Theoretical Study of Polar and Non-Polar Interfaces in Compound Semiconductors: A Thermodynamic Analysis Based on Electronic Structure Calculations

1992 ◽  
Vol 278 ◽  
Author(s):  
M. Kohyama ◽  
S. Kose ◽  
R. Yamamoto
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Compound Semiconductors ◽  
Binding Energies ◽  
Chemical Potentials ◽  
Zinc Blende ◽  
Thermodynamic Potentials ◽  
Symmetrical Tilt ◽  
The Stability ◽  
Structure Calculations

AbstractPolar and non-polar interfaces of grain boundaries in compound semiconductors can be defined by the stoichlometry in the interface region, and It Is possible to construct two polar and one non-polar Interfaces for a symmetrical tilt grain boundary In the zinc-blende structure of which the Interface Is polar surfaces. The atomic and electronic structures of polar and non-polar interfaces of the {122} Σ=9 grain boundary in SIC have been examined by using the SCTB method coupled with the supercell technique. By using the calculated binding energies, the relative stability of the polar and non-polar interfaces has been analyzed through calculations of the thermodynamic potentials as a function of the atomic chemical potentials. It has been shown that the wrong bonds and the stoichlometry much Influence the stability and properties of grain boundaries in SiC. The stability of polar Interfaces In heterovalent compound semiconductors has been discussed.

Effects of Alloying Elements on Iron Grain Boundary Cohesion

1997 ◽  
Vol 492 ◽  
Author(s):  
X. Chen ◽  
D. E. Ellis ◽  
G. B. Olson
Keyword(s):  
Molecular Dynamics ◽  
Free Surface ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
First Principles ◽  
Electronic Structure Calculations ◽  
Alloying Elements ◽  
Alloying Element ◽  
Long Time ◽  
Structure Calculations

For a long time, understanding the mechanisms of impurity-promoted embrittlement in iron and the consequent cohesion(decohesion) effects has been a challenge for materials scientists. The role alloying elements play in impurity-promoted embrittlement is important due to either their direct intergranular cohesion(decohesion) effects or effects upon embrittling potency of other impurities. Some alloying elements like Pd and Mo are known to be helpful for intergranular cohesion in iron and some other alloying elements like Mn are known to segregate to and weaken iron grain boundaries dramatically[1]. There have been intensive investigations on these mechanisms for a long time and especially, with the progress in computing techniques in recent years, calculations on more realistic models have become possible[2–4]. In this paper we briefly present our studies on some selected alloying-element/iron grain boundaries(GB) and free surface(FS) systems. The effects of Pd, Mo, Mn and Cr on the Fe Σ5 (031) grain boundary and its corresponding (031) free surface are examined, using a combination of molecular dynamics(MD) and first-principles electronic structure calculations. Section 2 gives a brief introduction to the methods used and Section 3 gives the main results.

Correlation between structure, energy, and ideal cleavage fracture for symmetrical grain boundaries in fcc metals

1990 ◽  
Vol 5 (8) ◽  
pp. 1708-1730 ◽  
Author(s):  
D. Wolf
Keyword(s):  
Phase Space ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Cleavage Fracture ◽  
Good Description ◽  
Random Boundary ◽  
Free Surfaces ◽  
Symmetrical Tilt ◽  
Boundary Model ◽  
Twist Boundaries

The misorientation phase space for symmetrical grain boundaries is explored by means of atomistic computer simulations, and the relationship between the tilt and twist boundaries in this three-parameter phase space is clucidated. The so-called random-boundary model (in which the interactions of atoms across the interface are assumed to be entirely random) is further developed to include relaxation of the interplanar spacings away from the grain boundary. This model is shown to include fully relaxed free surfaces naturally, thus permitting a direct comparison of the physical properties of grain boundaries and free surfaces, and hence the determination of ideal cleavage-fracture energies of grain boundaries. An extensive comparison with computer-simulation results for symmetrical tilt and twist boundaries shows that the random-boundary model also provides a good description of the overall structure-energy correlation for both low- and high-angle tilt and twist boundaries. Finally, the role of the interplanar spacing parallel to the grain boundary in both the grain-boundary and cleavage-fracture energies is elucidated.

A Comparative Atomistic Study of the Structure of Grain Boundaries in Tungsten

1992 ◽  
Vol 291 ◽  
Author(s):  
A. Marinopoulos ◽  
M. Sob ◽  
V. Vitek ◽  
A. E. Carlsson
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Structural Characteristics ◽  
Many Body ◽  
Electronic Density ◽  
Atomic Interactions ◽  
Symmetrical Tilt ◽  
Tilt Grain Boundary ◽  
Atomistic Study ◽  
Central Forces

ABSTRACTMost atomistic studies of grain boundaries have been carried out using central forces to describe atomic interactions. However, in transition metals with unfilled d-bands the angular dependence of interatomic forces may be important. The purpose of this paper is to investigate the significance of angular forces in the case of Tungsten. The calculations have been performed for the Σ5(210) symmetrical tilt grain boundary using two alternate approaches. First are the central-force many-body potentials of the Finnis-Sinclair type. The second are the angular dependent potentials obtained via a moment analysis of the electronic density of states. The results of these two approaches are compared by analyzing the boundary structures, the relative displacements of the adjoining grains and the expansion. Differences in structural characteristics are discussed in terms of the effect of angular forces.

