Electron microscopy of ceramic superconductors

1993 ◽  
Vol 51 ◽  
pp. 934-935
Author(s):  
M. Grant Norton ◽  
C. Barry Carter
Keyword(s):  
Electron Microscopy ◽  
Grain Boundaries ◽  
Analytical Techniques ◽  
Atomic Scale ◽  
Weak Links ◽  
Chemical Information ◽  
High Angle ◽  
Ceramic Superconductors ◽  
Transmission Electron ◽  
Current Densities

The microstructure of ceramic superconductors plays a crucial role in the transport properties of these materials. For example, it has been shown that high-angle grain boundaries can act as weak links and atomic scale defects can act as pinning centers. The nature and spatial distribution of such defects is related to the way in which the material is processed. Transmission electron microscopy (TEM) is an essential technique for understanding the relationship between microstructure, processing, and properties and for defect characterization. The advantage of TEM is that it is possible to combine various imaging modes with electron diffraction and other analytical techniques such as x-ray energy dispersive spectroscopy in order to obtain both structural and chemical information.Early measurements of critical current densities (Jc) across individual tilt grain boundaries in YBa2Cu3O7-δ (YBCO) thin films demonstrated that Jc decreased with increasing misorientation angle. More recently, however, it has been observed that this phenomenon may not be the case for all high-angle grain boundaries.

Composition variations near grain boundaries in YBa2Cu3O7-δ

1988 ◽  
Vol 46 ◽  
pp. 878-879
Author(s):  
S.E. Babcock ◽  
T.F. Kelly ◽  
D.C. Larbalestier
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Grain Boundaries ◽  
Electromagnetic Properties ◽  
Weak Links ◽  
Ion Milling ◽  
Transmission Electron ◽  
Field Independent ◽  
Scanning Transmission ◽  
Current Densities

Detailed electromagnetic characterization of samples of YBa2Cu3O7-δ (123) have shown this material, at least in its sintered form, is composed of islands of good superconductor which are separated from one another by “weak links” consisting of regions of poor superconductor or normal material. A number of researchers have suggested that these weak links are associated with grain boundaries. Therefore, conventional transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) coupled with energy dispersive x-ray analysis (EDAX) have been used to investigate the morphology, crystallography, and composition of typical grain boundaries in this material.The electromagnetic properties of the specific samples from which the TEM specimens were prepared had been studied in detail. Briefly, these samples possessed relatively low normal state resistivities and nearly field independent transport critical current densities, indicating that they were of relatively high quality.For these initial studies, specimens for TEM and STEM/EDAX were prepared by dimpling plus ion milling (3-4kV, 0.5mA per gun, liquid nitrogen cooled stage).

Low-Tc phase formation at the grain boundaries and electromagnetic granularity in (Bi,Pb)2Sr2Ca2Cu3Ox silver-sheathed tapes

1993 ◽  
Vol 51 ◽  
pp. 940-941
Author(s):  
Yi Feng ◽  
A. Umezawa ◽  
H. S. Edelman ◽  
D. C. Larbalestier
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Grain Boundaries ◽  
Critical Current ◽  
Ac Susceptibility ◽  
Transmission Electron ◽  
Heat Treated ◽  
Standard Powder ◽  
Current Densities ◽  
Powder In Tube

High resolution transmission electron microscopy (HRTEM) was performed on progressively heat treated Ag-clad (Bi,Pb)2Sr2Ca2Cu3Ox (2223) tapes and was correlated with their transport critical current densities, DC magnetization and AC susceptibility. HRTEM reveals the presence of a small number of half layers of the low Tc Bi2Sr2CaCu2Ox (2212) phase clustered at the numerous (001) twist grain boundaries. This residual 2212 phase produces electromagnetic granularity in a temperature range around 77K and thus directly controls the critical current.The Bi(Pb)-Sr-Ca-Cu-0 (BSCCO) Ag-clad tapes with the stoichiometric 2:2:2:3 starting composition were prepared by a standard powder-in-tube method. Sample A was heat treated at 817°C for 5 hours only. Sample B was first heat treated at 817°C for 24 hours, and then heat treated for 100 hours at the same temperature after two intermediate pressings. Sample C was heat treated at 830°C for 72 hours, and then heat treated for additional 196 hours after one intermediate pressing.

