (now known as the “first” universality) to the classical NCL behaviour (which Nowick termed “new” or “second” universality). We describe the details of our procedure and show that insights emerge with regard to both the high-frequency plateau of the conductivity component due to “ordinary” hopping and the NCL effect itself. 相似文献
13.
Indrani Coondoo Neeraj Panwar Amit Tomar A.K Jha S.K. Agarwal 《Physica B: Condensed Matter》2012,407(24):4712-4720
Complex impedance spectroscopy (CIS) technique has been utilized to investigate the intra- and intergranular contributions to the impedance in pristine and wolframium (tungsten, W) -substituted strontium bismuth tantalate [SrBi2(Ta1−xWx)2O9 (SBTW); x=0.0, 0.025, 0.05, 0.075, 0.1 and 0.2] ceramics as a function of temperature and frequency. CIS studies reveal that the electrical relaxation process was temperature dependent and non-Debye type. The temperature dependence of the relaxation time was found to obey the Arrhenius law. DC conductivity of the studied samples obtained from the CIS data decreased for W content upto x=0.05, followed by a subsequent increase with x>0.05. Electrical conductivity data including the typical values of the activation energies at high temperature indicated that the conductivity in the studied ceramics was essentially due to the contribution of doubly ionized oxygen vacancies to the conduction process. 相似文献
14.
Results of temperature and frequency dependent a.c. conductivity of pure and nickel-doped a-As2S3 are reported. The a.c. conductivity of pure As2S3 obeys a well-known relationship: σac ∝ω
s. Frequency exponents is found to decrease with increasing temperature. Correlated barrier hopping (CBH) model successfully explains the entire
behaviour of a.c. conductivity with respect to temperature and frequency for pure As2S3. But a different behaviour of a.c. conductivity has been observed for the nickel doped As2S3. At higher temperatures, distinct peaks have been observed in the plots of temperature dependence of a.c. conductivity. The
frequency dependent behaviour of a.c. conductivity (σac ∝ω
s) for nickeldoped As2S3 is similar to pure As2S3 at lower temperatures. But at higher temperatures, ln σac vs lnf curves have been found to deviate from linearity. Such a behaviour has been explained by assuming that nickel doping gives
rise to some neutral defect states (D
0′) in the band gap. Single polaron hopping is expected to occur between theseD
0‘ andD
+ states. Furthermore, allD
+,D
0′ pairs are assumed to be equivalent, having a fixed relaxation time at a given temperature. The contribution of this relaxation
to a.c. conductivity is found to be responsible for the observed peak in the plots of temperature dependence of a.c. conductivity
for nickel-doped As2S3. The entire behaviour of a.c. conductivity with respect to temperature and frequency has been explained by using CBH and
“simple pair” models. Theoretical results obtained by using these models, have been found to be in agreement with the experimental
results. 相似文献
15.
S. N. Mustafaeva Sh. G. Gasymov E. M. Kerimova M. M. Asadov 《Physics of the Solid State》2012,54(1):44-47
Pressure and temperature dependences of the conductivity anisotropy of TlGaTe2 chain single crystals have been investigated. It has been found that the conductivity anisotropy of TlGaTe2 can be controlled by choosing the values of temperature and pressure. The temperatures (216, 193, and 77 K) and corresponding
pressures (0, 0.31, and 0.71 GPa) have been determined, at which the conductivity of the TlGaTe2 single crystal becomes isotropic. 相似文献
16.
Monica Sindhu Neetu Ahlawat Sujata Sanghi Ashish Agarwal Reetu Dahiya Navneet Ahlawat 《Current Applied Physics》2012,12(6):1429-1435
Single phase perovskite CaTiO3 has been synthesized by conventional solid state reaction technique. The ceramic was characterized by XRD at room temperature and its Rietveld refinement inferred orthorhombic crystal structure with the space group Pbnm. The field dependence of dielectric relaxation and conductivity was measured over a wide frequency range from room temperature to 673 K. Analysis of Nyquist plots of CaTiO3 revealed the contribution of many electrically active regions corresponding to bulk mechanism, distribution of grain boundaries and electrode processes. The dc conductivity depicted a semiconductor to metal type transition. Frequency dependence of dielectric constant (ε′) and tangent loss (tan δ) show a dispersive behavior at low frequencies and is explained on basis of Maxwell-Wagner model and Koop's theory. Both conductivity and electric modulus formalisms have been employed to study the relaxation dynamics of charge carriers. The variation of ac conductivity with frequency at different temperatures obeys the universal Jonscher's power law (σac α ωs). The values of exponent ‘s’ lie in the range 0.13 ≤ s ≤ 0.33, which in light of CBH model suggest a large polaron hopping type of conduction mechanism. 相似文献
17.
