Grain boundary dislocation networks in YBa2Cu3O7-δ

1988 ◽  
Vol 46 ◽  
pp. 622-623
Author(s):  
S.E. Babcock
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Boundary Plane ◽  
Boundary Dislocation ◽  
Contrast Imaging ◽  
Plane Normal ◽  
Transmission Electron ◽  
Key Characteristics ◽  
Regular Networks ◽  
Beam Diffraction

The crystallography, morphology, and structure of typical grain boundaries in sintered samples of the high temperature superconducting oxide YBa2Cu3O7-δ (123) have been investigated by transmission electron microscopy using two-beam diffraction contrast imaging and selected area diffraction techniques.Since most of the grains present in sintered samples of 123 are plate shaped with the plate normal parallel to the c-axis of the crystal, the grain boundaries can be divided into two classes: (a) those for which the boundary plane normal is nearly parallel to the c-axis of one of the abutting grains (basal-plane-faced boundaries), and (b) those which are not basal-planefaced. Regular networks of grain boundary dislocations have been observed in high-angle grain boundaries of both types. These networks extend the length of the imagable portion (i.e., sufficiently thin) of the boundary without changing their basic geometry. The line contrast produced by the networks shows several of the key characteristics of dislocation images.

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.

Preferred inclinations of grain boundaries in epitaxially grown bicrystalline thin films of gold

1978 ◽  
Vol 36 (1) ◽  
pp. 434-435
Author(s):  
F. Cosandey ◽  
Y. Komem ◽  
C. L. Bauer
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Boundary Energy ◽  
Boundary Plane ◽  
Boundary Structure ◽  
Structural Elements ◽  
Grain Boundary Energy ◽  
Transmission Electron ◽  
A New Technique ◽  
Misorientation Of Grains

Energy and concomitant structure of grain boundaries are related to inclination of the boundary plane as well as misorientation of grains defining the boundary. Although increasing information is becoming available on variation of grain boundary energy with misorientation, still relatively little is known about variation of grain boundary energy with inclination. The purpose of this research is to examine preferred inclinations of preselected grain boundaries in gold by transmission electron microscopy (TEM) in order to identify principal structural elements and to relate these elements to the energy of special grain boundary configurations.Grain boundaries examined in this research are produced by a new technique involving vapor deposition of gold on common (001) surfaces of bicrystalline substrates of NaCl, characterized by preselected rotation about a common [001] axis, and subsequent epitaxial growth to form a bicrystalline thin film. These films are then removed from their substrates and examined by TEM. The principal advantage of this technique is that the grain boundary is formed during the deposition and growth process, thus resulting in a more perfect boundary structure while eliminating necessity of a separate bonding operation.

The Slip Transfer Process Through Grain Boundaries in HCP Ti

1993 ◽  
Vol 319 ◽  
Author(s):  
J. Shirokoff ◽  
I.M. Robertson ◽  
H.K. Birnbaum
Keyword(s):  
Grain Boundary ◽  
Slip System ◽  
Grain Boundaries ◽  
Slip Systems ◽  
Boundary Dislocation ◽  
Burgers Vector ◽  
Slip Transfer ◽  
Transmission Electron ◽  
Fcc Materials

AbstractInformation on the mechanisms of slip transfer across grain boundaries in an HCP α-Ti alloy has been obtained from deformation experiments performed In situ in the transmission electron microscope. Initially, lattice dislocations are accommodated within the grain boundary until a critical local dislocation density is reached. The boundary then responds by activating slip in the adjoining grain on the slip system experiencing the highest local resolved shear stress and producing the residual grain-boundary dislocation with the smallest Burgers vector. Slip on secondary slip systems may be initiated provided they reduce the magnitude of the Burgers vector of, or eliminate, the residual grainboundary dislocation. The selection rules used to predict the slip system activated by the grain boundary are the same as apply in ordered and disordered FCC materials.

The Intrinsic Formation Of Localized Electronic States At [001] Tilt Grain Boundaries In YBa2Cu3O7 And Their Effect On Jc

1999 ◽  
Vol 5 (S2) ◽  
pp. 156-157
Author(s):  
J. P. Buban ◽  
N. D. Browning
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Boundary Plane ◽  
Localized States ◽  
Contrast Imaging ◽  
Structural Units ◽  
Band Bending ◽  
Tilt Boundaries ◽  
Donor States ◽  
P Type

Grain boundaries have long been known to have a deleterious effect on the superconducting critical current that can be carried by YBa2Cu3O7-δ. Recent theoretical analyses have proposed that the origin of this behavior may be band bending, which results in the depletion of charge carriers at the grain boundaries. For this to occur in these p-type superconductors there must, by definition, be a high density of localized donor states in the boundary plane. Here we describe a structural feature intrinsic to all [001] tilt boundaries that may be the origin of these localized states.Direct atomic-resolution images of asymmetric [001] tilt grain boundary structures have been obtained using the Z-contrast imaging technique. The grain boundaries are observed to be composed of distinct structural units, as shown in figure 1. Within these structural units, a 2×1 reconstruction of the CuO columns is seen to occur. This reconstruction, which is caused by the constraint imposed on the structure by the sizes of the component atoms, leads to effective oxygen vacancies in the grain boundary plane (figure 2). Further oxygen annealing of the boundary cannot fill these vacancies as there is no space in the structure for more oxygen atoms.

