Determination of the lattice translation across {110} APBs in GaAs

1988 ◽  
Vol 46 ◽  
pp. 600-601
Author(s):  
D.R. Rasmussen ◽  
N.-H. Cho ◽  
C.B. Carter
Keyword(s):  
Grain Boundaries ◽  
Lower Energy ◽  
Antiphase Boundary ◽  
The Other ◽  
Boundary Structure ◽  
Interface Plane ◽  
Inversion Symmetry ◽  
High Angle ◽  
Equilibrium Distance

Domains in GaAs can exist which are related to one another by the inversion symmetry, i.e., the sites of gallium and arsenic in one domain are interchanged in the other domain. The boundary between these two different domains is known as an antiphase boundary [1], In the terminology used to describe grain boundaries, the grains on either side of this boundary can be regarded as being Σ=1-related. For the {110} interface plane, in particular, there are equal numbers of GaGa and As-As anti-site bonds across the interface. The equilibrium distance between two atoms of the same kind crossing the boundary is expected to be different from the length of normal GaAs bonds in the bulk. Therefore, the relative position of each grain on either side of an APB may be translated such that the boundary can have a lower energy situation. This translation does not affect the perfect Σ=1 coincidence site relationship. Such a lattice translation is expected for all high-angle grain boundaries as a way of relaxation of the boundary structure.

Grain boundary structure observed by T.E.M

1978 ◽  
Vol 36 (1) ◽  
pp. 410-411
Author(s):  
P.J. Goodhew
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Single Crystals ◽  
Lower Energy ◽  
Planar Defect ◽  
Boundary Structure ◽  
High Angle ◽  
Thin Specimen ◽  
Special Boundaries ◽  
Grain Boundary Structure

This paper reports some observations on gold by TEM which imply that the dissociation of a high angle grain boundary into two lower energy boundaries may occur extensively.It is well established that grain boundaries of any desired geometry can be created in gold by the welding together of thin single crystals. The resultant thin bicrystal specimens are ideally suited for immediate examination by TEM and many aspects of grain boundary structure and behaviour in such specimens have been studied or discussed. One particularly useful specimen configuration can be achieved if the bicrystal is annealed until its boundary migrates (lowering its total area) until it is perpendicular to the surface of the thin specimen. This specimen geometry has been used to study, inter alia, the faceting of grain boundaries.During a study of the behaviour of coincidence high angle boundaries (i.e. those special boundaries whose geometry is such that a fraction 1/Σ of the lattice sites in both crystals coincide) it was noticed that the boundary under observation was no longer a single planar defect.

Measurement of the Displacement Across a Coincidence Grain Boundary

1977 ◽  
Vol 35 ◽  
pp. 124-125
Author(s):  
J. W. Matthews ◽  
W. M. Stobbs
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Stacking Fault ◽  
The Other ◽  
Measuring Technique ◽  
High Angle ◽  
Twin Boundaries ◽  
Rigid Displacement ◽  
Cubic Crystals ◽  
Lattice Displacement

Many high-angle grain boundaries in cubic crystals are thought to be either coincidence boundaries (1) or coincidence boundaries to which grain boundary dislocations have been added (1,2). Calculations of the arrangement of atoms inside coincidence boundaries suggest that the coincidence lattice will usually not be continuous across a coincidence boundary (3). There will usually be a rigid displacement of the lattice on one side of the boundary relative to that on the other. This displacement gives rise to a stacking fault in the coincidence lattice.Recently, Pond (4) and Smith (5) have measured the lattice displacement at coincidence boundaries in aluminum. We have developed (6) an alternative to the measuring technique used by them, and have used it to find two of the three components of the displacement at {112} lateral twin boundaries in gold. This paper describes our method and presents a brief account of the results we have obtained.

Precipitation on Low Angle Boundaries in Al-Zn-Mg

1980 ◽  
Vol 38 ◽  
pp. 374-375
Author(s):  
Diane M. Vanderwalker
Keyword(s):  
Grain Boundaries ◽  
High Strength ◽  
Boundary Structure ◽  
Aircraft Industry ◽  
Precipitate Free Zone ◽  
High Angle ◽  
Adjacent Region ◽  
Free Zone ◽  
Widespread Interest

There is a widespread interest in understanding the properties of Al-base alloys so that progress can be made toward extending their present applications in the aircraft industry. Al-Zn-Mg is precipitation hardened to gain its high strength; however, during aging the formation of heterogeneous precipitates on the grain boundaries creates a precipitate-free zone in the adjacent region. Since high angle grain boundaries are not easily characterized, it is difficult to establish a relationship between the precipitate and the boundary structure. Therefore, this study involves precipitation on low angle grain boundaries where the boundary and the precipitate can be fully analyzed.

