Cluster structure of the surface in the amorphous,quasicrystalline, and liquid states

The electronic structure of the Zr₆₀Ni₂₀Ti₂₀, Al₆₅Cu₂₀Fe₁₅, and Al₈₆Mn₁₄ systems has been investigated by X-ray photoelectron spectroscopy and band calculations of the total and partial densities of electronic states have been carried out by the TB-LMTO-ASA method with the aim of studying the chemical bonds and the nearest environment of atoms in the liquid, amorphous, and quasicrystalline states. A direct proof of the inheritance of the chemical structure of the liquid state in the amorphous and quasicrystalline states has been obtained for the first time. The similarity of the electronic structure and the nearest environment of atoms indicates identity of clusters in the liquid, amorphous, and quasicrystalline states. The degree of hybridization of valence electrons of atoms in clusters increases in going from the quasicrystalline to the amorphous state due to the increase the number of transition metal atoms in clusters.     

Al-Cu-Fe二十面体准晶的深过冷研究

通过循环过热净化法研究了Ａｌ－Ｃｕ－Ｆｅ合金系中Al₆₅Cu₂₀Fe₁₅合金液的深过冷采用循环过热净化法净化Al₆₅Cu₂₀Fe₁₅合金液，获得了９８Ｋ的过冷度，并制备出直径为６ｍｍ的高纯度的Ａｌ－ＣＳ－ＦＳ二十面体准晶球．随着Al₆₅Cu₂₀Fe₁₅合金液过冷度的不同，Al₆₅Cu₂₀Fe₁₅合金液的第一形核相也发生变化．此外，提高对Al₆₅Cu₂₀Fe₁₅合金液的净化程度，可以提高合金液的形成Ａｌ－Ｃｕ－Ｆｅ二十面体准晶的能力．     

Short-range order of quasicrystals after ball milling

Thermodynamically stable icosahedral Al₆₅Cu₂₀Fe₁₅ alloy is studied using⁵⁷Fe Mössbauer experiments. Its quasicrystalline structure is subjected to a low energy process of mechanical grinding up to 800 hours. The influence of ball milling on the electric field gradient magnitudes is discussed using an analysis of the Mössbauer spectra to different fitting models. The presence of an amorphous phase which co-exists with the quasicrystalline one is revealed in the early stage of mechanical grinding.     

Al65Cu20Fe15 in amorphous,crystalline and quasicrystalline states

Three structurally distinct states (amorphous, crystalline, and quasicrystalline) of Al₆₅Cu₂₀Fe₁₅ and neighboring compositions, have been observed. A new metastable state. Intermediate between the amorphous and the quasicrystalline states, has been found. Mössbauer-effect measurements on these samples Al₆₅Cu_20xFe_15+x (?10≤x≤ 10, at.%) In the three different states show that the differences in the effective isomer shifts and quadrupole splittings among the three states are small despile diametrically different structures.     

Physical, mechanical, and tribological properties of quasicrystalline Al-Cu-Fe coatings prepared by plasma spraying

The physical, mechanical, and tribological properties of quasicrystalline coatings based on the Al₆₅Cu₂₃Fe₁₂ alloy prepared by plasma spraying have been investigated. The specific features of the phase formation due to the competitive interactions of the icosahedral ψ and cubic β phases have been elucidated. A correlation between the microhardness and the content of the icosahedral phase in the coating has been determined. The decisive role of the quasicrystalline phase in the formation of high tribological characteristics of the coatings has been revealed and tested.     

Synthesis and mechanical properties of mechanically alloyed Al-Cu-Fe quasicrystalline composites

Al-Cu-Fe alloys were prepared by mechanical alloying starting from elemental powders in a high-energy planetary ball mill. Three different alloy compositions with the same c _Cu : c _Fe ratio of 2:1 but different aluminium contents, that is Al₅₅Cu₃₀Fe₁₅, Al₆₃Cu₂₅Fe₁₂ and Al₇₀Cu₂₀Fe₁₀, were investigated. A sequence of solid-state reactions resulting in quasicrystalline phase formation in Al₆₃Cu₂₅Fe₁₂ proceeds during milling and during annealing of the as-milled powder. These reactions were studied by X-ray diffraction, transmission electron microscopy and differential scanning calorimetry. In order to form an aluminium-matrix composite, Al₆₃Cu₂₅Fe₁₂ single-phase quasicrystalline powders were blended with different amounts of aluminium. In an intermediate milling step the powder blend was homogenized. The powders were consolidated by hot extrusion. The bulk samples revealed a homogeneous dispersion of the particles in the matrix but a rather heterogeneous size distribution. The mechanical properties at room temperature were tested by constant-rate compression tests. A rule-of-mixtures dependence of the ultimate strength and the yield strength on the volume fraction of the quasicrystalline particles was found.     

