Bhadauria, P. P. S. and Gupta, Anurag and Kishan, Hari and Narlikar, A. V. (2013) Effect of excess Mg and nano-additives on the superconducting properties of weakly connected bulk MgB2. Journal of Applied Physics , 113 (6). 063908-063915. ISSN 0021-8979

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Abstract

Series of ex-situ polycrystalline MgB2 bulk samples, by adding different additives like more of excess Mg (5 wt. %), nanoparticles of Ag (3 wt. %), and SiC (10 wt. %) to a previously optimized composition MgB2 + Mg (5 wt. %), were prepared by solid state synthesis route. Detailed investigations were carried out by XRD, SEM, and thermoelectric power S(T), resistivity rho(T), and magnetization M(B) at temperatures T = 4.2-300K and applied fields B = 0-8 T. All the samples typically show low connectivity (i.e., normal state current carrying cross section similar to 0.9%-3%). The effect of different additives was different on the critical current density (J(c)) of the samples. The J(c), for instance at T = 4.2K and B = 1 T, varied between 4.8 x 10(7) and 2.8 x 10(8) A/m(2) for various samples. In comparison to the previously optimized values, the J(c) was enhanced by further addition of 5 wt. % Mg and degraded both by nano-SiC and nano-Ag addition. However, many of the other properties of the samples were not much affected. For instance, the samples did not show any change in the superconducting onsets, S(T) and the parallel upper critical field (B-c2(parallel to) (T) similar to 11-13 T at 20K and 20-21 T at 4.2 K). The J(c)(B) dependence also shows similar behavior in all the samples, where the J(c) is found to scale as B-1 up to a sample independent crossover field B-cr similar to 2 T and 1.3 T at T = 4.2 and 20 K, respectively. At higher fields B > B-cr, the J(c)(B) curves branch out and decrease rapidly towards zero at a sample dependent characteristic field. We try to understand these results quantitatively in terms of changes in connectivity, pinning, and anisotropy driven percolation. However, all our results and analysis point out that the intra-particle regions stay unaffected and mainly the inter-particle regions get affected by the additives leading to the J(c) variation in the weakly connected samples.

Item Type:	Article
Additional Information:	copyright for this article belongs to M/s Elsevier
Subjects:	Applied Physics/Condensed Matter
Divisions:	UNSPECIFIED
Depositing User:	Users 27 not found.
Date Deposited:	19 Aug 2026 10:16
Last Modified:	19 Aug 2026 10:16
URI:	https://npl.csircentral.net/id/eprint/3279

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