The ionic and electronic conductivities of Lisicon with compositions Li14Zn(GeO4)4-(A) and Li12Zn2(GeO4)4-(B) have been determined in the temperature range 306–578 K. It has thus been shown that the ionic transport number is nearly unity throughout the temperature range. The activation energies for lithium motion were found to be 0.6 eV and 0.47 eV for compounds A and B. These values are very close to the values of the heat of transport q1Li+ 0.59 eV and 0.50 eV respectively, obtained from thermoelectric power (θt) measurements. The total ionic conductivity of the pellets of Lisicon was found to decrease with increasing average grain size in the range 20–78 μ. Electrode effects on the ionic conductivity are also reported for silver and TiS2 electrodes. The electron/hole conductivity was studied using the Wagner cell technique. The activation energies for electron and hole transport for A were estimated as 1.02 eV and 1.39 eV and for B as 0.89 eV and 1.49 eV, respectively. The variation of the dielectric parameters ?', ?” and tan δ have been studied for sample A between 10 Hz-100 kHz. The high frequency dielectric constant (at 100 kHz) was 21.4. The ?' versus ?” (Cole-Cole plot) is also presented. 相似文献
18.
We address the optical conductivity of undoped bilayer graphene in the presence of a finite bias voltage at finite temperature. The effects of gap parameter and stacking type on optical conductivity are discussed in the context of tight binding model Hamiltonian. Green’s function approach has been implemented to find the behavior of optical conductivity of bilayer graphene within linear response theory. We have found the frequency dependence of optical conductivity for different values of gap parameter and bias voltage. Also the dependence of optical conductivity on the temperature has been investigated in details. A peak appears in the plot of optical conductivity versus frequency for different values of temperatures and bias voltage. Furthermore we find the frequency position of broad peak in optical conductivity goes to higher values with increase of gap parameter for both bernal and simple stacked bilayer graphenes. 相似文献
19.
Thin film of CaCu3Ti4O12 (CCTO) has been deposited on Nb-doped SrTiO3(100) single crystal using pulsed laser deposition. The dielectric constant and AC conductivity of CCTO film in the metal–insulator–metal
capacitor configuration over a wide temperature (80 to 500 K) and frequency (100 Hz to 1 MHz) range have been measured. The
small dielectric dispersion with frequency observed in the lower temperature region (<300 K) indicates the presence of small
defects in the deposited CCTO thin film. The frequency-dependent AC conductivity at lower temperature indicates the hopping
conduction. The dielectric dispersion data has been analyzed in the light of both conductivity relaxation and Debye type relaxation
with a distribution of relaxation times. Origin of dielectric dispersion is attributed to the distribution of barrier heights
such that some charge carriers are confined between long-range potential wells associated with defects and give rise to dipolar
polarization, while those carriers which do not encounter long-range potential well give rise to DC conductivity. 相似文献
20.
S. Kabi A. Ghosh 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,79(4):377-381
Electrical complex ac conductivity of the compound
Li0.9[Ni1/3Mn1/3Co1/3]O1.95 has been studied in the
frequency range 10 Hz–2 MHz and in the temperature range 93–373 K. It
has been observed that the frequency dependence of the ac conductivity obeys
a power law and the temperature dependence of the ac conductivity is quite
weak. The experimental data have been analyzed in the framework of several
theoretical models based on quantum mechanical tunneling and classical
hopping over barriers. It has been observed that the electron tunneling is
dominant in the temperature range from 93 K to 193 K. A crossover of
relaxation mechanism from electron tunneling to polaron tunneling is
observed at 193 K. Out of the several models discussed, the electron
tunneling and the polaron tunneling models are quite consistent with the
experimental data for the complex ac conductivity. The various parameters
obtained from the fits of the experimental results for the real and
imaginary parts of the conductivity to the predictions of these models are
quite reasonable. 相似文献