Influence of Impurities on Grain Boundaries Cohesion in B2-TiMe

2016 ◽  
Vol 258 ◽  
pp. 110-113
Author(s):  
Svetlana Kulkova ◽  
Alexander Bakulin ◽  
Sergey Kulkov
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
First Principles ◽  
Carbon Segregation ◽  
Accumulation Effect ◽  
Symmetrical Tilt ◽  
Pseudopotential Approach ◽  
Influence Of Impurities ◽  
Substitutional Impurities

The effect of interstitial and substitutional impurities on grain boundary (GB) cohesion in the series of B2-TiMe alloys is studied from first principles using pseudopotential approach. It is shown that the TiMe Σ5(310) symmetrical tilt GB cohesion is reduced by the segregation of hydrogen while it is increased due to boron or carbon segregation. We analyze also the combined and accumulation effect of interstitial B (C) and H impurities on the change of the Griffith work.

The Interaction of Twin Boundaries with Grain Boundaries in YBa2Cu3O7-δ

1994 ◽  
Vol 357 ◽  
Author(s):  
Jenn-Yue Wang ◽  
Alexander H. King
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Small Angle ◽  
Driving Force ◽  
The Other ◽  
Twin Boundaries ◽  
Domain Structures ◽  
Tilt Boundaries ◽  
Symmetrical Tilt ◽  
System Energy

AbstractTwins in YBa2Cu3O7-δ may be “correlated” at [001] tilt grain boundaries (i.e. twin boundaries from one grain may meet twin boundaries from the other grain in quadruple junctions) and the twins may also be narrowed or “constricted” at the boundary. These effects are more pronounced in the regime of small angle grain boundaries. Based on TEM observations, a tentative threshold misorientation angle of approximately 15° is identified, below which there is a significant driving force reducing the system energy by correlation. The energies of various grain boundary domain structures associated with the twins were estimated on the basis of the dislocations they contain. Success has been obtained in explaining twin correlation in symmetrical tilt boundaries.

Ab-Initio Determination of the Atomic Structure of Symmetrical Tilt Grain Boundaries in BCC Transition Metals

1997 ◽  
Vol 492 ◽  
Author(s):  
C. Elsässer ◽  
O. Beck ◽  
T. Ochs ◽  
B. Meyer
Keyword(s):  
Transition Metals ◽  
Grain Boundary ◽  
Ab Initio ◽  
Grain Boundaries ◽  
Density Functional ◽  
Local Density ◽  
High Symmetry ◽  
Many Body ◽  
Local Density Functional Theory ◽  
Symmetrical Tilt

ABSTRACTAtomistic simulations of grain-boundary structures in body-centered cubic transition metals have revealed that angle-dependent contributions to interatomic interactions are essential. Unfortunately, the results of presently available empirical many-body potentials are not yet always sufficiently reliable for quantitative theoretical predictions of grain-boundary structures, which are consistent with experimental observations, e.g. by high-resolution transmission electron microscopy.Ab-initio electronic-structure calculations based on the local-density-functional theory offer the possibility to determine accurately the microscopic structures of special, high-symmetry grain boundaries, which can be used as data bases for the improvement of empirical many-body potentials. Such ab-initio calculations, with a mixed-basis pseudopotential method and grain-boundary supercells, are presented for Σ5 (310) [001] 36.87° symmetrical tilt grain boundaries in Niobium and Molybdenum.

Anti-Site Bonds and the Structure of Interfaces in SiC

1990 ◽  
Vol 183 ◽  
Author(s):  
P. Pirouz ◽  
J. Yang
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Compound Semiconductors ◽  
High Resolution Electron Microscopy ◽  
High Energy ◽  
Dangling Bonds ◽  
Resolution Electron ◽  
Elemental Semiconductors

AbstractHigh resolution electron microscopy has been used to study the structure of the 3C/6H interface, Σ,=3 {111}and Σ.=3 {112}grain boundaries in 3C-SiC. In SiC, as in other compound semiconductors, anti-site bonds occur in a variety of defects. These are high energy bonds comparable to that of dangling bonds. But, while dangling bonds at the grain boundaries may be eliminated by reconstruction just as in elemental semiconductors, it may not be possible to avoid anti-site bonds.These problems are discussed for the Σ=3 {112} grain boundary, where the structures proposed for Ge and Si are used as starting models for SiC.

Solution of the Atomic Structure of the Σ=5 (310) [001] Grain Boundary in Nial by Hrem and Atomistic Simulations

1994 ◽  
Vol 364 ◽  
Author(s):  
R. W. Fonda ◽  
M. Yan ◽  
D. E. Luzzi
Keyword(s):  
Grain Boundary ◽  
Atomic Structure ◽  
High Resolution Electron Microscopy ◽  
Nial Phase ◽  
Consistent Model ◽  
Resolution Electron ◽  
Synergistic Approach ◽  
The Stability ◽  
Structure Calculations ◽  
Atomistic Structure

AbstractThe atomic structure of the Σ = 5 (310) [001] grain boundary in NiAl has been determined by a synergistic approach combining high resolution electron microscopy (HREM) and atomistic structure calculations. A bicrystal of controlled orientation was produced by diffusion bonding and imaged with the electron beam parallel to the [001] tilt axis. The results showed that the material remains chemically ordered up to the boundary plane. Atomistic structure calculations employed N-body empirical potentials developed for the NiAl phase to examine the changes in interfacial energy due to the incorporation of various point defects at the grain boundary. A self-consistent model structure was determined which was of lowest energy and produced calculated images which matched experimental images of the boundary. Monte Carlo simulations confirm the stability of this structure at finite temperatures.

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