EFG studies of the AlCuFe quasicrystal and related structures

It is known that the structure and thermal stability of the AlCuFe icosahedral quasicrystalline (i-QC) phase is extremely sensitive to the exact composition. A stable, ideally quasiperiodic phase exists only along a line around Al_62.0Cu_25.5Fe_12.5. The other i-QC samples show structural changes when annealed around 700 °C. The⁵⁷Fe Mössbauer EFG properties and isomer shifts of these various i-QC phases and of the new rhombohedral approximant phase are presented, and compared with the properties of the Al site investigated by NMR. Certain new systematic trends will be presented.     

机械合金化Fe100-xCux体系的X射线吸收精细结构研究

利用X射线吸收精细结构(XAFS)方法研究机械合金化制备的Fe_100-xCu_x(x=0,10,20,40,60,70,80,100,x为原子百分比)合金中Fe和Cu原子的局域环境结构.对于Fe_100-xCu_x(x≥40)二元混合物,球磨160h后,Fe原子的近邻配位结构从bcc转变为fcc,但Cu原子的近邻结构保持其fcc不变.与之相反,在Fe₈₀Cu₂₀和Fe₉₀Cu₁₀(x≤20)合金中,Fe原子的近邻配位保持其bcc结构而Cu原子的近邻配位结构从fcc转变为bcc结构.XAFS结果还表明,fcc结构的Fe_100-xCu_x样品中Fe的无序因子σ(0.0099nm)比bcc结构的Fe_100-xCu_x中的σ(0.0081nm)大得多;并且在机械合金化Fe_100-xCu_x(x≥40)样品中Fe原子的σ(0.0099nm)比其Cu原子的σ(0.0089nm)大.这表明机械合金化Fe_100-xCu_x样品中Fe和Cu原子可以有相同的局域结构环境但不是均匀的过饱和固溶体,而是由Fe富集区和Cu富集区组成的合金.我们提出互扩散和诱导相变机理来解释在球磨过程中Fe_100-xCu_x合金产生从bcc到fcc和从fcc到bcc变化的结构相变 关键词： XAFS 100-xCu_x合金')" href="#">Fe_100-xCu_x合金 机械合金化     

退火诱导亚稳态Fe80Cu20合金固溶体的结构相变

利用扩展x射线吸收精细结构和x射线衍射研究了机械合金化制备的体心立方(bcc)的亚稳态Fe₈₀Cu₂₀合金固溶体的结构随退火温度的变化特点.结果表明，在300—873 K温度范围内，随着退火温度的升高，bcc结构物相的晶格常数近于线性降低，这主要是由于Cu原子从bcc结构Fe₈₀Cu₂₀合金固溶体中逐渐偏析出来，生成面心立方(fcc)结构的Cu物相所致.经603K退火后，Cu原子的平均键长R_Cu—Cu增加了0.003 nm左右，大约有50%的Cu原子从bcc结构的Fe₈₀Cu₂₀合金固溶体中偏析出来.在773 K退火后，bcc结构Fe_８０Cu₂₀合金固溶体近于完全相分离，生成了bcc结构的α-Fe与fcc结构的Cu物相. 关键词： 扩展x射线吸收精细结构 x射线衍射 ８０Cu₂₀合金')" href="#">Fe_８０Cu₂₀合金 机械合金化     

A Mössbauer study on TiBaCa3(Cu1−xFex)3O8.5 superconductors

Two main superconducting phases, 1223 and 2223 in TiBaCa₃Cu₃O_8.5 superconductor, are identified by powder x-ray analysis and⁵⁷Fe Mössbauer spectroscopy analysis. The Mössbauer fitting results shown that iron atoms in the lattice substitute two inequivalent sites of copper atoms for each main phase. The temperature dependence of Mössbauer parameters are obtained, and several problems are discussed which relate to the electric charge transfer which takes place around the superconducting transition temperature, the lattice dynamics and the effect on oxygen deficiency at different temperatures.     

