Origin of grain boundary weak links in BaPb sub 1 minus x Bi sub x O sub 3 superconductor

Journal Article · Sat Dec 01 04:00:00 EST 1990 · Journal of Applied Physics; (USA)

DOI:https://doi.org/10.1063/1.346943· OSTI ID:6115695

Takagi, T; Chiang, Y ^[1]; Roshko, A ^[2]

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1. Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (USA)
2. Superconductor and Magnetic Measurements Group, National Institute of Standards and Technology, Boulder, Colorado 80303 (USA)

Although BaPb{sub 0.75}Bi{sub 0.25}O{sub 3} (BPB) has a comparatively large superconducting coherence length of {approximately}7 nm and no reported anisotropy in its superconducting parameters, polycrystalline BPB exhibits the same rapid decrease in transport critical current density ({ital J}{sub ct}) with low applied field ({lt}{approximately}50 Oe) that is characteristic of grain boundary weak links in cuprate superconductors (e.g., La{sub 2{minus}{ital x}}Sr{sub {ital x}}CuO{sub 4}, YBa{sub 2}Cu{sub 3}O{sub 7{minus}{ital x}} ). We have studied the effects of processing thermal history on the formation and morphology of grain boundary phases, and on the composition of BPB boundaries with and without second phase, in order to understand the origin of these weak links. Scanning transmission electron microscopy and Auger electron spectroscopy results show the presence of a Pb-Bi-Ba-O phase that is wetting and liquid above {approximately}570 {degree}C, but which retracts to three-grain junctions upon slow cooling or annealing at lower temperatures. However, weak-link behavior persists in materials with retracted secondary phase, as well as in hot isostatically pressed samples that never exceed the secondary phase melting temperature. It is found that the grain boundaries remain Bi- and Pb-rich even after the retraction of secondary phases; samples that never exceed the melting temperature of the secondary phase show absence of segregation at some but not all grain boundaries. The composition of the grain boundaries as well as {ital J}{sub ct} vs temperature measurements indicate that the boundaries act as SIS tunnel junctions.

• OSTI ID: 6115695
• Journal Information: Journal of Applied Physics; (USA), Journal Name: Journal of Applied Physics; (USA) Vol. 68:11; ISSN 0021-8979; ISSN JAPIA
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360202 -- Ceramics
Cermets
& Refractories-- Structure & Phase Studies
360204* -- Ceramics
Cermets
& Refractories-- Physical Properties
ALKALINE EARTH METAL COMPOUNDS
BARIUM COMPOUNDS
BARIUM OXIDES
BISMUTH COMPOUNDS
BISMUTH OXIDES
CHALCOGENIDES
COHERENCE LENGTH
CRYSTAL STRUCTURE
DIMENSIONS
ELECTRIC CONDUCTIVITY
ELECTRIC CONTACTS
ELECTRICAL EQUIPMENT
ELECTRICAL PROPERTIES
EQUIPMENT
GRAIN BOUNDARIES
JUNCTIONS
LEAD COMPOUNDS
LEAD OXIDES
LENGTH
MICROSTRUCTURE
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
SAMPLE PREPARATION
SUPERCONDUCTING JUNCTIONS
SUPERCONDUCTIVITY