Electronic structure and glass forming ability in early and late transition metal alloys

A correlation between the change in magnetic susceptibility (Δχ_exp) upon crystallisation of Cu–Zr and Hf metallic glasses (MG) with their glass forming ability (GFA) observed recently, is found to apply to Cu–Ti and Zr–Ni alloys, too. In particular, small Δχ_exp, which reflects similar electronic structures, ES, of glassy and corresponding crystalline alloys, corresponds to high GFA. Here, we studied Δχ_exp for five Cu–Ti and four Cu–Zr and Ni–Zr MGs. The fully crystalline final state of all alloys was verified from X-ray diffraction patterns. The variation of GFA with composition in Cu–Ti, Cu–Zr and Cu–Hf MGs was established from the variation of the corresponding critical casting thickness, d_c. Due to the absence of data for d_c in Ni–Zr MGs their GFA was described using empirical criteria, such as the reduced glass transition temperature. A very good correlation between Δχ_exp and d_c (and/or other criteria for GFA) was observed for all alloys studied. The correlation between the ES and GFA showed up best for Cu–Zr and NiZr₂ alloys where direct data for the change in ES (ΔES) upon crystallisation are available. The applicability of the Δχ_exp (ΔES) criterion for high GFA (which provides a simple way to select the compositions with high GFA) to other metal-metal MGs (including ternary and multicomponent bulk MGs) is briefly discussed.     

Bonding and short-range order effects in the theory of the electronic structure of liquids

A generalized coherent-wave approximation is suggested which takes into account the fact that the average environment of an atom in many liquids is not spherically symmetric but tends to have a point-group symmetry determined by its nearest neighbours. The effect of this generalization upon the theory of Phariseau and Ziman is discussed.     

First and second order Raman scattering in transition metal compounds

First and second order Raman scattering was observed in NbC and ZrN. The scattering spectra differ greatly in the two materials. The position of the Raman peaks shows satisfactory agreement with high values of the phonon density obtained from neutron scattering data. In addition to previous results second order Raman scattering has also been found in TiN.     

Resonant electron exchange scattering in late transition metal monoxides

Intra-atomic d-d transitions in NiO(100) and CoO(100) have been investigated with angle-resolved electron energy loss spectroscopy (EELS) at primary energies close to the metal 3s excitation threshold. Electron exchange scattering was found to be resonantly enhanced at the 3s threshold due to the temporary formation of a negative ion core state and its subsequent decay via Auger-like transitions. In both oxides the threshold is lowered several eV due to a strong electron- core hole interaction. Angle-dependent studies reveal a different dependency of exchange processes on the scattering angle as compared with nonresonant measurements and reveal a different angle dependence for each specific d-d transition. It is suggested that in these oxides large-angle single-step inelastic scattering contributes significantly to the EELS measurements in reflection mode.     

Icosahedral short-range order in amorphous alloys

We have characterized the icosahedral short-range order in amorphous solids using local environment probes. Such topological local order is pronounced even in an amorphous alloy that does not form quasicrystalline phases upon crystallization, as demonstrated by the extended x-ray absorption fine structure and x-ray absorption near-edge structure of a Ni-Ag amorphous alloy analyzed through reverse Monte Carlo simulations.     

Atomic short-range order in CuMn alloys

The establishment of atomic short-range order (SRO) has been investigated in CuMn alloys (5, 8,13,16,20 at. % Mn) by measurement of the electrical resistivity during isochronal and isothermal annealing. An increasing degree of SRO is accompanied by a reduction of resistivity; this effect increases with Mn concentration. For 8,13 and 16 at. % Mn SRO kinetics turn out to deviate significantly from single exponential behavior with a maximum at 13 at. % Mn, whereas at 5 and 20 at. % Mn SRO is adjusted in a single exponential process. For data analysis three methods are used: a sum of two and three exponentials as well as a log-normal spectrum of relaxation times. The strong interaction between second-nearest-neighbor atoms in CuMn seems to be essential for SRO kinetics but of minor importance for the value of SRO-induced resistivity change.     

