共查询到20条相似文献,搜索用时 28 毫秒
1.
The crystal structure of Y 3TaNi 6+xAl 26 (refined composition Y 4TaNi 6+[7]Al 20+[6]) was determined by single-crystal X-ray diffraction (λ(Mo K) −0.71073 A. μ −17.827 mm 1, F(000) = 700, T = 293 K, wR = 0.015 for [8] unique reflections). This new quaternary aluminide crystallizes with a cubic structure. Pearson code cP49-12.85, (221) Pm-3m-ji'gdba, a = 8.3600(1) Å. V = 584.28(2) Å, Z = 1, M1 = 1510.25, Dx = 4.292 mg mm 1. The structure of Y xTaNi 6+xAl 26 is filled-up substitution variant of the BaHg 11 structure type with one additional atom site, partly occupied (around 15%) by Ni atoms, located at the centre of a cube formed by Al atoms. Distinct atom coordinates were refined for Ni and Al atoms on a site for which mixed occupation (approximately 50% Ni/50% Al) was found. The Ta atoms centre regular Al atom cuboctahedra, and the Y atoms 20-vertex polyhedra, formed by Al and Ni atoms, similar to those observed in CeMn 4Al 8 and YbFe 2Al 10. 相似文献
2.
Single crystals of KCr 0.8Al 0.2Mo 2O 8 were prepared and investigated by the X-ray diffractometer technique. It shows a structure type related to trigonal KAIMo 2O 8, monoclinic NaCrMo 2O 8 or orthorhombic KInMo 2O 8, space group C2h6— C2/ c; a=17.445 Å, b=5.649 Å, c=8.997 Å, β=119.37°; Z=4. KCr 0.8Al 0.2Mo 2O 8 is characterized by isolated MoO 4 tetrahedra, isolated (Cr/Al)O 6 octahedra and a distorted square antiprism around K +. The crystal structure is discussed with respect to those of related compounds. ZusammenfassungEinkristalle von KCr0.8Al0.2Mo2O8 wurden synthetisiert und mit Vierkreisdiffraktometertechnik röntgenographisch untersucht. Sie zeigen einen mit trigonal-KA1Mo2O8, monoklin-NaCrMo2O8 oder orthorhombisch-KlnMo2O8 verwandten Strukturtyp, Raumgruppe C2h6—C2/c; a=17,445 Å, b=5,649 Å, c=8,997 Å, β=119,37°; Z=4. KCr0.8Al0.2Mo2O8 zeichnet sich durch isolierte MoO4-Tetraeder, isolierte (Cr/Al)O6-Oktaeder und ein verzerrtes quadratisches Antiprisma um K+ aus. Die Kristallstruktur wird mit solchen verwandter Verbindungen diskutiert. 相似文献
3.
The structure of the ternary phase Co 3Al 8Ga, Pearson symbol oI96, space group Immm, a=12.0081(7) Å, b=7.5701(6) Å, c=15.394(1) Å is isotypic with Co 2NiAl 9. Powder diffraction data are reported for this ternary intermetallic compound. Using liquid quenching, the metastable pseudoternary decagonal phase d-Co(Al, Ga) 3( m) was obtained in the aluminium-rich portion of the ternary system Co–Al–Ga. Gallium substitutes for aluminium atoms in the d-Co(Al, Ga) 3( m) phase up to a mol fraction xGa=0.10. In the phase of the binary system Co–Al richest in aluminium, Co 2Al 9, the aluminium atomic positions can be occupied by gallium up to a gallium content of xGa=0.05. 相似文献
4.
