共查询到20条相似文献,搜索用时 46 毫秒
1.
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
2.
The site preference of Fe in Cr23−xFexC6 is investigated based on the interatomic potentials obtained by the lattice inversion method. The calculated results show that Fe atoms preferentially substitute for Cr at 4a sites first and then 8c sites. The structural parameters of Cr23−xFexC6 with content x are calculated and the results are consistent with experimental results. The calculated cohesive energies indicate that the increase in x value is accompanied by the decrease in the stability of Cr23−xFexC6. The thermodynamic properties of Cr23C6, such as the phonon density of states and vibrational entropy, as well as the bulk modulus of Cr23−xFexC6 are evaluated. The calculated results are in good agreement with experimental results. This work provides a simple and promising method for studying the properties of carbides with complex structures. 相似文献
3.
Shi-Qiang Yang Ping-hua Lin Yin-sheng Dong Zhen-hua Chen 《Journal of Alloys and Compounds》2008,450(1-2):111-113
The effects of Mn partial substitution for Fe in TbFe10.5Mo1.5 on the structure and magnetic properties were investigated. TbFe10.5−xMnxMo1.5 samples (x = 1.5, 2.0, 3.0, 4.0, 5.0) were prepared by means of arc-melting and subsequent vacuum annealing. The structure and magnetic properties of TbFe10.5−xMnxMo1.5 compounds were investigated by X-ray powder diffraction and magnetic properties measurements. The following conclusions were obtained: all the TbFe10.5−xMnxMo1.5 compounds studied crystallize in the ThMn12-type structure; the unit-cell volume increases monotonically with increasing Mn concentration; a compensation temperature was observed in the magnetization-temperature curve of TbFe7.5Mn3Mo1.5 compounds. With increasing Mn concentration, the saturation magnetization at 4.4 K decreases to zero, and then increases again, the magnetic moments of the transition-metal sublattice of TbFe10.5−xMnxMo1.5 compounds decrease monotonically. 相似文献
4.
X.F. Liu S.B. Han J.Y. Lv X.J. Li Z.B. Hu D.F. Chen Y.J. Xue J.H. Li 《Journal of Alloys and Compounds》2005,400(1-2):178-183
The effects of the combined substitution of Y and Ga on the crystallographic structure of Nd2−xYxFe17−yGay compounds with x = 0, 0.5, 1.0, 1.5 and y = 0, 1, 2, 3 have been investigated using X-ray and neutron powder diffractions. Rietveld refinements of the diffraction data indicate that all the samples crystallize in the rhombohedral Th2Zn17-type structure with only small amounts of alpha iron. It is found that the addition of Ga atoms lessens the decreasing rates of the a-axis and unit cell volume V on the Y content but almost does not affect the decreasing rates of the c-axis. However, the substitution of Y has a positive effect on the increasing rates of the a-axis and unit cell volume V on the Ga content but has a very slight effect on the increasing rate of the c-axis. The c/a ratio of Nd2−xYxFe17−yGay as a function of Ga content exhibits a different increase for different Y content owe to the combined effects of Y and Ga on the crystallographic structure. The substitution of Y is found to have little effect on the site occupancy of Ga in Nd2−xYxFe17−yGay. The combined effects of Y and Ga on the bond lengths and ASBL of Nd2−xYxFe17−yGay indicate that more bonds detrimental to ferromagnetic exchange can be modulated into the desirable ferromagnetic exchange distance range through suitable combined substitution, which provides a valuable way to improve the magnetic properties of rare earth-transition intermetallic compounds. 相似文献
5.
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
6.
Hui-qun Guo Hong-ying Yang Bao-gen Shen Lin-yuan Yang Ru-qi Li 《Journal of Alloys and Compounds》1993,190(2):255-258
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
7.
