Interfaces in high-temperature superconductors

1992 ◽  
Vol 50 (1) ◽  
pp. 234-235
Author(s):  
K.L. Merkle ◽  
Y. Gao
Keyword(s):  
High Temperature ◽  
Critical Current ◽  
Weak Link ◽  
High Temperature Superconductors ◽  
Atomic Scale ◽  
Bulk Materials ◽  
Practical Applications ◽  
Metallic Contacts ◽  
Zero Resistance ◽  
Interfacial Characteristics

After the discovery of high-temperature superconductors (HTS) five years ago, it soon became apparent that their interfacial characteristics would play an extremely important role in any foreseeable applications of these materials. In recent commercial devices, the weak-link characteristics of grain boundaries (GBs) have in fact been exploited to manufacture Josephson junction SQUIDS. On the other hand, the low critical current density of HTS is a considerable limitation for practical applications of the zero-resistance property, particularly in bulk materials. The weak-link behavior of GBs is largely responsible for this, but other types of interfaces such as those formed by metallic contacts or the interfaces between the substrate and a HTS thin film are also critical to the application of these materials. We shall review here some of the important interface issues that have been addressed by TEM techniques, but shall focus largely on the connection between the critical current (Jc) that can be transported across a grain boundary and its atomic-scale structure and composition.

Electron irradiation effects in doped high temperature superconductors YBa2Cu3−x MxOy (M = Fe, Ni; x=0; x=0:01)

Open Physics ◽  
2008 ◽  
Vol 6 (4) ◽  
Author(s):  
Aram Sahakyan ◽  
Sergei Nikoghosyan ◽  
Hrant Yeritsyan
Keyword(s):  
High Temperature ◽  
Critical Current ◽  
Irradiation Dose ◽  
High Temperature Superconductor ◽  
Defect Formation ◽  
Weak Link ◽  
High Temperature Superconductors ◽  
Large Change ◽  
Impurity Doped ◽  
Intergranular Critical Current Density

AbstractThe influence of irradiation by electrons with an energy of 8 MeV, at dose intervals between 1013 and 2×1018el/cm2, on the properties of impurity doped, high-temperature superconductor YBa2Cu3−x MxOy (M = Fe, Ni; x=0; x=0:01) ceramics has been studied.It has been established that, as the irradiation dose is increased, the onset temperature of the transition to the superconducting state (T con), and the intergranular weak link coupling temperature between granules (T mJ), exhibit an oscillation around their initial values of approximately about 1–1.5 K. This oscillation indicates that the process of radiation defect formation in HTSC occurs in multiple stages. It was also found that the critical current (J c)decreases with an increase of the irradiation dose, and exhibits a local minimum at a dose of 8×1016el/cm2coinciding with minima for T con and T mJ at this dose. It was found that the introduction of Fe atoms to the ceramic decreases T mJ, while introducing Ni atoms decreases both T con and T mJ; it is suggested that this is a result of Ni substitution of Cu both in Cu2 plane sites and Cu1 chain sites. The introduction of Ni causes a large change in the intergranular critical current density, J c. A critical irradiation dose is obtained (2×1018)after which all HTSC parameters strongly decrease, i. e. the superconductivity of HTSC is destroyed.

COMPLEX SUSCEPTIBILITY AND CRITICAL CURRENT OF HIGH-TEMPERATURE SUPERCONDUCTORS

1990 ◽  
Vol 04 (21) ◽  
pp. 1361-1367 ◽  
Author(s):  
G. LU ◽  
K.X. CHEN ◽  
L.X. XUE ◽  
C.D. WEI ◽  
Q.R. FENG ◽  
...  
Keyword(s):  
High Temperature ◽  
Critical Current ◽  
Coupling Strength ◽  
Weak Link ◽  
Bulk Material ◽  
High Temperature Superconductors ◽  
High Critical Current Density ◽  
Link Structure ◽  
Complex Susceptibility ◽  
Very High

The ac complex susceptibility χ′−iχ″ of several bulk samples with very high critical current density Jc have been measured. The results show that these samples are all polycrystalline bulk material, the peak of χ″ still related to losses within “the weak link structure” of the intergrain material. But the intergrain coupling strength of the high Jc samples is much stronger than ordinary high-Tc superconductors. A parameter β=(Tc2(0) −Tc2(h0))/h02/3 has been proposed to characterize the coupling strength.