Onion-structured transition metal dichalcogenide nanoparticles by laser fabrication in liquids and atmospheres

Since the discovery of transition metal dichalcogenide (TMDC) nanoparticles (NPs) with the onion-like structure, many efforts have been made to develop their fabrication methods. Laser fabrication (LF) is one of the most promising methods to prepare onion-structured TMDC (or OS-TMDC) NPs due to its green, flexible, and scalable syntheses. In this mini-review article, we systematically introduce various laser-induced OS-TMDC (especially the OS-MoS₂) NPs, their formation mechanism, properties, and applications. The preparation routes mainly include laser ablation in liquids and atmospheres, and laser irradiation in liquids. The various formation mechanisms are then introduced based on the different preparation routes, to describe the formations of the corresponding OS-NPs. Finally, some interesting properties and novel applications of these NPs are briefly demonstrated, and a short outlook is also given. This review could help to understand the progress of the laser-induced OS-TMDC NPs and their applications.     

Magnetic anisotropies of late transition metal atomic clusters

We analyze the impact of the magnetic anisotropy on the geometric structure and magnetic ordering of small atomic clusters of palladium, iridium, platinum, and gold. We have employed a noncollinear implementation of density functional theory where the spin-orbit interaction has been included self-consistently. The size of the clusters ranges from two to five, six, or seven atoms, depending on the element. Our results highlight the relevance of the spin-orbit interaction in the magnetic properties of small atomic clusters made of fourth- and fifth-row elements.     

Multiatom interactions,order and stability in binary transition metal alloys

Interface delocalization or depinning transitions such as wetting or surface induced disorder are considered. At these transitions, the correlation length for transverse correlations parallel to the surface diverges. These correlations are studied in the framework of Landau theory. It is shown the t^–1/2 at all types of transitions for systems with short-range forces wheret measures the distance from bulk coexistence.     

Twinning and short-range order in ordered titanium monoxide

Electron diffraction was used to study the annealed titanium monoxide TiO_1.087 containing the monoclinic ordered phase Ti₅O₅. The diffraction pattern of titanium monoxide in the (112)* _B1 plane of the reciprocal lattice of the parent B1 cubic structure contains not only structural, superstructural, and additional reflections but also a system of planar diffuse strips. It has been established that part of the additional reflections are twins of the superstructure reflections of the monoclinic ordered phase; the twinning plane is the ( $\overline 1 \overline 1 1$ ) plane of the reciprocal lattice of the parent cubic phase. The diffuse scattering contours cover finite plane areas in the reciprocal space characterized by the wave vectors K ₁₀₀ ～ ± (h + 0.07)k ₁₀₀, K ₀₁₀ ～ ±(k + 0.07)k ₀₁₀, and K ₀₀₁ ～ ±(l + 0.07)k ₀₀₁ in the B1 structure. The diffuse scattering is caused by short-range displacement order. Short-range substitution order and the corresponding diffuse scattering are absent.     

Investigation of short-range order in magnesium-terbium alloy

Using the model potential method with Ashcroft form factors, we predict the existence of short-range order in the alloy Mg−2.9 at. % Tb, which is experimentally confirmed by diffuse x-ray scattering. We use the diffuse x-ray scattering method to determine the characteristic temperature of the alloy: θ _D = 325 K. M. V. Lomonosov Moscow State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 26–30, July, 1996     

Direct observation of medium-range crystalline order in granular liquids near the glass transition

Collective behavior of driven granular matter is often strikingly analogous to that of thermal systems. Here we use a vibrated quasi-two-dimensional granular matter as a model system and investigate the mechanism of the liquid-glass transition. We demonstrate by direct observation the existence of long-lived medium-range crystalline order, which is found to be closely related to both dynamic heterogeneity and slow dynamics. Our findings are remarkably similar to recent numerical results on model thermal liquids and thus open an intriguing possibility of understanding the dynamic arrest in both thermal and athermal systems in a unified manner.