共查询到20条相似文献,搜索用时 31 毫秒
1.
M. Aggarwal S. Khan M. Husain T. C. Ming M. Y. Tsai T. P. Perng Z. H. Khan 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(3):319-324
Using low-pressure chemical vapour deposition (LPCVD), multi-walled carbon nanotubes (MWNTs) are grown on nanocrystalline
Fe70Pt30 film. The Fe70Pt30 nanocrystalline film is deposited by vapour condensation technique. The size of the nanoparticles varies from 5–10 nm, as
inferred from SEM micrographs of Fe70Pt30 film. SEM and TEM observations of
as-grown CNTs film reveal that these are multi-walled and their diameter varies from 30–80 nm and length is of the order of
several micrometers respectively. There is a structural change from ordinary geometry of CNTs to bamboo shaped as suggested
by TEM image. Raman spectra shows sharp G and D bands with a higher intensity of G band showing the presence of graphitic
nature of the nanotubes. An experimental study of the temperature dependence of electrical conductivity of MWNTs film is done
over a wide temperature
range from (293–4 K). The measured data gives a good fit to variable-range hopping (VRH) and the results are interpreted using
Mott's (VRH) model. The conduction mechanism of the MWNTs film shows a crossover from the exp[ -(To/T)1/4] law in the temperature range (293–110 K) to exp[ -(Tm/T)1/3] in the low temperature range (110–4 K). This behaviour is attributed to temperature-induced transition from three-dimension
(3D) to two-dimension (2D) VRH. Various Mott's parameters like characteristic temperature (Tm), density of states at Fermi level N(EF), localization length (ξ), hopping distance (R), hopping
energy (W) have also been calculated using above-mentioned model. 相似文献
2.
A. Kh. Matiev A. N. Georgobiani V. V. Kodin M. A. Matiev 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(9):1326-1328
The electrical conductivity and magnetoresistance effect of n and p types of CuInSe2 single crystals were studied within the temperature range of 4.2–300 K and within magnetic fields of up to 6 T. It was found
that the hopping mechanism of conductivity dominates in the temperature range of 4.2–100 K. A peculiarity of electrical conductivity
behavior, accompanied by a change in the magnetoresistance sign in the vicinity of T ≈ 60 K, was revealed. 相似文献
3.
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
4.
L. S. Ewe I. Hamadneh H. Salama N. A. Hamid S. A. Halim R. Abd-Shukor 《Applied Physics A: Materials Science & Processing》2009,95(2):457-463
The magnetotransport and magnetoresistive (MR) properties of manganese-based La0.67Ca0.33MnO3 perovskite with different grain sizes are reported. The electrical resistivity was measured as a function of temperature
in magnetic fields of 0.5 and 1 T. The insulator–metal transition temperature, T
IM, shifted to a higher temperature with the application of the magnetic field. In zero field, T
IM is almost constant (∼271 K) for all samples except for the sample with the largest grain size, where T
IM=265 K. The temperature dependence of resistivity was fitted with several equations in the metallic (ferromagnetic) region
and the insulating (paramagnetic) region. The density of states at the Fermi level, N(E
F), and the activation energy of electron hopping were estimated by fitting the resistivity versus temperature curves. The
ρ–T
2 curves are nearly linear in the metallic regime, but the ρ–T
2.5 curves exhibit a deviation from linearity. The variable range hopping model and small polaron hopping model fit the data
well in the high-temperature region, indicating the existence of the Jahn–Teller distortion that localizes the charge carriers.
MR was found to increase with an increase in the magnetic field, an effect which is attributed to the intergrain spin tunneling
effect. 相似文献
5.