Crystal Growth of High Temperature Superconductors

MRS Bulletin ◽  
1988 ◽  
Vol 13 (10) ◽  
pp. 56-61 ◽  
Author(s):  
H.J. Scheel ◽  
F. Licci
Keyword(s):  
High Temperature ◽  
Critical Current Density ◽  
Single Crystals ◽  
Critical Current ◽  
Current Density ◽  
Large Scale ◽  
High Temperature Superconductivity ◽  
High Temperature Superconductors ◽  
Superconducting Transition ◽  
Theoretical Understanding

The discovery of high temperature superconductivity (HTSC) in oxide compounds has confronted materials scientists with many challenging problems. These include the preparation of ceramic samples with critical current density of about 106 A/cm2 at 77 K and sufficient mechanical strength for large-scale electrotechnical and magnetic applications and the preparation of epitaxial thin films of high structural perfection for electronic devices.The main interest in the growth of single crystals is for the study of physical phenomena, which will help achieve a theoretical understanding of HTSC. Theorists still do not agree on the fundamental mechanisms of HTSC, and there is a need for good data on relatively defect-free materials in order to test the many models. In addition, the study of the role of defects like twins, grain boundaries, and dislocations in single crystals is important for understanding such parameters as the critical current density. The study of HTSC with single crystals is also expected to be helpful for finding optimum materials for the various applications and hopefully achieving higher values of the superconducting transition temperature Tc than the current maximum of about 125 K. It seems unlikely at present that single crystals will be used in commercial devices, but this possibility cannot be ruled out as crystal size and quality improve.

Important Considerations for Processing Bi-Based High-Temperature Superconducting Tapes and Films for Bulk Applications

MRS Bulletin ◽  
1992 ◽  
Vol 17 (8) ◽  
pp. 45-51 ◽  
Author(s):  
Eric E. Hellstrom
Keyword(s):  
High Temperature ◽  
Magnetic Fields ◽  
Materials Science ◽  
Weak Link ◽  
High Temperature Superconductors ◽  
Electromagnetic Properties ◽  
High Magnetic Fields ◽  
Large Current ◽  
Current Densities ◽  
Made In

High-temperature superconductors are brittle oxide ceramics, yet they have been made into wire that has been wrapped into solenoids and used in demonstration magnets and motors. Fabricating wires from these ceramics is an extremely challenging materials science process that requires a precisely engineered microstructure with the correct chemical, mechanical, and electromagnetic properties if these wires are to transport large current densities (Jc) in high magnetic fields. Heine et al. first demonstrated that wires of these materials could carry high Jc in very high magnetic fields. At 4.2 K, the oxide superconducting wires can carry higher Jc at higher magnetic fields than conventional Nb-Ti or Nb3Sn wires (Figure 1), and as shown in the companion article in this issue by Kato et al. they can also have high Jc at 77 K.Of the three major families of high-temperature superconductors, YBa2Cu3O7-x, Bi-Sr-Ca-Cu-O (BSCCO), and Tl-Ba-Ca-Cu-O, the best wires to date have been made in the BSCCO system. At present, all YBa2Cu3O7-x wires are weak linked and have only small Jc in magnetic fields. In the Tl-based system, the superconducting properties are potentially very interesting, but the toxicity of Tl and the system's complex processing have limited conductor development. For the Bi-based system, the basic processing steps are becoming known, the grains are well connected, and the weak link problem can be controlled. This permits applications in the temperature range 4–77 K, depending on the field and current density requirements of the particular use.

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