Nano-probe microanalysis of grain boundary chemistry in YBa2Cu4O8 and its relationship to weak-link behavior

1993 ◽  
Vol 51 ◽  
pp. 598-599
Author(s):  
Z.L. Wang ◽  
J. Brynestad ◽  
D.M. Kroeger ◽  
Y.R. Sun ◽  
J.R. Thompson ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Weak Link ◽  
Oxygen Deficiency ◽  
High Temperature Superconductors ◽  
Cation Composition ◽  
X Ray ◽  
Transmission Electron ◽  
Boundary Chemistry ◽  
Electron Energy Loss

Weak-link behavior in high temperature superconductors limits bulk applications of polycrystalline high Tc compounds. Possible sources of the effect include grain boundary (GB) disorder, microcracks and nonstoichiometric material at grain boundaries. Recently, electron energy-loss spectroscopy (EELS) studies of YBa2Cu3O7-x (Y123) have shown that grain boundary oxygen deficiency is correlated with the crystallographic misorientations of between the Y123 grains. Studies of grain boundary chemistry in YBa2Cu4O8 (Y124) by nano-probe energy dispersive X-ray spectroscopy (EDS) and EELS are reported in this paper. Transmission electron microscopy (TEM) studies were performed at 100 kV in a Philips EM400 TEM/STEM equipped with a field emission gun (FEG), which generates an electron probe smaller than 2 nm in diameter. The cation composition was determined by EDS and the O:Ba composition was determined using EELS. Kikuchi patterns were recorded from both sides of the grain boundaries to determine the misorientation of the two adjacent grains.The observation of a pre-edge peak (Fig. 1) near the oxygen K ionization edge (O K) is related to the hole states produced by the O 2p state and Cu 3d states.

Effect of thermal annealing on grain boundary chemistry of polycrystalline TiBa2Ca2Cu3Oy films

1994 ◽  
Vol 52 ◽  
pp. 968-969
Author(s):  
Z. L. Wang ◽  
C. L. Briant ◽  
J. DeLuca ◽  
A. Goyal ◽  
D. M. Kroeger ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Weak Link ◽  
Zero Field ◽  
Stabilized Zirconia ◽  
Local Texture ◽  
Transmission Electron ◽  
Axis Alignment ◽  
Boundary Chemistry ◽  
Small Misorientation ◽  
Misorientation Angles

Recent studies have shown that spray-pyrolyzed films of the Tl-1223 compound (TlxBa2Ca2Cu3Oy, with 0.7 < × < 0.95) on polycrystalline yttrium stabilized zirconia substrates can be prepared which have critical current density Jc near 105 A/cm2 at 77 K, in zero field. The films are polycrystalline, have excellent c-axis alignment, and show little evidence of weak-link behavior. Transmission electron microscopy (TEM) studies have shown that most grain boundaries have small misorientation angles. It has been found that the films have a nigh degree of local texture indicative of colonies of similarly oriented grains. It is believed that inter-colony conduction is enhanced by a percolative network of small angle boundaries at colony interfaces. It has also been found that Jc is increased by a factor of 4 - 5 after the films were annealed at 600 °C in oxygen. This study is thus carried out to determine the effect on grain boundary chemistry of the heat treatment.

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.

STEM investigation of the chemistry and bonding changes associated with the grain boundary embrittlement of Cu by Bi

1996 ◽  
Vol 54 ◽  
pp. 526-527
Author(s):  
V. J. Keast ◽  
J. Bruley ◽  
D. B. Williams
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
High Current Density ◽  
High Current ◽  
Fracture Path ◽  
Scanning Electron Micrograph ◽  
Edge Structure ◽  
X Ray ◽  
Grain Boundary Embrittlement ◽  
Electron Energy Loss

It has long been known that trace amounts of Bi can embrittle Cu after appropriate heat treatments. The Bi segregates to the grain boundaries and weakens them such that failure occurs through intergranular fracture without plastic deformation. This behavior is demonstrated in the scanning electron micrograph of a typical Cu-Bi fracture surface in Figure 1. It is known that the Bi extends for only a few atomic layers into the grains on either side of the grain boundary. This narrow segregation width was been confirmed using Energy Dispersive X-ray Spectroscopy (EDS) on a VG HB603 STEM. Figure 2 shows the ratio of Bi to Cu as the probe is stepped across the grain boundary.The segregation behavior is well understood, however it is not yet properly understood how the Bi causes embrittlement once it is at the grain boundaries. The Bi must change the bonding at the boundaries so that the boundaries become weak and hence the most likely fracture path. The Electron Energy Loss Near Edge Structure (ELNES) coupled with the small probes and high current density available in a field emission STEM can provide information about the localized electronic structure and hence bonding at grain boundaries. Previous investigations indicated that the near edge structure of Cu was altered at the grain boundaries due to the presence of Bi.

