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1.
The electrical conductivity (σ), Seebeck coefficient (S), and power factor (σS2) of perovskite-type LaFeO3, La1−xSrxFeO3 [0.1 ≤ x ≤ 0.4] and LaFe1−yNiyO3 [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 LaFeO3 showed semiconducting behavior, and its Seebeck coefficient changed from positive to negative around 650 K with increasing temperature. The electrical conductivity of LaFeO3 increased with the substitutions of Sr and Ni atoms, while its Seebeck coefficient decreased. The Seebeck coefficient of La1−xSrxFeO3 was positive, whereas that of LaFe1−yNiyO3 changed from positive to negative with increasing Ni content. The substitutions of Sr and Ni were effective in increasing the power factor of LaFeO3; 0.0053 × 10−4 Wm−1 K−2 for LaFeO3 (1050 K), 1.1 × 10−4 Wm−1 K−2 for La1−xSrxFeO3 (x = 0.1 at 1100 K) and 0.63 × 10−4 Wm−1 K−2 for LaFe1−yNiyO3 (y = 0.1 at 1100 K).  相似文献   

2.
Two series of compositions with the general formula M1−xCexSiO4 (M = Th, Zr; = 0.0–0.5; 1.0) were prepared by a standard solid state route and characterized by powder XRD. About 10 mol% of ceria could be dissolved in the lattice of ThSiO4. A striking observation was the stabilization of tetragonal modification of ThSiO4, which is metastable, by ceria substitution. There was no solubility of ceria in zircon (ZrSiO4) lattice. The average linear thermal expansion coefficient (293–1123 K) of ZrSiO4, ThSiO4 and Th0.9Ce0.1SiO4 are 4.65 × 10−6, 4.97 × 10−6 and 5.14 × 10−6 K−1, respectively.  相似文献   

3.
The Li0.33La0.55TiO3 solid electrolyte has a maximum grain ionic conductivity of 1.13 × 10−3 S cm−1 among the Li3xLa2/3−xTiO3 oxides (0.21 ≤ 3x ≤ 0.50), but the total ionic conductivity of its polycrystalline phase is not the highest. Owing to the grain-boundary resistances controlling the total resistances of bulk samples, an excellent solid electrolyte is mainly characterized by the grain-boundary resistances. With regard to the role of lithium ions, the substitution of La3+ ions by the Li+ ions weakens the strength of inter-ionic forces, leading to the decrease in the sintering temperature. The presence of La3+/Li+-site vacancies promotes the densification and grain growth and further results in rapid decreases in porosity and grain-boundary resistances. Li0.21La0.60TiO3 with a larger amount of La3+/Li+-site vacancies can therefore exhibit the highest total ionic conductivity through rapidly decreasing its grain-boundary resistances by changing its microstructure, and it becomes a better polycrystalline solid electrolyte than Li0.33La0.55TiO3 in the Li3xLa2/3−xTiO3 system studied, in spite of its lower grain ionic conductivity.  相似文献   

4.
In this communication, we report on the bulk and lattice thermal expansion studies on a number of compounds, within the homogeneity range of solid solutions, in a series with the general composition Ce1−xSrxO2−x (0.0≤x≤0.10). The XRD pattern of each product was refined to determine the solid solubility of SrO into the lattice of CeO2, and the homogeneity range. The composition with maximum solid solubility limit of SrO in CeO2 lattice, under the slow cooled conditions, was delineated as Ce0.91Sr0.09O1.91 (i.e. 9 mol.% of SrO). The bulk thermal expansion measurements from ambient to 1123 K, as investigated by a dilatometer, revealed that the l (293 to 1123 K) values for the compositions within the homogeneity range increase from 11.58×10−6 to 12.13×10−6 K−1 on increasing the Sr2+ content from 0 mol.% (i.e. CeO2) to 9 mol.%, i.e. the upper solubility limit of SrO into the lattice of CeO2. A similar trend was observed in the lattice thermal expansion coefficients a (293 to 1473 K) as obtained by a high temperature-XRD.  相似文献   

