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1.
The electrical properties of pure and Li 2O-doped CuO/Fe 2O 3 solids were investigated. Pure and variously doped solids were subjected to thermal treatment at 1073–1273 K and the amount of dopant was varied between 0.84 to 3.36 mol%. The effect of precalcination temperature and amount of Li 2O added on the electrical conductivity σ, activation energy Ea and dielectric constant * were studied. The variation of ′ and ″ as a function of frequency for pure and variously doped solids precalcined at different temperatures was also investigated. The results obtained were discussed. 相似文献
2.
Results previously obtained in molecular dynamics experiment with Lennard-Jones ( n−6) (L-J ( n−6)) fluid were applied for the determination of viscous and elastic properties of real molecular fluids (shear viscosity coefficient and pressure). Parameters σ and of real liquids (liquid hydrocarbons) were determined by fitting p– ρ– T data of model fluids to experimental p– ρ– T data of real liquids. Using the data obtained in that way, parameters σ and viscous and elastic characteristics of real liquids were determined. The comparison of experimental and calculated viscous and elastic characteristics revealed lesser dependence of viscous properties from n in comparison with elastic properties. 相似文献
3.
本文用X射线和差热分析方法对BaO-Li 2O-B 2O 3三元系中的两个截面:BaB 2O 4-Li 2B 2O 4和BaB 2O 4-Li 2O作了研究。在BaB 2O 4-Li 2B 2O 4赝二元系中发现了一个新的化合物4BaB 2O 4·Li 2B 2O 4。化合物在930±3℃由包晶反应形成,并与Li 2B 2O 4形成共晶反应。共晶温度为797±3℃,共晶点组分为79mol%Li 2B 2O 4。在BaB 2O 4-Li 2O截面中也存在化合物4BaB 2O 4·Li 2B 2O 4,其包晶反应温度从930±3℃随Li 2O含量增加下降到908±3℃。在组分60mol%Li 2O处形成另一个新的化合物2BaB 2O 4·3Li 2O。该化合物在630±3℃也是由包晶反应形成,并与Li 2O和Li 2CO 3分别形成共晶反应,共晶温度分别为400±3℃和612±3℃。在BaB 2O 4-Li 2B 2O 4和BaB 2O 4-Li 2O体系中都没有观察到固溶体。用计算机程序分别对化合物4BaB 2O 4·Li 2B 2O 4和2BaB 2O 4·3Li 2O的X射线粉末衍射图案进行了指标化,其结果:4BaB 2O 4·Li 2B 2O 4的空间群为Pmma,a=13.033?,b=14.630?,c=4.247?,每个单胞包含两个化合式单位;2BaB 2O 4·3Li 2O的空间群为Pmmm,a=4.814?,b=9.897?,c=11.523?,每个单胞也含有两个化合式单位。
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4.
PbYb 1/2Ta 1/2O 3 single crystals were obtained for the first time. They were grown by the flux method. The PbOPbF 2B 2O 3 system was used as a solvent. Dielectric investigations were carried out in 1 0 0 c, 1 1 0 c and 1 1 1 c pseudocubic directions. These studies pointed to anisotropy of dielectric properties. Frequency-independent ε′( T) and ε″( T) maxima related to the antiferroelectric–paraelectric (AFE—PE) phase transition are observed for all directions at 562 K. The frequency-dependent ε′( T) and ε″( T) maxima near 400 K related to the ferroelectric (FE)–AFE phase transition are observed only in 1 1 1 c direction. The hysteresis loops were observed in this direction only. These results point that ferroelectric relaxor properties appear only in 1 1 1 c direction. We propose to consider the ferroelectric phase as ferrielectric one. 相似文献
5.
We have investigated the magnetic behavior of cobalt ferrite nanoparticles with a mean diameter of 7.2 nm. AC susceptibility of colloidal cobalt ferrite nanoparticles was measured as a function of temperature T from 2 to 300 K under zero external DC field for frequencies ranging from f=10 to 10,000 Hz. A prominent peak appears in both χ′ and χ″ as a function of T. The peak temperature T2 of χ″ depends on f following the Vogel–Fulcher law. The particles show superparamagnetic behavior at room temperature, with transition to a blocked state at TBm94 K in ZFC and 119 K in AC susceptibility measurements, respectively, which depends on the applied field. The saturation magnetization and the coercivity measured at 4.2 K are 27.3 emu/g and 14.7 kOe, respectively. The particle size distribution was determined by fitting a magnetization curve obtained at 295 K assuming a log-normal size distribution. The interparticle interactions are found to influence the energy barriers yielding an enhancement of the estimated magnetic anisotropy, K=6×10 6 erg/cm 3. Mössbauer spectra obtained at higher temperatures show a gradual collapse of the magnetic hyperfine splitting typical for superparamagnetic relaxation. At 4.2 K, the Mössbauer spectrum was fitted with two magnetic subspectra with internal fields Hint of 490, 470 and 515 kOe, corresponding to Fe 3+ ions in A and B sites. 相似文献
6.