Polycrystalline hydrogen storage alloys based on lanthanum (La) are commercially used as negative electrode materials for the nickel–metal hydride (Ni–MH x) batteries. In this paper, mechanical alloying (MA) was used to synthesize nanocrystalline LaNi 4−xMn 0.75Al 0.25Co x ( x=0, 0.25, 0.5, 0.75 and 1.0) hydrogen storage materials. XRD analysis showed that, after 30 h milling, the starting mixture of the elements decomposed into an amorphous phase. Following the annealing in high purity argon at 700 °C for 0.5 h, XRD confirmed the formation of the CaCu 5-type structures with a crystallite sizes of about 25 nm. The nanocrystalline materials were used as negative electrodes for a Ni–MH x battery. Cobalt substituting nickel in LaNi 4Mn 0.75Al 0.25 greatly improved the discharge capacity and cycle life of the LaNi 5 material. For example, in the nanocrystalline LaNi 3.75Mn 0.75Al 0.25Co 0.25 powder, discharge capacities up to 258 mA h g −1 (at 40 mA g −1 discharge current) were measured. Mechanical alloying is a suitable procedure to obtain LaNi 5-type alloy powders for electrochemical energy storage. 相似文献
5.
Ternary R 3Pd 4Ge 4 samples (R=Nd, Eu, Er) were investigated by means of X-ray single crystal (four circle diffractometer Philips PW1100, MoK radiation) and powder diffraction (MX Labo diffractometer, CuK radiation). The Er 3Pd 3.68(1)Ge 4 compound belongs to the Gd 3Cu 4Ge 4 structure type, space group Immm, a=4.220(2) Å, b=6.843(2) Å, c=14.078(3) Å, R1=0.0484 for 598 reflections with Fo>4σ( Fo) from X-ray single crystal diffraction data. No ternary R 3Pd 4Ge 4 compound when R is Nd or Eu was observed. The Nd and Eu containing samples appeared to be multiphase. Ternary phases observed in the Nd 3Pd 4Ge 4 and Eu 3Pd 4Ge 4 alloys and their crystallographic characteristics are the following: NdPd 2Ge 2, CeGa 2Al 2 structure type, space group I4/ mmm, a=4.3010(2) Å, c=10.0633(2) Å (X-ray powder diffraction data); NdPd 0.6Ge 1.4, AlB 2 structure type, space group P6/ mmm, a=4.2305(2) Å, c=4.1723(2) Å (X-ray powder diffraction data); Nd(Pd 0.464(1)Ge 0.536(1)) 2, KHg 2 structure type, space group Imma, a=4.469(2) Å, b=7.214(2) Å, c=7.651(3) Å, R1=0.0402 for 189 reflections with Fo>4σ( Fo) (X-ray single crystal diffraction data); Eu(Pd,Ge) 2, AlB 2 structure type, space group P6/ mmm, a=4.311(2) Å, c=4.235(2) Å; EuPdGe, EuNiGe structure type, space group P2 1/ c, and ternary compound with unknown structure (X-ray powder diffraction data). 相似文献
6.
The atomic structure of a new ternary phase UFe 2Al 10 appearing in the U–Fe–Al system was determined using direct methods applied to X-ray powder diffraction data. High resolution electron microscopy combined with the methods of crystallographic image processing was used for the verification of the structural model. The UFe 2Al 10 phase is orthorhombic and belongs to Cmcm space group, its unit cell contains 40 Al, eight Fe, and four U atoms. The lattice parameters obtained after Rietveld refinement are: a=8.919 Å, b=10.208 Å, and c=9.018 Å. The reliability factors characterizing the Rietveld refinement procedure are: Rp=5.9%, Rwp=8.1%, and Rb=2.9%. 相似文献
7.
The crystal structure of intermetallic compound Gd 6Cr 4Al 43 has been investigated by means of X-ray diffraction data (Ho 6Mo 4Al 43 structure type, space group P6 3/ mcm, Pearson symbol hP106, a = 10.9144(7) Å, c = 17.7361(13) Å). SQUID magnetic measurements carried out for the title compound point to the existence of two antiferromagnetic phase transitions observed at TN1 = 19.0(1) K and TN2 = 6.8(1) K, respectively. 相似文献
8.