Tailoring Grain-Boundary Segregation to Control Mechanical Properties

1999 ◽  
Vol 586 ◽  
Author(s):  
D. B. Williams ◽  
V. J. Keast
Keyword(s):  
Mechanical Properties ◽  
Grain Boundary ◽  
Boundary Segregation ◽  
X Ray ◽  
Transmission Electron ◽  
Intergranular Brittle Fracture ◽  
Properties Of Materials ◽  
Boundary Chemistry ◽  
First Time

ABSTRACTRecent advances in our understanding of the role of the chemistry of grain boundaries in controlling the mechanical properties of materials (in particular intergranular brittle fracture) are reviewed. It is now possible in a modem field-emission gun (FEG) analytical transmission electron microscope (AEM) to measure the chemistry of sub-nanometer films of GB segregants while at the same time observing the effect (if any) on the bonding of the atoms within a nanometer of the boundary plane. This has been accomplished by the development of X-ray mapping (XRM) a powerful new tool for the study of segregation. For the first time, in the same instrument, on the same grain boundary, any changes in the boundary chemistry can be correlated with the occurrence or absence of brittle failure, which is often associated with boundary segregation. There is strong evidence that boundary segregation is extremely nonuniform, even in some strongly embrittling systems (e.g. Cu-Bi) and in these same systems, embrittling segregants introduce subtle but consistent changes in the bonding. Non-embrittling segregants (e.g. Ag in Cu) do not introduce detectable bonding changes.

In-Plane Grain Boundary Effects on the Transport Properties of La0.7Sr0.3MnO3-δ Thin Films

1997 ◽  
Vol 494 ◽  
Author(s):  
J. Y. Gu ◽  
S. B. Ogale ◽  
K. Ghosh ◽  
T. Venkatesan ◽  
R. Ramesh ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Boundary Effects ◽  
Epitaxial Relationship ◽  
X Ray ◽  
Low Field ◽  
Grain Structures ◽  
Transmission Electron

ABSTRACTC-axis oriented La0.7Sr0.3MnO3.δ (LSMO) films were fabricated on the top of SrTiO3/YBa2Cu3O7 grown on MgO(001) substrates. From x-ray φ-scan and planar transmission electron microscopy measurements, the LSMO layer in the LSMO/SrTiO3/YBa2Cu3O7/MgO heterostructure is found to have coherent in-plane grain boundaries with a predominance of 45° rotations (between [100] and [110] grains) in addition to the cube-on-cube epitaxial relationship. Also, epitaxial LSMO/Bi4Ti3O12/LaAl03 (001) and c-axis textured LSMO/Bi4Ti3O12/SiO2/Si(001) with random in-plane grain boundaries are introduced as the counterparts for comparison. The resistivity and magnetoresistance (MR) of LSMO layer were measured and compared in these three different heterostructures. The low field MR at low temperature shows a dramatic dependence on the nature of the grain boundary. An attempt is made to interpret these results on the basis of correlation between the magnetic properties and grain structures.

Grain Boundary Chemical Analysis Using Intense Electron Beams

1998 ◽  
Vol 552 ◽  
Author(s):  
P. Shang ◽  
R. Keyse ◽  
I. P Jones ◽  
R. E. Smallman
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Large Angle ◽  
Scanning Transmission Electron Microscope ◽  
Al Content ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Intense Electron Beams ◽  
Boundary Chemistry ◽  
Intense Electron

ABSTRACTScanning Transmission Electron Microscope (STEM) Energy Dispersive X-Ray analysis (EDX) linescans and mapping have been used to examine the large angle grain boundary chemistry of Ni-rich Ni3AI both with and without boron. The results show that the Al content is reduced while the Ni content is unchanged at the grain boundaries in all these alloys, with the percentage of reduction of Al at the grain boundaries decreasing as boron concentration increases. This is ascribed to differential surface sputtering of the lighter Al atoms.

Grain-boundary compositional measurements in complex high-temperature Ni-base alloys using x-ray spectroscopy

1994 ◽  
Vol 52 ◽  
pp. 964-965
Author(s):  
E. L. Hall ◽  
C. P. Blankenship ◽  
M. F. Henry
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Base Alloy ◽  
Heat Treatments ◽  
Fatigue Crack Propagation Rate ◽  
Structure Property ◽  
X Ray ◽  
Collector Plate ◽  
Cr Depletion ◽  
Boundary Chemistry

