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215. Effects of Si and C Doping on the Superconducting Properties of MgB2.

Author

Zhou, S. H., Pan, A. V., Qin, M. J., Wang, X. L., Liu, H. K., and Dou, S. X.

Subjects
SILICON, CARBON, SUPERCONDUCTORS, METAL powders, SUPERCONDUCTIVITY, CRYOELECTRONICS, CRITICAL currents
Abstract

C and Si powders of different sizes were doped into MgB2 separately or together. Samples were made by a solid-state reaction method. It was found that the C doping had a strong negative effect on critical temperature (Tc) while the Si doping did not significantly depress Tc. All of these doping materials increased Jc at higher fields when the doping particles were of nanometer sizes. At 20 K and 4 T, Jc of the sample doped with nano-Si achieved 104A/cm2, which is 2 orders of magnitude higher than that of coarse Si doped MgB2. Jc of the sample doped with nano-carbon is one order of magnitude higher than for the sample doped with coarse carbon particles. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Published
2004
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225. Effect of various mechanical deformation techniques on pinning force densities in Ag/Bi-2223 tapes.

Author

Chen, W. M., Liu, H. K., Fu, X. K., Guo, Y. C., Shi, D. Q., and Dou, S. X.

Subjects
*DEFORMATION potential, *MAGNETIC fields
Abstract

Ag/Bi-2223 tapes were fabricated using the Powder-In-Tube method, involving intermediate deformation techniques of sandwich rolling (SR), pressing (P) and normal rolling (NR). Magnetic field B dependence of J[sub c] was measured. Depending on the relationship between J[sub c] and B, the irreversible magnetic field B[sub irr] was determined and pinning force density F was calculated. The experimental results showed that self-field-J[sub c] was linear with the relative density for SR-, P- and NR-tapes. Our experimental results support that NR-, P-, and SR-tapes have a same sort of pinning center and the intermediate deformation processing cannot change property of pinning centers, but can effect the pinning force strength. Our experimental results also support that sandwich rolling is the best technique for fabricating Ag/Bi-2223 tapes. [ABSTRACT FROM AUTHOR]

Published
2002

226. Flux dynamics of MgB[sub 2] superconductor by AC susceptibility measurements.

Author

Qin, M. J., Wang, X. L., Soltanian, S., Liu, H. K., and Dou, S. X.

Subjects
SUPERCONDUCTORS, MAGNETIC flux
Abstract

Flux dynamics of an MgB[sub 2] bulk sample have been studied by systematic measurements of the fundamental and third harmonic ac susceptibility. The irreversibility line T[sub irr](B) has been obtained by fitting the onset temperature T[sub on] (f,B) of the third harmonics at different frequencies to T[sub on](f,B) = C(2πf)[sup 1/[(z-1)ν]] + T[sub irr](B). The flux creep activation energy U(j,B,T) has been derived as U[sub 0][1-(T/T[sub irr])²]²(B/B[sub 0])[sup -n](j/j[sub 0])[sup -μ], with n=1.33 and μ=0.2. The steep decline of the activation energy as a function of the magnetic field U(B) ∝ B[sup -1.33] leads to the steep drop in the critical current density with magnetic field. The relaxation of the current density j(t) of the sample has been detected in a time window of 10[sup -4]∼10[sup -1]s, as the frequency is in the range of 10Hz-10kHz, which extends the time window l∼10[sup 4]s of the conventional dc magnetic relaxation to a much smaller one. The obtained activation energy and the irreversibility line indicate that the pinning properties of the MgB[sub 2] sample will need to be improved for practical applications. [ABSTRACT FROM AUTHOR]

Published
2002

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