静高压下有表面化学反应的非晶合金晶化研究

在静高压3—5GPa,510—660℃温度下,研究了在晶化过程中其表面与Al发生反应的非晶(Fe_0.99,Mo_0.01)₇₈Si₉B₁₃合金的晶化过程。发现在4GPa左右,510—660℃的温度范围内,非晶FMSB晶化为纳米α-Fe(Al)相,在其他压力下,晶化为α-Fe(Mo,Si),(Fe,Mo)₃B或Fe₂B相。利用简单固体模型对其晶化的热力学机制 关键词：     

Influence of segregation on magnetic order in Cr75(Fe x Mn1−x )25, 0.64 ≤x ≤ 0.85

Mössbauer and magnetic measurements on Cr₇₅(Fe,Mn)₂₅ alloys, which were segregated and re-disordered by appropriate heat treatments, are reported. A primary factor for the kind of magnetic order which appears is the Cr concentration around the Mössbauer probe atom. At around 15 K, a transition to a re-entrant spin-glass state occurs. For this state, the hyperfine field distributions of all investigated disordered and re-disordered samples are independent of the Fe concentration.     

Formation of Ni3Fe by mechanical alloying

Ni and Fe powders in a 7525 atomic proportion were mechanically alloyed using a high-energy ball mill.⁵⁷Fe Mössbauer measurements were made to determine the reaction mechanism for alloy formation by means of analysis of the evolution of the Fe hyperfine fields during milling. After a latent period of 2 hours, the spectral area of an Fe-like component decreased monotonically with milling time, disappearing after 8 hours. It was replaced by a well-resolved Zeeman pattern with hyperfine fieldH=29.1 T and outer lines of width 0.75 mm/s which is attributed to Fe in disordered Ni₃Fe. The evolution of hyperfine fields rules out alloy formation by dissolution of Ni in the Fe matrix or of Fe in the Ni matrix, so that formation must occur by reaction of Ni and Fe at the interfaces between their grains.     

Solid-state synthesis and magnetic properties of epitaxial FePd3(0 0 1) films

The solid-state synthesis of magnetically soft phase FePd₃ in epitaxial Pd(0 0 1)/Fe(0 0 1)/MgO(0 0 1) film systems was studied experimentally. The system had a Fe to Pd ratio of 1:3. An increase to 450 °C leads to the formation of three variants of ordered L1₀-FePd crystallites. At 500 °C, the solid-state reaction of unreacted Pd with L1₀-FePd crystallites initiates the growth of an ordered epitaxial L1₂-FePd₃(0 0 1) layer. When annealing at 650 °С, a gradual disordering is observed. The magnetic anisotropy (K₁=−2.0×10³ erg/cm³) and the saturation magnetization (M_S=650 emu/cm³) of the disordered FePd₃ phase were determined.     

Long-range chemical interactions in solid-state reactions: effect of an inert Ag interlayer on the formation of L10-FePd in epitaxial Pd(0 0 1)/Ag(0 0 1)/Fe(0 0 1) and Fe(0 0 1)/Ag(0 0 1)/Pd(0 0 1) trilayers

The effect of 0, 0.5, and 1?μm-thick Ag interlayers on the chemical interaction between Pd and Fe in epitaxial Pd(0?0?1)/Ag(0?0?1)/Fe(0?0?1)/MgO(0?0?1) and Fe(0?0?1)/Ag(0?0?1)/Pd(0?0?1)/MgO(0?0?1) trilayers has been studied using X-ray diffraction, ⁵⁷Fe Mössbauer spectroscopy, X-ray photoelectron spectroscopy, and magnetic structural measurements. No mixing of Pd and Fe occurs via the chemically inert Ag layer at annealing temperatures up to 400?°C. As the annealing temperature is increased above 400?°C, a solid-state synthesis of an ordered L1₀-FePd phase begins in the Pd(0?0?1)/Ag(0?0?1)/Fe(0?0?1) and Fe(0?0?1)/Ag(0?0?1)/Pd(0?0?1) film trilayers regardless of the thickness of the buffer Ag layer. In all samples, annealing above 500?°C leads to the formation of a disordered Fe_xPd_1?x(0?0?1) phase; however, in samples lacking the Ag layer, the synthesis of Fe_xPd_1?x is preceded by the formation of an ordered L1₂-FePd₃ phase. An analysis of the X-ray photoelectron spectroscopy results shows that Pd is the dominant moving species in the reaction between Pd and Fe. According to the preliminary results, the 2.2?μm-thick Ag film does not prevent the synthesis of the L1₀-FePd phase and only slightly increases the phase’s initiation temperature. Data showing the ultra-fast transport of Pd atoms via thick inert Ag layers are interpreted as direct evidence of the long-range character of the chemical interaction between Pd and Fe. Thus, in the reaction state, Pd and Fe interact chemically even though the distance between them is about 10⁴ times greater than an ordinary chemical bond length.     