The temperature dependence of the electrical conductivity of the compound 2,4,4-trimethyl-4,5-dihydro-3H-benzo[b] [1,4] diazepin-1-ium tetrachlorocadmiate in the different phases follows the Arrhenius law. The imaginary part of
the permittivity constant is analyzed with the Cole–Cole formalism. In the temperature range 348–394 K, the activation energy
of conductivity obtained from complex permittivity in regions I and II are, respectively, 1.03 and 0.33 eV, and E
m (in regions I and II are, respectively, 0.97 and 0.36 eV) obtained from the modulus spectra is close, suggesting that the
ion transport is probably due to a hopping mechanism. The Kohlrausch–Williams–Watts function,
j(t) = exp( - ( \fractt\textKWW )b ) \varphi (t) = \exp \left( { - {{\left( {\frac{t}{{{\tau_{\text{KWW}}}}}} \right)}^\beta }} \right) , and the coupling model are utilized for analyzing electric modulus at various temperatures. The decreasing of β at 373 K is due to approaching the temperatures of change in the conduction mechanism of the sample. 相似文献
6.
D. Parviz M. Kazemeini A. M. Rashidi Kh. Jafari Jozani 《Journal of nanoparticle research》2010,12(4):1509-1521
Molybdenum oxide nanostructures were synthesized utilizing the solution combustion method where the ammonium molybdate powder
and an organic additive were used as precursors. Different organic additives including ethylene diamine tetra-acetic acid
(EDTA), polyethylene glycol 200 (PEG 200), sorbitol and urea were used as surfactants in order to investigate the effect of
additive structure on morphology and particle size of products. Also various reaction parameters such as the additive/Mo molar
ratio, concentration of metal ion in solution, pH of the reaction, and temperature of the synthesis media were changed to
study effects on product morphology and size. Outcomes were characterized by Scanning Electron Microscopy (SEM), X-ray diffraction,
and Transmission Electron Microscopy (TEM) techniques. Results show a variety of MoO3 nanoparticles and nanorods produced within the size range of 10–80 nm. Furthermore, microrods and microsheets were also obtained
through this method whose length varied in the order of microns. 相似文献
7.
Preparation of pure phase CuIn0.75Ga0.25Se2 nanoparticle powder by ball milling technique has been confirmed for the milling time of more than 45 min at 1200 rpm. Formation
of shear bands responsible for breakdown of grains and generation of nanostructure during mechanical alloying, dislocation
and defects induced due to milling has been studied by High-Resolution Transmission Electron Microscopy (HRTEM) analysis.
Deviation in final composition of the products from those of starting materials has been discussed based on low volatilization
of Se. Effect of milling time on the phase formation, particle size, and composition has been discussed in detail. Decrease
in grain size from 12.44 to 7.96 nm has been observed with the increase in milling time. Mechanically induced self-propagating
reaction mechanism which occurred during milling process is also discussed. Nanoparticle precursor was mixed with organic
binder material for rheology of mixture to be adjusted for screen printing, and the films are subjected to heat treatment
at five different temperatures in nitrogen ambient for 25 min. Average grain size calculated by Scherrer’s formula was almost
the same irrespective of temperature. Reproducibility of precursor composition in the deposited films has been discussed in
detail. 相似文献
8.
A. V. Malakhovskii E. V. Eremin D. A. Velikanov A. V. Kartashev A. D. Vasil’ev I. A. Gudim 《Physics of the Solid State》2011,53(10):2032-2037
The magnetic properties of the Nd0.5Gd0.5Fe3(BO3)4 single crystal have been studied in principal crystallographic directions in magnetic fields to 90 kG in the temperature
range 2–300 K; in addition, the heat capacity has been measured in the range 2–300 K. It has been found that, below the Néel
temperature T
N = 32 K down to 2 K, the single crystal exhibits an easy-plane antiferromagnetic structure. A hysteresis has been detected
during magnetization of the crystal in the easy plane in fields of 1.0–3.5 kG, and a singularity has been found in the temperature
dependence of the magnetic susceptibility in the easy plane at a temperature of 11 K in fields B < 1 kG. It has been shown that the singularity is due to appearance of the hysteresis. The origin of the magnetic properties
of the crystal near the hysteresis has been discussed. 相似文献
9.
