A significant program in high T_c superconductivity is being conducted in MSEL and other Laboratories at NIST. The primary focus of the MSEL program is on bulk superconducting materials for wire and magnet applications. In carrying out this program, researchers in MSEL work closely with their counterparts in other NIST Laboratories, and collaborators in U.S. industry, universities, and other National Laboratories.

The primary thrusts of the program are as follows:

• Phase equilibria - Work is being performed in close collaboration with the U.S. Department of Energy (DOE) and its national laboratories to provide the phase diagrams necessary for processing these unique ceramic materials. A prime objective is the development of the portions of the phase diagram for the Pb-Bi-Sr-Ca-Cu-O system relevant to production of the high T_c materials.
  
  

• Flux pinning - Use is made of a unique magneto-optical imaging facility to examine flux pinning in a variety of materials, with much of this work being conducted in collaboration with American Superconductor Corporation. In addition techniques for better interpretation of magnetic measurements are being developed. Structure and dynamics of flux lattices and melting phenomena, critical to applications, are investigated with small-angle neutron scattering techniques.
  
  

• Damage mechanisms - Work is being carried out under a joint CRADA (cooperative research and development agreement) with American Superconductor Corporation as part of the "Wire Development Group" which involves a number of DOE National Laboratories and the University of Wisconsin to elucidate the effects of strain on the loss of current in superconducting wires. The primary tool being employed is the use of microfocus radiography available at the NIST beamline at the Brookhaven National Laboratory.
  
  

• Database - A high temperature superconductor database has been developed in collaboration with the National Research Institute for Metals (NRIM) in Japan. The High Temperature Superconductor Database (HTSD) includes evaluated open-literature data on numerous physical, mechanical, and electrical properties of a variety of chemical systems. The first version of the database is now for sale by the Office of Standard Reference Data.
  
  

• Crystal structure - Thermal neutron scattering techniques and profile refinement analyses are being utilized to investigate crystal and magnetic structures, composition, dynamics and crystal chemical properties. This research is being carried out in collaboration with a number of industrial and university experts and researchers at National Laboratories.

Project Title: MAGNETIC PROPERTIES OF SUPERCONDUCTORS

Investigators: L.J. Swartzendruber, L.H. Bennett, R.D. Shull, F.W. Gayle, A.J. Shapiro, M.J. Donahue, D.E. Mathews, H.J. Brown, R.V. Drew

Objectives:

This project seeks to improve present magnetic measurements and develop new measurements for superconductors, to provide support to the Ceramics Division in the determination of phase diagrams important for the processing of high temperature superconductors, and to determine the effect of various microstructural features such as inclusions, compositional modulation, and precipitates, on the flux pinning in high temperature superconductors.

Technical Description:

In collaboration with scientists from universities, industry, and other Divisions at NIST, superconducting materials are prepared and their microstructure and magnetic properties determined. The properties of impurities which form during processing of superconductors, or which are intentionally added to modify the properties, are also investigated. Measurements performed include AC and DC magnetization as a function of temperature and applied magnetic field, hysteresis loops, flux penetration and viscosity, critical fields, and critical temperatures. Microstructural studies are performed using scanning and transmission electron microscopy. Emphasis is on high temperature superconducting materials. When a Sn source becomes available, the structural and electronic properties of these compounds will be investigated by Mössbauer spectroscopy

Planned Outcome:

Results of this project will improve the ability of manufacturers and researchers to interpret magnetic measurements in high-temperature superconductors. It will also improve the ability of manufacturers to characterize and control the characteristics and quality of material they produce, will increase critical current densities by improvements in flux pinning, and provide better control over the flux pinning properties of materials for shielding and levitation bearings.

External Collaborations:

External collaborators include Dr. H.M. Seyoum at the University of the District of Columbia, Dr. M. Melamud of the Technion, Hiafa Israel, and M Rubinstein at the Naval Research Laboratory.

Accomplishments:

Diamagnetic shielding measurements were performed on pure and Sn-doped GeCuO. It was found that the low temperature spin-Peierls transition of the pure material was modified by the Sn doping. The effects of composition on the superconducting properties of

Sr_4-xCa_xPtO₆ were measured. This information was used to help determine phase relationships in this system. Compounds of (Sr,Ca)CuO prepared by the ceramics division were measured to determine if improved superconductivity could be achieved in this system by variations in the processing conditions.

Impact:

Phase diagrams determined at NIST are being used by industry to fabricate improved high temperature superconducting materials. Commercial devices using high temperature superconductors are currently available. Many of these devices are being fabricated using laser ablation, a method which was developed by NIST in cooperation with the Johns Hopkins Applied Physics Laboratory.

Our explanation of "inverse levitation" in terms of the effect of flux pinning on the magnetic properties of high temperature superconductors opens up many possibilities for the use of these materials in devices. An instrument, developed by NIST in cooperation with the Institute of Solid State Physics in Russia, for observing the flux distribution in superconductors and other magnetic materials won an IR100 award and has been commercialized by Phasemetrics, Inc.

Outputs:

Publications:

Effect of Barium Cuprate on High Temperature Superconductors, H.M. Seyoum, M. Melamud, W. Wong-Ng, L.H. Bennett, L.J. Swartzendruber, L. Cook, and H.J. Brown, J. Appl. Phys. 81, 4244 (1997).

U.S. Department of Commerce
Technology Administration
National Institute of Standards and Technology
Materials Science & Engineering Laboratory
Metallurgy Division

For further help finding information about specific NIST programs and publications,
please contact the Public Inquiries Unit, (301) 975-3058

Revised March 09, 1998