M. Tseggai P. Nordblad R. Tellgren H. Rundlf A.K. Azad S.G. Eriksson J. Eriksen 《Journal of Alloys and Compounds》2008,458(1-2):372-377
Perovskite oxides with the composition La1−xNdxFe0.5Cr0.5O3 (x = 0.10, 0.15 and 0.20) have been studied. The samples have been prepared using the standard solid-state reaction method in air. The X-ray and neutron diffractograms indicates that the samples crystallize in the orthorhombic perovskite structure with space group Pnma (No. 62). The Nd-substitution causes minor changes in the cell parameters and bond lengths but the nuclear structure remains orthorhombic in the whole range of substitutions and in the temperature range of 10–700 K. The magnetic structure of the samples at room temperature and below is G-type antiferromagnetic with an average magnetic moment of the Fe/Cr ions of 3.29(3) μB/atom at 10 K independent of the Nd content. At room temperature the average magnetic moment of the Fe/Cr ions reduces to 1.23 μB/atom. At temperatures below 250 K a weak but increasing uncompensated spontaneous magnetic moment develops that reaches a magnitude of about 0.5 emu/g (or 0.02 μB per Fe/Cr site) at 10 K. This moment saturates rather rapidly in the magnetization versus magnetic field curve and is at higher field superposed on the response of the antiferromagnetic spin system. 相似文献
8.
The effects of composition and heat treatment on the structure and magnetic properties of mechanically milled Nd2xFe100−3xBx alloys (x = 2–6) have been studied. High remanences have been obtained in isotropic samples consisting of a nanocrystalline mixture of Nd2Fe14B and -Fe. For optimally heat treated samples, an increase in the volume fraction of -Fe from 14% to 73%, increased the reduced remanence (Mr/Ms) from 0.56 to 0.64. The corresponding coercivities decreased from about 8 kOe to only 1.6 kOe. The magnetic behaviour of these Nd2Fe14B--Fe alloys is associated with exchange coupling between the hard and soft magnetic phases. 相似文献
9.
The a.c. susceptibility and high field magnetization on TbRh2−xPdxPdxSi2 and TbRu2−xPdxSi2 compounds were investigated up to 140 kOe. The (T,x) magnetic phase diagrams were determined. For both systems, an increase in the Pd content causes a decrease in the Néel temperature and changes the magnetization curves. 相似文献
10.
Z.W. Ouyang G.H. Rao H.F. Yang W.F. Liu G.Y. Liu X.M. Feng J.K. Liang 《Journal of Alloys and Compounds》2004,370(1-2):18-24
The crystal structure and magnetization of Hf0.8Ta0.2(Fe1−xCox)2 are investigated by X-ray powder diffraction and magnetization measurements. The compounds exhibit the Laves C14 structure for x=0.0–0.2 and the C15 structure for x≥0.3. The structural transition from C14 to C15 leads to an anomaly of the unit cell volume between x=0.2 and 0.3. When x=0.0, the compound undergoes a magnetic phase transition from ferromagnetic to paramagnetic state via the antiferromagnetic state, in which a field-induced metamagnetic transition is observed. When x=0.1 and 0.2, the compounds exhibit unusually small saturation moments, which are considered as antiferromagnetism (with weak ferromagnetic impurities) and weak ferromagnetism or ferrimagnetism, respectively. The formation of the AFM state is associated with a small bond length of Fe atom in the 6h site. When x≥0.3, the compounds exhibit a ferromagnetic to paramagnetic transition, which can be explained by itinerant electron metamagnetism. 相似文献
11.
