Poor intergrain connectivity of PbMo sub 6 S sub 8 in sintered Mo-sheathed wires and the beneficial effect of hot-isostatic-pressing treatments on the transport critical current density

Journal Article · Thu Aug 01 04:00:00 EDT 1991 · Journal of Applied Physics; (USA)

DOI:https://doi.org/10.1063/1.349525· OSTI ID:5557965

Yamasaki, H; Umeda, M; Kosaka, S; Kimura, Y ^[1]; Willis, T C; Larbalestier, D C ^[2]

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1. Electrotechnical Laboratory, MITI, 1-1-4 Umezono, Tsukuba-shi, Ibaraki 305, Japan (JP)
2. University of Wisconsin-Madison, 1500 Johnson Drive, Madison, Wisconsin 53706 (USA)

The microstructure of Mo-sheathed Chevrel-phase superconducting wires was investigated by high-resolution scanning electron microscopy (SEM). Excess Pb forms small nodules (10--30 nm) on the Chevrel-phase grains or wetting layers between the Chevrel grains. The critical current density {ital J}{sub {ital c}} is strongly reduced when wetting layers are present. However, second-phase Mo exists as islands as large as 2--10 {mu}m and has little harmful effect on {ital J}{sub {ital c}}. Although some Mo-sheathed wires sintered at 700 {degree}C show relatively high {ital J}{sub {ital c}} ( {ge} 2 {times} 10{sup 8} A/m{sup 2} at 8 T), the Chevrel phase in these wires has a very porous microstructure, and the {ital J}{sub {ital c}} values measured with a magnetic field parallel to the current, {ital J}{sub {ital c}}({parallel}), were only about 10% higher than the {ital J}{sub {ital c}} values measured with a field perpendicular to the current, {ital J}{sub {ital c}}({perpendicular}). This clearly suggests that the transport current flows percolatively in these wires. Much denser microstructures were obtained by hot-isostatic-pressing (HIP) treatments at 1200 {degree}C, and very high {ital J}{sub {ital c}} values, {gt} 5 {times} 10{sup 8} A/m{sup 2} at 8 T and 9.3 {times} 10{sup 7} A/m{sup 2} at 23 T, which are of the order of the highest {ital J}{sub {ital c}} values so far reported, were observed. High-resolution SEM observations of HIP'ed wires demonstrate that the interconnectivity between the Chevrel grains was much improved.

• OSTI ID: 5557965
• Journal Information: Journal of Applied Physics; (USA), Journal Name: Journal of Applied Physics; (USA) Vol. 70:3; ISSN 0021-8979; ISSN JAPIA
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360603* -- Materials-- Properties
CHALCOGENIDES
CRITICAL CURRENT
CRYSTAL STRUCTURE
CURRENTS
ELECTRIC CURRENTS
ELECTRON MICROSCOPY
FABRICATION
GRANULAR MATERIALS
HOT PRESSING
LEAD COMPOUNDS
LEAD SULFIDES
MATERIALS
MATERIALS WORKING
MICROSCOPY
MICROSTRUCTURE
MOLYBDENUM COMPOUNDS
MOLYBDENUM SULFIDES
PRESSING
REFRACTORY METAL COMPOUNDS
RESOLUTION
SCANNING ELECTRON MICROSCOPY
SINTERING
SULFIDES
SULFUR COMPOUNDS
SUPERCONDUCTING WIRES
TRANSITION ELEMENT COMPOUNDS
WIRES