共查询到20条相似文献,搜索用时 15 毫秒
1.
M.A. Afifi M.M. El-Nahass A.E. Bekheet I.T. Zedan 《Physica B: Condensed Matter》2007,400(1-2):248-251
Measurements of the dc and ac conductivity were made for polycrystalline CdSexTe1−x (0x0.4) at various frequencies (0.1–100 kHz) and at various temperatures (293–413 K). The temperature dependence of the dc conductivity was measured in the temperature range (293–413 K). It was found that the obtained dc activation energy for the investigated compositions decrease with the increase of Se content. The ac conductivity is found to be frequency and temperature dependent and obeys the Aωs law, where s decreases with the increase of temperature. The ac conductivity of these compositions are explained on the basis of the correlated barrier hopping model. 相似文献
2.
In the paper some experimental results on the dependence of thermal conductivity, temperature conductivity coefficient, heat capacity, dc conductivity and ac conductivity on integrated neutron flux within the range from 1016
n cm–2 to 1019
n cm–2 are described. At integrated neutron flux of 1017
n cm–2 an extreme in all parameters was observed. This effect can be explained by means of compensation of unsaturated bonds in the glass due to defects caused by irradiation. 相似文献
3.
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
4.
The absorption constantK of amorphous As2S3 was determined at the absorption edge in the range 1 to 105 cm–1. It is shown that at low energy levels up to about 103 cm–1
K depends exponentially on the photon energy; at higher absorption levels the energy dependence ofK is quadratic. The significance of these results is discussed. When sulphur is added to As2S3 the absorption edge has similar properties but is shifted towards lower energies. 相似文献
5.
M. G. Ramazanzade S. A. Aliev N. A. Berdieva A. M. Agaev 《Russian Physics Journal》1981,24(10):919-923
To obtain information on the temperature and concentration dependence of thermoelectric quality factor Z and to clarify the nature of scattering in Ag2Se a study was made of electrical conductivity , thermo-emf , and thermal conductivity in silver selenide over the temperature range T=80–450°K at concentration levels of 2–43·1024 m–3. It is shown that in Ag2Se the Lorentz number L, determined experimentally from the electronic fraction of the thermal conductivity, is less than the Sommerfeld number Lo. Calculation of L/Lo(n) performed with a theory considering inelastic scattering of carriers, shows that the inelasticity is produced by electron interaction. Comparison of experimental data on the temperature dependence of lattice thermal conductivity with theory permits the conclusion that in Ag2Se in range 80–300°K the basic role in phonon scattering is played by three-phonon Umklapp processes. It is shown that with increase in T and decrease in n the thermoelectric quality factor of silver selenide increases. The highest value of Z was achieved in a specimen with electron concentration n=2·1024 m–3 at T=320°K. The rapid decrease in Z upon phase transition is related to discontinuous decrease in and at this point.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 27–31, October, 1981. 相似文献
6.
在单电子紧束缚近似下,建立了准一维多链无序体系直流、交流电子跳跃输运模型,通过计算探讨了无序模式、维度效应、温度及外场对其直流、交流电导率的影响.计算结果表明:准一维多链无序体系的直流、交流电导率随着格点能量无序度的增大而减小,非对角无序具有增强体系电子输运能力的作用.随着链数的增加,体系的直流、交流电导率增大,但格点能量无序度较小时,维度效应的影响不明显.在对角无序情况下准一维多链无序体系的交流电导率随温度的升高而增大,而在非对角无序模式下却随温度的升高而减小,但对于直流情况,体系的直流电导率随温度的升 相似文献
7.
In the present paper we report the first experimental results on ac and dc conductivity and permittivity of adenine hemisulphate hydrate and adenine sulphate measured at atmospheric and high hydrostatic pressures. For both materials ac conductivity is of
s type, where:s 1·1· Room temperature dc conductivity of adenine hemisulphate hydrate equals approximately 5×10–15
–1 cm–1 with an activation energy of 0·86 eV; dc conductivity of adenine sulphate is less than 10–16 cm–1. On the basis of these measurements and those carried out at high pressure, it is concluded that conductivity of adenine hemisulphate hydrate is of electronic type.The authors wish to thank Dr. J. Zachová for the preparation of adenine salts single crystals. 相似文献
8.