L. Nedelcu A. Ioachim M. I. Toacsan M. G. Banciu I. Pasuk M. Buda N. Scarisoreanu V. Ion M. Dinescu 《Applied Physics A: Materials Science & Processing》2008,93(3):675-679
Ba0.6Sr0.4TiO3 (BST) bulk ceramic synthesized by solid state reaction was used as target for thin films grown by pulsed laser deposition
(PLD) and radiofrequency beam assisted PLD (RF-PLD). The X-ray diffraction patterns indicate that the films exhibit a polycrystalline
cubic structure with a distorted unit cell. Scanning Electron Microscopy investigations showed a columnar microstructure with
size of spherical grains up to 150 nm. The capacitance–voltage (C–V) characteristics of the BST films were performed by applying
a DC voltage up to 5 V. A value of 280 for dielectric constant and 12.5% electrical tunability of the BST capacitor have been
measured at room temperature. 相似文献
10.
D. Golberg P.S. Dorozhkin Y. Bando Z.-C. Dong C.C. Tang Y. Uemura N. Grobert M. Reyes-Reyes H. Terrones M. Terrones 《Applied Physics A: Materials Science & Processing》2003,76(4):499-507
Transport and field-emission properties of as-synthesized CNx and BNCx (x<0.1) multi-walled nanotubes were compared in detail. Individual ropes made of these nanotubes and macrofilms of those
were tested. Before measurements, the nanotubes were thoroughly characterized using high-resolution and energy-filtered electron
microscopy, electron diffraction and electron-energy-loss spectroscopy. Individual ropes composed of dozens of CNx nanotubes displayed well-defined metallic behavior and low resistivities of ∼10–100 kΩ or less at room temperature, whereas
those made of BNCx nanotubes exhibited semiconducting properties and high resistivities of ∼50–300 MΩ. Both types of ropes revealed good field-emission
properties with emitting currents per rope reaching ∼4 μA(CNx) and ∼2 μA (BNCx), albeit the latter ropes se- verely deteriorated during the field emission. Macrofilms made of randomly oriented CNx or BNCx nanotubes displayed low and similar turn-on fields of ∼2–3 V/μm. 3 mA/cm2 (BNCx) and 5.5 mA/cm2 (CNx) current densities were reached at 5.5 V/μm macroscopic fields. At a current density of 0.2–0.4 mA/cm2 both types of compound nanotubes exhibited equally good emission stability over tens of minutes; by contrast, on increasing
the current density to 0.2–0.4 A/cm2, only CNx films continued to emit steadily, while the field emission from BNCx nanotube films was prone to fast degradation within several tens of seconds, likely due to arcing and/or resistive heating.
Received: 29 October 2002 / Accepted: 1 November 2002 / Published online: 10 March 2003
RID="*"
ID="*"Corresponding author. Fax: +81-298/51-6280, E-mail: golberg.dmitri@nims.go.jp 相似文献
11.
Zishan H. Khan 《Applied Surface Science》2009,255(21):8874-8878
Electrical and optical properties of thin film of amorphous silicon nanoparticles (a-Si) are studied. Thin film of silicon is synthesized on glass substrate under an ambient gas (Ar) atmosphere using physical vapour condensation system. We have employed Field Emission Scanning Electron Microscopy (FESEM), Transmission Electron Microscopy (TEM) and Atomic Force Microscopy (AFM) to study the morphology and microstructure of this film. It is observed that this silicon film contains almost spherical nanoparticles with size varying between 10 and 40 nm. The average surface roughness is about 140 nm as evident from the AFM image. X-ray diffraction analysis is also performed. The XRD spectrum does not show any significant peak which indicates the amorphous nature of the film. To understand the electrical transport phenomena, the temperature dependence of dc conductivity for this film is studied over a temperature range of (300-100 K). On the basis of temperature dependence of dc conductivity, it is suggested that the conduction takes place via variable range hopping (VRH). Three-dimensional Mott's variable range hopping (3D VRH) is applied to explain the conduction mechanism for the transport of charge carriers in this system. Various Mott's parameters such as density of states, degree of disorder, hopping distance, hopping energy are estimated. In optical properties, we have studied Fourier transform infra-red spectra and the photoluminescence of this amorphous silicon thin film. It is found that these amorphous silicon nanoparticles exhibits strong Si-O-Si stretching mode at 1060 cm−1, which suggests that the large amount of oxygen is adsorbed on the surface of these a-Si nanoparticles. The photoluminescence observed from these amorphous silicon nanoparticles has been explained with the help of oxygen related surface state mechanism. 相似文献
12.