5.
Measurements of magnetic properties, X-ray diffraction and magnetostriction were made on Tb0.27Dy0.73(Fe1 − xAlx)2 (x = 0.1, 0.2, …, 0.7) compounds. It was found that the system has the cubic MgCu2 structure over almost the whole (Fe,Al) concentration range investigated, except for a narrow intermediate range (x = 0.4–0.6) where the hexagonal MgZn2 structure appears. With increasing Al content x, the lattice constant a increases linearly with x. The first replacement of Fe results in a marked decrease in the Curie temperature, which is followed by a slight decrease in TC with x. A linear decrease in magnetostriction of |λ| − λ| at room temperature with x was also observed from 1530 × 10−6 for x=0 to 36×10−6 for x=0.3. The saturation magnetization σs exhibits a complex concentration dependence in the Tb0.27Dy0.73(Fe)1 − xAlx)2 system: in the range x < 0.5, σs increases linearly with x and, for x = 0.5–0.6, σs decreases and then increases again. An enhancement of the magnetic ‘hardness’ in this system was also observed at low temperature.  相似文献   

6.
La- and K-doped perovskite-type ceramics, (Sr0.6Ba0.4)1−xLaxPbO3 with x = 0.0−0.1 and (Sr0.6Ba0.4)1−xKxPbO3 with x = 0.00−0.15, were prepared to modify thermoelectric properties of semi-metallic Sr0.6Ba0.4PbO3 via the doping of electrons and holes, respectively. The electrical conductivity σ and Seebeck coefficient S for the ceramics were measured at temperatures of 373–1073 K in air. With the La doping, electron carriers were successively doped and the material changed from a semi-metal for the undoped Sr0.6Ba0.4PbO3 to a metal for the (Sr0.6Ba0.4)0.9La0.1PbO3. With the K doping, the thermoelectric properties were essentially unchanged probably due to the carrier compensation effect by the generation of oxygen deficiencies. The thermoelectric power factor S2σ was maximized to a value of 3.1 × 10−4 Wm−1 K−2 at 773 K for the undoped Sr0.6Ba0.4PbO3 ceramic.  相似文献   

7.
The effect of iron substitution on the electrochemical behaviour of LaNi3.55Mn0.4Al0.3Co0.75−xFex compounds (x=0, 0.15, 0.55) has been studied by chronopotentiometry and cyclic voltammetry techniques. The maximum capacity decreases linearly from 308 to 239 mAhg−1 when the iron content increases from 0 to 7.3 wt.% (x=0.55). This decrease can be explained by the corrosion of the alloy in the aqueous KOH electrolyte. In spite of this decrease and of the long time needed for the activation, a good stability of discharge capacity was observed in LaNi3.55Mn0.4Al0.3Co0.75−xFex compounds. The reversibility of the electrochemical redox reaction of LaNi3.55Mn0.4Al0.3Co0.75−xFex alloy electrodes has been observed in the alloys least rich in iron. The hydrogen diffusivity in LaNi3.55Mn0.4Al0.3Co0.75−xFex alloy electrodes decreases when increasing the iron content. The obtained values of the hydrogen diffusion coefficient DH, varies between 2.1×10−7 and 8.2×10−9 cm2 s−1 depending on the iron content of the electrode.  相似文献   

8.
Series of perovskite-type compounds La1−aCaaCr0.8Ti0.2O3−δ (a=0–1.0) were synthesized by the ceramic technique in air (final heating 1350 °C). The crystal structure of the compounds after cooling in air to room temperature was characterized as orthorhombic in space group Pbnm. Analysis of the lattice constants shows a noticeable decrease with increasing Ca content. All compounds prepared were stable in air and in a stream of Ar/1 Pa O2 at 20–1400 °C, as also in Ar/5% H2 (pH2O/pH2=0.01) at 850–1000 °C. Oxygen stoichiometry and electrical conductivity of the solid solutions with a=0.0–1.0 are investigated. Increasing Ca contents decrease the stability of the oxides in respect to the thermal dissociation of oxygen. All compounds are p-type semiconductors in the temperature range 20–1000 °C at oxygen partial pressures of 10−15 to 0.21×105 Pa. A maximum conductivity of about 30 S/cm in air at 1000 °C is observed for the composition with a=0.6 corresponding to a ratio of Cr3+/Cr4+=1 at an oxygen stoichiometry near 3.0, and oxidation states of La, Ca, Ti, and O ions of 3+, 2+, 4+, and 2−, respectively.  相似文献   