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
9.
J. Lu A. Günther F. Schrettle F. Mayr S. Krohns P. Lunkenheimer A. Pimenov V. D. Travkin A. A. Mukhin A. Loidl 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,75(4):451-460
Magnetic dc susceptibility between 1.5 and 800 K, ac
susceptibility and magnetization, thermodynamic properties, temperature
dependence of radio and audio-wave dielectric constants and conductivity,
contact-free dielectric constants at mm-wavelengths, as well as
ferroelectric polarization are reported for single crystalline BiFeO3.
A well developed anomaly in the magnetic susceptibility signals the onset of
antiferromagnetic order close to 635 K. Beside this anomaly no further
indications of phase or glass transitions are indicated in the magnetic dc
and ac susceptibilities down to the lowest temperatures. The heat capacity
has been measured from 2 K up to room temperature and significant
contributions from magnon excitations have been detected. From the
low-temperature heat capacity an anisotropy gap of the magnon modes of the
order of 6 meV has been determined. The dielectric constants measured in
standard two-point configuration are dominated by Maxwell-Wagner like
effects for temperatures T > 300 K and frequencies below 1 MHz. At lower
temperatures the temperature dependence of the dielectric constant and loss
reveals no anomalies outside the experimental errors, indicating neither
phase transitions nor strong spin phonon coupling. The temperature
dependence of the dielectric constant was measured contact free at microwave
frequencies. At room temperature the dielectric constant has an intrinsic
value of 53. The loss is substantial and strongly frequency dependent
indicating the predominance of hopping conductivity. Finally, in small thin
samples we were able to measure the ferroelectric polarization between 10
and 200 K. The saturation polarization is of the order of 40 μC/cm2, comparable to reports in literature. 相似文献
10.
Experimental data of the ac conductivity in polymers and other disordered materials are discussed in terms of theoretical models, especially with respect to a common universal behaviour, as proposed by Summerfield. Two parameters can be extracted from such an analysis, the frequency exponents=0.69±0.04, describing the behaviour at higher frequencies, and a model dependent factorA, ranging between 10–2 and 10–5, that characterizes the crossover from frequency independent values to an ac conductivity increasing with frequency like 5.Dedicated to Professor Harry Thomas on the occasion of his 60th birthday 相似文献
11.
Measurements of electrical conductivity of NaCl 10–5 molar fr. CaCl2 (1–80)×10–5 molar fr. Na2CO3 crystals have been used to determine the temperature dependence of the solubility of CO3-ions over the temperature range from 75 to 530 °C. The total solubility of CO3-ions and that of [CO
3
2–
-vacancy] complexes may be expressed by simple relationships
andc
ka=3·19× 10–2 exp (–0·25 eV/kT), resp. The heat of solution of complexes is equal to 0·25 eV and that of free CO
3
2–
ions is higher than 1·2 eV. Under conditions of the thermal equilibrium between the solid solution and precipitate, the ratio of Na2CO3 and CaCO3 components in the precipitate has been calculated at various temperatures and CO3 concentrations. 相似文献
12.
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
13.
The experimental results obtained with the chalcogenide glass Ge15Te81S2As2 with imposed overall pressure up to 700 MPa are presented. The material exhibits the switching effect and the memory effect. It is shown that the overall pressure changes remarkably d.c. electrical conductivity of the amorphous semiconductor. It is assumed that the changes in conductivity are caused by changes in activation energy. The changes in activation energy within the range of considered pressures are, as follows from our measurements, E/p–10·95×10–5 eV/MPa +p × 10·41 W 10–7 eV/MPa2. The assumption of the activation energy dependence on pressurep are confirmed also by measurements of dependence In vs. 1/T at various pressures. 相似文献
14.
S. Bala Murali Krishna P. Srinivasa Rao B. Sreedhar D. Krishna Rao 《Physica B: Condensed Matter》2009,404(21):3898-3905
ZnO–As2O3–Sb2O3 glasses of varying concentrations of Sb2O3 with ZnO (ranging from 5 to 45 mol%) are prepared. A number of studies, including differential thermal analysis, and study of spectroscopic properties (viz., optical absorption and IR spectra) and dielectric properties (constant ε′, loss tan δ and ac conductivity σac) over a wide range of frequency and temperature of these glasses are carried out. Analyses of the results of these investigations have indicated that the glasses containing higher concentrations of Sb2O3 are more suitable for non-linear optical (NLO) applications. 相似文献
15.