通过Thermo-Calc软件计算、微观组织多尺度表征以及热模拟试验等研究了Al 25Nb 20Ti 30Zr 25合金的组织结构、高温组织稳定性和热加工性能。结果表明,Al 25Nb 20Ti 30Zr 25合金的铸锭组织主要由BCC基体相和Zr 5Al 3析出相组成,Zr 5Al 3相在BCC晶界连续析出,晶粒内部的Zr 5Al 3相呈块状分布,平均尺寸在750 nm左右;合金在750~1000 ℃保温24 h后,基体中的晶粒尺寸并未发生明显变化;随着温度的增加,Zr 5Al 3相含量小幅度降低,合金的高温组织稳定性较好。建立了合金的本构方程为$\dot{ε}$=4.5×10 14×[sinh(0.0063 σp)] 2.8exp(-419/ RT),并绘制了合金的能量耗散系数图;在1050 ℃/1 s -1变形条件下,能量耗散系数达到峰值0.69,在该变形条件下等温锻造出尺寸为$\phi$ 180 mm×20 mm完整无开裂的圆形块体材料。锻造消除了原始晶界处连续分布的Zr 5Al 3相,使其分解成短杆状均匀分布于合金基体中,BCC基体组织发生了动态回复和部分再结晶。 相似文献
9.
The studies of the thermoelectric power and band structure calculations for CeNi 4Si are reported. These studied are supported by magnetic susceptibility, electrical resistivity, specific heat and X-ray photoemission spectroscopy measurements. CeNi 4Si is paramagnetic down to 2 K and follows the Curie–Weiss law with μeff = 0.52 μB/f.u. and the paramagnetic Curie temperature θP = −2 K. This effective paramagnetic moment is lower than the free Ce 3+ value. The obtained values for the f occupancy nf and for the coupling Δ of the f level with the conduction states are in good agreement with the values found for mixed valence compounds. Below the Fermi energy the total density of states contains mainly the d states of Ni atoms. The narrow peaks of the f states of Ce atoms were found above the Fermi level. CeNi 4Si is characterized by γ = 16 mJ mol −1 K −2 and θD = 335 K. 相似文献
10.
The peritectoid formation of Ni 5Al 3 from the two phases NiAl and Ni 3Al was studied in a Ni---Al alloy containing 66 at% Ni by means of transmission electron microscopy. The product phase does not form as a uniform layer between the two initial phases as expected and already observed in a few systems. In the system studied here there are only very few nucleation sites located at the NiAl/Ni 3Al interface. The further growth of Ni 5Al 3 takes place only into one of the initial phases which is NiAl. A strict orientation relationship between NiAl and Ni 5Al 3 was observed; the growth direction was [221]. The transformation is presumably diffusion controlled; it is very sluggish and it can be described by a nucleation and growth process. From the study presented here we conclude that the formation of Ni 5Al 3 proceeds by a micromechanism which differs from that normally assumed for peritectoid reactions. 相似文献
11.
Rapidly solidified LaNi 4.25Al 0.75 alloy was prepared by melt spinning and its hydrogen storage properties were examined. The hydrogen storage capacities and the equilibrium pressures of the unannealed melt-spun (UMS) LaNi 4.25Al 0.75 alloy were found to be nearly identical to those of the annealed induction-melt (AIM) alloy. However, the resistance to pulverization was greatly improved and the hysteresis was markedly decreased for the UMS alloy, while its activation became rather difficult. 相似文献
12.
The bottleneck effect observed in electron spin resonance (ESR) was removed by replacing the Gd 3. spins by non-magnetic lanthanum ions in two compounds: the most bottlenecked GdCu 2Si 2 and GdNi 2Si 2 where the bottleneck is weaker. The unbottlenecked limit was reached for very small Gd concentrations to (1 −x) = 0.0005. From these results the ν( EF) JSc values have been estimated, where ν( EF) is the electron density of states at the Fermi level and JSc is the exchange coupling constant between conduction electrons and Gd spins. It was found that these values are twice as large for Ni compounds (15 × 10 3) as for Cu compounds (7.5 × 10 3). On the basis of X-ray photoemission spectra of the valence band and theoretical calculations of ν( EF) for LaCu 2Si 2, the density of states is estimated as 0.15 states per eV spin atom for GdCu 2Si 2 and 0.3 states per eV spin atom for GdNi 2Si 2 (for JSc = 0.05 eV). The relaxation processes in the investigated compounds are also discussed. 相似文献
13.