YFe2B2电子结构的第一性原理计算

基于密度泛函理论,从头计算了具有ThCr₂Si₂型四方晶系的稀土金属化合物Yfe₂B₂体相的物理特性.能量计算结果表明Yfe₂B₂体相处于顺磁金属态;而能带结构、态密度、布居数以及差分电荷　分布的计算结果表明Y原子的5s,5p电子具有很强的局域性;Fe原子的3d电子和B的1s,2s和2p电子强烈耦合,使得最近邻Fe原子与B原子形成了Fe—B共价键;最近邻的两个Fe原子之间由于 关键词： 稀土金属化合物 第一性原理计算 能带结构 态密度     

Medium range ordering and its effect on plasticity of Fe–Mn–B–Y–Nb bulk metallic glass

Glass formation, thermal properties and mechanical behavior were investigated in a series of Fe_{65? x} Mn₁₃B₁₇Y₅Nb _x (x = 0, 3, 5 and 7) alloys. Appropriate partial substitution of Fe by Nb in a Fe₆₅Mn₁₃B₁₇Y₅ bulk glassy alloy simultaneously enhances the glass-forming ability and the mechanical properties of the alloys. The Nb-containing glassy alloys exhibit an additional exothermic event in the supercooled liquid region. This exothermic reaction is correlated with the formation of medium range ordered (MRO) clusters originated from the large difference in mixing enthalpy between constituent elements such as Nb–Y (+30 kJ/mol) and Nb–B (?39 kJ/mol). The presence of MRO clusters in the as-cast state is dependent on the cooling condition from the liquid state, and plays a crucial role in providing plasticity in as-cast Fe–Mn–B–Y–Nb bulk metallic glass.     

Deformation hardening and the temperature dependence of the mechanical properties of ternary ordering alloys. Part II

Yield point, hardening factor, and elastic modulus are reported as functions of quenching and test temperatures for the alloys Ni₃(Fe + 3 at% Al), Ni₃(Fe + 3 at% Mn). A maximum is found in the mechanical properties near the critical temperature T_cr; this does not occur for alloys in the disordered state. The deformation aging under load is examined near this maximum and at 200 ° C. A range of linear hardening occurs up to e of 15–18% in ordered alloys, which is replaced by a range of decreasing hardening coefficient at higher . The results are discussed by reference to earlier ones for Ni₃Fe, Ni₃(FeCr). Ni₃(FeMo).     

A Mössbauer study of some new trinuclear Fe−S cluster compounds

The reaction of (u-RS)₂ (XMgS) Fe₂ (CO)₂ with CpFe (CO)₂I gave thirteen new compounds (u-RS) [CpFe (CO)₂S] Fe₂ (CO)₄. Mossbauer spectra were obtained at 80K. Two quadrupote doubles (A set and B set) were present. The ratio of areas between A set and B set was close to 21. The molecule of every compound contained two Fe (2+) which were in the same chemical environment of low spin state with a coordination number of six, and the Mossbauer parameters of the two Fe (2+), IS=0.2–0.3 mm/s, QS=0.7–0.8 mm/s. In addition, the molecule contained a Fe (3+) in low spin state which was proved by ESR. Its Mossbauer parameters, IS=0.4–0.5 mm/s. QS=1.5±1.6 mm/s, The molecular structure of (u-MeS) [u-CpFe (CO)₂S] Fe₂ (CO)₄ was determined by X-ray diffraction, monoclinic form, space group P21/n z=4, unit cell parameters, a=7.90A, b=10.77A, c=22.53A.     

57Fe Mössbauer study of the electrochemical reaction of Li with FeP y (y = 1,2)

A complete ⁵⁷Fe Mössbauer study was undertaken to elucidate the electrochemical mechanism occuring during the cycling of the FeP _x (x?= 1,2)/Li batteries. Upon discharge, for FeP, the conversion reaction FeP + 3Li → Fe + Li₃P was confirmed, whereas for FeP₂, FeP and a disordered magnetic unknown phase A are observed. On charge, the starting material is partially reconstructed only in the case of FeP. Once the first cycle is achieved, the same redox process occurs in both the FeP/Li and FeP₂/Li cells, between LiFeP, FeP, Fe° (or phase A) and Li₃P.     

