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1.
The 57Fe Mössbauer effect study at 5.0 K and in an external magnetic field of 9.0 T on a high-quality stable decagonal quasicrystal Al65Co15Cu19.9Fe0.1 is presented. It is shown that the iron atoms are located in two distinct classes of sites. The values of the principal component of the electric field gradient tensor and the asymmetry parameter at these sites are, respectively, ?1.90(10)?×?1021 V/m2, 0.97(15) and ?3.95(12)?×?1021 V/m2, 0.00(17). 相似文献
2.
The concept of crystalline module, that is, an unambiguously isolated, repeated quasi-molecular element, is introduced. This concept is more general than the concept of crystal lattice. The generalized modular approach allows extension of the methods and principles of crystallography to quasi-crystals, clusters, amorphous solids, and periodic biological structures. Principles of construction of aperiodic, nonequilibrium regular modular structures are formulated. Limitations on the size of icosahedral clusters are due to the presence of spherical shells with non-Euclidean tetrahedral tiling in their structure. A parametric relationship between the structures of icosahedral fullerenes and metal clusters of the Chini series was found. 相似文献
3.
R.?T.?Savalia K.?N.?Lad A.?PratapEmail author G.?K.?Dey S.?Banerjee 《Journal of Thermal Analysis and Calorimetry》2004,78(3):745-751
The formation of nano-quasicrystals on isothermal annealing of melt-spun ribbons of Zr69.5Al7.5Ni11Cu12 metallic glass has been investigated using transmission electron microscopy (TEM). The crystallization study of this metallic glass has been carried out using differential scanning calorimetry (DSC) in non-isothermal (linear heating) mode. It exhibits two-stage crystallization where the first stage corresponds to the precipitation of icosohedral nano-quasicrystalline phase. This has been confirmed with the help of TEM investigations. The crystallization parameters like the activation energy (E
c) and frequency factor (k
0) have been derived using the Kissinger peak shift analysis. The activation energies for the first and second crystallization peak are found to be 278 and 295 kJ mol–1, respectively. The frequency factors obtained for the two peaks are respectively 7.16·1019 and 1.42·1020 s–1. E
c, k
0 and the Avrami exponent (n) have also been derived by fitting the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation for the transformed volume fraction (x) to the crystallization data. JMAK results of E
c for the first and second crystallization peak turn out to be 270 and 290 kJ mol–1 respectively. However, k
0 and n are found to be heating rate dependent as reported in similar studies. The values of n for the first crystallization stage ranges between 1.66 and 2.57 indicating diffusion-controlled transformation in agreement with earlier reports. 相似文献
4.
The zero field cooled (ZFC) and field cooled (FC) low-field magnetic moment m of a dense frozen ferrofluid containing Fe55Co45 particles of size 4.6nm in hexane exhibits irreversibility at temperatures T?T b≈ 30?K. FC in μ 0 H ≤ 1?T gives rise to shifted minor hysteresis loops below T b. At T c≈ 10?K, sharp peaks of m ZFC and of the ac susceptibility χ ′, a kink of the thermoremanent magnetic moment m TRM, a sizeable reduction of the coercive field H c, and the appearance of a spontaneous moment m SFM indicate a phase transition with near mean-field critical behaviour of both m SFM and χ ′ . These features are explained within a core-shell model of nanoparticles, whose strongly disordered shells gradually become blocked below T b, while their soft ferromagnetic cores couple dipolarly and become superferromagnetic (SFM) below T c. 相似文献
5.
Fe-based amorphous ribbons with excellent soft magnetic properties and mechanical properties were prepared in the Fe–Si–P ternary system. Enhanced soft magnetic properties could be achieved through annealing treatment of the ribbons for 1 h at 325 °C, which is far below the glass transition temperatures (462–474 °C). Icosahedral medium-range ordering with a size range of around 2 nm occurred throughout the amorphous matrix during the low-temperature annealing treatment. The annealed ribbons exhibited improved magnetic saturation of over 185 emu/g while maintaining good mechanical flexibility. During icosahedral ordering, the distance between the Fe atoms and the coordination number within the amorphous ribbon can be optimised for achieving high magnetic saturation. However, nanocrystallisation of the SiP and Fe2P transition phases embedded within the amorphous matrix occurred after the annealing treatment for 1 h at 385 °C, which caused deterioration of the soft magnetic properties and mechanical flexibility of the ribbons. Therefore, the combination of high magnetic saturation and mechanical flexibility of the amorphous ribbons could be optimised through low-temperature annealing treatment without any nanocrystallisation. 相似文献
6.
