Structural–microstructural characteristics and its correlationswith the superconducting properties of in situ PIT-processedMgB2 tapes with ethyltoluene and SiC powder added

Abstract

We performed structural–microstructural investigations of pureMgB2, ethyltoluene and both ethyltoluene- and SiC-addedMgB2/Fe tapes. The analysis of the microstructure shows that the grain size for the pure and ethyltoluene-addedMgB2 tape sample is in the range of 10–100 nm. However, with the addition ofboth ethyltoluene and SiC, the grain size decreases to about 5–80 nm. Thea-axis length of the ethyltoluene-added tape samples is slightlydecreased, whereas for both ethyltoluene- and SiC-added samples, thea-axis length is decreased by 0.4% as compared to the pureMgB2 tape sample, showing the amount of carbon substitution is lessin ethyltoluene-added tape samples. The reason for the higherJc values of theethyltoluene-added MgB2 tape sample as compared to the pureMgB2 tapes is the presence of a lesser amount of the impurity phase, MgO. The large improvement inJc–B properties for the ethyltoluene- and SiC-addedMgB2 tape sample is attributed to (1) the enhancement of upper critical field,Bc2, by the substitution of carbon for boron, (2) pinning by nanosized (5–20 nm) particles ofMg2Si and other silicides, (3) enhanced grain boundary pinning due to the smaller grain size and(4) the presence of a lesser amount of impurity phase, MgO, as compared to the puresample.