M. D. Volnyanskii S. N. Plyaka M. P. Trubitsyn Yahia A. H. Obaidat 《Physics of the Solid State》2012,54(3):499-503
The electrical properties of a lithium heptagermanate (Li2Ge7O15) crystal have been studied in DC and AC measuring fields at temperatures from 500 to 700 K. In a DC field, a substantial
decrease of electrical conductivity σ with time has been detected. On the basis of kinetic dependences σ(t), estimates of the charge carrier diffusion coefficient D have been obtained. In the frequency range 101–105 Hz, the spectra of complex impedance ρ*(f) have been measured. The analysis of diagrams in the complex plane (ρ″–ρ′) has been performed within the equivalent circuit
approach. It has been shown that, in the considered temperature and frequency intervals, the electrical properties of Li2Ge7O15 crystals have been determined by the hopping conduction of interstitial lithium ions A
Li and accumulation of charge carriers near the blocking Pt electrodes. 相似文献
13.
G. Li S.-J. Feng F. Liu Y. Yang R.-K. Zheng T. Qian X.-Y. Guo X.-G. Li 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(1):5-11
The magnetic transport properties have been measured for La0.67-xYxCa0.33MnO3 ( 0 ⩽
x
⩽ 0.14) system. It was found that the transition temperature T
p
almost linearly moves to higher temperature as H increases. Electron spin resonance confirms that above T
p
, there exist ferromagnetic clusters. From the magnetic polaron point of view, the shift of T
p
vs. H was understood, and it was estimated that the size of the magnetic polaron is of 9.7 ∼ 15.4 ? which is consistent with the magnetic correlation length revealed by the small-angle neutron-scattering technique. The
transport properties at temperatures higher than T
p
conform to the variable-range hopping mechanism.
Received 27 August 2002 / Received in final form 2 December 2002 Published online 14 March 2003 相似文献
14.
The AC conductivity of the LiCaPO4 compound has been measured in the temperature range 634–755 K and the frequency range 300 Hz–5 MHz. The impedance data were
fitted to an equivalent circuit consisting of series combination of grains, grains boundary, and electrode elements. Dielectric
data were analyzed using complex electrical modulus M* at various temperatures. The modulus plots are characterized by the presence of two relaxation peaks thermally activated.
The activation energies obtained from the analysis of M″ (0.90 eV) and conductivity data (0.94 eV) are very close, revealing an ionic hopping mechanism. 相似文献
15.
Xiao-Ping Shen Hua-Juan Miao Hui Zhao Zheng Xu 《Applied Physics A: Materials Science & Processing》2008,91(1):47-51
Well-aligned Co3O4 nanotubes were synthesized within the nanochannels of porous anodic alumina membranes using a single-source chemical vapor
deposition method. Scanning electron microscopy and transmission electron microscopy showed that the Co3O4 nanotubes are highly ordered with uniform diameter in the range of 100–300 nm and length up to tens of microns. X-ray diffraction,
the Raman spectrum, energy-dispersive spectroscopy and selected-area electron diffraction demonstrated that the nanotubes
are composed of pure cubic phase polycrystalline Co3O4. Magnetic measurements using a SQUID magnetometer suggested the presence of a strong antiferromagnetic interaction with Weiss
constant θ= -248 K. The real and imaginary parts of the ac susceptibility at f= 10 Hz had a maximum at 4.0 K, and the field
dependence of the magnetization at 1.8 K showed a small hysteresis loop with a coercivity of ∼ 98 Oe.
PACS 81.07.De; 81.15.Gh; 78.30.-j; 75.75.+a; 61.46.Np 相似文献
16.
