Defects Near the Y2BaCuO5/YBa2Cu3O7−x Interface and their Effect on Flux-Pinning in Melt-Processed and Quench-Melt-Growth Processed YBa2Cu3O7−x

1992 ◽  
Vol 275 ◽  
Author(s):  
Z. L. Wang ◽  
A. Goyal ◽  
D. M. Kroeger ◽  
T. Armstrong
Keyword(s):  
Applied Field ◽  
Flux Pinning ◽  
Volume Fraction ◽  
Analytical Electron Microscopy ◽  
Stacking Faults ◽  
Detailed Examination ◽  
Dislocation Loops ◽  
Fault Density ◽  
Analytical Electron ◽  
X Interface

ABSTRACTA detailed examination of the Y2BaCuO5 (211)/ YBa2Cu3O7−x (123) interface in several melt-processed 123 samples prepared using different methods was undertaken using analytical electron microscopy. It is found that there exists a significant increase in the a-b planar stacking fault density in 123, near the 211/123 interface. When viewed along [001], these faults appear as disks with diameter from a few to 30 nm and are bounded by dislocation loops. Most stacking faults are confined to the (001) basal plane. The size and density of defects around the 211 particles suggest that these defects could act as effective flux-pinning sites and may explain the observations of increased Jc with increasing volume fraction of 211 and a maximum in Jc when the applied field parallel to the c-axis.

Defect Formation During Zn Diffusion into GaAs

1989 ◽  
Vol 163 ◽  
Author(s):  
Martina Luysberg ◽  
W. Jäger ◽  
K. Urban ◽  
M. Perret ◽  
N.A. Stolwijk ◽  
...  
Keyword(s):  
Defect Formation ◽  
Analytical Electron Microscopy ◽  
Surface Region ◽  
Dislocation Loops ◽  
Diffusion Front ◽  
Near Surface ◽  
Zn Diffusion ◽  
Zn Concentration ◽  
Analytical Electron ◽  
Type Dislocation

AbstractThe microstructure induced by the Zn diffusion at 1170 K into doped and undoped semi-insulating GaAs single crystals was characterized for various diffusion times t < 1740 min by analytical electron microscopy. The results were compared with Zn concentration profiles obtained by spreading resistance measurements (SRM) on the same samples. At the diffusion front the formation of prismatic interstitial dislocation loops, dislocation networks, and of cavities partly filled with Ga was observed. Closer to the surface facetted voids and, for the undoped samples, vacancy-type dislocation loops formed. The near surface region of highest Zn-concentration showed a high density of Zn-rich precipitates. A model is presented which accounts .for these observations. It is based on fast interstitial Zn diffusion and the kick-out mechanism for interstitial-substituional exchange.

Microstructural inhomogeneities in chemically derived Ba2YCu3O7−x thin films: Implications for flux pinning

1994 ◽  
Vol 9 (11) ◽  
pp. 2778-2788 ◽  
Author(s):  
P.C. McIntyre ◽  
M.J. Cima
Keyword(s):  
Thin Films ◽  
Critical Current Density ◽  
Flux Pinning ◽  
Stacking Faults ◽  
Stacking Fault ◽  
Cross Sectional ◽  
Abrupt Transition ◽  
Fault Density ◽  
Defective Layer ◽  
Film Substrate

A gradient in the density of polytypoidal stacking faults was observed through the thickness of chemically derived epitaxial Ba2YCu3O7−x (BYC) films on (001) LaAlO3. Cross-sectional TEM studies indicated that films of less than 100 nm thickness were faulted, with a high density of polytypoidal stacking faults. A decrease in stacking fault density in thicker films (300-500 nm thick) was found with increasing distance from the most defective layer near the film/substrate interface. An abrupt transition from highly faulted material near the substrate to essentially stacking fault-free BYC in the upper part of the films was observed in several cases. The present observations are compared with the previously reported1 decrease in critical current density with increasing thickness of these films. Possible implications for flux pinning in BYC thin films are discussed.