AB 5-type intermetallic compounds were prepared by arc-melting in argon atmosphere. The composition of a stoichiometric compound LaNi 3.6Al 0.4Co 0.7Mn 0.3 with a hexagonal CaCu 5 structure was varied by stoichiometric and nonstoichiometric addition of Ti. With the increase of the Ti y0.05 content in LaNi 3.6Al 0.4Co 0.7Mn 0.3Ti y, the hydrogen storage capacity is enhanced, whereas when y=0.1–0.3, it is decreased. The discharge capacity and cyclability are increased considerably by addition of titanium in the range of 0.02–0.1 with a maximum value at about 0.1%. The highest maximum capacity is achieved for a nonstoichiometric addition of 0.05% Ti. The kinetic properties are also additionally improved by the formation of a titanium-rich second phase. This can explain the improvement of the capacity for alloys with low Ti content. The decrease in capacity for high Ti content was also correlated with the amount of the Ti-rich phase. Therefore, the improvement of kinetics are due to the catalytic effect, grain boundary diffusion effect or more pronounced alloy pulverization upon cycling. This study has been aimed to improve the electrode properties of a series of multicomponent LaNi 3.6Al 0.4Co 0.7Mn 0.3Ti y ( y=0.0, 0.02, 0.05, 0.1, 0.2, 0.3) alloys which have mutual complementary properties. All the prepared alloys have been subjected to analyses by EDS, SEM and XRD. In order to determine the hydrogen storage capacity, the pressure composition isotherms ( P– C– T curves) have been used. The metal hydride electrodes were characterized by galvanostatic cycling test. 相似文献
14.
在Ni基体电沉积不同厚度的Ni-CeO 2复合镀层并对其进行620 °C低温渗铝,制备了剩余复合镀层厚度分别约为10和45 μm厚的 δ-Ni 2Al 3-CeO 2/Ni-CeO 2涂层体系。1000 °C真空退火5 h后,以上两种涂层体系均可在铝化物/镀层界面形成CeO 2富集层。但剩余复合镀层厚度为10 μm的涂层体系由于氧化物富集程度不足,涂层退化程度较剩余复合镀层厚度为45 μm的涂层体系严重。可见,在镀层氧化物颗粒含量一定的情况下,渗铝后剩余镀层厚度是影响扩散障有效性的重要因素。 相似文献
15.
CaO-Al 2O 3基保护渣在解决高铝钢连铸过程渣-金反应性问题中展现了巨大潜力,但仍存在结晶能力过强、熔化温度偏高等问题。因此,研究了BaO对CaO-Al 2O 3-CaF 2-B 2O 3-Na 2O-Li 2O-MgO多元渣系熔化温度、结晶行为和微观结构的影响。研究结果表明,BaO的加入降低了渣系软化温度和熔化温度,随着BaO含量的增加,降低程度减弱;BaO的加入使渣系结晶相由Ca 12Al 14O 33和Ca 3B 2O 6 2相共同析出转变为Ca 12Al 14O 33、Ca 3B 2O 6和BaAl 2O 4 3相共同析出,且随着BaO 的增加,渣系结晶温度降低,结晶能力减弱;Ba2+对[AlO 4]5-具有较强电价补偿效应,使其能够稳定存在,Al-O网络结合更为紧密,游离O2-难以进入孔隙中破坏桥氧链接,从而导致网络聚合度轻微升高,原子扩散能力降低,提高了结晶动力学势垒,抑制了结晶。 相似文献
16.