Analysis of Grain Boundaries, Twin Boundaries and Te Precipitates in Cd1−xZnxTe Grown bY High-Pressure Bridgman Method

1997 ◽  
Vol 487 ◽  
Author(s):  
J. R. Heffelfinger ◽  
D. L. Medlin ◽  
R. B. James
Keyword(s):  
Electron Microscopy ◽  
High Pressure ◽  
Light Microscopy ◽  
Grain Boundaries ◽  
Local Density ◽  
Infrared Light ◽  
High Angle ◽  
Twin Boundaries ◽  
Transmission Electron ◽  
Te Precipitates

AbstractGrain boundaries and twin boundaries in commercial Cd1−xZnxTe, which is prepared by a high-pressure Bridgeman technique, have been investigated with transmission electron microscopy, scanning electron microscopy, infrared-light microscopy and visible-light microscopy. Boundaries inside these materials were found to be decorated with Te precipitates. The shape and local density of the precipitates were found to depend on the particular boundary. For precipitates that decorate grain boundaries, their microstructure was found to consist of a single, saucer-shaped grain of hexagonal Te (space group P3121). Analysis of a Te precipate by selected-area diffraction revealed the Te to be aligned with the surrounding Cd1−xZnxTe grains. This alignment was found to match the (111) Cd1−xZnxTe planes with the (0111) planes of hexagonal Te. Crystallographic alignments between the Cd1−xZnxTe grains were also observed for a high-angle grain boundary. The structures of the grain boundaries and the Te/C1−xZnxTe interface are discussed.

Analysis of Grain Boundaries, Twin Boundaries and Te Precipitates in Cd1−xZnxTe Grown by High-Pressure Bridgman Method

1997 ◽  
Vol 484 ◽  
Author(s):  
J. R. Heffelfinger ◽  
D. L. Medlin ◽  
R. B. James
Keyword(s):  
Electron Microscopy ◽  
High Pressure ◽  
Light Microscopy ◽  
Grain Boundaries ◽  
Local Density ◽  
Infrared Light ◽  
High Angle ◽  
Twin Boundaries ◽  
Transmission Electron ◽  
Te Precipitates

AbstractGtain boundaries and twin boundaries in commercial Cd1−xZnxTe, which is prepared by a high-pressure Bridgeman technique, have been investigated with transmission electron microscopy, scanning electron microscopy, infrared-light microscopy and visible-light microscopy. Boundaries inside these materials were found to be decorated with Te precipitates. The shape and local density of the precipitates were found to depend on the particular boundary. For precipitates that decorate grain boundaries, their microstructure was found to consist of a single, saucer-shaped grain of hexagonal Te (space group P3,2 1). Analysis of a Te precipate by selected-area diffraction revealed the Te to be aligned with the surrounding Cd1−xZnxTe grains. This alignment was found to match the (111) Cd1−xZxTe planes with the (0 111) planes of hexagonal Te. Crystallographic alignments between the Cd1−xZnxTe grains were also observed for a high-angle grain boundary. The structures of the grain boundaries and the Te/Cd1−xZnxTe interface are discussed.