57Fe Mössbauer study of Eu1−x Sr x FeO3−y

The samples of Eu_1–x Sr _x FeO_3–y (x=0.0–1.0) were prepared by the solid state reaction method. Their X-ray diffraction patterns and⁵⁷Fe Mössbauer spectra at room temperature were measured. It is found that Sr ions incorporate in the lattice of EuFeO₃, the change of crystal structure is related to the dopant.⁵⁷Fe Mössbauer spectra consist of one magnetic, one doublet and one single paramagnetic components. The Fe ions in the cubic phase are in intermediate valence state between Fe(III) and Fe(IV) and may participate in electron hopping.     

Effects of Gd<Superscript>3+</Superscript> doping on structural and dielectric properties of PZT (Zr:Ti = 52:48) piezoceramics

The purpose of this research is to study the effect of doping Gd into Pb(Zr_0.52Ti_0.48)O₃ ceramics prepared by solid state reaction. X-ray diffraction patterns show that all PGZT samples are of tetragonal structure and the highest doping should be no more than 2 mole % Gd at which the unreacted oxides start to appear. The electron spin resonance (ESR) spectra of PGZT's indicate that Gd³⁺ can enter both A site of the perovskite structure instead of only A site as widely believed. The ESR peaks resonance shift towards low fields as the concentration is higher, which is due to the change in crystal field experienced by Gd³⁺ ions. At x =0.001, 0.005 and 0.01 dopings, two sets of powder ESR signals arising from Gd³⁺ (4f⁷, spin 7/2) ions at A site. The first set shows some fine structure having strong absorption peaks centered at 76.26 mT (g = 8.550). The second is a seven-peak spectrum centered at 206.01 mT (g = 3.165), which belongs to the Gd³⁺ ions at B sites. Furthermore, the overlapped ESR strong absorption peaks from 309.17 mT to 314.49 mT (g = 2.2818-2.1087) belong to Gd³⁺ of unreacted Gd₂O₃. The local environments of Gd³⁺ ions were verified from the calculated ESR spectra using appropriate spin Hamiltonian parameter, i.e. gyromagnetic tensor g, zero-field splitting D and hyperfine tensor A.     

Pr基大块纳米晶合金及其特性研究

研究了Pr₆₀Al₁₀Ni₁₀Cu₂₀ 大块金属玻璃 的结构和磁性随Fe含量 的变化关系，结果表明Pr基合金逐步从玻璃状态，转变为非晶与纳米晶的复合状态，最后成 为纳米晶合金，Pr基合金的磁性也相应地发生变化.提出了一种通过对大块稀土基金属玻璃 进行Fe掺杂，制备出微观结构和性能具有可调控性的大块纳米晶合金的方法, 并讨论了纳米 晶结构和性能的关系. 关键词： 金属玻璃 大块纳米晶 掺杂     

Effect of severe plastic deformation on the properties of the Pt<Subscript>3</Subscript>Fe antiferromagnet

The effect of atomic disordering on the magnetic, electrical, and optical properties of the Pt_74.1Fe_25.9alloy close in composition to the stoichiometric Pt₃Fe alloy has been studied. It has been shown that, as a result of severe plastic torsional deformation under high pressure, the alloy transforms from the antiferromagnetic state (T _N=164 K) into the ferromagnetic state (T _C≈400 K). In this case, the residual electrical resistivity increases by a factor of more than two and the thermopower changes its sign from positive to negative. The results of the studies of the optical conductivity agree with the previously calculated electronic spectra of the atomically ordered and disordered Pt₃Fe alloys in the range of interband transitions and with the obtained data on the electrical properties in the infrared range.     

Kinetics of the nanocrystalline structure formation

The kinetics of the nanocrystalline structure formation in the Fe_73.5Cu₁Nb₃Si_22.5?xB_x (x=6. 7. 8. 9 at. %) was followed during the annealing runs interrupted between 300 and 700°C.⁵⁷Fe room temperature Mössbauer spectra were taken and complemented by the electrical resistivity and X-Ray diffraction measurements. It has been found that for the 50 K/min temperature increase the formation of the nanocrystalline phase begins above 450°C reaching a maximum around 500°C and is followed by the second stage of crystallization of the disordered intergranular remainder above ca 600°C accompanied by the changes in the occupation of the iron sites in the crystalline α?Fe?Si phase. Thus gained composition-temperature dependence seems to witness for the inhibiting influence of the substitution of B by Si on the crystallization process.     

