An Ab Initio Study of Thermodynamic and Mechanical Stability of Heusler-Based Fe2AlCo Polymorphs

We use quantum-mechanical calculations to test a hypothesis of Glover et al. (J. Mag. Mag. Mater. 15 (1980) 699) that Co atoms in the Fe 2 AlCo compound have on average 3 Fe and 3 Co atoms in their second nearest neighbor shell. We have simulated four structural configurations of Fe 2 AlCo including the full Heusler structure, inverse Heusler polymorph and two other phases matching this idea. The highest thermodynamic stability at T = 0 K is indeed predicted for one of the phases with the distribution of atoms according to Glover and et al. However, small energy differences among three of the studied polymorphs lead to a disordered CsCl-structure-like (B2-like) phase at elevated temperatures. The fourth variant, the full Heusler phase, is predicted to be mechanically unstable. The global magnetic states are predicted to be ferromagnetic but local magnetic moments of Fe and Co atoms sensitively depend on the composition of the first and second coordination shells.

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Mechanical and thermal stability of retained austenite in plastically deformed bainite-based TRIP-aided medium-Mn steels

Archives of Civil and Mechanical Engineering ◽

10.1007/s43452-021-00284-6 ◽

2021 ◽

Vol 21 (3) ◽

Author(s):

Aleksandra Kozłowska ◽

Adam Grajcar ◽

Aleksandra Janik ◽

Krzysztof Radwański ◽

Ulrich Krupp ◽

...

Keyword(s):

Electron Microscopy ◽

Thermal Stability ◽

Retained Austenite ◽

Elevated Temperatures ◽

Mechanical Performance ◽

Mechanical Stability ◽

Electron Backscatter Diffraction ◽

Cost Effective ◽

Tensile Tests ◽

Thermal Stability Of

AbstractAdvanced medium-Mn sheet steels show an opportunity for the development of cost-effective and light-weight automotive parts with improved safety and optimized environmental performance. These steels utilize the strain-induced martensitic transformation of metastable retained austenite to improve the strength–ductility balance. The improvement of mechanical performance is related to the tailored thermal and mechanical stabilities of retained austenite. The mechanical stability of retained austenite was estimated in static tensile tests over a wide temperature range from 20 °C to 200 °C. The thermal stability of retained austenite during heating at elevated temperatures was assessed by means of dilatometry. The phase composition and microstructure evolution were investigated by means of scanning electron microscopy, electron backscatter diffraction, X-ray diffraction and transmission electron microscopy techniques. It was shown that the retained austenite stability shows a pronounced temperature dependence and is also stimulated by the manganese addition in a 3–5% range.

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Bi-Functional Composting the Sulfonic Acid Based Proton Exchange Membrane for High Temperature Fuel Cell Application

Polymers ◽

10.3390/polym12051000 ◽

2020 ◽

Vol 12 (5) ◽

pp. 1000

Author(s):

Guoxiao Xu ◽

Juan Zou ◽

Zhu Guo ◽

Jing Li ◽

Liying Ma ◽

...

Keyword(s):

High Temperature ◽

Fuel Cell ◽

Composite Membrane ◽

Sulfonic Acid ◽

Elevated Temperatures ◽

Mechanical Stability ◽

Strong Dependence ◽

Proton Exchange ◽

Nafion Membrane ◽

Silica Nanofiber

Although sulfonic acid (SA)-based proton-exchange membranes (PEMs) dominate fuel cell applications at low temperature, while sulfonation on polymers would strongly decay the mechanical stability limit the applicable at elevated temperatures due to the strong dependence of proton conduction of SA on water. For the purpose of bifunctionally improving mechanical property and high-temperature performance, Nafion membrane, which is a commercial SA-based PEM, is composited with fabricated silica nanofibers with a three-dimensional network structure via electrospinning by considering the excellent water retention capacity of silica. The proton conductivity of the silica nanofiber–Nafion composite membrane at 110 °C is therefore almost doubled compared with that of a pristine Nafion membrane, while the mechanical stability of the composite Nafion membrane is enhanced by 44%. As a result, the fuel cell performance of the silica nanofiber-Nafion composite membrane measured at high temperature and low humidity is improved by 38%.

