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1.
The structure and magnetic properties of Nd1−xYxMn2Ge2 (0.0≤x≤0.6) were studied by X-ray powder diffraction and magnetization measurements. All compounds crystallize in the ThCr2Si2-type structure with space group I4/mmm. Substitution of Y for Mn led to a linear decrease in the lattice constants and the unit cell volume. Increasing substitution of Y for Nd in NdMn2Ge2 shows a depression of ferromagnetic ordering and the gradual development of antiferromagnetic ordering. 相似文献
2.
I. Nehdi M. Abdellaoui L. Bessais C. Djega-Mariadassou H. Zarrouk 《Journal of Alloys and Compounds》2003,360(1-2):14-20
The crystallographic and the Curie temperature of the Sm2Fe17−xCrxC2 (x=0.5, 1, 1.5 and 2) carbides have been extensively studied. X-ray diffraction studies have shown that all these alloys are approximately single phases corresponding to the Th2Zn17 type rhombohedral structure with a small amount of -Fe. The amount of this residual -Fe phase decreases with increasing the Cr atomic content. It decreases from 1 wt% for x=0.5 to 0.4 wt.% for x=2. The lattice parameter c increases as a function of the Cr atomic content x from x=0 to x=1.5 and then decreases. This is due to the Cr atoms which prefer to substitute the Fe atoms in the 6c sites located along the c-axis. The lattice parameter a and the unit-cell volume decrease in all substitution ranges. The insertion of the C atoms leads essentially to an increase of the distances between the 9d and 18h sites and the 9d–18f sites. The Curie temperature reaches a maximum value of 583 K for x=1.5 and then decreases to 551 K for x=2. The enhancement of the Tc for lower Cr contents is due to a lowering of the hybridization of the iron atoms with their neighbors, the magnetovolume effect and the reduction of antiferromagnetic interactions. However, the decrease in Tc for higher Cr content is due to the reduction in the number of Fe–Fe pairs due to the magnetic dilution effect. For given interatomic distances, the exchange coupling of the Cr–Cr atoms is not of antiferromagnetic type and the exchange integral of the Cr–Cr pair is higher than that of the Fe–Fe pair. 相似文献
3.
The structure and magnetic properties of CeMn2−xCoxGe2 (0.0≤x≤1.0) were studied by X-ray powder diffraction and magnetization measurements. All compounds crystallize in the ThCr2Si2-type structure with space group I4/mmm. Substitution of Co for Mn leads to a linear decrease in the lattice constants and the unit cell volume. Increasing substitution of Co for Mn shows a depression of ferromagnetic ordering. 相似文献
4.
The TiCr2−xVx compounds with 0.0≤x≤1.2 series have been synthesised and characterised by X-ray powder diffraction. X-Ray qualitative and quantitative phase analysis has been carried out on the as-cast alloys using the Rietveld method. The refinements of the structure shows that the materials crystallise either in the hexagonal or in the cubic Laves phase type for low V contents. For x>0.6, the system is found of b.c.c.-type structure only. The pressure–composition–temperature (P–C–T) isotherms measured at 298 K show that the as-cast alloys absorb large amounts of hydrogen, from 4 to 5.2 H/f.u. The P–C–T diagrams reveal also the presence of a relatively flat plateau, and a large hysterisis effect, and correspondingly the hydride cannot be completely dehydrogenated. 相似文献
5.
C. Khaldi H. Mathlouthi J. Lamloumi A. Percheron-Gugan 《Journal of Alloys and Compounds》2003,360(1-2):266-271
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
6.
The HfFe6Ge6-type RMn6Sn6−xXx′ solid solutions (R=Tb, Dy, X′=Ga, In; x≤1.4) have been studied by powder magnetization measurements. All the series are characterized by ferrimagnetic ordering and by a decrease in Curie temperatures with the substitution (ΔTc/Δx≈−39 K for X′=Ga and ΔTc/Δx≈−75 K for X′=In). The RMn6Sn6−xGax systems are characterized by a strong decrease in the spin reorientation temperature with substitution (ΔTt/Δx≈−191 K and −78 K for R=Tb and Dy, respectively) while this transition almost does not change in systems containing indium. The coercive fields drastically decrease with the substitution in the TbMn6Sn6−xGax system while the substitution of In for Sn has a weaker effect. The coercive fields of the Dy compounds do not vary greatly with the substitution in both series. The behaviour of the TbMn6Sn6−xGax is compared with the evolutions observed in the TmMn6Sn6−xGax series. This comparison strongly suggests that the replacement of Sn by Ga changes the sign of the A02 crystal field parameter. 相似文献
7.
