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1.
The phase composition and the temperature dependence of the magnetization of the Er0.45Ho0.55Fe2 compound in coarse-grained, microcrystalline, and submicrocrystalline states are investigated experimentally. It is found
that, upon heating under vacuum, the Er0.45Ho0.55Fe2 microcrystalline powder with a crystalline grain size of ∼1 μm undergoes decomposition into pure iron and rare-earth (erbium
and holmium) oxides and nitrides at a temperature of 500 K. The changes observed in the phase composition of the microcrystalline
powder due to annealing are confirmed by x-ray diffraction analysis. Heating of the Er0.45Ho0.55Fe2 submicrocrystalline sample leads to a partial change in the phase composition. The phase composition of a large crystal (∼1
mm in size) remains unchanged upon heating to 1080 K. It is shown that the thermal stability of the Er0.45Ho0.55Fe2 compound depends on the crystalline grain size.
__________
Translated from Fizika Tverdogo Tela, Vol. 44, No. 6, 2002, pp. 1060–1063.
Original Russian Text Copyright ? 2002 by Mulyukov, Sharipov, Korznikova. 相似文献
2.
Thin films of Sb2Te3 and (Sb2Te3)70(Bi2Te3)30 alloy and have been deposited on precleaned glass substrate by thermal evaporation technique in a vacuum of 2?×?10?6 Torr. The structural study was carried out by X-ray diffractometer, which shows that the films are polycrystalline in nature. The grain size, microstrain and dislocation density were determined. The Seebeck coefficient was determined as the ratio of the potential difference across the films to the temperature difference. The power factor for the (Sb2Te3)70 (Bi2Te3)30 and (Sb2Te3) is found to be 19.602 and 1.066 of the film of thickness 1,500 Å, respectively. The Van der-Pauw technique was used to measure the Hall coefficient at room temperature. The carrier concentration was calculated and the results were discussed. 相似文献
3.
In this work, Li2SnO3 has been synthesized by the sol–gel method using acetates of lithium and tin. Thermogravimetric analysis (TGA) has been applied to the precursor of Li2SnO3 to determine the suitable calcination temperature. The formation of the compound calcined at 800 °C for 9 h has been confirmed by X-ray diffraction (XRD) analysis. The Li2SnO3 is then pelletized and electrically characterized by using electrochemical impedance spectroscopy (EIS) in the frequency range from 50 Hz to 1 MHz. The complex impedance spectra clearly show the dominating presence of the grain boundary effect on electrical properties whereas the complex modulus plots reveal two semicircles which are due to the grain (bulk) and grain boundary. The spectra of imaginary parts of both impedance and modulus versus frequency show the existence of peaks with the modulus plots exhibiting two peaks that are ascribed to the grain and grain boundary of the material. The peak maximum shifts to higher frequency with an increase in temperature and the broad nature of the peaks indicates the non-Debye nature of Li2SnO3. The activation energy associated with the dielectric relaxation obtained from the electrical impedance spectra is 0.67 eV. From the electric modulus spectra, the activation energies related to conductivity relaxation in the grain and grain boundary of Li2SnO3 are 0.59 and 0.69 eV, respectively. The conductivity–temperature relationship is thermally assisted and obeys the Arrhenius rule with the activation energy of 0.66 eV. The conduction mechanism of Li2SnO3 is via hopping. 相似文献
4.
T. M. Ul’yanova N. P. Krut’ko L. V. Titova Yu. G. Zonov 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2010,4(4):603-608
The correlation between temperature treatment conditions and the ratio of components in nanostructured fibrous powders with
a composition of ZrO2-Y2O3-Al2O3 and their porous crystal structure and physicochemical properties is studied. The dependences of the ratio between zirconia
tetragonal and monoclynic phases on the treatment temperature and the alumina content are found to have a nonmonotonic character.
The growth of zirconia crystallite size is suppressed by introduced nanocrystalline alumina in a temperature range of 600–1200°C,
which is caused by the processes of ternary solid solution formation. The bulk and picnometric density values of materials
are proportional to the temperature of heat treatment. The temperature dependence of the specific surface and the size of
oxide grain particles has an inversely proportional character. With increasing alumina content in the powders, the specific
surface increases, while the picnometric and bulk densities decrease. 相似文献
5.
. The dependence of electron structure on the grain size in Mn2O3 nanocrystals has been investigated using X-ray photoelectron spectroscopy. It is found that the electron structure is sensitively dependent on the average grain size. The experimental results indicate that the O–1s core-level spectra are hardly shifted with decreasing average grain size; however, for a sample with a small grain size (e.g. a 9-nm sample), the shoulder peak evidently appears on the higher-binding-energy side. The main peak width of the Mn–2p core-level spectra becomes wide for samples with decreasing average grain size. The remarkable aspect of the Mn–3s core-level spectra is that the peak is multiply split, with a complex peak structure. The exchange interaction of the 3s and 3d electrons in the Mn3+ ion can be used to explain this behavior. PACS 71.23.-k; 73.22.-f 相似文献
6.
