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

Technical Description:

Working with other scientists fron NIST, universities, and industry, high temperature superconducting materials are prepared and their microstructure and magnetic properties determined. Measurements 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. Microstructure studies are performed using scanning and transmission electron microscopy.

Technical Objectives:

• Develop and improve magnetic measurements of superconductors.

• Develop relationships between ac and dc susceptibilities and the impurities and phase distributions present in the material.

• Study the flux pinning properties of high temperature superconductors as a function of their microstructure and processing variables.

• Explore superconducting properties of new materials and of materials prepared under varying processing conditions.

• Provide support to the Ceramics Division in the determination of phase diagrams of materials important for the production of high temperature superconductors.

Anticipated Outcome:

• Improvements in the ability of manufacturers and researchers to interpret magnetic measurements in high-temperature superconductors.

• Increased critical current densities by improvements in flux pinning.

• Better quality control in the production of high-temperature superconductors.

• Better control over the flux pinning properties of materials used in shielding and levitation bearings.

Accomplishments for FY 1995:

• Determined that small field gradients have a large effect when measuring the Meissner fraction of high temperature superconductors with large pinning.

• Developed a method for measuring Meissner fraction in the presence of field gradients.

Impacts and Technical Highlights:

• 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. An instrument, developed by NIST in cooperation with the Institute of Solid State Physics in Russia, for observing the flux distribution in superconductors has been commercialized by a US Company. Phase diagrams developed using the aid of magnetic measurements are currently being used for scientific investigation and industrial development.

• After the discovery of high temperature superconductors, a so-called "positive Meissner effect" was observed in many laboratories. Such an effect is often observed in SQUID magnetometers. Rather than being a real effect, we have shown how such an observation is an artifact of the measurement process. We have also shown how the true Meissner fraction in a sample can be properly measured. Such measurements are important for assessing the flux pinning properties high-temperature superconductors.

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Last modified: Mon Jan 06 09:46:15 1997 Metallurgy Webmeister