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Abstract:
The effect of the quality of starting powders on the microstructure and superconducting properties of in situ processed Fe-sheathed MgB2 tapes has been investigated. Three different types of commercial atomized spherical magnesium powder and two different purities of amorphous boron powder were employed. When using the 10 mu m magnesium as precursor powders, the Mg reacted with boron more uniformly and quickly; thus the uniformity of the fabricated MgB2 was improved and the grain size of the MgB2 was decreased. Hence significant critical current density ( Jc) enhancements were achieved for MgB2 tapes. J(c) at 4.2 K for MgB2 tapes made from the 10 mu m Mg and high purity boron powders was at least a factor of ten higher than values measured for MgB2 samples made from all other starting powders. At 20 K, 5 T, the typical J(c) values of the tapes were over 1.0 x 10(4) A cm(-2) and were much better than those of tape samples reported recently.