Application of Analytical Electron Microscopy to glass-bonded aluminas

1986 ◽  
Vol 44 ◽  
pp. 436-439
Author(s):  
B.J. Hockey
Keyword(s):  
Electron Microscopy ◽  
Volume Fraction ◽  
Sintered Material ◽  
Analytical Electron Microscopy ◽  
Microstructural Characterization ◽  
Ceramic Materials ◽  
Liquid Phase Sintering ◽  
Binder Phase ◽  
Analytical Electron ◽  
Polycrystalline Body

Liquid phase sintering represents one of the most common methods of producing aluminas and other ceramic materials. Regardless of the specific processing details, this sintering procedure invariably results in a polycrystalline body containing a certain volume fraction of an intergranular binder phase. This phase is typically a glass, which can control many important properties of the sintered material. Clearly, microstructural characterization - describing not only the physical distribution of the binder phase but also its chemical composition - represents its an important part in the study of these materials.

Interface microstructures in melt-textured YBa2Cu3O7-δ on Ag-Pd and flux pinning centers introduced by Y2BaCuO5 particles

1992 ◽  
Vol 50 (1) ◽  
pp. 72-73
Author(s):  
Z. L. Wang ◽  
A. Goyal ◽  
D. M. Kroeger
Keyword(s):  
Electron Microscopy ◽  
Electron Probe ◽  
Flux Pinning ◽  
Thick Films ◽  
Analytical Electron Microscopy ◽  
Pinning Centers ◽  
X Ray ◽  
Transmission Electron ◽  
Analytical Electron ◽  
Pd Alloy

Transmission electron microscopy (TEM) and energy dispersion X-ray spectroscopy (EDS) were used to study the microstructure of the melt-textured YBa2Cu3O7-δ (123) thick films on Ag-Pd substrate. The samples used for this study were melt-textured thick films of 123 on a Ag10%Pd alloy substrate. The film was prepared using a paint-on technique and was processed according to a schedule described elsewhere, Domains of 123, as large as 5-6 mm, are formed in the film. Analytical electron microscopy (AEM) studies of this material were made using a Philips EM400 TEM/STEM (100 kV) with a field emission gun (FEG). A small electron probe of diameter approximately 2 nm was generated, and used in determining the compositional change across grain boundaries.

Analytical Electron Microscopy of Precipitates in Ion-Implanted Mgal2O4 Spinel

1994 ◽  
Vol 373 ◽  
Author(s):  
N. D. Evans ◽  
S. J. Zinkle ◽  
J. Bentley
Keyword(s):  
Electron Microscopy ◽  
Energy Loss ◽  
Volume Fraction ◽  
Analytical Electron Microscopy ◽  
Metallic Aluminum ◽  
X Ray ◽  
Electron Energy Loss Spectrometry ◽  
Analytical Electron ◽  
Electron Energy Loss ◽  
Ion Implanted

AbstractAnalytical electron microscopy (AEM) has been used to investigate precipitates in MgAl2O4 spinel implantated with Al+, Mg+, or Fe2+ ions. Experiments combining diffraction, energy dispersive X-ray spectrometry (EDS), electron energy-loss spectrometry (EELS), and energy-filtered imaging were employed to identify and characterize precipitates observed in the implanted ion region. Diffraction studies suggested these are metallic aluminum colloids, although EELS and energy-filtered images revealed this to be so only for the Al+ and Mg+ implantations, but not for Fe2+ ion implantations. Multiple-least-squares (MLS) fitting of EELS plasmon spectra was employed to quantify the volume fraction of metallic aluminum in the implanted ion region. Energy-filtered plasmon images of the implanted ion region clearly show the colloid distribution in the Al+ and Mg+ implanted spinel. Energy-filtered images from the Fe2+ ion implanted spinel indicate that the features visible in diffraction contrast cannot be associated with either metallic aluminum or iron-rich precipitates.

Chemical partitioning of elements in Ni-base MC-carbide reinforced eutetic superalloys

1983 ◽  
Vol 41 ◽  
pp. 250-251
Author(s):  
E. F. Koch ◽  
E. L. Hall ◽  
S. W. Yang
Keyword(s):  
Alloy Composition ◽  
Volume Fraction ◽  
Lattice Mismatch ◽  
Turbine Blades ◽  
Eutectic Alloys ◽  
Alloy Matrix ◽  
X Ray ◽  
Gas Turbine Blades ◽  
Analytical Electron ◽  
Analytical Electron Microscope

The plane-front solidified eutectic alloys consisting of aligned tantalum monocarbide fibers in a nickel alloy matrix are currently under consideration for future aircraft and gas turbine blades. The MC fibers provide exceptional strength at high temperatures. In these alloys, the Ni matrix is strengthened by the precipitation of the coherent γ' phase (ordered L12 structure, nominally Ni3Al). The mechanical strength of these materials can be sensitively affected by overall alloy composition, and these strength variations can be due to several factors, including changes in solid solution strength of the γ matrix, changes in they γ' size or morphology, changes in the γ-γ' lattice mismatch or interfacial energy, or changes in the MC morphology, volume fraction, thermal stability, and stoichiometry. In order to differentiate between these various mechanisms, it is necessary to determine the partitioning of elemental additions between the γ,γ', and MC phases. This paper describes the results of such a study using energy dispersive X-ray spectroscopy in the analytical electron microscope.