9.
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 U2Ti3Si4 (U2Mo3Si4-type) with a small homogeneity region of about 3 at.% exchange U/Ti and (2) U2−xTi3+xSi4 (Zr5Si4-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 U2Ti and U3Si. U2Ti3Si4 is weakly paramagnetic following a Curie–Weiss law above 50 K with μeff.=2.67 μB/U, ΘP=−150 K and χ0=1.45×10−3 emu/mol (18.2×10−9 m3/mol).  相似文献   

10.
Lithium lanthanoid silicate, a high temperature lithium ion conducting solid electrolyte, synthesized by sol–gel method, has been characterized by TGA/DTA, XRD, FTIR and SEM. Conductivity was found to be 0.847 × 10−6 Ω−1 cm−1 at 750 °C and activation energy was 0.5 eV.  相似文献   

11.
The formation of cation solid solution in the (La1−xGdx)OCl:Eu3+ (0≤xGd≤1; ΔxGd=0.1) series was studied by photoluminescence spectroscopy. The luminescence from the 5D0–2 to the 7F0–4 levels of the Eu3+ ion in the (La1−xGdx)OCl series was recorded at 77 K by using argon ion laser excitation (457.9 nm). The interpretation of the spectra according to the C4v site symmetry of the Eu3+ ion in the tetragonal PbFCl-type structure yielded nearly complete sets (18 to 19 levels) for the 7F0–4 levels. Simulations of the Stark level schemes were carried out with the aid of a phenomenological c.f. theory utilizing the five non-zero c.f. Bqk parameters (B02, B04, B44, B06 and B46) allowed for the C4v site symmetry. By using the calculated c.f. parameter sets a quantitative measure was obtained to monitor the formation of cation solid solutions. The strength of the c.f. effect was estimated with the c.f. strength parameters S and Sk (k=2, 4 and 6). The c.f. parameter sets reproduced the experimental 7FJ (J=0–4) energy level schemes with the rms deviations between 4 and 11 cm−1. The individual parameters as well as the c.f. strength parameters were found to evolve in a smooth manner indicating complete solid solubility in the (La1−xGdx)OCl series. Some local distortions from the C4v symmetry — probably of long range—leading to the splitting of the 7F1 doubly degenerate E level were observed, however.  相似文献   

12.
The hydrogen storage alloys MmNi3.55Mn0.4Al0.3Co0.75−xFex (x = 0.55 and 0.75) were used as negative electrodes in the Ni-MH accumulators. The chronopotentiommetry and the cyclic voltammetry were applied to characterize the electrochemical properties of these alloys. The obtained results showed that the substitution of the cobalt atoms by iron atoms has a good effect on the life cycle of the electrode. For the MmNi3.55Mn0.4Al0.3Co0.2Fe0.55 compound, the discharge capacity reaches its maximum of 210 mAh/g after 12 cycles and then decreases to 190 mAh/g after 30 charge–discharge cycles. However, for the MmNi3.55Mn0.4Al0.3Fe0.75 compound, the discharge capacity reaches its maximum of 200 mAh/g after 10 cycles and then decreases to 160 mAh/g after 30 cycles.

The diffusion behavior of hydrogen in the negative electrodes made from these alloys was characterized by cyclic voltammetry after few activation cycles. The values of the hydrogen coefficient in MmNi3.55Mn0.4Al0.3Co0.2Fe0.55 and MmNi3.55Mn0.4Al0.3Fe0.75 are, respectively, equal to 2.96 × 10−9 and 4.98 × 10−10 cm2 s−1. However, the values of the charge transfer coefficients are, respectively, equal to 0.33 and 0.3. These results showed that the substitution of cobalt by iron decreases the reversibility and the kinetic of the electrochemical reaction in these alloys.  相似文献   


13.
The PrBa2−xSrxCu3Oδ solid solution was investigated by means of X-ray powder diffraction in combination with Rietveld analysis. The Sr-doped Pr123 single phase could be synthesized at 950 °C in air. The solubility of PrBa2−xSrxCu3Oδ solid solution is 0.2≤x≤0.6. The structure of PrBa2−xSrxCu3Oδ is orthorhombic for x=0.2. The structure transforms into tetragonal for 0.3≤x≤0.6. In the PrBa2−xSrxCu3Oδ structure, Sr ions can replace Ba ions, the highest value is x=0.6 under our experimental condition. But Sr ions could not replace Pr ions. Furthermore Pr ions could not occupy the sites of Ba ions in the PrBa2−xSrxCu3Oδ system. Both ionic radii and chemical properties play an important role in the mutual substitution of Pr, Ba and Sr ions in the Pr123 structure of the PrBa2−xSrxCu3Oδ system.  相似文献   

