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Superconducting MgB2 ceramics and tapes prepared from mechanically milled powders

P. BADICA1,* , T. KONDO2, K. TOGANO3, G. ALDICA1

Affiliation

  1. National Institute of Materials Physics, Bucharest-Magurele ,POBox MG-7, 077125 Romania
  2. Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577, Japan
  3. National Institute for Materials Science,1-2-1 Sengen, Tsukuba, Ibaraki, 305-0047, Japan

Abstract

Bulks and tapes of MgB2 with 5 wt.% SiC were prepared from Mg, B and SiC. Mixing of the raw powders was performed in Ar atmosphere by high energy milling using a planetary mill. Number of balls (10 or 20), size (10 mm or 7 mm, respectively), rotation speed (200 rpm or 400 rpm) and milling time (up to 3 h) were varied. Powders were compared through XRD and SEM. From the as-prepared powders, bulk and tape samples were prepared and investigated by magnetic (SQUID) and transport (four-probe method) measurements. Results suggest that through variation of the milling conditions such as rotation speed, size and number of balls it is possible to control the value of the critical current density, Jc and the slope of the Jc(B) curve. For different heat treatment conditions milling with 400 rpm and using 20 balls of 7 mm always resulted in lower Jc(B) than for the tapes or bulks produced from hand-milled mixture. Use of 10 balls of 10 mm keeping all the other conditions constant changed the slope of the Jc(B) curve possibly improving Jc above a crossover at 4 T. Mild milling with a rotation speed of 200 rpm (20 balls x 7 mm) resulted in enhancement of Jc in the entire investigated region B ≤ 14 T, but the slope was steeper than for the best sample produced from the hand-milled mixture and a crossover is likely to occur for B > 14 T leading to lower Jc-values. The best samples had at 4.2 K Jc = 3.6 x 102 A􀂂cm-2 at 14 T and Jc = 5 x 103 A􀂂cm-2 at 10 T..

Keywords

MgB2, superconductor, bulk, tape, milling, critical current density.

Submitted at: May 21, 2008
Accepted at: Oct. 7, 2008

Citation

P. BADICA, T. KONDO, K. TOGANO, G. ALDICA, Superconducting MgB2 ceramics and tapes prepared from mechanically milled powders, Journal of Optoelectronics and Advanced Materials Vol. 10, Iss. 10, pp. 2753-2756 (2008)