Improvement of ex-situ MgB2 powder in tube processed tapes using MgH2 powder

The critical current density, J(c), in applied magnetic field, B, of MgB2 tape fabricated by a powder-in-tube (PIT) method via ex-situ process was dramatically improved by using MgB2 Powder made from MgH2 and amorphous boron. The starting powder was obtained from the core of an MgB2 tape prepared via an in-situ process of PIT method. The highest J(c) at 10 T and 4.2 K (4.5 x 10(3) A/cm(2)) exceeds not only that of conventional ex-situ processed MgB2 tape made from commercial MgB2 powder (< 100 A/cm(2)), but also that of in-situ processed tape (3.4 x 10(3) A/cm(2)). This drastic improvement in J(c)-B property of ex-situ MgB2 tape is considered to be due to the enhancement in the B-irr of MgB2 core. On the other hand, we also found that the slope of J(c)-B line was different between ex-situ MgB2 tape and in-situ processed tape, and it resulted in the higher J(c) of ex-situ processed tape than that of in-situ processed tape. This difference is considered to originate in the difference of the effective pinning mechanism between in-situ processed and ex-situ processed tapes, and the J(c)-B property of ex-situ processed tape is affected by the introduction of extra lattice distortion via mechanical pressure of PIT process. (c) 2006 Elsevier B.V. All rights reserved.