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.

Structure and misorientation angle distributions of (001) twist grain boundaries in Bi2Sr2Ca1Cu2Oy/Ag composite tapes processed in different oxygen partial pressures

1999 ◽  
Vol 14 (2) ◽  
pp. 349-353 ◽  
Author(s):  
Hiroki Fujii ◽  
Hiroaki Kumakura ◽  
Kazumasa Togano
Keyword(s):  
Grain Boundaries ◽  
Misorientation Angle ◽  
Small Angle ◽  
Large Angle ◽  
Amorphous Layer ◽  
High Energy ◽  
Boundary Structure ◽  
Partial Pressures ◽  
Small Angle Boundary ◽  
Twist Boundaries

We investigated the relationship between the structure and misorientation angle of (001) twist grain boundaries in Bi2Sr2Ca1Cu2Oy/Ag composite tapes processed in different oxygen partial pressures (PO2 = 0.01, 0.21, and 1 atm). Large-angle misoriented twist boundaries (>10°) essentially had no amorphous layers at the interface, and the misorientation angles of these boundaries mostly corresponded to low-energy misorientations. This large-angle misoriented boundary structure was independent of PO2. Small-angle misoriented twist boundaries (<10°), on the other hand, corresponded to high-energy misorientations and sometimes had amorphous layers at the interface. The population of the small-angle boundary with an amorphous layer was very low in the tape processed in PO2 = 1 atm. This suggests that high PO2 during the heat treatment is effective in the improvement of grain coupling, and hence, to increase critical current density.

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.

Quantitative High Resolution Electron Microscopy of Grain Boundaries and Comparison with Atomistic Simulations

2001 ◽  
Vol 7 (S2) ◽  
pp. 244-245
Author(s):  
G.H. Campbell ◽  
W.E. King ◽  
J.M. Plitzko ◽  
J. Belak ◽  
S.M. Foiles
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Grain Boundaries ◽  
Atomic Structure ◽  
Radiation Effects ◽  
Crystal Defects ◽  
Boundary Structure ◽  
Atomistic Simulations ◽  
Simulated Image ◽  
Good Test

The technique of high-resolution transmission electron microscopy (HREM) produces images that contain information about the atomic structure of the specimen. Within additional, very stringent, constraints, the HREM image can contain information about atomic structure of crystal defects, including grain boundaries and interfaces. to extract this information from the image it is necessary to compare the experimental image with a simulated image calculated based upon an atomic model of the specimen.2 in this comparison, investigators have been aided by the use of quantitative techniques.Atomistic simulations are often used to predict the atomic structure of crystal defects or to simulate the evolution of dynamic processes in crystals, e.g. radiation effects or dislocation motion and interaction. During the development of new models of interatomic interactions, the predictions of simulations are tested against experimental observations to validate new potentials. Grain boundary structure is a good test because atoms residing in the boundary experience environments (interatomic distances and angles) that are significantly different from those experienced by atoms residing in a perfect crystal lattice site.

On the Role of Schottky Disorder on the Stability and Structure of (100) Twist Grain Boundaries in Nio

1983 ◽  
Vol 24 ◽  
Author(s):  
D. Wolf
Keyword(s):  
Grain Boundaries ◽  
Point Defects ◽  
Coincidence Site Lattice ◽  
Unit Cell ◽  
Twist Boundary ◽  
Site Lattice ◽  
Metastable Structures ◽  
The Stability ◽  
Twist Boundaries

ABSTRACTRecent calculations on (100) coincidence-site lattice (CSL) twist boundaries in the NaCl structure have shown that without point defects these boundaries are only marginally stable. Following an earlier suggestion that point defects are the likely source for the considerable stability of these boundaries observed experimentally for Mgo and NiO, Tasker and Duffy have shown recently that the creation of a Schottky pair can, indeed, stabilize a (100) twist boundary in NiO. In this article a variety of configurations in which one or more Schottky pairs have been created in the perfect CSL or anti-CSL unit cell are investigated. It is concluded that many metastable structures may exist which differ mainly with respect to their different interfacial mass densities and the relative translation of the two halves of the bicrystal.

