| 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. |
- Liu, H.K., et al.
(författare)
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Cu valence states in superconducting BiPbSrCaCuO system
- 1990
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Ingår i: Journal of Solid State Chemistry. - 0022-4596 .- 1095-726X. ; 87:2, s. 289-297
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Tidskriftsartikel (refereegranskat)abstract
- The oxidation states of Bi, Pb, and Cu in the BiPbSrCaCuO (BPSCCO) system have been determined by a combination of volumetric measurement technique and iodometric titration. It was found that, in contrast to previous reports, the concentration of the Cu3+ ions decreased with increasing Pb content, and Cu3+ ions were absent in samples of Bi1.6Pb0.4Sr1.6Ca2Cu3O9.8, while a Tc at 108 K and a Jc of greater than 12,000 A/cm2 at 77 K were observed. The 110 K phase in BPSCCO was stabilized and showed a high tolerance to change in oxygen partial pressure during sintering. In Pb-doped materials, Bi appears to be trivalent while Pb was determined to be mixed-valence Pb4+ Pb2+. It is suggested that superconductivity in BPSCCO may result from a dynamic transfer of holes from Bi PbO layers toward CuO2 planes
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| 3. |
- Antzutkin, Oleg, et al.
(författare)
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Suppression of sidebands in magic-angle-spinning nuclear magnetic resonance : general principles and analytical solutions
- 1994
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 100:1, s. 130-140
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Tidskriftsartikel (refereegranskat)abstract
- Several theoretical and experimental aspects of sideband suppression in the nuclear magnetic resonance (NMR) spectra of rotating solids are considered. The principles of sideband suppression are explored using general symmetry arguments and previous treatments are examined critically. Analytical solutions are given for sideband suppression pulse sequences employing four, five, six, and nine pulses. The analytical solutions for four pulses are complete. Experimental demonstrations are given. The Journal of Chemical Physics is copyrighted by The American Institute of Physics.
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| 4. |
- Song, Zhiyan, et al.
(författare)
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Sideband suppression in magic-angle-spinning NMR by a sequence of 5 π pulses
- 1993
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Ingår i: Solid State Nuclear Magnetic Resonance. - 0926-2040 .- 1527-3326. ; 2:3, s. 143-146
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Tidskriftsartikel (refereegranskat)abstract
- We report a symmetrical sequence of 5 π pulses for total sideband suppression in magic-angle-spinning NMR. The sequence is almost evenly spaced and shorter than previous 4 and 6 π pulse methods.
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