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1.
We have calculated the electronic structures of Co2FeAl1-xSix(101) surface using first-principles method based on the density functional theory. Because of the surface effect, the minority spin band gap at the Fermi level disappears at the surface of bulk Co2FeAl1-xSix. However, beneath the surface, the minority spin gap opens at the Fermi level, which indicates that the electronic structures of Co2FeAl1-xSix(101) be-come close to that of bulk phase. Accordingly, the Co2FeAl1-xSix(101) surface is a composite tri-layer structure that corresponds to the weakening of half-metallic property in Co2FeAl1-xSix films. Even though, the spin polarization of Co2FeAl1-xSix(101) surface is still larger than that of Co2FeAl or Co2FeSi materials, making Co2FeAl1-xSix a promising spintronics material.  相似文献   

2.
The process of the nanocrystallization of magnetically soft Fe72.5Cu1Nb2Mo1.5Si14B9 alloy has been studied using dilatometry and thermomagnetic analysis, together with structural investigations. It has been shown that the amount of nanocrystalline phase precipitated upon heating of the amorphous precursor is in good agreement with a shortening of the ribbon length in the course of crystallization. Thermal expansion at the different stages of heating and cooling depends on the structural and phase states, as well as on the magnetic state of the alloy. The numerical value of the coefficient of linear thermal expansion decreases with an increase in the fraction of the ferromagnetic crystalline phase.  相似文献   

3.
Nano-TiO2/Co4Sb11.7Te0.3 composites were prepared by mechanical alloying (MA) and cold isostatic pressing (CIP) process.The phase composition,microstructure,and thermoelectric properties were characterized.The diffraction spectra of all samples well corresponds to CoSb3 skutterudite diffraction plane.TiO2 agglomerates into irregular clusters.They locate at the grain boundaries or some are distributed on the surface of Co4Sb11.7Te0.3 particles.For composites with high TiO2 content (0.6% and 1.0% TiO2),the phonon scattering by TiO2 particle,pores,and small size grains can result in a remarkable reduction in thermal conductivity.The maximum value of ZT is 0.79 for sample with 0.6 wt.% TiO2 at 700 K,which is 11% higher than that of non-dispersed sample.  相似文献   

4.
In this study, indium-filled CoSb3 skutterudite is synthesized via encapsulated induction melting and subsequent annealing at 823 K for six days, and the crystal structure, lattice constant, filler position, phase homogeneity and stability were investigated. All of the In-filled CoSb3 samples were n-type conducting samples. The temperature dependence of the electrical resistivity showed InzCo4Sb12 is a highly degenerate semiconducting material. The thermal conductivity was reduced considerably by In filling. The highest thermoelectric figure of merit value was achieved when the In filling fraction is 0.25. It was found that the ZT of the In-filled CoSb3 (InzCo4Sb12) was higher than that of the In-substituted CoSb3 (Co3.75In0.25Sb12 and Co4Sb11.75In0.25). This is mainly due to the lower thermal conductivity and higher Seebeck coefficient.  相似文献   

5.
Perovskite-type Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCFO) powders were synthesized using two methods, solid-state reaction (SSR) method and citrate-EDTA complexing method (CC-EDTA). Then the powders were pressed to green disks of 19 mm in diameter and sintered at 1140°C for 5 h. The shrinkage rate and relative density of the membranes prepared from the perovskite-type powders were determined and calculated, and the powders and derived membranes were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that the shrinkage rates of the two kinds of disks are nearly the same (about 10%). The disks prepared by the SSR method had a bigger grain size and lower relative density than those prepared by the CC-EDTA method. The conductivity of the membranes prepared by the SSR method was about 38 S/cm, higher than that of the membranes prepared by the CC-EDTA method, which was about 30 S/cm, at the same temperature of 600°C.  相似文献   

6.
Nanostructured Bi2Se3 and Sn0.5-Bi2Se3 were successfully synthesized by hydrothermal coreduction from SnCl2·H2O and the oxides of Bi and Se. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and field emission scanning electron microscope (FESEM). Bi2Se3 powders obtained at 180°C and 150°C consist of hexagonal flakes of 50–150 nm in side length and nanorods of 30–100 nm in diameter and more than 1 μm in length. The product obtained at 120°C is composed of thin irregular nanosheets with a size of 100–200 nm and several nanometers in thickness. The major phase of Sn0.5-Bi2Se3 synthesized at 180°C is similar to that of Bi2Se3. Sn0.5-Bi2Se3 powders are primarily nanorod structures, but small amount of powders demonstrate irregular morphologies.  相似文献   

