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

Abstract

Abstract V–I characteristics of monocore MgB 2 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 MgB 2 (+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. MgB 2 conductors with the larger I c can lead to the higher n -value.