Accession Number:

ADA067310

Title:

Controlled Grain Boundary Structures in Superconductors.

Descriptive Note:

Annual technical rept. 1 Jan-31 Dec 78,

Corporate Author:

CORNELL UNIV ITHACA N Y

Personal Author(s):

• Kramer,Edward J.

Report Date:

1979-02-01

Pagination or Media Count:

22.0

Abstract:

The relationship between grain boundary structure and chemistry and the critical current properties of superconductors is being investigated. The critical current flux pinning contributed by single grain boundaries in Nb bicrystals has been observed and shown to be suprisingly large even for boundaries that should have no crystal anisotropy or stress field contribution to the elementary interaction force between a grain boundary and the flux line lattice. Transmission electron microscopy and X-ray topography have been used to characterize the grain boundary structure, and bicrystal substructure respectively. The first high angle symmetric tilt examined is straight, shows no periodic structure and appears to be free of precipitates or detectable segregation. The electron float zone welding method of bicrystal manufacture is shown to give rise to very low angle subboundaries lying approximately parallel to the main grain boundaries. These contribute an annoyingly high background critical current which makes isolation of the main boundary contribution somewhat uncertain.

Descriptors:

• *SUPERCONDUCTORS
• *GRAIN BOUNDARIES
• CRYSTAL STRUCTURE
• FLUX(RATE)
• X RAY DIFFRACTION
• CURRENT DENSITY
• ELECTRON MICROSCOPY
• ANISOTROPY
• NIOBIUM
• LEAD COMPOUNDS
• POLYCRYSTALLINE
• BISMUTH COMPOUNDS

Subject Categories:

• Crystallography
• Electricity and Magnetism

Distribution Statement:

APPROVED FOR PUBLIC RELEASE