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Peculiarities of the pre-transitional low-stability structural-phase states of BCC alloys during thermocycling
Published in A. I. Potekaev, A. M. Glezer, V. V. Kulagina, M. D. Starostenkov, A. A. Klopotov, Structure and Properties of Intermetallics in Pre-Transitional Low-Stability States, 2020
A. I. Potekaev, A. M. Glezer, V. V. Kulagina, M. D. Starostenkov, A. A. Klopotov
The behaviour of the short-range order parameter on the first coordination sphere of both the CuZn alloy (Fig. 1.30a) and the NiAl intermetallic compound (Fig. 1.30b) indicates the tendency of the alloy or intermetallic compound to ordering (a negative value of the short-range order parameter indicates a tendency towards ordering). However, with increasing temperature, the short-range order decreases. A system with a complex of shear APBs is more prone to ordering than a system with a complex of thermal APBs. Naturally, the structural-phase transition in the NiAl intermetallic compound occurs at higher temperatures than the order–disorder phase transition in the CuZn alloy. Changes in the short-range order parameter for all considered configurational variants of the alloy (Fig. 1.30) are consistent with changes in configurational energy (Fig. 1.28).
Formulation and Classification of Electronic Devices
Published in Michael Olorunfunmi Kolawole, Electronics, 2020
We know from basic chemistry that silicon dioxide (SiO2), like some ceramic materials, can exist in either crystalline or non-crystalline (amorphous) form. In crystalline materials, a lattice point is occupied either by atoms or ions depending on the bonding mechanism. These atoms (or ions) are arranged in a regularly repeating pattern, as shown in Figure 1.13, in long-range order (i.e. in three dimensions). Each silicon atom corresponds to a volume of 2 × 10−23 cm3(= 0.02 nm3). In contrast, in amorphous (non-crystalline) materials, the atoms exhibit only short-range order. The type of bonding (ionic or covalent) and the internal structure (crystalline or amorphous) affect the mechanical, electrical, thermal, and optical properties of ceramic materials. Note that chemical bonding is about the rearrangement of electrons due to the arrangement of the nuclei.
Structural Description of Materials
Published in Snehanshu Pal, Bankim Chandra Ray, Molecular Dynamics Simulation of Nanostructured Materials, 2020
Snehanshu Pal, Bankim Chandra Ray
Condensed matter, such as liquids and solids, is specifically characterized by the dynamics and structure of the constituent atoms. Solids are divided into two types according to their specific static structures: crystalline and amorphous. In crystalline solids, long-range periodicity is observed, whereas in metallic glass, such long-range order or periodicity is absent. Rather, short-range order, medium-range order, and efficient atomic packing around both solute and solvent atoms can characterize the metallic glass. Short-range order may be referred to as the nearest-neighbor atomic environment containing both geometric and chemical short-range ordering. Medium-range ordering refers to the second or third nearest-neighbor arrangement. However, the medium-range ordering plays a greater role in the formation and properties of metallic glass in comparison with the short-range ordering. Detailed structural evolution of metallic glass can be determined via two approaches: (a) experimentally (X-ray diffraction, atom probe tomography, and high-resolution transmission electron microscope) and (b) computer simulation (Monte Carlo simulation, molecular dynamics, and ab initio molecular dynamics). The determination of atomic structure reveals the intrinsic properties and glass formation behavior of super-cooled solids.
Study on amorphous surface modification of iron-based alloys and their epoxy wettability
Published in Surface Engineering, 2021
Qiang Zou, Ruru Bai, Zhenghou Zhu, Qi Zhong, Wei Zhou
The atomic structures of amorphous alloys have the characteristics of long-range disorder and short-range order. The amorphous alloys have no grain boundaries and dislocations, and their elements are uniformly distributed (no segregation). Owing to the excellent mechanical properties and soft magnetic properties, amorphous alloys have huge application potential in many fields [1–4]. Iron-based amorphous alloys are generally obtained by rapid cooling and solidification of molten metals. They have the characteristics of low surface energies, weak surface activities, strong water-repellent, and oil-repellent. When the polymer material is used to encapsulate the iron-based amorphous alloy material, there is a serious interface non-wetting problem between the two, which prevents to achieve ideal packaging effect. Hence, improving the wettability is the biggest challenge in the application of iron-based amorphous alloys [5–7].
Molecular dynamics simulation for studying the stability of structure H clathrate-hydrates of argon and large guest molecules
Published in Journal of Dispersion Science and Technology, 2018
Pourya Reshadi, Hamid Modarress, Bahram Dabir, Sepideh Amjad-Iranagh
The host–host RDF can be considered as a robust tool to identify hydrate crystal structure. As we know, in a crystalline solid with long-range order, due to the periodic arrangement of the system, the RDF plots has an infinite number of sharp peaks corresponding to coordination of the nearest and next-nearest shells, whose separations and heights exhibit the characteristic of the lattice structure.[44] This is in contrast with gas or liquid, which has short-range order and long-range disorder. The liquids (and amorphous solids) have short-range order, where the nearest coordination shells around a given molecule can be identified. However, the well-defined positional relationships disappear gradually with increasing the distance r because of missing the long-range order.[45] In real gases, it is equally likely to find a molecule at any distance r from a given molecule and the g(r) is completely featureless.[46] These states demonstrate that the lattice structure of the simulated clathrate-hydrates in this work, preserve their crystalline phase over the length of simulation procedure.
Local configurations and atomic intermixing in as-quenched and annealed Fe1−xCrx and Fe1−xMox ribbons
Published in Philosophical Magazine, 2018
A. E. Stanciu, S. G. Greculeasa, C. Bartha, G. Schinteie, P. Palade, A. Kuncser, A. Leca, G. Filoti, A. Birsan, O. Crisan, V. Kuncser
The structural characterisation of binary AB alloys is described very well by the statistical short-range order (SRO) parameters, such as the Warren–Cowley parameters, αn, quantifying the deviation from the binomial distribution [31]. While clustering describes the tendency for like atoms to be near neighbours, short-range order indicates arrangements where alike atoms have the tendency to be near neighbours. The αn parameters account for the site occupancy in the nth shell, being influenced by concentration, nature, temperature and sample history [32]. Based on the Warren–Cowley parameters, the type of order can be mentioned as short range for negative αn, and clustering or local order for positive αn, and random distribution for null αn. Within the two-shell model, the SRO parameters are described by the general formulas [20]: