  Fe-sheathed MgB2 tapes were prepared through the in situ powder-in-tube
technique by 5 at.% ZrSi2, ZrB2 and WSi2 doping, respectively. The doping
effect of these compounds on the microstructure and superconducting properties
of MgB2 tapes has been investigated by using x-ray diffraction, scanning
electron microscope, transport measurements and DC susceptibility measurements.
Compared to the undoped samples, Jc for all the doped samples were much
improved; the best result in terms of Jc was achieved for ZrSi2 doping, by up
to a factor of 3.4 at 4.2 K in magnetic fields up to 12 T. Moreover, these
dopants did not significantly decrease the transition temperature. The Jc-B
curves of WSi2-doped tapes show better performance in higher magnetic fields in
comparison to undoped tapes, suggesting that pinning centers effective in a
high-field region were possibly introduced.
