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1.
The electrical conductivity ( σ), Seebeck coefficient ( S), and power factor ( σS2) of perovskite-type LaFeO 3, La 1−xSr xFeO 3 [0.1 ≤ x ≤ 0.4] and LaFe 1−yNi yO 3 [0.1 ≤ y ≤ 0.6] were investigated in the temperature range of 300–1100 K to explore their possibility as thermoelectric materials. The electrical conductivity of LaFeO 3 showed semiconducting behavior, and its Seebeck coefficient changed from positive to negative around 650 K with increasing temperature. The electrical conductivity of LaFeO 3 increased with the substitutions of Sr and Ni atoms, while its Seebeck coefficient decreased. The Seebeck coefficient of La 1−xSr xFeO 3 was positive, whereas that of LaFe 1−yNi yO 3 changed from positive to negative with increasing Ni content. The substitutions of Sr and Ni were effective in increasing the power factor of LaFeO 3; 0.0053 × 10 −4 Wm −1 K −2 for LaFeO 3 (1050 K), 1.1 × 10 −4 Wm −1 K −2 for La 1−xSr xFeO 3 ( x = 0.1 at 1100 K) and 0.63 × 10 −4 Wm −1 K −2 for LaFe 1−yNi yO 3 ( y = 0.1 at 1100 K). 相似文献
2.
The secondary ion mass spectrometry (SIMS) technique was used to study grain boundary diffusion along (100) twist grain boundaries in the Cu(Ni) system. Concentration profiles of Ni down Cu twist grain boundaries with nominal disorientation angles of 10°, Σ5 (36.87°), and 45°, were measured using the SIMS technique. The average activation energy for grain boundary diffusion, Qb, was found to be 245±22, 140±10, and 102±15 kJ/mol, for the 10°, Σ5, and 45° twist grain boundaries, respectively. The average grain boundary diffusion pre-exponential term, s δDbo, was found to be 9.6±1.24×10 −9, 1.1±0.17×10 −14, and 1.3±0.36×10 −16 m 3/s, for the 10°, Σ5, and 45° twist grain boundaries, respectively. 相似文献
3.
The standard enthalpies of formation of some congruent-melting compounds in the binary systems Re---X, where Re Ce, Pr or La and X C, Si or Ge have been determined by direct-synthesis calorimetry at 1473 ± 2 K. The following values of Δ Hfo are reported: CeC 2, −25.4 ± 1.4 kJ (mol atom) −1; CeSi 2, −60.5 ± 2.0 kJ (mol atom) −1; CeSi, −71.1 ± 3.3 kJ (mol atom) −1; Ce 5Ge 3, −73.4 ± 2.3 kJ (mol atom) −1; CeGe 1.6, −75.6 ± 1.9 kJ (mol atom) −1; PrC 2, −29.4 ± 1.6 kJ (mol atom) −1; PrSi 2, −61.5 ± 1.7 kJ (mol atom) −1; PrSi, −78.1 ± 1.9 kJ (mol atom) −1; Pr 5Ge 3, −70.4 ± 2.3 kJ (mol atom) −1; PrGe 1.6, −81.7 ± 1.7 kJ (mol atom) −1; LaSi 2, −56.8 ± 2.5 kJ (mol atom) −1. The results are compared with earlier experimental data, with predicted values from Miedema's semiempirical model, and with available data obtained for Sn and Pb compounds by Borzone et al., by Palenzona and by Palenzona and Cirafici. 相似文献
4.
Organoheterobimetallic compounds of the type, [PhHg] 2[M(dithio) 2] {M=Ni(II), Cu(II) or Zn(II); dithio=isomaleonitriledithiolate (i-MNT 2−), 1,1-dicarboethoxy-2,2-ethylenedithiolate (DED 2−) or trithiocarbonate (CS 32−)} have been synthesized and investigated by molecular spectroscopies and conductivity techniques. Magnetic behaviour, together with electronic spectra, are compatible with square planar coordination geometry around nickel(II) in [PhHg] 2[Ni(dithio) 2]. Magnetic moments, 1.6 BM and 1.25 BM for [PhHg] 2[Cu(i-MNT) 2] and [PhHg] 2[Cu(DED) 2] showed involvement of some sort of Cu–Cu interaction. Their electronic and EPR spectra show distorted square planar geometry with tetragonal/rhombic symmetry around copper(II). Powder X-ray diffraction patterns of the complexes have been compared. All the complexes show σrt in 2.29×10 −10−4.38×10 −4 S cm −1 range. [PhHg] 2[Ni(DED) 2] and [PhHg] 2[Cu(i-MNT) 2] show semiconducting behaviour as their conductivity increases with increase in temperature with band gaps 0.39 eV; 0.57 eV and 2.38 eV, respectively. 相似文献
5.
The electrical resistivity, Seebeck coefficient, and thermal conductivity of Nd 2(Cu 0.98M 0.02)O 4 (M: Ni and Zn) have been measured in the temperature range from room temperature to about 1000 K. Ni- and Zn-doping decreases the electrical resistivity and the absolute values of the Seebeck coefficient. The thermal conductivity decreases with increasing temperature, showing phonon conduction, and also decreases by doping. The power factor of Nd 2(Cu 0.98Ni 0.02)O 4 reaches 1.02×10 −4 W m −1 K −2 and the figure of merit is 1.35×10 −5 K −1 at 320 K. The relatively low figure of merit compared with that of the state-of-the-art thermoelectric materials is due to the high thermal conductivity. 相似文献
6.
Phase equilibria in the system Si–Ti–U were established at 1000 °C by optical microscopy, EMPA and X-ray diffraction. Two ternary compounds were observed and were characterised by X-ray powder data refinement: (1) stoichiometric U 2Ti 3Si 4 (U 2Mo 3Si 4-type) with a small homogeneity region of about 3 at.% exchange U/Ti and (2) U 2−xTi 3+xSi 4 (Zr 5Si 4-type) extending at 1000 °C for 0.7< x<1.3. Mutual solubility of U-silicides and Ti-silicides was found to be below about 1 at.%. The Ti,U-rich part of the diagram was also investigated at 850 °C establishing the tie-lines to the low temperature compounds U 2Ti and U 3Si. U 2Ti 3Si 4 is weakly paramagnetic following a Curie–Weiss law above 50 K with μeff.=2.67 μ B/U, ΘP=−150 K and χ0=1.45×10 −3 emu/mol (18.2×10 −9 m 3/mol). 相似文献
7.
The effects of Y 2O 3 solute concentration, strain rate, and temperature on solid-solution strengthening in single crystal yttria-stabilized cubic zirconia was investigated. Previous work was extended by studying the flow behaviour at strain rates from 1.5 × 10 −5 s −1 to 8 × 10 −8 s −1 at 1200, 1300 and 1400°C in the harder 001 orientation. Solute hardening in this system is sensitive to strain rate down to 8 × 10 −8 s −1, but at 1400°C there was no difference in flow stress between a 9.4 mol% alloy and 21 mol% alloy at a strain rate of 8 × 10 −8 s −1. The results were explained by the solute drag model. 相似文献
8.
Tracer diffusion of 44Ti was measured between 1373 and 1126 K in four alloys in the composition range from 25 to 35 at% Al in ordered Ti 3Al using the standard precision grinding sectioning technique and polycrystalline samples. The self-diffusion coefficient D*Ti was found to be lower than self-diffusion in pure -Ti and to increase very little with Al concentration. D*Ti reveals Arrhenius behaviour which is described by the frequency factor D0 = (2.44 −1.04+1.81) · 10 −5 m 2/s and the activation enthalpy QTi = (288.2 ± 5.7) kJ/mol. Especially, the stoichiometric composition shows no distinguished diffusion behaviour. Interdiffusion was measured in single phase conditions by combining samples of 25 and 35 at% Al. The interdiffusion coefficient
was evaluated by Boltzmann-Matano analysis between 26 and 34 at% Al at different temperatures. Again, only a weak concentration dependence of
and an Arrhenius behaviour were detected. Applying Darken's equation, the self-diffusion coefficient of aluminium D*Ti was calculated by combining
with the thermodynamic factor Φ(XAl, T) in Ti3Al. D*Al turned out to be smaller than D*Ti, e.g. by a factor of 6 at 1170 K. The Arrhenius relation is characterized by D0 = (2.32 −1.20+2.48) · 10−1 m2/s and QAl = (394.5 ± 7.5) kJ/mol. Different jump possibilities of the Al atoms are discussed. From the overall diffusion behaviour in the Ti3Al-phase it is concluded that atomic migration proceeds via thermal vacancies. There is no indication regarding the formation of constitutional vacancies. Diffusion behaviour of the components Al and Ti in Ti3Al is compared with our recent results of Al impurity diffusion (SIMS analysis) and self-diffusion in pure -Ti. 相似文献
9.