J.J. Rieger W.W. Kim G. Fraunberger A. Mielke E.-W. Scheidt G.R. Stewart 《Journal of Alloys and Compounds》1993,200(1-2):59-63
The heat capacity, magnetic susceptibility and magnetization of Y1−xUxRh4B4 were determined within the range from x = 0 to X = 0.65. The influence of the local magnetic moments of the U atoms (dU-U = 5.27 Å) in the CeCo4B4 structure of the tetragonal RERh4B4 was studied. A.c. susceptibility measurements showed a rather large value for the Tc depression of dTc/dx = −1.88 K per at. % U in the lower concentration range x = 0.0 to x = 0.06. In comparison with the (Bardeen-Cooper-Schrieffer) BCS theory and the Abrikosov-Gorkov model for dilute magnetic impurities, the decrease in the jump in specific heat at Tc vs. the depression of Tc is rather strong in these samples, so the existence of a demagnetizing Kondo cloud around the U moments seems likely. In the samples containing more U, the magnetization and d.c. susceptibility showed a tendency towards magnetic behaviour, but no evidence for long-range magnetic order was found. 相似文献
12.
J. Pospíil J. Poltierov Vejpravov M. Divi V. Sechovský 《Journal of Alloys and Compounds》2008,450(1-2):118-127
We have studied influence of the Pt–Ni substitution on the crystal structure and magnetic behavior of the PrNixPt1−x compounds. Polycrystalline samples with x = 1, 0.9, 0.75, 0 were prepared and characterized by X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM). The analysis of XRPD data confirmed that the orthorhombic CrB-type structure owned by the parent binary compounds remains conserved through the entire series. The samples were subsequently investigated by specific heat (Cp), magnetization (M) and ac susceptibility measurements in the temperature range 2–350 K and in magnetic fields up to 9 T. All compounds were found to order ferromagnetically. The TC values monotonously increase with increasing Ni content. To inspect the crystal-field (CEF) effects and magnetocaloric properties specific-heat data were analyzed in detail and the magnetic contribution to the specific heat together with the magnetic entropy have been determined. The results of first principles electronic structure calculations of the PrNi and PrPt confirmed that besides the stable Pr magnetic moments due to localized 4f-electrons only a very small magnetic moments of at most 0.2μB is induced at the Ni (Pt) site due to the polarized 3d-electron states (5d-electron states) hybridizing with the Pr 5d-electron states, i.e. the Ni (Pt) moment plays only minor role in the total balance of the magnetic moments in these compounds. 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.
A. Yücel A. Elmali M. Kabak P. Sevgi Y. Elerman 《Journal of Alloys and Compounds》2005,400(1-2):11-15
The magnetic properties of DyFe10−xNixSi2 compounds with x = 0, 1, 2, 3, 4, 6, 9 and 10 have been investigated by means of X-ray diffraction and magnetic measurements. Substitution of Ni for Fe leads to a decrease in the lattice constants a, c and the unit-cell volume V. The Curie temperature reaches a maximum of 590 K at x = 2, then decreases strongly for x ≥ 2. The spin reorientations are observed for the compounds with x = 0, 1, 2 and 3. The spin reorientation temperature decreases strongly from 255 to 60 K as the Ni content is increased from x = 0 to 3. Below the spin reorientation temperature, the compounds exhibit ferrimagnetic ordering. For the Ni-rich compounds with x = 9 and 10, the magnetization of the Dy sublattice decreases strongly since the magnetization of the Dy sublattice is strongly affected by the molecular field produced by the 3d sublattice. 相似文献
15.
Room temperature 57Fe Mössbauer studies of the 2:17 compounds Sm2Fe17−xGax with x=0, 1, 2, 3, 4 and 5 are reported. These measurements yield values of the Fe hyperfine field and relative concentration of Fe atoms at the four inequivalent transition metal sites, 6c, 9d, 18f and 18h, in the rhombohedral Th2Zn17 structure. Changes in the Fe hyperfine field as a function of Ga content can be correlated to changes in lattice parameter and Curie temperature and are the result of changes in the transition metal-transition metal exchange coupling. The relative intensity of the various spectra components shows that for small concentrations, Ga preferentially enters into the 18h sites. For x & 1 a substantial quantity of Ga also enters into the 18f sites. It is the Ga which enters into the 18f sites which is responsible for the formation of a uniaxial anisotropy in these materials for higher Ga content. 相似文献
16.