Structure of Low- And High-Angle Grain Boundaries In YBCO/MgO Films

1998 ◽  
Vol 4 (S2) ◽  
pp. 676-677
Author(s):  
S. Oktyabrsky ◽  
R. Kalyanaraman ◽  
K. Jagannadham ◽  
J. Narayan
Keyword(s):  
Electron Microscopy ◽  
Thin Films ◽  
Transmission Electron Microscopy ◽  
High Resolution ◽  
Grain Boundaries ◽  
Atomic Structure ◽  
Boundary Plane ◽  
Dislocation Model ◽  
High Angle ◽  
Transmission Electron

Grain boundaries (GBs) in laser deposited YB2Cu3O7-δ/MgO(001) thin films have been investigated by high-resolution transmission electron microscopy (TEM) and scanning TEM (STEM). We report both statistics and atomic structure of low-angle and high-angle [001] tilt grain boundaries resulting from almost perfect c-axis textured YBCO films.Atomic structure of low-angle GBs was analyzed using a dislocation model. These boundaries have been found to be aligned primarily along (100) and (110) interface planes. For (100) boundary plane, the GB consists of a periodic array of [100] dislocations (Fig.l). For (110) boundary plane, the array is also periodic but every [110] dislocation is split by ∼ 1.5 nm into two [100] and [010] dislocations (Fig.2). We have calculated energy of various configurations and shown that the energy of the (110) boundary with dissociated dislocations is comparable to that of (100) boundary, which explains the coexistence of (100) and (110) interface facets along the boundary.

Investigation of Grain Boundaries in an Al-Mg-Si-Cu Alloy

2014 ◽  
Vol 794-796 ◽  
pp. 951-956 ◽  
Author(s):  
Jon Holmestad ◽  
Martin Ervik ◽  
Calin D. Marioara ◽  
John Charles Walmsley
Keyword(s):  
Electron Microscopy ◽  
Heat Treatment ◽  
Transmission Electron Microscopy ◽  
Grain Boundaries ◽  
Solution Heat Treatment ◽  
High Angle ◽  
Corrosion Properties ◽  
X Ray ◽  
Cu Alloy ◽  
Transmission Electron

The grain boundaries of a fibrous Al-Mg-Si-Cu alloy have been investigated with Transmission Electron Microscopy. The compositions have been mapped by Energy Dispersive X-ray Spectroscopy. The alloy has been aged for 12 hours at 155°C after solution heat treatment and is in a slightly underaged condition. The precipitates nucleated on the high angle grain boundaries are coarse, while the precipitates on the low angle grain boundaries are smaller and more numerous. The precipitates on both types of grain boundaries has been identified as Q'-type. Copper is segregated to both the low and high angle grain boundaries. The effect of this segregation will be discussed with regards to the corrosion properties of the alloy.

Electron Microscopy Studies of The Chemistry And Microstructure of BaF2 / YBa2Cu3O7-x Thin Films

1994 ◽  
Vol 52 ◽  
pp. 796-797
Author(s):  
J. L. Lee ◽  
C. A. Weiss ◽  
R. A. Buhrman ◽  
J. Silcox
Keyword(s):  
Thin Film ◽  
Electron Microscopy ◽  
Thin Films ◽  
Scanning Transmission Electron Microscope ◽  
Atomic Scale ◽  
Island Growth ◽  
Multilayer Systems ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Mgo Substrate

BaF2 thin films are being investigated as candidates for use in YBa2Cu3O7-x (YBCO) / BaF2 thin film multilayer systems, given the favorable dielectric properties of BaF2. In this study, the microstructural and chemical compatibility of BaF2 thin films with YBCO thin films is examined using transmission electron microscopy and microanalysis. The specimen was prepared by using laser ablation to first deposit an approximately 2500 Å thick (0 0 1) YBCO thin film onto a (0 0 1) MgO substrate. An approximately 7500 Å thick (0 0 1) BaF2 thin film was subsequendy thermally evaporated onto the YBCO film.Images from a VG HB501A UHV scanning transmission electron microscope (STEM) operating at 100 kV show that the thickness of the BaF2 film is rather uniform, with the BaF2/YBCO interface being quite flat. Relatively few intrinsic defects, such as hillocks and depressions, were evident in the BaF2 film. Moreover, the hillocks and depressions appear to be faceted along {111} planes, suggesting that the surface is smooth and well-ordered on an atomic scale and that an island growth mechanism is involved in the evolution of the BaF2 film.

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