Synthesis, X-Ray analysis, and Mössbauer investigation of Al-Cu-Fe quasicrystals

Alloys with nominal compositions Al₆₂Cu_25.5Fe_12.5, Al₆₃Cu₂₄Fe₁₃, Al_62.7Cu_24.8Fe_12.5 Al_62.8Cu_24.5Fe_12.7, Al₆₃Cu_24.3Fe_12.7, Al_63.2Cu₂₄Fe_12.8 and Al₆₅Cu₂₀Fe₁₅ are fabricated by a solid-state reaction. Synthesis is performed in the temperature range 550–750°C. The reaction time varies from 2 to 20 h. X-ray diffraction and nuclear γ-resonance spectroscopy are used to study phase formation during synthesis. The samples with the nominal compositions Al₆₃Cu₂₄Fe₁₃, Al_63.2Cu₂₄Fe_12.8 and Al₆₃Cu_24.3Fe_12.7 annealed at 650°C for 20 h contain only the thermodynamically stable icosahedral phase.     

A triple potential model for the structural transition in Cu2Mo6S8

A simple model for the structural phase transition in Cu₂Mo₆S₈ is proposed. The model uses a triple well potential for copper atoms. In the molecular field approximation a first order transition of the order—disorder type involving the rearrangement of the copper atoms is obtained.     

Study of the magnetic properties of GdZn compound using PAC spectroscopy with 140Ce and 111Cd as probe nuclei

Nanocrystalline Al₆₄Cu₂₃Fe₁₃ icosahedral quasicrystal has been obtained by milling of solid quasicrystal precursors prepared by arc-melt. The local structure around Fe atoms was studied by Mössbauer spectroscopy using a quadrupole splitting distribution method. Mössbauer results of annealed and milled samples show the existence of a broadened distribution of Fe sites which is associated to intrinsic disorder. The structural characterization was determined using x-ray diffraction. The average grain-size of the nanostructured quasicrystal, obtained from the line broadening of the X-ray diffraction peaks, was estimated to be of the order of 10 nm for a sample milled by 5 h.     

Structural evolutions of the mechanically alloyed Al<Subscript>70</Subscript>Cu<Subscript>20</Subscript>Fe<Subscript>10</Subscript> powders

Elemental mixtures of Al, Cu, Fe powders with the nominal composition of Al₇₀Cu₂₀Fe₁₀ were mechanically alloyed in a planetary ball mill for 80 h. Subsequent annealing of the as-milled powders were performed at 600–800°C temperature range for 4 h. Structural characteristics of the mechanically alloyed Al₇₀Cu₂₀Fe₁₀ powders with the milling time and the heat treatment were investigated by X-ray diffraction (XRD), differential scanning calorimeter (DSC) and differential thermal analysis (DTA). Mechanical alloying of the Al₇₀Cu₂₀Fe₁₀ did not result in the formation of icosahedral quasicrystalline phase (i-phase) and a long time milling resulted in the formation of β-Al(Cu,Fe) solid solution phase (β-phase). The i-phase was observed only for short-time milled powders after heat treatment above 600°C. The β-phase was one of the major phases in the Al₇₀Cu₂₀Fe₁₀ alloy. The w-Al₇Cu₂Fe₁ phase (w-phase) was obtained only after heat treatment of the short-time milled and unmilled samples. The present investigation indicated that a suitable technique to obtain a large amount of quasicrystalline powders is to use a combination of short-time milling and subsequent annealing.     

Atomic dynamics of an Al<Subscript>0.62</Subscript>Cu<Subscript>0.255</Subscript>Fe<Subscript>0.125</Subscript> icosahedral quasicrystal

The atomic dynamics of an Al_0.62Cu_0.255Fe_0.125 icosahedral quasicrystal is investigated using inelastic neutron scattering (the isotopic contrast method). The partial vibrational spectra of copper, iron, and aluminum atoms in the icosahedral quasicrystal and the total spectrum of thermal vibrations of the compound are directly reconstructed from the experimental data for the first time. It is found that the vibrational energies of copper and iron atoms fall in relatively narrow ranges near 16 and 30 meV, respectively, whereas the vibrational energies of aluminum atoms lie in a wide range (up to 60 meV).     