7.
A series of Cd x Zn1−x S (x = 0.1–0.9) photocatalysts were prepared by coprecipitation. They could form solid solution semiconductors with hexagonal phase in agreement with pure CdS by characterization of XRD. The photophysical properties of Cd x Zn1−x S photocatalysts were measured by UV-Vis diffuse reflectance spectrum and surface photovoltage spectroscopy (SPS). The band gap energy gradually reduced with the increasing of x value in CdxZn1−x S, and when x = 0.7, the Cd0.7Zn0.3S photocatalyst had the strongest surface photovoltage. Cd x Zn1−x S photocatalysts were used in the photodecomposition of H2S to H2. The evolution rate of H2 over the Cd0.7Zn0.3S photocatalyst was also the highest among Cd x Zn1−x S photocatalysts. And the effect of calcination temperature on the evolution rate of H2 was investigated and the optimum temperature was 650°C.  相似文献   

8.
Stoichiometric Ni0.5Zn0.5Fe2O4 powders were produced by self-propagating high temperature synthesis (SHS). The effects of NiCO3 content in the raw materials on the microstructure and magnetic properties of Ni-Zn ferrite powders were systematically studied. The Ni0.5Zn0.5Fe2O4 powders were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The magnetic properties of the powders were evaluated by vibrating sample magnetometry (VSM). The results show that the introduction of NiCO3 into reactants improves the conversion percentage and refines the Ni0.5Zn0.5Fe2O4 particles. The increase of NiCO3 content enhances the magnetic properties of Ni0.5Zn0.5Fe2O4. Particularly, the saturation magnetization reaches the maximum when the NiCO3 content is 3 at.%.  相似文献   

9.
An isothermal section of the system Al2O3-CaO-CoO at 1500 K has been established by equilibrating 22 samples of different compositions at high temperature and phase identification by optical and scanning electron microscopy, X-ray diffraction, and energy dispersive spectroscopy after quenching to room temperature. Only one quaternary oxide, Ca3CoAl4O10, was identified inside the ternary triangle. Based on the phase relations, a solid-state electrochemical cell was designed to measure the Gibbs energy of formation of Ca3CoAl4O10 in the temperature range from 1150 to 1500 K. Calcia-stabilized zirconia was used as the solid electrolyte and a mixture of Co + CoO as the reference electrode. The cell can be represented as: From the emf of the cell, the standard Gibbs energy change for the Ca3CoAl4O10 formation reaction, CoO + 3/5CaAl2O4 + 1/5Ca12Al14O33 → Ca3CoAl4O10, is obtained as a function of temperature: /J mol−1 (±50) = −2673 + 0.289 (T/K). The standard Gibbs energy of formation of Ca3CoAl4O10 from its component binary oxides, Al2O3, CaO, and CoO is derived as a function of temperature. The standard entropy and enthalpy of formation of Ca3CoAl4O10 at 298.15 K are evaluated. Chemical potential diagrams for the system Al2O3-CaO-CoO at 1500 K are presented based on the results of this study and auxiliary information from the literature.  相似文献   

10.
The thermodynamic database of the ZrO2-Gd2O3-Y2O3-Al2O3 system is up-dated taking into account new data on lattice stabilities of ZrO2, Gd2O3 and Y2O3 and heat capacity measurements for the monoclinic phase Gd4Al2O9 and phase with garnet structure Gd3Al5O12. New data for the heat capacities of Gd2Zr2O7 (pyrochlore) and GdAlO3 (perovskite) as well as on the enthalpy of formation of fluorite solid solutions (Zr1−x Gd x )O2−x/2 were found to be in good agreement with calculated results. In comparison with the previous assessment, taking into account new experimental data resulted in a change of the melting character of the Gd4Al2O9 phase from a peritectic one to a congruent one in the Gd2O3-Al2O3 system. Correspondently, in the ternary system ZrO2-Gd2O3-Al2O3, the melting character of the three-phase assemblage Gd2O3 (B), Gd4Al2O9 and GdAlO3 changed from eutectic to transition type U. The T 0-lines for T/M and F/T diffusionless transformations and driving force of partitioning to equilibrium assemblage T + F were calculated in the ZrO2-Gd2O3-Y2O3 system.  相似文献   

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