PROGRAM TITLE: Superconductivity

Principal investigator(s):

NIST Staff:

Designated Project Leader:

Kaiser, Debra L.
Mailing Address:
NIST
Materials (223), A329
Gaithersburg, MD 20899
Telephone: (301) 975-6759
Fax Number: (301) 990-8729
E-mail Address: dkaiser@enh.nist.gov

Other NIST Principal investigator(s):

Turchinskaya, Marina (Guest Scientist)
Mailing Address:
NIST
Materials (223), A329
Gaithersburg, MD 20899
Telephone: (301) 975-4073
Fax Number: (301) 990-8729

Technical Description:

A magneto-optic imaging system originally developed in Russia has been placed into operation at NIST in order to study flux pinning mechanisms in high temperature superconductors. High flux pinning densities are needed for increasing the electrical current carrying capabilities of high temperature superconductors. Magneto-optic imaging is proving to be highly useful in visualizing and evaluating flux pinning densities.

Technical Objectives:

To provide U.S. industry with evaluation techniques and data which will accelerate the commercialization of high temperature superconductors for electrical power transport.

Accomplishments:

Magneto-optic has been very useful in evaluating the performance of cast tapes of the superconductor Bi₂Sr₂CaCu₂O_z (hereafter called BSCCO), a leading candidate material for electrical power applications.

Microscopic flux flow in undoped and Li-doped BSCCO cast tapes before and after neutron irradiation was studied by means of a magneto-optical imaging technique in order to correlate flux flow with the microstructure. Flux penetration was very nonuniform, indicating that current flow in the specimens is inhomogeneous. The neutron irradiation treatment increased flux pinning in both the undoped and Li-doped tapes. These results are important in understanding the effect of microstructure and irradiation on the critical current density of BSCCO.

More recently, the magneto-optical imaging system was used to study magnetization and demagnetization in composite tapes from American Superconductor Corporation that are composed of superconducting BSCCO filaments embedded in a silver matrix. BSCCO filaments located up to 112 µm below the unpolished surface of a composite tape could be imaged directly through the outer silver sheath. The magneto-optical images provided information on the morphology and alignment of the upper layer filaments in the tape, the relative depths of these filaments from the tape surface, and the homogeneity of the magnetic flux distribution within these filaments. These characteristics should prove useful in predicting the performance of the composite in service. Furthermore, our results demonstrate that magneto-optical imaging could be a routine diagnostic tool for these materials. These measurements demonstrate the utility of that magneto-optical imaging for nondestructive analysis of composites containing high T_c superconductors.

Outputs:

Technical Papers:

"Magnetic Flux Penetration in Undoped and Li-Doped Bi2Sr2CaCu2Oz Cast Tapes Before and After Neutron Irradiation," M. Turchinskaya, D. L. Kaiser, A. J. Shapiro, and J. Schwartz, Physica C 246, 375 (1995).

"Magneto-transport Behavior of Polycrystalline YBa₂Cu₃O₇: A Possible Role for Surface Barriers," Shi Li, M. Fistul, J. Deak, P. Metcalf, G. F. Giuliani, M. McElfresh, and D. L. Kaiser, Phys. Rev. B. in press.

Impact:

The NIST measurements are enabling American Superconductor Corporation to monitor progress in developing tapes made of high temperature superconductors for transmission of electrical power.