The Pressure–Composition–Temperature ( P– C– T) relations for the LaNiIn, LaNi 0.95Cu 0.05In and LaNiIn 0.98Al 0.02–H systems were measured by a volumetric Sieverts’ method at 398–423 K. All isotherms show plateau pressure regions indicating equilibria between two hydride phases. The replacements of Ni by Cu and In by Al affect the P– C– T diagrams, stability of the hydrides, homogeneity regions of the hydrides formed, slope of the isotherms and critical temperatures of the β–γ transition. In addition, the Cu-doping induces a significant hysteresis between the hydrogen absorption and desorption processes. The relative partial molar thermodynamic properties for the studied systems are: Δ HH = −34.6 ± 2.1 kJ (mol H) −1, Δ SH = −70.7 ± 3.6 J (K·mol H) −1 for LaNiIn–H; Δ HH = −34.1 ± 0.5 kJ (mol H) −1, Δ SH = −74.9 ± 1.0 J (K·mol H) −1 for LaNi 0.95Cu 0.05In–H; Δ HH = −33.2 ± 0.8 kJ (mol H) −1, Δ SH = −68.3 ± 1.2 J(K·mol H) −1 for LaNiIn 0.98Al 0.02–H. 相似文献
10.
Kinetics for lithium ion transfers in the fast ionic conductor Li 2.8(V 0.9Ge 0.1) 2(PO 4) 3 prepared by solid-state reaction method has been studied by electrochemical impedance spectroscopy (EIS) at various temperatures and the results were correlated with observed cathodic behavior. The specific conductivities of Li x(V 0.9Ge 0.1) 2(PO 4) 3 ( x = 0.9–2.8) versus temperatures were analyzed from blocking-electrodes by Wagner's polarization method and the activation energy was calculated. It was observed that electronic conductivities of Li x(V 0.9Ge 0.1) 2(PO 4) 3 increased with lithium contents in the materials. The compounds show a reversible capacity of 131 mAh g −1 at low current density (13 mA g −1). Modeling the EIS data with equivalent circuit approach enabled the determination of charge transfer and surface film resistances. The Li ion diffusion coefficient ( DLi+) versus voltage plot shows three valleys during the first charge cycle coinciding with the irreversible plateau of the voltage versus lithium content profiles reflecting the irreversible phase change in the compound. The obtained DLi+ from EIS varies within 10 −8 to 10 −7 cm 2 s −1, so Li 2.8(V 0.9Ge 0.1) 2(PO 4) 3 shows excellent chemical diffusion performance. 相似文献
11.
A direct isoperibolic differential calorimeter was used to measure the formation heats of the Sm---Al intermetallic compounds. X-ray powder diffraction, optical and scanning electron microscopy and electron probe microanalysis were used to check the composition of the samples. The following values of Δ fH0 for the different compounds were obtained in the solid state at 300 K: Sm 2Al, = −38.0 ± 2 kJ (mol atoms) −1; SmAl, −49.0 ± 2 kJ (mol atoms) −1; SmAl 2, −55.0 ± 2 kJ (mol atoms) −1; SmAl 3, −48.0 ± 2 kJ (mol atoms) −1. The results are discussed and compared with earlier experimental data. 相似文献
12.
In this paper we report on the characterization of predominantly single phase, fully dense Ti 2InC (Ti 1.96InC 1.15), Hf 2InC (Hf 1.94InC 1.26) and (Ti,Hf) 2InC ((Ti 0.47,Hf 0.56) 2InC 1.26) samples produced by reactive hot isostatic pressing of the elemental powders. The a and c lattice parameters in nm, were, respectively: 0.3134; 1.4077 for Ti 2InC; 0.322, 1.443 for (Ti,Hf) 2InC; and 0.331 and 1.472 for Hf 2InC. The heat capacities, thermal expansion coefficients, thermal and electrical conductivities were measured as a function of temperature. These ternaries are good electrical conductors with a resistivity that increases linearly with increasing temperatures. At 0.28 μΩ m, the room temperature resistivity of (Ti,Hf) 2InC is higher than the end members (0.2 μΩ m), indicating a solid solution scattering effect. In the 300 to 1273 K temperature range the thermal expansion coefficients are: 7.6×10 −6 K −1 for Hf 2InC, 9.5×10 −6 K −1 for Ti 2InC, and 8.6×10 −6 K −1 for (Ti,Hf) 2InC. They are all good conductors of heat (20 to 26 W/m K) with the electronic component of conductivity dominating at all temperatures. Extended exposure of Ti 2InC to vacuum (10 −4 atm) at 800 °C, results in the selective sublimation of In, and the conversion of Ti 2InC to TiC x. 相似文献
13.