The amounts of decreased charge at Al sites of Al-based (Al–Pd–Cr–Fe, Al–Si–Mn, and Al–Re–Si) and at Zn sites of Zn-based (Zn–Mg–Zr) quasicrystals and approximant crystals were estimated. The evaluation was done by comparisons between chemical shifts experimentally observed by soft-X-ray emission spectroscopy and the amount of valence charge obtained by Bader analysis for first principle calculations of reference materials (Al, α-Al2O3, Zn, and ZnO). Decreased charges at Al sites of Al-based quasicrystals and at Zn sites of Zn-based quasicrystals were evaluated to be 1.0–2.5 e–/atom and 1.1–1.2 e–/atom, respectively. A covalent bonding nature alloy of Al–Re–Si also showed a decrease in valence charge at Al sites. 相似文献
7.
Shan Jin Manman Zhou Xi Kang Xiaowu Li Wenjun Du Xiao Wei Shuang Chen Shuxin Wang Manzhou Zhu 《Angewandte Chemie (International ed. in English)》2020,59(10):3891-3895
The high‐dimensional (that is, three‐dimensional (3D)) assembly of nanomaterials is an effective means of improving their properties; however, achieving this assembly at the atomic level remains challenging. Herein, we obtained a novel nanocluster, [Au8Ag57(Dppp)4(C6H11S)32Cl2]Cl (Dppp=1,3‐bis(diphenylphosphino)propane) showing a 3D octameric assembly mode involving the kernel penetration of eight complete icosahedral Au@Ag10Au2 units for the first time. The atomically precise structure was determined by single‐crystal X‐ray diffraction, and further confirmed by thermogravimetric analysis, X‐ray photoelectron spectroscopy, and electrospray ionization mass spectrometry measurements. Furthermore, ligand‐induced transformation prompted the conversion of [Au8Ag57(Dppp)4(C6H11S)32Cl2]Cl, with complete octameric fusion into [Au8Ag55(Dppp)4(C6H11S)34][BPh4]2, with incomplete octameric fusion. These observations will hopefully facilitate further research on the assembly of M13 nanobuilding blocks. 相似文献
8.
One of the long standing problems in quantum chemistry had been the inability to exploit full spatial and spin symmetry of an electronic Hamiltonian belonging to a non‐Abelian point group. Here, we present a general technique which can utilize all the symmetries of an electronic (magnetic) Hamiltonian to obtain its full eigenvalue spectrum. This is a hybrid method based on Valence Bond basis and the basis of constant z‐component of the total spin. This technique is applicable to systems with any point group symmetry and is easy to implement on a computer. We illustrate the power of the method by applying it to a model icosahedral half‐filled electronic system. This model spans a huge Hilbert space (dimension 1,778,966) and in the largest non‐Abelian point group. The C60 molecule has this symmetry and hence our calculation throw light on the higher energy excited states of the bucky ball. This method can also be utilized to study finite temperature properties of strongly correlated systems within an exact diagonalization approach. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012 相似文献
9.
Mackay introduced two important crystallographic concepts in a short paper published 40 years ago. One is the icosahedral shell structure (iss) consisting of concentric icosahedra displaying fivefold rotational symmetry. The number of atoms contained within these icosahedral shells and subshells agrees well with the magic numbers in rare gas clusters, (C60)
N
molecules, and some metal clusters determined by mass spectroscopy or simulated on energy considerations. The cluster of 55 atoms within the second icosahedral shell occurs frequently and has been called Mackay icosahedron, or simply MI, which occurs not only in various clusters, but also in intermetallic compounds and quasicrystals. The second concept is the hierarchic icosahedral structures caused by the presence of a stacking fault in the fcc packing of the successive triangular faces in the iss. For instance, a fault occurs after the ABC layers resulting an ABCB packing. This is, in fact, a hierarchic icosahedral structure of a core icosahedron connected to 12 outer icosahedra by vertex sharing, or an icosahedron of icosahedra (double MI. Contrary to Mackay's iss, a faulted hierarchic icosahedral shell is, in fact, a twinlike face capping of the underlying triangles; it is, therefore, called an anti-Mackay cluster. The hierarchic icosahedral structure in an Al-Mn-Pd icosahedral quasicrystal has a core of body-centered cube rather than an icosahedron and, therefore, is called a pseudo-Mackay cluster. The hierarchic icosahedral structures have been studied separately in the past in the fields of clusters, nanoparticles, intermetallic compounds, and quasicrystals, but the underlying geometry should be the same. In the following a unified geometrical analysis is presented. 相似文献
10.