In this work, the investigation of the interface state density and series resistance from capacitance–voltage ( C– V) and conductance–voltage ( G/ ω− V) characteristics in In/SiO 2/p-Si metal–insulator–semiconductor (MIS) structures with thin interfacial insulator layer have been reported. The thickness of SiO 2 film obtained from the measurement of the oxide capacitance corrected for series resistance in the strong accumulation region is 220 Å. The forward and reverse bias C– V and G/ ω− V characteristics of MIS structures have been studied at the frequency range 30 kHz–1 MHz at room temperature. The frequency dispersion in capacitance and conductance can be interpreted in terms of the series resistance ( Rs) and interface state density ( Dit) values. Both the series resistance Rs and density of interface states Dit are strongly frequency-dependent and decrease with increasing frequency. The distribution profile of Rs– V gives a peak at low frequencies in the depletion region and disappears with increasing frequency. Experimental results show that the interfacial polarization contributes to the improvement of the dielectric properties of In/SiO 2/p-Si MIS structures. The interface state density value of In/SiO 2/p-Si MIS diode calculated at strong accumulation region is 1.11×10 12 eV −1 cm −2 at 1 MHz. It is found that the calculated value of Dit (≈10 12 eV −1 cm −2) is not high enough to pin the Fermi level of the Si substrate disrupting the device operation. 相似文献
7.
We studied the electronic structure of a chemically Li-intercalated V 2O 5 xerogel. The technique used in the study was V 2p and O 1s X-ray absorption spectroscopy (XAS). The V ions in the as-prepared V 2O 5 xerogel are mostly in a pentavalent V 5+ state. The spectra show that the V ions are partially reduced to V 4+ and V 3+ states upon Li intercalation. The results also show that low Li intercalation ( x<1) affects mostly O 2p–V 3d mixed states, whereas for higher Li intercalation ( x>1), this mechanism saturates and leads to Li 2O formation. 相似文献
8.
Formation of the La 2Cu 1−xCo xO 4+δ solid solutions with orthorhombic K 2NiF 4-type structure was found to be in the range of 0≤ x≤0.30 at temperatures above 1270 K. Incorporating cobalt into the copper sublattice of lanthanum cuprate leads to increasing oxygen hyperstoichiometry and decreasing electrical conductivity. Thermal expansion coefficients of the La 2Cu 1−xCo xO 4+δ ( x=0.02–0.30) ceramics at 470–1100 K were calculated from the dilatometric data to vary in the range (12.2–13.2)×10 −6 K −1. Studying the dependence of oxygen permeation fluxes through La 2Cu(Co)O 4+δ on the membrane thickness demonstrated that the oxygen transport at the thickness values below 1 mm is limited by both surface exchange rate and bulk ionic conductivity. Oxygen permeability of the La 2Cu 1−xCo xO 4+δ solid solutions was ascertained to increase with cobalt concentration at x=0.02–0.10 and to decrease with further dopant additions, indicating a participation of interstitial oxygen in the ionic transport. 相似文献
9.
The thermal expansion of Lu 2Fe 17−xSi x solid solutions has been measured by X-ray powder diffraction. The magnetic ordering in all compounds within the homogeneity range ( x3.4) is accompanied by a large spontaneous volume magnetostriction, distributed anisotropically over the principal axes of the hexagonal crystal structure. The volume effect ωs in the ground state reaches 14.7×10 −3 in Lu 2Fe 17 and decreases monotonously to 8.9×10 −3 for x=3.4, following the reduction of magnetic moment. Despite a still large ωs, the Invar behavior observed in Lu 2Fe 17 changes to a positive thermal expansion for x>1 due to an increasing Curie temperature. 相似文献
10.
