First-Principles Study of Structural and Defect Properties in FeCo Intermetallics

2004 ◽  
Vol 842 ◽  
Author(s):  
M. Krcmar ◽  
C. L. Fu ◽  
J. R. Morris
Keyword(s):  
Shear Stress ◽  
Ab Initio ◽  
Structural Stability ◽  
First Principles ◽  
Statistical Thermodynamic ◽  
Internal Stresses ◽  
Applied Shear Stress ◽  
Defect Energies ◽  
Antisite Defects ◽  
B2 Structure

ABSTRACTEmploying ab-initio calculations and statistical thermodynamic modeling, we investigated the structural stability, defect energies, and ordering of B2 FeCo intermetallics. We find that FeCo in the B2 structure is a marginally stable and weakly ordered system, with a high density of antisite defects on both sublattices and low APB energies for the <111> slip on both {110} and {112} planes. The structural stability of B2 FeCo is very sensitive to the change in local atomic environment, as the system transforms to a lower-symmetry L10 phase under the effects of reduced dimensionality or applied shear stress. We suggest that internal stresses near dislocation cores might be closely connected with the intrinsic brittleness of ordered FeCo, as it is likely to induce a local structural transformation from the B2 structure to the L10 structure.

Dislocation mobility and the concept of flow stress

1975 ◽  
Vol 344 (1638) ◽  
pp. 375-385 ◽  
Keyword(s):  
Shear Stress ◽  
Flow Stress ◽  
First Principles ◽  
Unstable State ◽  
Burgers Vector ◽  
Applied Shear Stress ◽  
Set Up ◽  
The Stability ◽  
Definition Of ◽  
Hurwitz Theorem

A formal definition of the flow stress of a metal is established rigorously from first principles for a certain model by studying the stability of equilibrium of the leader in a group of n ( n large) coplanar screw dislocations with Burgers vector b, moving on a plane a distance h from a non-coplanar locked dislocation with Burgers vector mb ( m < n ) under the action of an applied shear stress p yz = o.A ‘ characteristic equation’ of the model is set up and the onset of instability of the leader is identified with the bifurcation of its equilibrium state, which is predicted by the Routh-Hurwitz theorem, well-known in the theory of stability. As an aid in simplifying this process recourse is had to another well-known the orem -that due to Liénard & Chipart. The applied shear stress required to achieve this unstable state is specified within certain bounds. Since these bounds are very close to each other, especially for small m , the critical flow stress can be estimated accurately. It is shown that the flow stress is closer to the lower bound obtained previously and that the superdislocation approach overestimates the critical stress. The paper also discusses certain implications of the present work.

Influence of Shear Stress on Screw Dislocations in a Model Sodium Lattice

1971 ◽  
Vol 49 (16) ◽  
pp. 2160-2180 ◽  
Author(s):  
Z. S. Basinski ◽  
M. S. Duesbery ◽  
Roger Taylor
Keyword(s):  
Shear Stress ◽  
First Principles ◽  
Dislocation Core ◽  
The Body ◽  
Peierls Stress ◽  
Screw Dislocations ◽  
Hexagonal Close Packed ◽  
Applied Shear Stress ◽  
Dislocation Movement ◽  
Twinning Direction

The behavior of the screw dislocation core in the presence of an external shear stress has been examined for the body-centered cubic and hexagonal close-packed phases of a model sodium lattice, using an effective ion–ion potential calculated from first principles. The Peierls stress for screw dislocations in the b.c.c. lattice at 0 °K is dependent on the orientation of the applied shear stress, and has a minimum value of 0.0105G, where G is the shear modulus, for slip in the twinning direction on {112} planes. The Peierls stress in the h.c.p. lattice is at least 25 times smaller. Dislocation movement in the model b.c.c. lattice takes place by unit translations on {110} planes, with the selection rule that no two consecutive translations can take place on the same slip plane.

scholarly journals Modulating the thermal and structural stability of gallenene via variation of atomistic thickness

2021 ◽  
Author(s):  
Stephanie Lambie ◽  
Krista G. Steenbergen ◽  
Nicola Gaston
Keyword(s):  
Molecular Dynamics ◽  
Ab Initio ◽  
Structural Stability ◽  
Variable Thickness

Using ab initio molecular dynamics, we show that a recently discovered form of 2D Ga—gallenene—exhibits highly variable thickness dependent properties.

Flexoelectricity in atomic monolayers from first principles

Nanoscale ◽  
2020 ◽  
Author(s):  
Shashikant Kumar ◽  
David Codony ◽  
Irene Arias ◽  
Phanish Suryanarayana
Keyword(s):  
Density Functional Theory ◽  
Transition Metal ◽  
Ab Initio ◽  
First Principles ◽  
Density Functional ◽  
Transition Metal Dichalcogenides ◽  
Functional Theory ◽  
Group Iii ◽  
Flexoelectric Effect ◽  
Metal Dichalcogenides

We study the flexoelectric effect in fifty-four select atomic monolayers using ab initio Density Functional Theory (DFT). Specifically, considering representative materials from each of Group III monochalcogenides, transition metal dichalcogenides...

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