V-I characteristics of MgB2 PIT composite tapes:: n-values under strain, in high fields, or at high temperatures

V-I characteristics of monocore MgB2 PIT composite tapes are examined in n-values under strain, in high fields, or at high temperatures. n-values are determined by using V-I curves that are obtained for short samples by dc four-probe resistive method. The n-value increases with increasing external tensile strain up to 0.5% in the same way that critical current, I-c, increases with increasing the strain. When the strain exceeds 0.5%, I-c and n-value show a large degradation. In high field tests, in situ processed MgB2(+10 at.% SiC) tapes show n-values of 25.8-29.0 (J(c)(core) = 12,000-15,000 A/ cm(2)), 18.3-20.1 (5300-6200 A/cm(2)), and 4.8-6.5 (970-1100 A/cm(2)) at 10, 12, and 16 T, respectively. In high temperature tests, the tapes show n-values around 40 at 18 K in 4 T, 21 K in 3 T, 25.5 K in 2 T, and 29 K in 1 T. I-c and n-value show a strong correlation. MgB2 conductors with the larger I-c can lead to the higher n-value. (C) 2003 Elsevier B.V. All rights reserved.