Polycrystalline samples of modified lead germanate Pb 4.9A 0.1Ge 2.7Si 0.3O 11 (A=Ca,Sr,Ba) have been prepared by solid-state reaction technique. X-ray studies have been carried out to check the formation of single-phase composition and to obtain preliminary structural data. Measurements of dielectric permittivity ( ) and loss (tan δ) have been studied both as a function of frequency (10 2–10 4 Hz) and temperature (room temperature to 180°C). Phase transition was observed in all three cases but with different Tc value. From the plots of conductivity vs. temperature using dielectric data, collected at 10 kHz activation energy was calculated to investigate the conduction mechanism in them. 相似文献
11.
Cation deficient spinels Ni xMn 3−x□ 3δ/4O 4+δ (0≤ x≤1) have been prepared by thermal decomposition of mixed oxalates Ni x/3Mn (3−x)/3(C 2O 4)· nH 2O in air at 623 K. They have been characterised by temperature programmed reduction (TPR) under H 2, the reaction being followed by gravimetric and powder X-ray diffraction measurements. It has been shown that TPR proceeds in several steps. The first steps correspond to the loss of nonstoichiometric oxygen leading to the formation of a stoichiometric oxide. During the following stages the manganese cations are reduced, causing the spinel structure to be destroyed, and the formation of solid solution of NiO in a cubic MnO. Subsequently, Ni 2+ cations undergo a reduction to metallic nickel, and, finally, a mixture of nonstoichiometric MnO 1−δ and metallic nickel is formed. These oxides contain a high level of vacancies which vary with the nickel content with a maximum of δ≈1 near x=0.6. This nonstoichiometry is ascribed both to the presence of Ni 3+ and excess of Mn 4+. 相似文献
12.
The lithium insertion characteristics of lithium vanadate, Li 4V 3O 8, were investigated using LiV 3O 8 prepared by the precipitation technique as the starting material. The Li 4V 3O 8 phase was formed by lithiation over x=1.5 in Li 1+xV 3O 8, and the diffusion of lithium in this phase determined the reaction rate of insertion more than x=1.5. Improvement of insertion kinetics in the Li 4V 3O 8 phase extended the lithium insertion limit from x=3.2 to x=4.0, compared with the case of LiV 3O 8 by conventional high temperature synthesis. Lithium insertion proceeds as the single-phase reaction in the range of 3.2< x<4.0. 相似文献
13.
Polycrystalline lithium-ammonium sulphate samples were subjected to X-ray diffraction analysis for determining the lattice parameters of the prepared mixed crystals. The compositions of the samples were determined using X-ray microanalysis. The Li0.5(NH4)0.5SO4 samples were irradiated with different doses of γ-radiation in order to investigate the effect of this ionizing radiation on the phase transition temperatures Tc1 and Tc2. The temperature dependence of the d.c. resistivity ρd.c. and dielectric constant of irradiated samples showed (i) a shift of Tc1 to higher temperatures; (ii) a shift of Tc2 to lower temperatures; and (iii) the appearance of a new anomaly near 128°C at moderately high γ-doses. The mechanisms giving rise to this behaviour are discussed. 相似文献
15.
Magnetoelectric composites, namely, xNiFe 2O 4+(1− x)Ba 0.9Sr 0.1TiO 3 were prepared by standard double sintering ceramic method. The X-ray diffraction analysis was carried out to check the phases formed during sintering and to calculate the lattice parameters. Scanning electron microscope (SEM) micrographs were taken to understand the microstructure of the samples. The dielectric constant ( ε′) and loss tangent (tan δ) were measured as a function of frequency in the frequency range 100 Hz–1 MHz. Variation of dielectric constant and loss tangent with temperature and composition has been reported. The hysteresis measurements were done to determine saturation magnetization ( MS) and coersivity ( Hc). The variation of saturation magnetization and magnetic moment is interpreted in terms of composition. 相似文献
16.