EBSD Analysis of Friction Stir Welded 7136-T76 Aluminum Alloy

2013 ◽  
Vol 203-204 ◽  
pp. 258-261 ◽  
Author(s):  
Izabela Kalemba ◽  
Krzysztof Muszka ◽  
Mirosław Wróbel ◽  
Stanislaw Dymek ◽  
Carter Hamilton
Keyword(s):  
Grain Size ◽  
Aluminum Alloy ◽  
Grain Boundaries ◽  
Texture Analysis ◽  
Crystallographic Texture ◽  
High Frequency ◽  
The Other ◽  
Ebsd Analysis ◽  
High Angle ◽  
Friction Stir

This research addresses the EBSD analysis of friction stir welded 7136-T76 aluminum alloy. The objectives of this study were to evaluate the grain size and their shape, character of grain boundaries in the stirred and thermo-mechanically affected zones, both on the advancing and retreating side as well as to investigate changes in the crystallographic texture. Results of texture analysis indicate the complexity of the FSW process. The texture gradually weakens on moving from the thermo-mechanically affected zone toward the weld center. The stirred zone is characterized by very weak texture and is dominated by high angle boundaries. On the other hand, the thermo-mechanically affected zone exhibits a high frequency of low angle boundaries.

Observations and implications of grain boundary dislocation networks in high-angle YBa2Cu3O7−δ grain boundaries

1990 ◽  
Vol 5 (5) ◽  
pp. 919-928 ◽  
Author(s):  
S. E. Babcock ◽  
D. C. Larbalestier
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Weak Link ◽  
Coincidence Site Lattice ◽  
Boundary Structure ◽  
High Angle ◽  
Grain Boundary Structure ◽  
Transmission Electron ◽  
Means Of Transmission ◽  
Regular Networks

Regular networks of localized grain boundary dislocations (GBDs) have been imaged by means of transmission electron microscopy in three different types of high-angle grain boundaries in YBa2Cu3O7-δ, implying that these boundaries possess ordered structures upon which a significant periodic strain field is superimposed. The occurrence of these GBD networks is shown to be consistent with the GBD/Structural Unit and Coincidence Site Lattice (CSL)/Near CSL descriptions for grain boundary structure. Thus, these dislocations appear to be intrinsic features of the boundary structure. The spacing of the observed GBDs ranged from ∼10 nm to ∼100 nm. These GBDs make the grain boundaries heterogeneous on a scale that approaches the coherence length and may contribute to their weak-link character by producing the “superconducting micro-bridge” microstructure which has been suggested on the basis of detailed electromagnetic measurements on similar samples.

scholarly journals Diffraction Studies of the Atomic Structure of Grain Boundaries

1984 ◽  
Vol 41 ◽  
Author(s):  
K. R. Milkove ◽  
P. A. Lamarre ◽  
F. Schmückle ◽  
M. D. Vaudin ◽  
S. L. Sass
Keyword(s):  
Grain Boundaries ◽  
Atomic Structure ◽  
Large Angle ◽  
Boundary Structure ◽  
Twist Boundary ◽  
Bonding Type ◽  
Metal Type ◽  
Twist Boundaries

AbstractThe application of diffraction techniques to study the atomic structure of grain boundaries is reviewed. The determination of the projected structure of a large angle [001] twist boundary is described. The influence of f.c.c. metal type and bonding type on boundary structure is examined. Generalizations are made concerning the structure of large angle [001] twist boundaries based on the results of the diffraction studies.

Grain Boundaries in Nanophase Materials and Conventional Polycrystals – Are They Distinct?

1994 ◽  
Vol 351 ◽  
Author(s):  
S. C. Mehta ◽  
D. A. Smith ◽  
U. Erb
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
The Other ◽  
Boundary Structure ◽  
Triple Junctions ◽  
Grain Sizes ◽  
Grain Boundary Structure ◽  
Nanophase Materials ◽  
20 Nm ◽  
Boundary Diffusivity

ABSTRACTNanograined materials, with grain sizes in the range of 1–20 nm, exhibit significant enhancement of grain boundary dependent properties such as yield strength, intergranular fracture toughness, grain boundary diffusivity, specific heat and thermal expansion coefficient. Measurements by indirect techniques suggest that the grain boundaries in nanophase materials are structurally different from the boundaries in their conventional polycrystal counterparts. Exploratory HRTEM observations, on the other hand, indicate that the grain boundary structure in nanophase materials is the same as that found in grain boundaries in conventional polycrystals. This paper reports an HRTEM investigation of the microstructure in electrodeposited nanocrystalline (nc) Ni1wt.%P alloy. These observations reveal the presence of about 8-10 vol. % porosity in the microstructure. There is also evidence for the presence of an amorphous phase at some grain boundaries and triple junctions. A comparison of grain boundary structures with boundaries in conventional materials suggests that grain boundaries in the nc Ni-P alloy are, for the most part, normal.