Electron Beam Damage of Biomolecules Assessed by Energy Loss Spectroscopy

1978 ◽  
Vol 36 (3) ◽  
pp. 61-69
Author(s):  
M. Isaacson ◽  
M.L. Collins ◽  
M. Listvan
Keyword(s):  
Electron Microscopy ◽  
Radiation Damage ◽  
Structural Integrity ◽  
Analytical Electron Microscopy ◽  
High Dose ◽  
Dose Rates ◽  
Special Cases ◽  
Analytical Electron ◽  
Atom Migration ◽  
Beam Damage

Over the past five years it has become evident that radiation damage provides the fundamental limit to the study of blomolecular structure by electron microscopy. In some special cases structural determinations at very low doses can be achieved through superposition techniques to study periodic (Unwin & Henderson, 1975) and nonperiodic (Saxton & Frank, 1977) specimens. In addition, protection methods such as glucose embedding (Unwin & Henderson, 1975) and maintenance of specimen hydration at low temperatures (Taylor & Glaeser, 1976) have also shown promise. Despite these successes, the basic nature of radiation damage in the electron microscope is far from clear. In general we cannot predict exactly how different structures will behave during electron Irradiation at high dose rates. Moreover, with the rapid rise of analytical electron microscopy over the last few years, nvicroscopists are becoming concerned with questions of compositional as well as structural integrity. It is important to measure changes in elemental composition arising from atom migration in or loss from the specimen as a result of electron bombardment.

Analytical Electron Microscopy (AEM) of Meningeal Cells Exposed to Particulate Cobalt During Studies of Experimental Epilepsy

1982 ◽  
Vol 40 ◽  
pp. 186-187
Author(s):  
R.G. Frederickson ◽  
R.G. Ulrich ◽  
J.L. Culberson
Keyword(s):  
Electron Microscopy ◽  
Analytical Electron Microscopy ◽  
Experimental Epilepsy ◽  
Metallic Cobalt ◽  
Experimental Animals ◽  
X Ray ◽  
Brain Surface ◽  
Meningeal Cells ◽  
Analytical Electron ◽  
The Brain

Metallic cobalt acts as an epileptogenic agent when placed on the brain surface of some experimental animals. The mechanism by which this substance produces abnormal neuronal discharge is unknown. One potentially useful approach to this problem is to study the cellular and extracellular distribution of elemental cobalt in the meninges and adjacent cerebral cortex. Since it is possible to demonstrate the morphological localization and distribution of heavy metals, such as cobalt, by correlative x-ray analysis and electron microscopy (i.e., by AEM), we are using AEM to locate and identify elemental cobalt in phagocytic meningeal cells of young 80-day postnatal opossums following a subdural injection of cobalt particles.

Optimizing conditions for x-ray microchemical analysis in analytical electron microscopy

1978 ◽  
Vol 36 (1) ◽  
pp. 548-549 ◽  
Author(s):  
N. J. Zaluzec
Keyword(s):  
Solid Angle ◽  
Analytical Electron Microscopy ◽  
Incident Beam ◽  
Thin Foil ◽  
Experimental Conditions ◽  
X Ray ◽  
Microchemical Analysis ◽  
Analytical Electron ◽  
Image Position ◽  
Incident Beam Energy

The ultimate sensitivity of microchemical analysis using x-ray emission rests in selecting those experimental conditions which will maximize the measured peak-to-background (P/B) ratio. This paper presents the results of calculations aimed at determining the influence of incident beam energy, detector/specimen geometry and specimen composition on the P/B ratio for ideally thin samples (i.e., the effects of scattering and absorption are considered negligible). As such it is assumed that the complications resulting from system peaks, bremsstrahlung fluorescence, electron tails and specimen contamination have been eliminated and that one needs only to consider the physics of the generation/emission process.The number of characteristic x-ray photons (Ip) emitted from a thin foil of thickness dt into the solid angle dΩ is given by the well-known equation

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