In this paper, the electrochemical properties of the MmNi 3.55Mn 0.4Al 0.3Co 0.4Fe 0.35 alloy used as a negative electrode in Ni–MH accumulators, have been investigated by different electrochemical methods such as cyclic voltammetry, chronopotentiometry, chronoamperometry and electrochemical impedance spectroscopy. The experimental results indicate that the discharge capacity reaches a maximum value of 260 mAh g −1 after 12 cycles and then decreases to about 200 mAh g −1 after 70 cycles. The value of the mean diffusion coefficient DH, determined by cyclic voltammetry, is about 3.44 × 10 −9 cm 2 s −1, whereas the charge transfer coefficient , determined by the same method, is about 0.5 which allows us to conclude that the electrochemical reaction is reversible. The hydrogen diffusion coefficients in this compound, corresponding to 10 and 100% of the charge state, determined by electrochemical impedance spectroscopy, are, respectively, equal to 4.15 × 10 −9 cm 2 s −1 ( phase) and 2.15 × 10 −9 cm 2 s −1 (β phase). These values are higher, for the phase and less, for the β phase, than the mean value determined by cyclic voltammetry. We assume that this is related to the number of interstitial sites susceptible to accept the hydrogen atom, which are more numerous in the phase than in the β phase. The chronoamperometry shows that the average size of the particles involved in the electrochemical reaction is about 12 μm. 相似文献
14.
Particulate sol–gel LiNi 0.8Co 0.2O 2 has been synthesized by a maleic-acid-assisted process using de-ionized water or ethanol as the solvent. A comparison of the effect on these two different solvents was made on the basis of thermal studies, Fourier transform infrared spectroscopy, X-ray diffraction analysis, chemical diffusion coefficients measurement, and electrochemical cyclability tests. An esterification reaction occurred on the xerogel prepared with ethanol as solvent, reducing Ni and Co from their nitrate salts. LiNi 0.8Co 0.2O 2 grew at the expense of Li 2CO 3, NiO, and CoO during calcination. Better results of capacity and cyclability were obtained in a DI-water-solvent sample associated with a larger interslab thickness between OLiO and lower Ni occupancy on the Li site. The activation energy for the calcinations of DI-water-solvent sample is one-half of that of the ethanol-solvent one, which could be the reason for its better properties. Chemical diffusion coefficients of Li + ion are of the same order 10 −10 cm 2/s, is not affected by the solvents used and/or the temperature raise to 55 °C. 相似文献
15.
The effects of mechanical grinding with or without nickel powder on microstructure and electrochemical properties of Ce 2Mg 17 hydrogen storage alloy in 6 M KOH solution were investigated. The microstructure and electrochemical properties depend greatly on the amount of nickel powder introduced during mechanical grinding. For the alloy ball-milled with nickel powder, the more nickel powder added, the more advantageous it is for the formation of a homogeneous amorphous structure, and the larger discharge capacity obtained. After 90 h ball-milling, the Ce 2Mg 17 + 200 wt.% Ni composite exhibited a large discharge capacity of 1014 mAh g(Ce 2Mg 17) −1[338 mAh g(Ce 2Mg 17 + 200 wt.% Ni) −1] at 303 K. The improvement of electrochemical capacity can be attributed to the formation of a homogeneous amorphous structure as well as the modification of the surface state by Ni addition. 相似文献
16.
The addition of 5 wt.% SiO 2, a viscous second phase, to 8 mol% Y 2O 3 cubic stabilized ZrO 2 (8Y-CSZ) made superplastic 8Y-CSZ. This material had a fine grain size of 0.4 μm and exhibited deformations in tension as large as 520% at 1430 °C with a strain rate of 1.0 × 10 −4 s −1. 相似文献
17.