Mössbauer isomer shift and hyperfine fields of ordered and disordered Fe3Al alloys

The Mössbauer technique was used to measure the hyperfine magnetic field and isomer shift of⁵⁷Fe nucleus in the ordered and disordered Fe₃Al alloys. The Mössbauer spectra were analyzed to yeld the hyperfine magnetic field distribution curves. A linear correlation has been revealed between the average hyperfine field and the average number of Al atoms in the first two nearest neighbour shells of⁵⁷Fe nucleus,N _Al, for both ordered and disordered alloys. The measured values of the mean isomer shift agree very well with the values expected from the Miedema-Van der Woude model.     

Formation of amorphous Al1−x Au x films as a consequence of low-temperature Al/Au-interface reactions in a multilayered system

Al/Au multilayers (average composition Al₂Au, individual layer thicknesses 1 nm Al and 0.71 nm Au) are prepared at 90 K by ion beam sputtering. The electrical resistance of the growing films is monitored in situ. From the results obtained in this way it can be concluded that interface reactions occur transforming the ultrathin layers into an amorphous phase, which is stable up to 255 K.For larger individual layer thicknesses (2.1 nm Au and 3 nm Al), the interface reaction into the amorphous state is incomplete. Based on a simple parallel-resistor model, one finds that the interface reaction into the amorphous phase is restricted to a thickness of less than 3.5 nm. The temperature dependence of the resistance of such thicker multilayers indicates the onset of interdiffusion of the yet unreacted material at T=200 K resulting in the crystalline Al₂Au-phase.     

Mean field analysis of exchange coupling in amorphous DyFe2–B alloy ribbons

Experimental magnetization-temperature curves for melt-spun ribbons of amorphous alloys (Dy_0.33Fe_0.67)_1−xB_x with x=0, 0.05, 0.1 and 0.15 (in atomic fraction) are fitted with theoretical equations based on the mean field theory in order to investigate exchange couplings between constituent elements as a function of the B content. The sign of the exchange coupling between Dy and Fe is negative, indicating that the magnetization direction of Dy is antiparallel to that of Fe. The sign of the other two couplings are positive. The exchange coupling between Fe ions are greatest, while that between Dy ions is negligible. The exchange couplings between Fe ions, and between Dy and Fe increase with increasing B content, the increase of the latter being much greater than the former. Resultantly, the exchange coupling between Dy and Fe becomes about one half of that between Fe ions at the highest B content. The increase of the exchange coupling between Fe ions may be explained by the increase of the Fe–Fe separation with the increase of the B content. The total magnetization is dominated by the Dy sublattice magnetization. As the B content increases, the magnetization decreases over the whole temperature range, and the Curie temperature also decreases.     

Hard mode infrared spectroscopy of CaTiO3—CaFeO2.5 perovskites

Abstract

Powder-absorption infrared (IR) spectra of perovskites CaFe_xTi_1?x O_3?x/2 (0≤x≤1) annealed at different temperatures were investigated at room temperature in the range 135–2000 cm^?1. The spectra change as a function of composition, annealing temperature and structural state (order-disorder of oxygen vacancies). Autocorrelation analysis has been used to determine variations of average line widths of groups of peaks in the primary IR spectra. The band widths increase on increasing Fe content in the region of the structures with disordered oxygen vacancies and they decrease on going through the order-disorder boundary. High degrees of local structural heterogeneity are suggested by the effective line widths of the phases at intermediate compositions. The intensity of bands at ～150 and ～443 cm^?1 decreases with increasing Fe content in the compositional range of the disordered structures. Finally, for every annealing temperature, the frequency of the band at ～600cm^?1 systematically shifts to higher values on increasing Fe content, these values decreasing again for the fully ordered structures.     

Magnetic ordering of Fe atoms in icosahedral Al70−x BxPd30−y Fey quasicrystals

Novel icosahedral quasicrystals, in which Fe atoms possess a magnetic moment, have been found in Al_70?x B_xPd_30?y Fe_y compounds with 5<x<10 and 10<y<20. The compounds have ferromagnetic properties, and their Curie temperature ranges between 280 and 340 K, the saturation magnetization σ _s(5 K)≈7.5 emu/g. It follows from Mössbauer spectra that only a fraction of Fe atoms (12 to 15%) are magnetically ordered at 4.2 K, and the mean saturation field 〈H _hf〉=96 kOe. The isomer shift values confirm that the atomic volume of magnetic Fe sites is larger than that of nonmagnetic Fe sites. The magnetic properties of these quasicrystals can be interpreted in terms of large magnetic clusters with a size of 185 to 290 Å. This size correspond to about 4×10⁴ “unit cells,” hence the magnetic state can be described in terms of bulk parameters. The localized magnetic moment of Fe atoms is tentatively ascribed to bonding between Fe and B, similarly to that in the amorphous Fe_～50B_～50 alloy.