Fifth DOE Information Meeting on High Tc Superconductors Explores Effects of Microstructure
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Fifth DOE Information Meeting on High Tc Superconductors Explores Effects of Microstructure Terry L. Aselage and Keith D. Keefer The theme of the Fifth U.S. Department of Energy Information Meeting on High Temperature Superconductivity was the "Effect of Microstructure on the Properties of High Temperature Superconducting Materials." Sponsored by the Materials Science Division of the Office of Basic Energy Sciences of DOE, the meeting was held at Sandia National Laboratories, Albuquerque, New Mexico, January 25 and 26, 1988. Approximately 150 scientists from around the United States attended. The purpose of these meetings has been to exchange information on the new high temperature superconductors in a timely fashion and to coordinate superconductivity research among the various DOE-sponsored programs. To broaden participation, this meeting feat u r e d a live, n a t i o n w i d e television broadcast of the program by satellite hookup through the National Technical University. Special requirements dictated by the broadcast necessitated a different format than that used in previous meetings, according to Jim Schirber of Sandia National Laboratories, who organized the meeting. In order to keep to the tight schedule yet allow for free discussion, a panel format was utilized. Five panels were assigned the task of discussing the following topics: (1) interconnects and critical currents, (2) structural properties and twins, (3) oxygen stoichiometry, vacancies and doping, (4) pinning, magnetic anisotropy and critical fields, and (5) theory. Each panel member had five minutes to describe an aspect of the topic, after which the
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V. Narayanamurti, vice president of research at Sandia , welcomes participants to the DOE information meeting on the "Effect of Microstructure of the Properties of High Temperature Superconductors." (Photo, R. Montoya, Sandia)
panel m e m b e r s a n s w e r e d questions from other panelists, the studio audience, and television viewers who telephoned their questions. A late afternoon session, which was not televised, allowed for the presentation of recent research results. Panel 1 — Interconnects and Critical Currents The first panel on interconnects and critical currents focused on intergranular weak links in polycrystalline ceramic materials. A number of effects at or near grain b o u n d a r i e s were identified, i n c l u d i n g second p h a s e s (primarily B a C u 0 2 and C u O ) , cracks resulting from thermal expansion anisotropy, carbonate impurities, nonstoichiometry, and anisotropy in transport properties
(grain alignment). G. Fisanick (AT&T Bell Laboratories) reported scanning Auger results suggesting that a 10 A insulating carbonate layer is present at grain boundaries. R. McCallum (Ames Laboratory) followed by p r e s e n t i n g results that showed that much of the carbonate found at grain boundaries in their samples results from exposure to laboratory air for long periods of time. Cracks at grain boundaries were cited as an important factor. D. Kroeger (Oak Ridge National La
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