Thermal treatment of advanced Ni-base alloys used in critical aircraft engine components can have a significant effect on both the microstructure and properties of these alloys. One important property that can be strongly affected by heat treatment is the time-dependent fatigue crack propagation rate along grain boundaries. It is possible for heat treatments to affect the morphology, chemistry, andphase distribution along the grain boundaries in these complex multiphase alloys. Structure-property correlations require the measurement of each of these parameters. By far, the least tractable of these is the measurement of grain boundary chemistry.X-ray spectroscopy in the AEM has been shown to be a very powerful method for measuring grain boundary chemistry in single-phase Fe and Ni-base alloys, among others. In the case of a singlephase Ni-base alloy such as IN600, heat treatments in the range of 500-750&C cause precipitation of Crrich carbides at grain boundaries and the depletion of Cr from the grain-boundary segments between precipitates via a collector-plate mechanism. Measurement of Cr-depletion at the grain boundaries and Cr-depletion profiles across boundaries is straightforward.

Chemistry, Bonding and Fracture of Grain Boundaries in Ni3Si

1996 ◽  
Vol 460 ◽  
Author(s):  
Shanthi Subramanian ◽  
David A. Muller ◽  
John Silcox ◽  
Stephen. L. Sass
Keyword(s):  
Electronic Structure ◽  
Grain Boundary ◽  
Energy Loss ◽  
Grain Boundaries ◽  
Electron Energy Loss Spectroscopy ◽  
Cohesive Energy ◽  
Large Angle ◽  
X Ray ◽  
Electron Energy Loss ◽  
Insight Into

ABSTRACTTo obtain insight into the effect of dopants on the bonding and cohesive energy of gram boundaries in Ll2 intermetallic compounds, the chemistry and electronic structure at grain boundaries in B-free and B-doped Ni-23 at % Si alloys were examined, with electron energy loss spectroscopy (EELS) providing information on the former and energy dispersive X-ray spectroscopy (EDX) on the latter. Ni-enrichment was seen at large angle boundaries, both in the absence and presence of B. EELS of the Ni L3 edge showed that the bonding at Ni-rich grain boundaries was similar in both undoped and doped alloys. Comparison of the Ni L3 edge recorded at the grain boundary and in the bulk suggests that reduced hybridization and weaker bonding occurs at Ni-rich grain boundaries in both doped and undoped alloys. These changes in bonding are interpreted in terms of changes in the cohesive energy of the boundaries.

scholarly journals The Effects of a New Grain Boundary Phase in Ni-Al Alloy

2000 ◽  
Vol 652 ◽  
Author(s):  
Y.L. Chiu ◽  
A.H.W. Ngan ◽  
I.P. Jones
Keyword(s):  
Grain Boundary ◽  
Lattice Parameter ◽  
Boundary Phase ◽  
Al Alloy ◽  
Nickel Aluminum ◽  
X Ray ◽  
Boundary Precipitate ◽  
Transmission Electron ◽  
Electron Energy Loss ◽  
New Phase

ABSTRACTIn a γ/γ' nickel-aluminum alloy, a new phase has been identified along grain boundaries by conventional transmission electron microscopy. This phase is identified to be of the C6Cr23 type structure with lattice parameter 10.48Å, which is approximately three times that of Ni 3Al or nickel. This grain boundary precipitate is found to be coherent with the γ' phase in one grain. The chemical composition of this grain boundary precipitate is determined by energy dispersive x-ray spectroscopy and parallel electron energy loss spectroscopy. The deformation mechanism of this grain boundary precipitate is investigated on post-mortem specimens which have been carefully deformed by nanoindentation after jet-polishing.

scholarly journals Microstructure of Josephson Junctions: Effect on Supercurrent Transport in YBCO Grain Boundary and Barrier Layer Junctions

1998 ◽  
Vol 4 (S2) ◽  
pp. 792-793
Author(s):  
K. L. Merkle ◽  
Y. Huang
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Electrical Transport ◽  
Josephson Junctions ◽  
Quantum Interference ◽  
Weak Link ◽  
High Temperature Superconductors ◽  
Boundary Structure ◽  
Electric Transport ◽  
Electrical Transport Properties

The electric transport of high-temperature superconductors, such as YBa2Cu307-x (YBCO), can be strongly restricted by the presence of high-angle grain boundaries (GB). This weak-link behavior is governed by the macroscopic GB geometry and the microscopic grain boundary structure and composition at the atomic level. Whereas grain boundaries present a considerable impediment to high current applications of high Tc materials, there is considerable commercial interest in exploiting the weak-link-nature of grain boundaries for the design of microelectronic devices, such as superconducting quantum interference devices (SQUIDs). The Josephson junctions which form the basis of this technology can also be formed by introducing artifical barriers into the superconductor. We have examined both types of Josephson junctions by EM techniques in an effort to understand the connection between microstructure/chemistry and electrical transport properties. This knowledge is a valuable resource for the design and production of improved devices.

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