The HfFe6Ge6-type YbMn6Ge6−xGax solid solution (0.07≤x≤0.72) has been studied by X-ray diffraction, microprobe analysis and powder magnetization measurements. All the compounds order antiferromagnetically between TN=481 K for x=0.07 and TN=349 K for x=0.72 and display more or less pronounced spontaneous magnetization at lower temperature. The corresponding Curie points increase from 40 K for x=0.07 to 319 K for x=0.72. The maximum magnetization values of the Ga-rich compounds (M≈5 μB/f.u. at 6 K) is compatible with a ferrimagnetic order of the Mn and Yb sublattices whereas the smaller values measured in the Ga-poor compounds suggest the stabilization of non-colinear magnetic structures. All the studied compounds are characterized by rather large coercive fields at low temperature (4.0≤Hc≤8.2 kOe). 相似文献
8.
D. Brardan C. Godart E. Alleno E. Leroy P. Rogl 《Journal of Alloys and Compounds》2003,350(1-2):30-35
We report on sample preparation, annealing effects, electron microprobe analysis in the series CeyFe4−xCoxSb12 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 CeyFe4Sb12 or CeyCo4Sb12 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
9.
H.H. Cheng H.G. Yang S.L. Li X.X. Deng D.M. Chen K. Yang 《Journal of Alloys and Compounds》2008,458(1-2):330-334
Rapidly solidified LaNi4.25Al0.75 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) LaNi4.25Al0.75 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
10.
Mössbauer spectrometry (57Fe and 119Sn) was used to investigate phase separation in coarse-grained Fe0.55Cr0.45 and in mechanically-alloyed nanocrystalline Fe0.55Cr0.45, Fe0.52Cr0.45Sn0.03 and Fe0.49Cr0.45Sn0.06 alloys during isothermal annealing at 748 K. Phase separation occurs faster in nanocrystalline Fe–Cr than in cold-rolled coarse-grained alloys. The effect of the interconnected microstructure on room-temperature hyperfine magnetic field distributions of alloys aged for hundreds of hours is qualitatively discussed. Tin hinders grain growth of nanocrystalline alloys. 相似文献
11.
K. Young T. Ouchi Y. Liu B. Reichman W. Mays M.A. Fetcenko 《Journal of Alloys and Compounds》2009,480(2):521-528
Simple ternary alloys with formula TixZr7−xNi10 (x between 0 and 2.5) were studied as a potential replacement for Laves phase alloys used in the negative electrodes of nickel metal hydride batteries. The samples were prepared by arc-melting and were not annealed. The samples retained a high degree of disorder, which contributed positively to activation and other electrochemical properties. Before hydrogenation, the alloys have a Zr7Ni10 orthorhombic structure mixed with some C15 and ZrO2 secondary phases. The amount of C15 secondary phase is important to the bulk diffusion of hydrogen and the surface electrochemical kinetics. That is, the diffusion coefficient and the exchange current both increase in the presence of C15 secondary phase. The proportion of C15 secondary phase is controllable by stoichiometry design. For instance, a slightly higher Zr content reduces the C15 content. Further, as the titanium substitution level increases: (1) the lattice constants decrease; (2) the PCT plateau pressure increases; (3) activation becomes easier; and (4) the high rate dischargeability improves. 相似文献
12.
《Journal of Alloys and Compounds》2004,370(1-2):47-52
The structure and magnetic properties of the Pr1−xGdxMn2Ge2 (0.0≤x≤1.0) compounds have been investigated by means of X-ray diffraction (XRD), differential scanning calorimetry (DSC) techniques and AC magnetic susceptibility measurements. All compounds crystallize in the ThCr2Si2-type structure with the space group I4/mmm. The lattice constants and the unit cell volume obey Vegard’s law. Samples in this alloy system exhibit a crossover from ferromagnetic ordering for PrMn2Ge2 to antiferromagnetic ordering for GdMn2Ge2 as a function of Gd concentration x. At low temperatures, the rare earth sublattice also orders and reconfigures the ordering in the Mn sublattice. The results are summarized in the x–T magnetic phase diagram. 相似文献
13.
