  A MgB2 superconducting tape has been successfully prepared by a new way of
boron diffusion into Mg tape. This tape superconductor has a Tc of 39 K with a
sharp transition width of 0.4 K, high bulk critical current density jc of
6.7*10^5 A/cm^2 in zero field at 6 K, higher irreversibility line comparing to
that of a high pressure synthesized bulk sample and very small crystalline
grain with size in the scale of 10-200 nm.