A novel radical cation salt based on of the donor (4,5-ethylenedithio-4′,5′-vinylenedithio)tetrathiafulvalene (EVT) with the square planar anion Pt(CN) 42− has been synthesized: (EVT) 4·[Pt(CN) 4] (1). According to the X-ray analysis its crystal structure includes EVT cation layers alternating with anion layers along the a-axis of the unit cell. The radical cation layer is formed by EVT stacks with β-packing type, the donors in stacks are tetramerized. The EPR spectra of a plate-like crystal of (EVT) 4·[Pt(CN) 4] salt shows a very weak signal with typical parameters of TTF derivative. The room temperature conductivity of salt 1 is 8×10 −2 Ω −1 cm −1 and the temperature dependence of the conductivity exhibits semiconducting character. 相似文献
18.
The electrochemical behaviour of LaNi 3.55Mn 0.4Al 0.3Co 0.75−xFe x ( x = 0, 0.15, 0.55, 0.75) intermetallic compounds has been studied and presented [C. Khaldi, H. Mathlouthi, J. Lamloumi, A. Percheron-Guégan, Int. J. Hydrogen Energy 29 (2004) 307–311; C. Khaldi, H. Mathlouthi, J. Lamloumi, A. Percheron-Guégan, J. Alloys Compd. 360 (2003) 266–271; C. Khaldi, H. Mathlouthi, J. Lamloumi, A. Percheron-Guégan, J. Alloys Compd. 384 (2004) 249–253]. It has been deduced that the LaNi 3.55Mn 0.4Al 0.3Co 0.4Fe 0.35 compound has interesting electrochemical properties. In this paper we present the electrochemical study of LaNi 3.55Mn 0.4Al 0.3Co 0.4Fe 0.35 compound properties compared with the parent LaNi 3.55Mn 0.4Al 0.3Co 0.75 compound. Several techniques, such as, the chronopotentiometry, the constant potential discharge (CPD), the cyclic voltammetry (CV) and the linear polarization (LP) were applied to characterize these electrochemical properties. The electrochemical discharge capacity of the LaNi 3.55Mn 0.4Al 0.3Co 0.75 alloy increases to reach 294 mAh g −1 after few cycles only (five cycles). However, the activation of the LaNi 3.55Mn 0.4Al 0.3Co 0.4Fe 0.35 alloy takes more than 20 cycles to be achieved and the obtained maximum discharge capacity is 194 mAh g −1. The hydrogen diffusion coefficient DH was determined by constant potential discharge and cyclic voltammetry techniques. The obtained values of the LaNi 3.55Mn 0.4Al 0.3Co 0.75 and LaNi 3.55Mn 0.4Al 0.3Co 0.4Fe 0.35 compounds are 6.29 × 10 −11 and 7.62 × 10 −11, and 2 × 10 −8 and 7.5 × 10 −8 cm 2 s −1 by CPD and CV techniques, respectively. The exchange current density values, determined by a linear polarization technique, are 44 and 27 mA g −1, respectively, for LaNi 3.55Mn 0.4Al 0.3Co 0.75 and LaNi 3.55Mn 0.4Al 0.3Co 0.4Fe 0.35 alloys. 相似文献
19.
Two sets of Er 3+-doped alkaline-free glass systems, MgF 2–BaF 2–Ba(PO 3) 2–Al(PO 3) 3 (MBBA) and Bi(PO 3) 3–Ba(PO 3) 2–BaF 2–MgF 2 (BBBM), have been prepared and investigated with the aim of using them as active media. Radiative lifetimes ( τrad) and branching ratios ( β) have been obtained for the excited states of Er 3+. The absorption spectra were recorded to obtain the intensity parameters ( Ωt) which are found to be Ω2 = 4.47 × 10 −20 cm 2, Ω4 = 1.31 × 10 −20 cm 2, Ω6 = 0.81 × 10 −20 cm 2 for the MBBA system and Ω2 = 4.03 × 10 −20 cm 2, Ω4 = 1.34 × 10 −20 cm 2, Ω6 = 0.53 × 10 −20 for the BBBM system, respectively. The emission cross-section for the 4I 13/2 → 4I 15/2 transition is determined by the Fuchtbauer–Ladenburg method and found to be 2.35 × 10 −20 cm 2 and 3.54 × 10 −20 cm 2 for the MBBA and BBBM system, respectively. Comparison of the measured values to those of Er 3+ transitions in other glass hosts suggests that our new glass systems are good candidates for broadband compact optical fiber and waveguide amplifier applications. 相似文献
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