A series of the Chevrel phases, Mo6−xRuxTe8 and Mo6Te8−xSx (x=0, 1, 2), has been prepared and the various physical properties, such as the elastic modulus, Debye temperature, and electrical resistivity, have been evaluated. The relationships between several properties of the compounds have also been studied. Young’s modulus and Debye temperature of Mo6−xRuxTe8 and Mo6Te8−xSx increase with increasing x value. The relationship between the Vickers hardness and Young’s modulus shows ceramic characteristics for Mo6−xRuxTe8, while they show glass-like characteristics for Mo6Te8−xSx. The electrical resistivities of Mo6−xRuxTe8 and Mo6Te8−xSx increase with increasing x value. 相似文献
14.
L. Vasylechko W. Schnelle U. Burkhardt R. Ramlau R. Niewa H. Borrmann K. Hiebl Z. Hu Yu. Grin 《Journal of Alloys and Compounds》2003,350(1-2):9-16
The ternary phase Yb4Ni10+xGa21−x has been synthesised from the elements by high frequency melting in argon atmosphere. The homogeneity region has been established from X-ray powder data and confirmed by EDX analysis for 0.3≤x≤1. The crystal structure of Yb4Ni10+xGa21−x has been estimated from X-ray single crystal data: space group C2/m (no. 12), Z=2, a=20.6815(9) Å, b=4.0560(4) Å, c=15.3520(7) Å, β=124.800(3)°, R(F)=0.023 for 1701 symmetry independent reflections with F(hkl)>4σ(F). A special feature of the structure is the local disorder within the gallium/nickel network. Neglecting atomic disorder in the region of the Ga9 and Ga11 positions, the Yb4Ni10+xGa21−x structure is an occupation variant of the Ho4Ni10Ga21 type with nickel atoms partially replacing the Ga atoms in the 2d sites at the centers of distorted icosahedra. From magnetic susceptibility and from LIII-XAS spectra, the valence state of ytterbium is near 3+. 相似文献
15.
Hongzhong Chi Changpin Chen Lixin Chen Qidong Wang 《Journal of Alloys and Compounds》2003,360(1-2):312-315
The hydrogen storage properties of La2Mg16Ni alloy prepared by mechanical milling in benzene were investigated. The ball-milling times (0, 5, 10 and 20 h) significantly influence the hydriding process. Compared with the unmilled sample, these as-milled alloys are ready to be activated and the absorption kinetics are relatively fast even at low temperature. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to examine the microstructure and morphology. 相似文献
16.
A high-energy ball milling technique using the mechanical alloying method has been employed for fabrication of glassy Co100−xTix (25≤x≤67) alloy powders at room temperature. The fabricated glassy alloys in the Co-rich (33≥x) side exhibit good soft magnetic properties. The binary glassy alloys for which the glass transition temperatures (Tg) have rather high temperatures (above 800 K), show large supercooled liquid regions before crystallization (ΔTx larger than 50 K). The reduced glass transition temperature (ratio between Tg and liquidus temperatures, Tl (Tg/Tl)) was found to be larger than 0.56. We have also performed post-annealing experiments on the mechanically deformed Co/Ti multilayered composite powders. The results show that annealing of the powders at 710 K leads to the formation of a glassy phase (thermally enhanced glass formation reaction), of which the heat of formation was measured directly. The similarity in the crystallization and magnetization behaviors between the two classes of as-annealed and as-mechanically alloyed glassy powders implies the formation of the same glass state. 相似文献
17.
C. Rizzoli P. S. Salamakha O. L. Sologub G. Bocelli 《Journal of Alloys and Compounds》2002,340(1-2):146-150
The crystal structure of the new ternary stannide YbNi2−xSn [space group P63/mmc (N 194), z=4] was investigated using single crystal X-ray diffraction data (automatic single crystal diffractometers Philips PW1100 and Bruker SMART CCD, Mo K radiation). Three crystals with different composition YbNi1.695Sn [a=4.424(4) Å, c=15.232(6) Å, V=258.2(4) Å3, ρ=10.066 g cm−3, μ=57.32 mm−1], YbNi1.705Sn [a=4.424(5) Å, c=15.179(7) Å, V=257.3(4) Å3, ρ=10.116 g cm−3, μ=57.59 mm−1] and YbNi1.745Sn [a=4.303(6) Å, c=16.001(9) Å, V=256.7(5) Å3, ρ=10.199 g cm−3, μ=58.00 mm−1] were refined to R=0.0494, wR2=0.1330, to R=0.0782, wR2=0.1916 and to R=0.0643, wR2=0.1460, respectively. The compounds belongs to a new structure type of intermetallic compounds and are formed from two hypothetical structures YbNi1.5Sn (space group P63/mmc, z=4) and YbNi2Sn (space group P63/mmc, z=4) containing segments of the MnCu2Al, ZrBeSi and ZrPt2Al structures. 相似文献
18.
K. Asada K. Konno M. Matsuura M. Sakurai A. Fujita K. Fukamichi 《Journal of Alloys and Compounds》2003,350(1-2):47-51
Studies on the structure and the crystallographic site of Mn in LaCo13−xMnx compounds were carried out by using X-ray diffraction and X-ray absorption fine structure (XAFS) of the Mn K-edge. These compounds with x≤3.0 adopt a NaZn13-type structure consisting of icosahedral clusters. The lattice constant increases with the Mn concentration. The calculated XAFS curves of the center and the corner sites in the icosahedral clusters for the Mn K-edge are obtained by using the program
. The fitting result for the corner site agrees much better with the observed XAFS spectrum than that for the center site. Therefore, the Mn site is determined to be the corner Co site in the icosahedral clusters of all the compounds. In comparison with the crystallographic parameters of LaCo13, the icosahedral clusters composed of Mn atoms expand and the crystallographic Mn site is slightly more close to the La atom. 相似文献
19.
The hexagonal ErMn6−xFexSn6 solid solution (0.2 < x < 4) has been studied by magnetisation measurements and neutron diffraction. The ordering temperature of the T = (Mn,Fe) sublattice almost continuously increases from T = 386 K for x = 0.2 to T = 498 K for x = 4. The T sublattice orders in the successive magnetic structures helimagnetic H1, antiferromagnetic AF2, helimagnetic H2 and antiferromagnetic AF1 with increasing iron content. While structures AF2 and H1 were already observed in ternary Mn compounds and AF1 in ternary iron compounds, the structure H2 is of a new kind characterized by an AF slab around the Er(1a) site. At low temperature, a change of the easy direction of the Er moment from easy plane to easy axis is observed. The iron-rich compounds display a ferromagnetic order of the Er sublattice. A new kind of magnetic structure characterized by a sine-wave modulated arrangement with a propagating vector Q = (0, 0, qz) is also observed. The evolution of the magnetic properties (enhancement of the AF character of the (Mn,Fe) sublattice and magnetocrystalline anisotropy of erbium) is discussed. 相似文献
20.
C. P. Yang Y. Z. Wang B. P. Hu J. L. Wang Z. X. Wang Z. L. Jiang C. L. Ma J. Zhu 《Journal of Alloys and Compounds》1999,290(1-2)
The magnetocrystalline anisotropy and magnetic structure of DyFe12−xMox (1.00≤x≤3.00) have been investigated in detail by X-ray diffraction, thermomagnetic analysis, AC magnetic susceptibility, singular point detection technique and angular-magnetization measurement. A magnetic phase diagram of DyFe12−xMox (1.00≤x≤3.00) has been proposed. At room temperature, all DyFe12−xMox compounds exhibit uniaxial anisotropy. At low temperature, a spin reorientation transition of axis-to-cone was observed for DyFe12−xMox compounds with low Mo concentration, x<2.00. The spin reorientation temperature decreases with increasing Mo concentration. For DyFe12−xMox compounds with high Mo concentration, magnetohistory effects were observed below 48 K. 相似文献