The 45° grain boundaries in YBa2Cu3O7−δ

1992 ◽  
Vol 7 (5) ◽  
pp. 1052-1059 ◽  
Author(s):  
Stuart McKernan ◽  
M. Grant Norton ◽  
C. Barry Carter
Keyword(s):  
Thin Films ◽  
Grain Boundaries ◽  
Electrical Transport ◽  
Weak Link ◽  
High Resolution Electron Microscopy ◽  
Boundary Region ◽  
Boundary Structure ◽  
High Angle ◽  
Electrical Transport Properties ◽  
The Stability

High-angle grain boundaries in YBa2Cu3O7−δ thin films are of technological interest because of the weak coupling observed between the grains; however, not all high-angle grain boundaries show this weak-link behavior. The microstructure of both these boundaries is not understood, nor is the reason for the differing electrical transport properties. High-angle grain boundaries in YBa2Cu3O7−δ thin films on MgO, where the angular misorientation between the grains is ∼45°, have been examined using high-resolution electron microscopy. The results show that the boundary structure can appear quite different even when the angular misorientation between the two grains is the same. The stability of the grain boundaries under the electron irradiation in the electron microscope was found to be a function of the accelerating voltage—400 kV leads to rapid disordering of the boundary region.

Intrinsic Structure in Grain Boundaries and Boundary Mobility

1978 ◽  
Vol 36 (3) ◽  
pp. 380-391
Author(s):  
L.M. Clarebrough ◽  
C.T. Forwood
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Low Energy ◽  
Boundary Structure ◽  
Boundary Mobility ◽  
High Angle ◽  
Intrinsic Structure ◽  
Cornell University ◽  
Grain Boundary Structure ◽  
Energy Configurations

An outstanding experimental contribution to the knowledge of grain boundary structure in the 1970's is the work of Balluffi and his colleagues at Cornell University on artificially fabricated boundary interfaces in thin films of gold (e.g., Balluffi, Komem and Schober, 1972; Balluffi, Goodhew, Tan and Wagner, 1975). In particular, for high-angle boundaries they have shown that secondary grain boundary dislocations (g.b.d's.) do exist and accommodate a deviation from a low-energy misorientation corresponding to an exact C.S.L. relationship. Further, following the results of Spyridelis, Delavignette and Amelinckx (1967) they have shown that a network of g.b.d's. can act as a diffraction grating, causing extra reflections whose spacing is reciprocally related to the separation of the g.b.d's. (Balluffi, Sass and Schober, 1972). The description of high-angle grain boundaries in terms of secondary g.b.d's. accommodating a departure from an exact C.S.L. orientation is based solely on geometrical considerations, but it has been pointed out that other low-energy configurations may be preferred when account is taken of the nature of interatomic forces (Gleiter and Pumphrey, 1976; Hermann, Gleiter and Baro, 1976; Smith, Vitek and Pond, 1977).

Theoretical analysis of tilt grain boundaries in GaN at the atomic scale

2002 ◽  
Vol 743 ◽  
Author(s):  
Jun Chen ◽  
Pierre Ruterana ◽  
Gérard Nouet
Keyword(s):  
Grain Boundaries ◽  
Rotation Angle ◽  
The Other ◽  
Atomic Scale ◽  
Threading Dislocations ◽  
High Angle ◽  
Structural Units ◽  
Atomic Structures ◽  
Very High ◽  
Weber Potential

ABSTRACTEpitaxial layers of GaN contain a very high density of threading dislocations. In the first stage of growth they may form low and high angle grain boundaries. Energetic calculations of <0001> tilt grain boundaries have been performed with the Stillinger-Weber potential modified to take into account the wrong bonds Ga-Ga and N-N. The variation of the energy has been calculated as a function of the rotation angle. Two minima exist with special atomic structures based on a limited number of structural units. They are used to describe the other misorientations in terms of dislocation cores.

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