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Investigation of the structural competing and atomic ordering in Heusler compounds Fe 2 NiSi and Ni 2 FeSi under strain condition

Royal Society Open Science ◽

10.1098/rsos.191007 ◽

2019 ◽

Vol 6 (9) ◽

pp. 191007 ◽

Cited By ~ 5

Author(s):

Tie Yang ◽

Liyu Hao ◽

Rabah Khenata ◽

Xiaotian Wang

Keyword(s):

First Principles ◽

Magnetic Moments ◽

Applied Strain ◽

First Principles Calculation ◽

Cubic Phase ◽

Strain Condition ◽

Heusler Compounds ◽

Atomic Ordering ◽

Nearest Neighbours ◽

Full Heusler

The structural competing and atomic ordering of the full Heusler compounds Fe 2 NiSi and Ni 2 FeSi under uniform and tetragonal strains have been systematically studied by the first-principles calculation. Both Fe 2 NiSi and Ni 2 FeSi have the XA structure in cubic phase and they show metallic band structures and large magnetic moments (greater than 3 μ B ) at equilibrium condition. Tetragonal distortion can further decrease the total energy, leading to the possible phase transformation. Furthermore, different atom reordering behaviours have been observed: for Fe 2 NiSi, atoms reorder from cubic XA-type to tetragonal L1 0 -type; for Ni 2 FeSi, there is only structural transformation without atom reordering. The total magnetic moments of Fe 2 NiSi and Ni 2 FeSi are mainly contributed by Fe atoms, and Si atom can strongly suppress the moments of Fe atoms when it is present in the nearest neighbours of Fe atoms. With the applied strain, the distance between Fe and Si atoms play an important role for the magnetic moment variation of Fe atom. Moreover, the metallic band nature is maintained for Fe 2 NiSi and Ni 2 FeSi under both uniform and tetragonal strains. This study provides a detailed theoretical analysis about the full Heusler compounds Fe 2 NiSi and Ni 2 FeSi under strain conditions.

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Impact of Nano-Scale Distribution of Atoms on Electronic and Magnetic Properties of Phases in Fe-Al Nanocomposites: An Ab Initio Study

Nanomaterials ◽

10.3390/nano8121059 ◽

2018 ◽

Vol 8 (12) ◽

pp. 1059 ◽

Cited By ~ 5

Author(s):

Ivana Miháliková ◽

Martin Friák ◽

Yvonna Jirásková ◽

David Holec ◽

Nikola Koutná ◽

...

Keyword(s):

Ab Initio ◽

Density Functional ◽

Nearest Neighbor ◽

Magnetic Moments ◽

Generalized Gradient ◽

Functional Theory ◽

Α Phase ◽

Ordered Intermetallic ◽

Random Structures ◽

The Impact

Quantum-mechanical calculations are applied to examine magnetic and electronic properties of phases appearing in binary Fe-Al-based nanocomposites. The calculations are carried out using the Vienna Ab-initio Simulation Package which implements density functional theory and generalized gradient approximation. The focus is on a disordered solid solution with 18.75 at. % Al in body-centered-cubic ferromagnetic iron, so-called α -phase, and an ordered intermetallic compound Fe 3 Al with the D0 3 structure. In order to reveal the impact of the actual atomic distribution in the disordered Fe-Al α -phase three different special quasi-random structures with or without the 1st and/or 2nd nearest-neighbor Al-Al pairs are used. According to our calculations, energy decreases when eliminating the 1st and 2nd nearest neighbor Al-Al pairs. On the other hand, the local magnetic moments of the Fe atoms decrease with Al concentration in the 1st coordination sphere and increase if the concentration of Al atoms increases in the 2nd one. Furthermore, when simulating Fe-Al/Fe 3 Al nanocomposites (superlattices), changes of local magnetic moments of the Fe atoms up to 0.5 μ B are predicted. These changes very sensitively depend on both the distribution of atoms and the crystallographic orientation of the interfaces.