Jianjun Tian Shengen Zhang Xuanhui Qu Farid Akhtar Siwu Tao 《Journal of Alloys and Compounds》2007,440(1-2):89-93
When sintered Sm(Co, Fe, Cu, Zr)z permanent magnets are prepared by metal injection molding, some organic binders are added in alloy powder, which leads to much residual carbon in the magnets. The residual carbon decreases magnetic properties and destroys the microstructure of the magnets. In this paper, the behavior of carbon in Sm(Co, Fe, Cu, Zr)z permanent magnets has been studied. The results indicate that Sm(Co, Fe, Cu, Zr)z magnets can keep excellent magnetic properties when the carbon content is below 0.1 wt.%: Br ≥ 10 kGs, Hcj ≥ 22 kOe, BHmax ≥ 25 MGOe. When the carbon content is above 0.1 wt.%, Br, Hcj and BHmax decrease with increasing carbon content evidently. Carbon consumes Zr content and forms ZrC, which reduces the volume fraction of the lamella and Sm(Co, Cu)5 phases. Thus, the cell size increases and the cellular microstructure deteriorates. When the carbon content reaches 0.43 wt.%, there is not enough Sm(Co, Cu)5 phase to form a uniform cellular microstructure. Br, Hcj and BHmax are approximate to zero. Since carbon has little influence on the content of Sm2(Co, Fe)17 phase, Ms can keep a high value (≥100 emu/g). ZrC has high melting point (3420 °C) and acts as dispersion particle in the magnets, which prevents the grains of SEM structure growing and reduces the liquid content of green compacts during sintering. Therefore, the density of the magnets decreases. 相似文献
17.
Mineo Sato Takahito Suzuki Kenji Yoshida Kazuyoshi Uematsu Kenji Toda Zuo-Guang Ye 《Journal of Alloys and Compounds》1997,250(1-2):510-514
Lithium ion conductors, Li3−2x(Sc1−xZrx)2(PO4)3 (0
x
0.3), were prepared by a solid-state reaction. TG–DTA analysis indicated no phase transition in the samples with x superior to 0.05. X-ray powder diffraction analysis of these samples clearly showed the stabilization of a superionic conduction phase at room temperature with an orthorhombic system Pbcn. The highest conductivity was observed for the sample with x=0.05, and ascribed to the stabilization of the superionic conduction phase and the introduction of vacancies on the Li+ sites by substituting Zr4+ for Sc3. 相似文献
18.
G.B Song J.K Liang L.T Yang Q.L Liu G.Y Liu H.F Yang G.H Rao 《Journal of Alloys and Compounds》2004,370(1-2):302-306
The PrBa2−xSrxCu3O7±δ 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−xSrxCu3O7±δ solid solution is 0.2≤x≤0.6. The structure of PrBa2−xSrxCu3O7±δ is orthorhombic for x=0.2. The structure transforms into tetragonal for 0.3≤x≤0.6. In the PrBa2−xSrxCu3O7±δ 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−xSrxCu3O7±δ 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−xSrxCu3O7±δ system. 相似文献
19.
Magnetization measurements on zero field cooled (ZFC) and field cooled (FC) samples as a function of temperature where made on Fe0.70−xMnxAl0.30 alloys with 0≤x≤0.10. Our data show the existence of two regimes of the spin glass temperature Tf when increasing the concentration x of the Mn atoms. We found that Tf decreases slowly with increasing x up to x=0.06 and then shows a rapid linear decrease above this concentration. The existence of two regimes of Tf behavior with x may be attributed to the disappearance of ferromagnetic clusters which exist for low values of x (x<0.06). Compared to the Mn-free alloy, the relative changes in Tf are bigger and exceed 40% at x=0.10. The second regime (x>0.06) is associated with more influence of x on Tf. 相似文献
20.
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