| 1. |
- Dou, S.X., et al.
(författare)
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Improvement of critical current density in the Bi-Pb-Sr-Ca-Cu-O system through hot isostatic pressing
- 1990
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Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 167:5-6, s. 525-528
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Tidskriftsartikel (refereegranskat)abstract
- The effects of hot isostatic pressing (HIPing) on densification and the superconducting properties of the Bi-Pb-Sr-Ca-O system were investigated. A relative density up to 95% and a critical current density greater than 1100 A/cm2 at 77 K were achieved through HIPing at 650°C for 2 h under 200 MPa argon. Under these conditions, the product gave a value of Jc four times that without HIPing. To was unaffected by HIPing for samples encapsulated with a combination of glass and silver tubes. However, To was suppressed from 103 K to 86 K for samples encapsulated with stainless steel and silver tubes while Jc increased from 260 A/ cm2 to 1086 A/cm2 during HIPing, indicating that the weak links were significantly improved. A new minor phase, having a composition of Bi/Pb/Sr/Ca/Cu=0.58/2.8/3.0/2.1/1.1, was observed in HIPed samples but its effect on Jc is not clear
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| 2. |
- Dou, S.X., et al.
(författare)
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Microstructure and flux pinning in superconducting Bi-Pb-Sr-Ca-Cu-O wires
- 1990
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Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 172:1-2, s. 63-70
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Tidskriftsartikel (refereegranskat)abstract
- The critical current density (Jc) of Ag-clad Bi-Pb-Sr-Ca-Cu-O wire has been measured to be 1.2×104 A/cm2 at 77 K in zero field. The high Jc is attributed to a combination of elimination of the poisoning effect of Ag on superconductivity, grain alignment, and enhancement of flux pinning. Jc-H dependence was significantly improved in the Ag-clad tape, which has a Jc of 1.0×103 A /cm2 at 77 K and 4000 Oe, while the Jc of the sintered pellet drops two orders of magnitude at only 100 Oe. A pronounced anisotropy in Jc under high magnetic field is attributed to the grain alignment. Planar defects, such as heavy stacking faults parallel to the a-b plane in the rolled tape, are considered to be effective pinning centres.
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| 3. |
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| 4. |
- Guo, S.J., et al.
(författare)
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Improved single crystal growth in the Bi-Sr-Ca-Cu-O system using a sealed cavity technique
- 1990
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 100:1-2, s. 303-308
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Tidskriftsartikel (refereegranskat)abstract
- Bi-Sr-Ca-Cu-O single crystals obtained thus far commonly have a very small thickness in the c-axis because of the weak bonding between two adjacent BiO layers and the high vapour pressure of Bi2O3 at high temperature. To overcome these difficulties a presintered SrCaCu4O6 was used to seal the Bi-Sr-Ca-Cu-O melt from which the single crystals grew during slow cooling. In the SrCaCu4O6 sealed cavity the Bi loss through vaporization was prevented and Sr and Ca were enriched in the superconducting crystals. The resulting single crystals have a dimension of up to 3.0×1.5×0.7 mm3, which is two orders of magnitude thicker than those grown from alkali chloride flux. The composition of the crystals is Bi2.2Sr1.8Ca0.75Cu1.8Ox and they possess a zero resistance at temperature above liquid nitrogen
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| 5. |
- Guo, S.J., et al.
(författare)
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Magnetic field dependence of the critical current density for the bismuth-based bulk high-Tc superconductors
- 1992
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Ingår i: Journal of Materials Science. - 0022-2461 .- 1573-4803. ; 27:11, s. 3043-3049
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Tidskriftsartikel (refereegranskat)abstract
- Three types of bismuth-based bulk samples were prepared through uniaxial pressing at room temperature, hot isostatic pressing (HIP) and drawing and rolling. Transport current properties were characterized in a steady field up to 1.12 T at 77 K (T/T c=0.75). The Josephson weak-link decoupling fields have been found to be 5 mT for the cold-pressed pellet and 30 mT for the HIPed pellet and the rolled tape. At the decoupling field the transport critical current density,J c, drops 80% from 124 (OT) to 29 A cm-2 (5 mT) for the cold-pressed pellet, 80% from 582 (OT) to 126 A cm-2 (30 mT) for the HIPed sample and 50% from6500 (0 T) to 2850 A cm-2 (30 mT) for the rolled tape. In the flux flow regime, whereB is perpendicular to thec-axis a modified Kim's modelJ c=(α/B 0)/[(1+B/B 0)] n can be used to describe the field dependence of the critical current density, Jc, in the field range 0.2-1.12 T. The effective upper critical fields were estimated to be 0.98, 1.54 and 1.94 T for the three types of samples, respectively. An adjustable range ofB c2 for bismuth-based bulk highT c superconductors is given. Flux shear may operate in these materials. The prediction of this pinning mechanism is yielded from fitting the equation qualitatively. WhenB is parallel to thec-axis, the absence of strongly intragranular flux-pinning is emphasized by the poor flux flow regime for the rolled tape sample.
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