The role of boundary plane: HREM investigation of the atomic structure of grain boundaries in gold

1988 ◽  
Vol 46 ◽  
pp. 588-589
Author(s):  
K. L. Merkle
Keyword(s):  
Grain Boundaries ◽  
Atomic Structure ◽  
Large Angle ◽  
Boundary Plane ◽  
Low Energy ◽  
Site Density ◽  
Atomic Relaxation ◽  
Tilt Boundaries ◽  
Misorientation Angles

Computer simulations of large-angle grain boundaries (GBs) have indicated the importance of local atomic relaxation, rigid body translations, and of the boundary plane in determining GB energy. Experimental observations of GB structure often find GB faceting, which is an indication that some GB planes are preferred over others. Investigations of the atomic structure of large-angle >001> tilt GBs in NiO have shown, along with symmetrical GB con-figuations, the presence of asymmetric GBs of the type which has at least one of the crystals terminated at the boundary by a low index plane. Such boundaries are thought to be of low energy. For studying the role of the GB plane in a metallic GB we chose in the present work two <011> tilt boundaries in Au. The misorientation angles (θ) were selected such that one bicrystal orientation (θ=39°) was close to the Σ=9 reciprocal coincident site density, while the other (θ=55°) was near the misorientation for which (111) and (100) planes are parallel to each other (θ=54.74°). The latter misorientation is also close to Σ=41 (θ=55.88°).

High-resolution z-contrast imaging of YBa2Cu3O7-δ grain boundaries

1989 ◽  
Vol 47 ◽  
pp. 198-199
Author(s):  
M. F. Chisholm ◽  
S. J. Pennycook
Keyword(s):  
High Resolution ◽  
Grain Boundaries ◽  
Critical Current ◽  
Tilt Angle ◽  
Large Angle ◽  
Boundary Segregation ◽  
Boundary Structure ◽  
Contrast Imaging ◽  
Transmission Electron ◽  
Tilt Boundaries

A rapid reduction of the critical current density across grain boundaries with increasing tilt angle up to ∽10° has been observed in YBa2Cu3O7−δ superconductors. These results fit nicely with an investigation of the structure of low-angle tilt boundaries in these materials. The boundaries are observed to be composed of an asymmetric array of dislocations with a Burgers vector of 1.17 nm for [100] tilt boundaries (Fig. 1) and 0.389 nm for [001] tilt boundaries. It is observed that at 7.5° tilts, the dislocation cores begin to overlap (Fig. 2). Increasing the tilt angle beyond this value is not expected to significantly change the boundary structure which corresponds closely to the point where tilt angle had little further effect on critical current. A complication which was not completely addressed in the study of the structure of these low-angle boundaries is that ceramic materials have a strong tendency to form thin intergranular glass phases and to exhibit enhanced segregation of impurities to the grain boundaries. Conventional transmission electron microscopy and x-ray microanalysis with emitted photons using an energy dispersive spectrometer is of questionable use for this application. A new method for forming high resolution images with strong chemical sensitivity using large-angle elastically scattered electrons in a scanning transmission electron microscope has been used in this study to directly address the grain boundary segregation question.

Tilt and twist grain boundaries

2009 ◽  
Vol 42 (2) ◽  
pp. 308-311 ◽  
Author(s):  
A. Morawiec
Keyword(s):  
Grain Boundaries ◽  
Mixed Type ◽  
Twist Boundary ◽  
Dual Character ◽  
Twist Boundaries

Grain boundaries are frequently classified into tilt, twist and mixed-type boundaries. However, the classification (into tilt and twist) is not a dichotomy; due to crystal symmetries, some boundaries may be concurrently tilt and twist boundaries. Formal conditions for a planar homophase boundary between crystals withm3msymmetry to be a tilt as well as a twist boundary are determined, and a procedure for verification of whether a boundary has such dual character is given.

DIFFRACTION STUDIES OF THE ATOMIC STRUCTURE OF LARGE ANGLE [001] TWIST BOUNDARIES

1985 ◽  
Vol 46 (C4) ◽  
pp. C4-71-C4-84 ◽  
Author(s):  
K. R. Milkove ◽  
P. Lamarre ◽  
F. Schmückle ◽  
M. D. Vaudin ◽  
S. L. Sass
Keyword(s):  
Atomic Structure ◽  
Large Angle ◽  
Twist Boundaries
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