Li3V2(PO4)3/C samples were synthesized by two different synthesis methods. Their influence on electrochemical performances of Li3V2(PO4)3/C as cathode materials for lithium-ion batteries was investigated. The structure and morphology of Li3V2(PO4)3/C samples were characterized by X-ray diffraction and scanning electron microscopy. Electrochemical performance was characterized
by charge/discharge, cyclic voltammetry, and alternating current (AC) impedance measurements. Li3V2(PO4)3/C with smaller grain size showed better performances in terms of the discharge capacity and cycle stability. The improved
electrochemical properties of the Li3V2(PO4)3/C were attributed to the decreasing grain size and enhanced electrical conductivity produced via low temperature route. AC
impedance measurements also showed that the Li3V2(PO4)3/C synthesized by low temperature route significantly decreased the charge-transfer resistance and shortened the migration
distance of lithium ion. 相似文献
7.
Li3V2(PO4)3 glass-ceramic nanocomposites, based on 37.5Li2O-25V2O5-37.5P2O5 mol% glass, were successfully prepared via heat treatment (HT) process. The structure and morphology were investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM). XRD patterns exhibit the formation of Li3V2(PO4)3 NASICON type with monoclinic structure. The grain sizes were found to be in the range 32–56 nm. The effect of grain size on the dynamics of Li+ ions in these glass-ceramic nanocomposites has been studied in the frequency range of 20 Hz–1 MHz and in the temperature range of 333–373 K and analyzed by using both the conductivity and modulus formalisms. The frequency exponent obtained from the power law decreases with the increase of temperature, suggesting a weaker correlation among the Li+ ions. Scaling of the conductivity spectra has also been performed in order to obtain insight into the relaxation mechanisms. The imaginary modulus spectra are broader than the Debye peak-width, but are asymmetric and distorted toward the high frequency region of the maxima. The electric modulus data have been fitted to the non-exponential Kohlrausch–Williams–Watts (KWW) function and the value of the stretched exponent β is fairly low, suggesting a higher ionic conductivity in the glass and its glass-ceramic nanocomposites. The advantages of these glass-ceramic nanocomposites as cathode materials in Li-ion batteries are shortened diffusion paths for Li+ ions/electrons and higher surface area of contact between cathode and electrolyte. 相似文献
8.
Polycrystalline Li2WO4 was sintered at temperatures, 400, 450, 500, 550, 600, 650, and 700 °C. After sintering at each particular temperature, the
Li2WO4 was cooled to room temperature. The X-ray diffraction pattern of Li2WO4 exhibits dominant peaks attributable to 7Li2WO4.4H2O (cubic) and Li2WO4 (hexagonal) and thus reveals the extent of hydration of the material. The composition varies on heating at several temperatures
as shown by the presence of new peaks in the diffractogram. Thermogravimetric analysis is used to correlate respective structural
and thermal properties in variation. The impedance spectra show the presence of a semicircle in the higher frequency regions
and straight line behaviors at lower frequencies. SEM micrographs depict the image of sintered Li2WO4. Grain growth studies reveal the sensitiveness of grain toward temperature. The maximum grain size is observed to be ≈5.7 μm
at 700 °C. 相似文献
9.
I.?A.?Santos R.?G.?Mendes J.?A.?Eiras J.?de?Los?S.?Guerra E.?B.?Araújo 《Applied Physics A: Materials Science & Processing》2009,95(3):757-760
The dielectric properties of Sr0.75Ba0.25Nb2O6 relaxor ferroelectric thin films were carefully analyzed. In contrast to bulk samples which present three distinct dielectric
relaxation phenomena Sr0.75Ba0.25Nb2O6 thin films present only two of them. The suppression of the third anomaly can be mainly attributed to the narrow grain size
distribution of nanograins and weak tensile strains imposed to the film from the substrate. The whole set of results point
to the interpretation of a dielectric response characteristic of mesoscopic structure, which is composed of clusters and nanodomains. 相似文献
10.
The lead pyrophosphate, Pb2P2O7, compound was prepared by conventional solid-state reaction and identified by X-ray powder diffractometer. Pb2P2O7 has a triclinic structure whose electrical properties were studied using impedance spectroscopy technique. Both impedance
and modulus analysis exhibit the grain and grain boundary contribution to the electrical response of the sample. The temperature
dependence of the bulk and grain boundary conductivity were found to obey the Arrhenius law with activation energies E
g = 0.66 eV and E
gb = 0.67 eV, respectively. The scaling behavior of the imaginary part of the complex impedance suggests that the relaxation
describes the same mechanism at various temperatures. 相似文献
11.