Ag +/Na + ion-exchanged aluminosilicate glasses with uniform concentration profiles were prepared, and their electrical conductivities were investigated as functions of the ion-exchange ratio and the initial glass compositions. In the case of the ion-exchanged glasses of x20Ag 2O–(1− x)20Na 2O–10Al 2O 3–70SiO 2 in mol%, the conductivity, σ, and its activation energy, Eσ, showed a minimum and a maximum at the same ion-exchange ratio x=0.3, respectively, and the mixed mobile ion effect (MMIE) was observed. The fully ion-exchanged sample attained σ=3.5×10 −5 S/cm at 200 °C, which was 1.5 orders of magnitude larger than that of initial glass. In the case of x25Ag 2O–(1− x)25Na 2O–25Al 2O 3–50SiO 2, the mixed mobile ion effect was also observed at x=0.5. The maximum conductivity of 2×10 −4 S/cm at 200 °C was obtained in the fully ion-exchanged glass sample. The electric relaxation analysis was also conducted on both systems, and Kohlrausch–Williams–Watts (KWW) fractional exponent β was obtained as a function of x. The decrease of β was observed near x≈0.3 in the former system, while that of the later system was independent of the ion-exchange ratio. Based on the structural analysis results, the observed behaviors were investigated from the point of view of the occupation of Ag+ ions on the non-bridging oxygen-site (NBO-site) and the charge compensation-site (CC-site) of AlO4 tetrahedral unit. 相似文献
17.
Ionic conductivity, σi, of dilute pseudobinary alloys (CuBr) 1−x(Cu 2Se) x ( x≤0.1) in their γ-phase has been measured by an ac method. The increase of the ionic conductivity propertional to x has been observed, which is attributed to interstitial ions brought by Cu 2Se dissolved in CuBr. It is found that the temperature dependence of mobility of interstitial ions, μ, evaluated by the relation Δ σi/ x= kμ ( k is a constant) is bent at the temperature corresponding to the extrinsic–intrinsic transition of the based material CuBr. 相似文献
18.
Lithium insertion to distorted ReO 3-type metastable solid solution Nb xW 1−xO 3−x/2 (0≤ x<0.25) has been studied by chemical and electrochemical methods. In the course of lithium insertion into tetragonal compounds, transition to a cubic phase was found to occur in the region where values of y (in Li yNb xW 1−xO 3−x/2) fall between 0.2 and 0.3, and the phase transition was found to depend on the conditions of the reaction. Changes in OCV and lattice parameters in tetragonal region ( y<0.2) were discussed from the viewpoint of the ordering of lithium ions. Also, the component diffusion coefficient of lithium in tetragonal compounds Li 0.1Nb xW 1−xO 3−x/2 (0≤ x≤0.23) was found to increase with niobium content when x≤0.10, and to saturate at 4×10 −9 cm 2/s. 相似文献
19.
The polycrystalline sample of LiFe 1/2Ni 1/2VO 4 was prepared by a standard solid-state reaction technique and confirmed by X-ray diffractometry. LiFe 1/2Ni 1/2VO 4 has orthorhombic crystal structure whose dielectric and electric modulus properties were studied over a wide frequency range (100 Hz–1 MHz) at different temperatures (296–623 K) using a complex impedance spectroscopy (CIS) technique. The frequency and temperature dependence of dielectric constant ( εr) and tangent loss (tan δ) of LiFe 1/2Ni 1/2VO 4 are studied. The variation of εr as a function frequency at different temperatures exhibits a dispersive behavior at low frequencies. The variation of the εr as a function of temperature at different frequencies shows the dielectric anomaly in εr at 498 K with maximum value of dielectric constant 274.49 and 96.86 at 100 kHz and 1 MHz, respectively. Modulus analysis was carried out to understand the mechanism of the electrical transport process, which indicates the non-exponential type of conductivity relaxation in the material. The activation energy calculated from electric modulus spectra is 0.38 eV. 相似文献
20.
We report on solid state 7Li NMR measurements of electrochemically lithiated SnO. At low Li contents (Li/SnO≤2), the results are consistent with the formation of amorphous Li 2O. For Li/SnO ratio of 4.3, in addition to the amorphous Li 2O phase, there are at least two distinct Sn/Li alloy environments which are similar to those observed in a reference Li 2.3Sn alloy. However the Li + environments in a sample with Li/SnO ratio equal to 6.4 and an Li 4.4Sn reference alloy differ markedly. The NMR data are thus consistent with the simple model of Li insertion proposed by other groups, involving the formation of Li 2O and Li xSn alloys (SnO+ xLi→Li 2O+Li x−2Sn), at low and intermediate Li contents. At high Li content, however, the Li x−2Sn alloy structure is significantly different in the electrochemically lithiated SnO material, compared to that in the reference alloy. 相似文献
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