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Magnetic Condition Flat Core/Shell Nanoparticles

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.752-753.238 ◽

2015 ◽

Vol 752-753 ◽

pp. 238-242 ◽

Cited By ~ 1

Author(s):

Leonid Afremov ◽

Artur Elovskii

Keyword(s):

Phase Diagrams ◽

Equilibrium Position ◽

Magnetic Moments ◽

Core Shell ◽

Geometrical Parameters ◽

Shell Nanoparticles ◽

Two Phase ◽

Magnetic Condition ◽

Core Shell Nanoparticles ◽

Magnetic States

In terms two-phase nanoparticles model, dependence equilibrium position of magnetic moments of parameters size and elongation nanoparticles core is investigated. Phase diagrams of magnetic states were shown and determine geometrical parameters core, in equilibrium states.

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LOCAL MAGNETIC MOMENTS OF Fe1/CrN NANOINCLUSIONS EMBEDDED IN BULK Fe

Surface Review and Letters ◽

10.1142/s0218625x02004335 ◽

2002 ◽

Vol 09 (05n06) ◽

pp. 1747-1752

Author(s):

J. L. MORÁN-LÓPEZ ◽

P. G. ALVARADO-LEYVA ◽

J. M. MONTEJANO-CARRIZALES

Keyword(s):

Magnetic Properties ◽

Nearest Neighbor ◽

Magnetic Moments ◽

Zero Temperature ◽

Hartree Fock ◽

The Matrix

Local magnetic moments of Fe 1/ Cr N inclusions in an Fe matrix are calculated as a function of the Cr number of atoms N at zero temperature, and for N ≤ 64. We use a realistic spd-band Hamiltonian to determine their magnetic properties. The local magnetic moments μ(i) at the various cluster sites i are calculated self-consistently in the unrestricted Hartree–Fock approximation. The matrix Fe atoms couple always antiferromagnetically with the Cr atoms. The μ(i) of Cr atoms at the interface are enhanced by the presence of Fe atoms in their first nearest neighbor shell. In most cases the Fe moments close to the cluster are reduced. A remarkable interplay between the antiferromagnetism of Cr and the ferromagnetism of Fe is obtained.

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Quantum-mechanical stability of solitons and the correspondence principle

Physical Review A ◽

10.1103/physreva.48.2361 ◽

1993 ◽

Vol 48 (3) ◽

pp. 2361-2369 ◽

Cited By ~ 21

Author(s):

F. X. Kärtner ◽

H. A. Haus

Keyword(s):

Correspondence Principle ◽

Mechanical Stability ◽

Quantum Mechanical

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Controlled On-Chip Single-Photon Transfer Using Photonic Crystal Coupled-Cavity Waveguides

Advances in OptoElectronics ◽

10.1155/2011/893086 ◽

2011 ◽

Vol 2011 ◽

pp. 1-13 ◽

Cited By ~ 4

Author(s):

Hubert Pascal Seigneur ◽

Matthew Weed ◽

Michael Niklaus Leuenberger ◽

Winston Vaughan Schoenfeld

Keyword(s):

High Efficiency ◽

Nearest Neighbor ◽

Single Photon ◽

Tight Binding ◽

Quantum Mechanical ◽

Single Photons ◽

Quantum Network ◽

On Chip ◽

Quantum Mechanical Approach ◽

Coupled Cavity

To the end of realizing a quantum network on-chip, single photons must be guided consistently to their proper destination both on demand and without alteration to the information they carry. Coupled cavity waveguides are anticipated to play a significant role in this regard for two important reasons. First, these structures can easily be included within fully quantum-mechanical models using the phenomenological description of the tight-binding Hamiltonian, which is simply written down in the basis of creation and annihilation operators that move photons from one quasimode to another. This allows for a deeper understanding of the underlying physics and the identification and characterization of features that are truly critical to the behavior of the quantum network using only a few parameters. Second, their unique dispersive properties together with the careful engineering of the dynamic coupling between nearest neighbor cavities provide the necessary control for high-efficiency single-photon on-chip transfer. In this publication, we report transfer efficiencies in the upwards of 93% with respect to a fully quantum-mechanical approach and unprecedented 77% in terms of transferring the energy density contained in a classical quasibound mode from one cavity to another.

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