Malgorzata Adamczyk Lucjan Kozielski Dariusz Bochenek Daria Radoszewska Marian Pawełczyk Beata Wodecka-Duś 《The European Physical Journal B - Condensed Matter and Complex Systems》2016,89(2):37
In recent years a wide range of Aurivillius layered materials have been introduced. These novel materials are produced in many various forms such as fibers, thin films as well as bulk by using a number of processing routes. As advanced materials they are they have many interesting properties which include a number of useful electrical properties related to separated grain and grain boundary conductivity, impedance, activation energies, etc. In this paper these properties are described and discussed in detail. The electrical properties of the vanadium doped BaBi2Nb2O9 ceramic was measured over a wide range of temperatures by impedance spectroscopy (IS). The separated grain activation energy, calculated from Arrhenius characteristics at temperatures between room temperature and 600 °C, was 1 eV for 0 at.% of vanadium dopant and 1.2 eV for 10 at.%, whereas the activation energies in the grain boundary region were 0.97 and 1.15 eV, respectively. The obtained results suggest the significant role of vanadium dopant, causing ordering the crystalline structure. 相似文献
12.
Sh. M. Khaliullin A. Sh. Khaliullina A. Ya. Neiman 《Russian Journal of Physical Chemistry B, Focus on Physics》2016,10(1):62-68
The magnitude and character of conductivity were studied for Y2(WO4)3 ceramics synthesized by the ceramic (from oxides) and organic-nitrate procedures. Investigation of the dependence \(\sigma \left( {{\alpha _{{o_2}}}} \right)\) and measurements of the ion transport numbers of charge carriers by the EMF method showed that Y2(WO4)3 is basically an ion conductor. The conductivity is largely determined by the sample preparation conditions related to the dependence of the specific surface area and powder grain size on the synthetic procedure. The maximum high-temperature conductivity of Y2(WO4)3 was 2.51 × 10–4 S/cm, which roughly corresponds to the conductivities of Sc2(WO4)3 and In2(WO4)3 measured under the same conditions. It was confirmed that Y2(WO4)3 crystallizes as a mixed monoclinic-orthorhombic structure at 1000°C. The character of water incorporation in hydrated Y2(WO4)3 crystals was studied by thermogravimetry and diffuse reflectance IR spectroscopy. A qualitative model of water intercalation was suggested. 相似文献
13.
E. Govea-Alcaide I. García-Fornaris P. Muné R. F. Jardim 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(4):373-378
Measurements of the electrical resistivity as a function
of temperature, ρ(T), for different values of applied
magnetic field, Ba (0 ≤ Ba ≤ 50 mT), were performed in
polycrystalline samples of Bi1.65Pb0.35Sr2Ca2
Cu3O10+δ subjected to different uniaxial compacting
pressure (UCP). We have found appreciable differences in the grain
orientation between samples by using X-ray diffractometry. From
the X-ray diffraction patterns performed, in powder and pellet
samples, we have estimated the Lotgering factor along the (00l)
direction, F(00l). The results indicate that F(00l)
increases ~23% with increasing UCP suggesting that grains
of these samples are preferentially aligned along the c-axis,
which is parallel to the compacting direction. The resistive
transition of the samples have been interpreted in terms of the
thermally activated flux-creep model. In addition, the effective
intergranular pinning energy, U0, have been determined for
different applied magnetic field. The magnetic field dependence of
U0, for Ba > 8 mT, was found to follow a H- α
dependence with α = 0.5 for all samples. The analysis of the
experimental data strongly suggested that increasing UCP results
in appreciable changes in both the grain alignment and the grain
connectivity of the samples. We have successfully interpreted the
data by considering the existence of three different
superconducting levels within the samples: the superconducting
grains, the weak-links, and the superconducting clusters. 相似文献
14.
M.J. Šćepanović M. Grujić-Brojčin Z.D. Dohčević-Mitrović Z.V. Popović 《Applied Physics A: Materials Science & Processing》2007,86(3):365-371
Nanosized titanium dioxide (TiO2) powder was prepared by a laser-induced pyrolysis. Specific surface area of the as-grown powder measured by BET method was
109 m2/g. The grain size (14.5 nm) estimated from these data coincides well with the crystallite size (12.3 nm) determined by XRD
measurements. The average grain size (∼35 nm) obtained from the subsequent SEM measurements refers to considerable agglomeration
of nanoparticles. Raman spectroscopy has been used to investigate the structural properties of TiO2 nanopowder and its anatase structure is confirmed. The blueshift and broadening of the lowest frequency Eg Raman mode at temperature range ∼25–550 K have been analyzed using a phonon-confinement model. Dominant influence of the
strong anharmonic effect at higher temperatures was demonstrated.
PACS 81.07.Wx; 78.30.-j; 63.22.+m 相似文献
15.
The nanocrystalline La0.8Sr0.2MnO3 (LSM) is prepared by varying the revolutions per minute and milling time of planetary monomill during the mechanochemical
method. The LSM forms in a relatively shorter milling time with an increase in the milling speed from 250 to 600 rpm. The
structural phase transition from orthorhombic to rhombohedral phase in the LSM prepared by ball milling at the speed 250 rpm
for 36 h is seen due to sintering it at 700 °C for 4 h. The crystallite size reduces with the increase in both the milling
speed and the milling time individually or combined. The microhardness (HV) and sintered density increase with the reduction
in the crystallite size. The temperature-activated transition temperature is suppressed by reducing the grain size in the
nanometer range. The electrical dc conductivity increases with the reduction in the grain/crystallite size. 相似文献
16.
ZK60A nanocomposite containing Al2O3 nanoparticle reinforcement (50 nm average size) was fabricated using solidification processing followed by hot extrusion.
The nanocomposite exhibited similar grain size to the monolithic alloy, reasonable Al2O3 nanoparticle distribution, non-dominant (0 0 0 2) texture in the longitudinal direction, and 15% higher hardness than the
monolithic alloy. Compared to the monolithic alloy (in tension), the nanocomposite exhibited lower yield strength (0.2%TYS)
(−4%) and higher ultimate strength (UTS), failure strain, and work of fracture (WOF) (+13%, +170%, and +200%, respectively).
Compared to the monolithic alloy (in compression), the nanocomposite exhibited lower yield strength (0.2%CYS) (−5%) and higher
ultimate strength (UCS), failure strain, and WOF (+6%, +41%, and +43%, respectively). The effects of Al2O3 nanoparticle addition on the enhancement of tensile and compressive properties of ZK60A are investigated in this article. 相似文献
17.
Jungang Hou R. V. Kumar Yuanfang Qu Dalibor Krsmanovic 《Journal of nanoparticle research》2010,12(2):563-571
Bi4Ti3O12 (BIT) nanoparticles with a narrow average particle size distribution in the range of 11–46 nm was synthesized via a metal-organic polymeric precursor process. The crystallite size and lattice parameter of BIT were determined by XRD analysis. At annealing temperatures >550 °C, the orthorhombic BIT compound with lattice parameters a = 5.4489 Å, b = 5.4147 Å, and c = 32.8362 Å was formed while at lower annealing temperatures orthorhombicity was absent. Reaction proceeded via the formation of an intermediate phase at 500 °C with a stoichiometry close to Bi2Ti2O7. The particle size and the agglomerates of the primary particles have been confirmed by FESEM and TEM. The decomposition of the polymeric gel was ascertained in order to evaluate the crystallization process from TG-DSC analysis. Raman spectroscopy was used to investigate the lattice dynamics in BIT nanoparticles. In addition, investigation of the dependence of the visible emission band around the blue–green color emission on annealing temperatures and grain sizes showed that the effect of grain size plays important roles, and that oxygen vacancies may act as the radiative centers responsible for the observed visible emission band. 相似文献
18.
Y. D. Kolekar S. B. Kulkarni Keka Chakraborty A. Das S. K. Paranjpe P. B. Joshi 《Pramana》2004,63(2):189-197
Nd2Sn2O7 pyrochlores with the substitution of Zr4+ were prepared by conventional ceramic double sintering technique. The single-phase formation was confirmed by X-ray diffraction
and neutron diffraction techniques. Relative intensity calculations for X-ray diffraction analysis were performed for oxygen
positional parametersx = 0.331 and 0.375, while Rietveld refinements were employed for neutron diffraction data. The neutron diffraction study revealed
that there are only two anion sites with 48f and 8b positions. This indicates that the 8a site, i.e. O(3) sublattice, is completely
vacant and the structure is a perfect cubic pyrochlore with space group Fd3m (O
h
7
). From the conductivity measurements, it is observed that the electronic conductivity dominates from room temperature up
to about 525 K and forT > 525 K, the oxygen ion conduction dominates the charge transport in these compositions. Complex impedance spectroscopy indicates
the existence of grain and grain boundary as two separate elements. 相似文献
19.
L. G. Mamsurova N. G. Trusevich K. S. Pigalskiy N. B. Butko A. A. Vishnev 《Bulletin of the Russian Academy of Sciences: Physics》2011,75(8):1136-1139
It was proven experimentally that the structural disordering inherent to fine-grained high-temper- ature YBa2Cu3O
y
superconductors (with an average grain size of 〈D〉 < 2 μm) leads to a reduction of the level of hole doping and the creation of features inherent to the pseudogap state (antiferromagnetic
correlations and the lowered density of states at the Fermi level) even in samples with optimum oxygen content y ≈ 6.92. 相似文献
20.
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