14.
Superplastic behavior of a 7055 aluminum alloy   总被引:1,自引:0,他引:1  
It is shown that a high strength 7055 aluminum alloy with partially recrystallized initial structure exhibits superplastic behavior in the temperature interval 400–490 °C within a wide strain rate range from 8.3×10−5 to 3.3×10−2 s−1. Maximum total elongation of about 960% and strain rate sensitivity coefficient, m, of 0.6 were obtained at a temperature of 450 °C and a strain rate of 3.3×10−4 s−1.  相似文献   

15.
In this paper we report on the characterization of predominantly single phase, fully dense Ti2InC (Ti1.96InC1.15), Hf2InC (Hf1.94InC1.26) and (Ti,Hf)2InC ((Ti0.47,Hf0.56)2InC1.26) 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 Ti2InC; 0.322, 1.443 for (Ti,Hf)2InC; and 0.331 and 1.472 for Hf2InC. 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 Hf2InC, 9.5×10−6 K−1 for Ti2InC, 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 Ti2InC to vacuum (10−4 atm) at 800 °C, results in the selective sublimation of In, and the conversion of Ti2InC to TiCx.  相似文献   

16.
The high temperature phase transitions of orthorhombic La0.95MnO3 from room temperature to 1273 K were studied using high temperature XRD technique in air. Two-phase transitions were found in temperature ranges, 373–473 K and 973–1273 K, respectively. The crystal symmetry increases from orthorhombic to rhombohedral then cubic, while the second transition was not completed in the observation of the present study. The first transition could be due to the depression of Jahn–Teller distortion, while the second one could be caused by the ionic oscillation at high temperature. The lattice thermal expansion coefficients of rhombohedral La0.95MnO3 from 473 to 973 K were also calculated using lattice parameters.  相似文献   

17.
Organoheterobimetallic compounds of the type, [PhHg]2[M(dithio)2] {M=Ni(II), Cu(II) or Zn(II); dithio=isomaleonitriledithiolate (i-MNT2−), 1,1-dicarboethoxy-2,2-ethylenedithiolate (DED2−) or trithiocarbonate (CS32−)} 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   

18.
Nanocrystals La1−xSrxFeO3 (x = 0.0, 0.1, 0.2, 0.4 and 0.6), containing crystal grains of mean diameter 12.4 nm (x = 0.0) and 4–7 nm (x = 0.1–0.6), were compacted into nanocrystalline solid materials under static pressures of 0.5, 1.0 and 1.5 GPa in the axial direction at ambient temperature. The results showed that the peak intensities of the electron paramagnetic resonance (EPR) spectra for the nanocrystalline solid materials were about 103–104 times stronger than those of conventional crystals. The EPR spectra changed with grain size and compacting pressure. The characteristics of the EPR spectra of these nanocrystalline solid materials are discussed.  相似文献   

19.
The electromagnetic field of lasers and non-equilibrium doping conditions enable laser doping of SiC with increased dopant diffusivity. Chromium, which acts as a double acceptor, has been laser-doped in SiC wafers. A thermal model is utilized to determine the temperature distribution at various depths of the wafer and a diffusion model is presented including the effects of Fickian diffusion, laser electromagnetic field and thermal stresses due to localized laser heating on the mass flux of dopant atoms. The dopant diffusivity is calculated as a function of temperature at different depths of the wafer based on measured dopant concentration profile. The maximum diffusivities achieved in this study are 4.61 × 10−10 cm2 s−1 at 2898 K and 6.92 × 10−12 cm2 s−1 at 3046 K for 6H-SiC and 4H-SiC, respectively. The maximum concentration is found to be 2.29 × 1019 cm−3 for 6H-SiC, which is two orders of magnitude higher than the reported value (3 × 1017 cm−3 solid solubility limit).  相似文献   

20.
A large and transparent Yb3+:GdYCOB crystal with dimensions up to 30 mm× 58 mm have been grown by the Czochralski method. The spectral properties of Yb3+:GdYCOB crystal has been investigated. The absorption cross-section (σa) is 1.65 × 10−20 cm2 at 977 nm. The emission cross-section (σe) is 0.25 × 10−20 cm2 with an FWHM of 37.2 nm at 1020 nm. The fluorescence lifetime is 3.00 ms.  相似文献   

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