铸锭凝固组织对相应非晶合金晶化过程中二十面体准晶相形成动力学的影响

通过在真空电弧熔炼炉内对合金铸锭进行反复熔炼处理，获得到了凝固组织不同的Zr₆₅Al_7.5Cu_12.5Ni₁₀Ag₅合金铸锭.在相同的制备条件下，由凝固组织不同的合金铸锭通过吸铸法制备得到了薄片非晶合金.利用差示扫描量热法(DSC)对非晶合金的晶化动力学进行了分析.x射线衍射谱表明，在Zr₆₅Al_7.5Cu_12.5Ni₁₀Ag₅非晶合金晶化过程中，二十面体准晶相(I相)作为初生相析出.Kissinger分析结果表明，合金铸锭的凝固组织细化，相对应的非晶合金发生晶化时，I相形成与分解的有效激活能都增大，说明非晶合金及析出的I相的热稳定性都提高.从结构的遗传性角度就合金铸锭凝固组织对相应非晶合金晶化过程中二十面体准晶相的形成动力学的影响进行了讨论. 关键词： 二十面体准晶相 晶化动力学 凝固组织     

XAFS和XRD研究高能球磨对Fe70Cu30合金结构的影响

利用XRD和XAFS方法研究机械合金化Fe₇₀Cu₃₀二元金属合金随球磨时间的结构变化.XRD结果表明，球磨2 h后，部分金属Fe与Cu生成Fe-Cu合金；球磨20h后，金属Fe与Cu已完全合金化生成Fe-Cu合金，并只在2θ=44°处出现一个宽化的弱衍射峰，认为是在球磨20h后的Fe₇₀Cu₃₀合金中共存着fcc和bcc结构的Fe-Cu合金相.XAFS结果进一步表明，在球磨的初始阶段(2h)，fcc结构的Cu颗粒的晶 关键词： XAFS XRD 70Cu₃₀合金')" href="#">Fe₇₀Cu₃₀合金 机械合金化     

EXAFS analysis of Zr-based quasicrystals

The character of transformation of the local environment of zirconium and palladium atoms in Zr₇₀Pd₃₀ binary alloy at a transition from the amorphous state to the quasicrystalline and crystalline states and in Zr₇₀Be₃₀ and Zr₈₀Pt₂₀ binary alloys at a transition from the amorphous to the quasicrystalline state have been investigated by extended X-ray absorption fine-structure (EXAFS) spectroscopy and X-ray diffraction. The parameters of the zirconium, palladium, and platinum local environment are determined, and the general features and differences in the local atomic rearrangement during formation of icosahedral clusters around zirconium atoms in these three compounds are established.     

The local and electronic structures of Al90FexCe10−x alloys (x=3, 5, 7): XANES analysis

The x-ray absorption near-edge structure (XANES) of Al₉₀Fe_xCe_10?x (x=3, 5, 7) is measured above the Fe K edge and analyzed theoretically by the multiple scattering method. By comparing the experimental data with the theoretical findings, the most adequate model for describing the neighbor environment of Fe atoms is chosen. Since the dipole transition matrix element is a smoothly varying function of energy near the Fe K edge, the x-ray absorption fine structure in this energy range characterizes the density of free p states of Fe in the conduction band of Al₉₀Fe_xCe_10?x alloys.     

Structure and reflective properties of Al-Cu-Fe quasicrystalline thin film prepared by laser induced arc method

Al-Cu-Fe thin films were prepared by laser induced arc (laser-arc) method from a single source—Al₆₃Cu₂₅Fe₁₂ alloy, which was proved to consist of quasicrystalline phase together with approximant phase. The composition of the deposited films meets the requirement for formation of icosahedral symmetry phase. Quasicrystalline phase was obtained after annealing the amorphous as-deposit film samples. The optical properties of the samples were investigated. Thin film samples of Al, Cu and Fe deposited under the same condition were employed for comparison. The results showed specific reflective properties of Al-Cu-Fe quasicrystal thin film in some wavelength range. The optical conductivity of the films exhibited a negative peak, centered about 440 nm in range of 190 to 800 nm. The Al-Cu-Fe quasicrystal thin films could absorb almost all the ray in the wavelength range from 420nm to 450 nm. The ratio of absorption was greater than 99%.