Atomic Scale Analysis of a YSZ Bicrystal Grain Boundary

2001 ◽  
Vol 7 (S2) ◽  
pp. 400-401
Author(s):  
Y. Lei ◽  
Y. Ito ◽  
N. D. Browning
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Bulk Material ◽  
Atomic Scale ◽  
Structure Property ◽  
Contrast Imaging ◽  
Structure Property Relationships ◽  
Commercial Applications ◽  
Z Contrast ◽  
Electron Energy Loss

Yttria-stabilized zirconia (YSZ) has been the subject of many experimental and theoretical studies, due to the commercial applications of zirconia-based ceramics in solid state oxide fuel cells. Since the grain boundaries usually dominate the overall macroscopic performance of the bulk material, it is essential to develop a fundamental understanding of their structure-property relationships. Previous research has been performed on the atomic structure of grain boundaries in YSZ, but no precise atomic scale compositional and chemistry characterization has been carried out. Here we report a detailed analytical study of an [001] symmetric 24° bicrystal tilt grain boundary in YSZ prepared with ∼10 mol % Y2O3 by Shinkosha Co., Ltd by the combination of Z-contrast imaging and electron energy loss spectroscopy (EELS).The experimental analysis of the YSZ sample was carried out on a 200kV Schottky field emission JEOL 201 OF STEM/TEM4.

Effect of Grain Boundary Energy Anisotropy on Faceting and Migration of Low Angle Grain Boundaries

2014 ◽  
Vol 783-786 ◽  
pp. 1634-1639
Author(s):  
Dmitri A. Molodov ◽  
Jann Erik Brandenburg ◽  
Luis Antonio Barrales-Mora ◽  
Günter Gottstein
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Elevated Temperatures ◽  
Boundary Energy ◽  
Migration Behavior ◽  
Grain Boundary Energy ◽  
Contrast Imaging ◽  
Orientation Contrast ◽  
And Migration ◽  
Twist Boundaries

The faceting and migration behavior of low angle <100> grain boundaries in high purity aluminum bicrystals was investigated. In-situ technique based on orientation contrast imaging was applied. In contrast to the pure tilt boundaries, which remained straight/flat and immobile during annealing at elevated temperatures, mixed tilt-twist boundaries readily assumed a curved shape and steadily moved under the capillary force. Computational analysis revealed that this behavior is due to the inclinational anisotropy of grain boundary energy, which in turn depends on boundary geometry – the energy of pure tilt low angle <100> boundaries is anisotropic, whereas that of mixed tilt-twist boundaries isotropic with respect to boundary inclination.

Grain Boundary Analysis of Crept Alloy 617

2012 ◽  
Vol 1383 ◽  
Author(s):  
Fan Zhang ◽  
David P. Field
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Electron Backscatter Diffraction ◽  
Creep Damage ◽  
Original Material ◽  
Alloy 617 ◽  
Plane Normal ◽  
Lattice Misorientation ◽  
Two Parameters ◽  
Backscatter Diffraction

ABSTRACTAlloy 617, a high-temperature creep-resistant, nickel-based alloy, is being considered for the primary heat exchanger for the next generation nuclear plant, which is highly influenced by thermal creep. The main objective of this study is to inspect the crept grain boundaries under its imitated working condition, and to determine which boundaries are susceptible to damage and which are more resistant, in order to help improve its creep resistance in future manufacturing. Electron backscatter diffraction was used to measure the proportions of each boundary by observing and analyzing these crept microstructures. The grain-boundary distribution can be expressed in terms of five parameters including three parameters of lattice misorientation and two parameters of the grain-boundary plane normal. Three conditions were analyzed: the original material, metal that was annealed without stress, and ones that were crept at 1000ºC at 19 MPa and 25 MPa for various times. Though observation, it is found that the voids seldom occur at low angle grain boundaries, and coherent twin boundaries are also resist to creep damage.

scholarly journals Coupling Automated Electron Backscatter Diffraction with Transmission Electron and Atomic Force Microscopies

2000 ◽  
Vol 6 (S2) ◽  
pp. 940-941
Author(s):  
A.J. Schwartz ◽  
M. Kumar ◽  
P.J. Bedrossian ◽  
W.E. King
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Thermomechanical Processing ◽  
Electron Backscatter Diffraction ◽  
Grain Boundary Character Distribution ◽  
Atomic Force ◽  
Transmission Electron ◽  
Electron Backscatter ◽  
Network Engineering ◽  
Backscatter Diffraction

Grain boundary network engineering is an emerging field that encompasses the concept that modifications to conventional thermomechanical processing can result in improved properties through the disruption of the random grain boundary network. Various researchers have reported a correlation between the grain boundary character distribution (defined as the fractions of “special” and “random” grain boundaries) and dramatic improvements in properties such as corrosion and stress corrosion cracking, creep, etc. While much early work in the field emphasized property improvements, the opportunity now exists to elucidate the underlying materials science of grain boundary network engineering. Recent investigations at LLNL have coupled automated electron backscatter diffraction (EBSD) with transmission electron microscopy (TEM)5 and atomic force microscopy (AFM) to elucidate these fundamental mechanisms.An example of the coupling of TEM and EBSD is given in Figures 1-3. The EBSD image in Figure 1 reveals “segmentation” of boundaries from special to random and random to special and low angle grain boundaries in some grains, but not others, resulting from the 15% compression of an Inconel 600 polycrystal.

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