The isothermal section of the Yb---Cu---Al phase diagram at 870 K over the whole concentration region has been constructed using X-ray structure and phase analysis. We have confirmed the existence of earlier reported ternary compounds: YbCuAl (ZrNiAl type) and YbCu 4Al 8 (CeMn 4Al 8 type); the previously reported compound YbCu 4Al proved to be a solid solution of aluminium in the binary compound YbCu 5 (CaCu 5). New ternary aluminides such as Yb 4(Cu 0.26Al 0.74) 33 (new structure type), Yb 2(Cu 0.57Al 0.43) 17 (Th 2Zn 17), Yb(Cu 0.85Al 0.15) 6 (YbMo 2Al 4) 7 Yb 6(Cu 0.74Al 0.26) 23 (Th 6Mh 23) and Yb(Cu 0.30Al 0.70) 3 (PuNi 3) have been prepared for the first time and their crystal structures have been determined. The limits of solid solutions of the binary compound YbCu 5 and the homogeneity ranges of the ternary phases Yb(CuAl) 12, Yb(CuAl) 17 and Yb(CuAl) 2 have been established. 相似文献
17.
A novel molybdenum diphosphate, Mo 1.3O(P 2O 7), was obtained by electrochemical lithium deintercalation. The diphosphate crystallises in space group I2/ a with the lattice parameters a=22.88(1), b=22.94(2), c=4.832(1) Å, γ=90.36°, Z=8. Its original framework is built up from MoO 6 octahedra, P 2O 7 groups and also from MoO 4, Mo 2O 4 and Mo 3O 8 units containing Mo 2 and Mo 3 clusters. These polyhedra delimit large octagonal and z-shaped tunnels running along c, in which the inserted cations may be located. 相似文献
18.
We report on sample preparation, annealing effects, electron microprobe analysis in the series Ce yFe 4−xCo xSb 12 which shows that a phase separation occurs for substituted samples (0< x<4) annealed at 650 and 550 °C. Single phase samples are obtained for either Ce yFe 4Sb 12 or Ce yCo 4Sb 12 samples annealed at 650 °C and for all compositions when annealed at 700 °C. The valence state of Ce in homogeneous samples has been studied using X-ray absorption spectroscopy (XAS). Ce ions are trivalent throughout the series and the XAS spectra does not show effect of the crystal field on the 5d-final state. 相似文献
19.
The magnetocrystalline anisotropy of R 2Fe 17 (R=Y, Gd, Tb, Ho and Er) and their hydrides are studied by analyzing the magnetization curves of single crystal samples in the temperature range 4.2–300 K in magnetic fields up to 140 kOe. There is no noticeable influence of hydrogenation on the magnetic anisotropy in the Y 2Fe 17 and Gd 2Fe 17 compounds. An easy-plane to easy-cone transition is detected for a Tb 2Fe 17H 3 single crystal after hydrogenation. A significant change of the magnetization process has been observed in the hydrides Ho 2Fe 17H 3 and Er 2Fe 17H 3. Hydrogenation induces a FOMP-type transition in the Ho 2Fe 17H 3 compound and, on the contrary, leads to the disappearance of the FOMP type transition in the Er 2Fe 17H 3 compound. The obtained results are discussed on the basis of a model based on the interaction of the quadrupolar moment and the magnetic moment of the 4f electron shell of the rare earth ion with the interstitial hydrogen. It is established that the orientation of the quadrupolar moment of the asymmetric 4f shell with respect to the direction of the resulting magnetic moment of 4f electrons plays an important role. 相似文献
20.
The compound CsTi 5Te 8 was obtained as a crystalline product by an “U-assisted” reaction of Cs, Ti, U, and Cs 2Te 3 in a CsCl flux at 1173 K. The structure of CsTi 5Te 8 contains a three-dimensional network of face-sharing and edge-sharing TiTe 6 octahedra that form one-dimensional channels. The Cs + cations reside in channels that propagate in the [0 1 0] direction. The structure is closely related to several other types of channel structures including those of the minerals of the hollandite and psilomelane families, and those of the TlV 5S 8 and TlCr 3S 5 structure types. 相似文献
|