Influence of MgB2 powder quality on the transport properties of Cu-sheathed MgB2 tapes

We fabricated Cu-sheathed MgB2 tapes by a powder-in-tube method without hea t treatment using commercially available two different MgB2 powders. One po wder composed of fine MgB2 grains which were fully covered with thick MgO l ayers caused transport critical current density (J(c)) values of zero at 4. 2 K and 0 T, while another powder composed of relatively large MgB2 grains which were partially covered with thin MgO layers did Jc values of about 10 kA/cm(2). These results indicate that the quality of powder is very import ant to obtain good grain connectivity for supercurrent flow. Neither micros tructural change of the large MgB2 grains nor J(c) decrease of the correspo nding tapes was appreciable after an exposure in air for one month, suggest ing that the large MgB2 grains are unlikely to receive damages by moisture and oxygen rapidly. Heat treatment of these Cu-sheathed tapes resulted in a deterioration of J(c) due to the reaction of Cu and Mg. (C) 2001 Elsevier Science B.V. All rights reserved.