A. U. Sheleg V. G. Hurtavy S. N. Mustafaeva E. M. Kerimova 《Physics of the Solid State》2011,53(3):472-475
The temperature dependences of the electrical conductivity and the permittivity of TlInSe2 and TlGaTe2 crystals unirradiated and irradiated with 4-MeV electrons at a doze of 1016 cm−2 have been investigated. It has been established that electron irradiation leads to a decrease in the electrical conductivity
σ and the permittivity ɛ over the entire temperature range under study (90–320 K). It has been revealed that the TlInSe2 and TlGaTe2 single crystals undergo a sequence of phase transitions characteristic of crystals of this type, which manifest themselves
as anomalies in the temperature dependences σ = f(T) and ɛ = f(T). Electron irradiation at a doze of 1016 cm−2 does not affect the phase transition temperatures of the crystals under investigation. 相似文献
17.
G. A. Komandin A. S. Prokhorov V. I. Torgashev E. S. Zhukova B. P. Gorshunov A. A. Bush 《Physics of the Solid State》2011,53(4):736-744
The spectra of complex permittivity of a Ba2Mg2Fe12O22 single crystal belonging to the family of Y-type hexaferrites have been measured over a wide temperature range (10–300 K) with the aim of determining the dynamic parameters
of the phonon and magnetic subsystems in the terahertz and infrared frequency ranges (3–4500 cm−1). A factor-group analysis of the vibrational modes has been performed, and the results obtained have been compared with the
experimentally observed resonances. The oscillator parameters of all nineteen phonon modes of E
u
symmetry, which are allowed by the symmetry of the Ba2Mg2Fe12O22 crystal lattice, have been calculated. It has been found that, at temperatures below 195 and 50 K, the spectral response
exhibits new absorption lines due to magnetic excitations. 相似文献
18.
We have synthesized nanosized La0.67Ca0.33MnO3 by a simple low-cost novel synthesis route without calcination at high temperature. The study of these nanoparticles indicates
excellent properties similar to colossal magnetoresistance (CMR) materials sintered at ∼1600°C for 20 h. The resulting particle
size is in the range of 50–160 nm as determined by scanning electron microscopy. Resistivity measurement has been carried
out down to 12 K. The sample shows metal-to-insulator (M–I) transition at 205 K.
相似文献
19.
The temperature behavior of I-U curves and the field and temperature dependences of the electrical resistivity and dielectric permittivity of crystals of the LiCu2O2 phase have been studied. It was established that the crystals belong to p-type semiconductors and that their static resistivity in the range 80–260 K follows the Mott law ρ=Aexp(T0/T)1/4 describing variable-range hopping over localized states. At comparatively low electric fields, the crystals exhibit threshold switching and characteristic S-shaped I-U curves containing a region of negative differential resistivity. In the critical voltage region, jumps in the conductivity and dielectric permittivity are observed. Possible mechanisms of the disorder and electrical instability in these crystals are discussed. 相似文献
20.
The Ac electrical conductivity and the dielectric relaxation properties of the [(C3H7)4N]2Cd2Cl6 polycrystalline sample have been investigated by means of impedance spectroscopy measurements over a wide range of frequencies
and temperatures, 209 Hz–5 MHz and 361–418 K, respectively. The purpose is to make a difference between the electrical and
dielectric properties of the polycrystalline sample and single crystal. Besides, a detailed analysis of the impedance spectrum
suggests that the electrical properties of the material are strongly temperature-dependent. Plots of (Z" versus Z') are well
fitted to an equivalent circuit model consisting of a series combination of grains and grains boundary elements. Moreover,
the temperature dependence of the electrical conductivity in the different phases follows the Arrhenius law and the frequency
dependence of σ (ω) follows the Jonscher’s universal dynamic law. Furthermore, the modulus plots can be characterized by full
width at half height or in terms of a nonexperiential decay function φ(t) = exp(t/t)β. Finally, the imaginary part of the permittivity constant is analyzed with the Cole–Cole formalism. 相似文献