Summary Reflectivity measurements have been done on dopedn-type HgCr2Se4 (n≈(1015÷1019) cm−3), at various temperatures ((4÷300) K) in the infra-red range
. The spectra show the structure of a plasma edge and reststrahlbands. Data have been analysed by a Kramers-Kronig procedure.
The deduced dynamical conductivity shows an anomaly near the plasma frequency ωp. The transmitivity measurements show a strong temperature dependence of the conduction band.
Paper presented at the ?V International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16,
1982. 相似文献
16.
The changes in the dielectric properties and temperature dependence of the d.c. conductivity of α-exposed poly allyl diglycol carbonate (PADC) have been studied. On α-irradiation the dielectric constant (′) as a function of frequency has been found to decrease significantly. The temperature dependence of resistivity in pristine and γ-irradiated samples is of the form ρ(T)=ρ∝ exp(T0/T) which can be attributed to conduction of thermally generated carriers. In case of (γ+α) irradiated samples the temperature dependence of resistivity is of the form ρ(T)=ρ∝ exp(T0/T)1/2 which is due to one-dimensional hopping of carriers. 相似文献
17.
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
18.
Imran Murtaza Ibrahim Qazi Khasan S. Karimov Muhammad H. Sayyad 《Physica B: Condensed Matter》2011,406(6-7):1238-1241
We use experimental results of low signal impedance spectroscopy to investigate the conduction mechanism in organic semiconductor, zinc phthalocyanine (ZnPc). The first 10 nm, of a total of 150 nm thermally deposited ZnPc, was doped with molybdenum oxide (MoO3) by co-evaporation to obtain a 20% doping concentration. The ac electrical parameters were measured at room temperature in the dc bias and frequency ranges of 0–5 V and 100 Hz–0.1 MHz, respectively. The variation of bulk resistance with applied bias presents a clear indication of space charge limited conduction in the fabricated device. The experimental results show a strong frequency dependence of capacitance and loss tangent at low frequencies and high applied bias, while at higher frequencies and low applied bias a weak dependence is observed. Moreover, the ac conductivity shows a strong dependence on frequency and is found to vary as ωs with the index s≤1.15 suggesting a dominant hopping mechanism of conduction. 相似文献
19.
R. Feile P. Leiderer J. Kowalewski W. Assmus J. Schubert U. Poppe 《Zeitschrift für Physik B Condensed Matter》1988,73(2):155-160
We have performed detailed investigations on the temperature dependence of the 335 cm–1 phonon in single crystals and thin films of the YBa2Cu3O7 superconductor. The frequency of this phonon exhibits a downshift of about 5 cm–1 on passing the superconducting transition from above. The shift of the phonon in thin epitaxial films on MgO or SrTiO3 substrates is only about 2.5 cm–1. The width of the asymmetric phonon line displays a slight increase belowT
c due to the electron-phonon interaction in these systems. 相似文献
20.
The structural, electrical, magnetic, and thermal properties were investigated for the nanocomposites of polypyrrole (PPy) and inorganic clay (Na+-montmorillonite) prepared by emulsion polymerization. Dodecylbenzenesulfonic acid (DBSA) was used as emulsifier (surfactant) and dopant. The X-ray diffraction (XRD) patterns and transmission electron microscopy (TEM) images showed that the conducting PPy was intercalated into the clay layers in nanoscale (<10 Å). The dc conductivity (σdc) of PPy–DBSA with clay was 6 S/cm, while that of PPy–DBSA without clay was 20 S/cm at room temperature (RT). Temperature dependence of σdc of both samples followed the three dimensional variable range hopping (VRH) model. From the g-value and the temperature dependence of EPR linewidth, paramagnetic signals were strongly affected by the partially negatively charged clay layers. The thermogravimetric analysis (TGA) and differential scanning calorimeter (DSC) showed that the clay induced the thermal stability of the systems. 相似文献