Superconducting properties of PIT-processed MgB₂ tapes using Mg(BH₄)₂ precursor

We have fabricated MgB₂ superconducting tapes with a powder-in-tube (PIT) technique using Mg(BH₄)₂ precursor. Heat treatment decomposes Mg(BH₄)₂ and subsequently forms MgB₂ as nearly single phase. Although the tapes carry supercurrent at 4.2 K and 0 T, the transport critical current (I_c) values of the tapes decrease down to 0 A by applying a magnetic field as small as 1 T. This is due to the weak grain coupling brought about by the large reduction in volume at the formation of MgB₂ from Mg(BH₄)₂. On the other hand, the use of the intermediates obtained by the calcination of Mg(BH₄)₂ powder successfully improves the critical current density (J_c) property close to the level of tapes using conventional Mg + B powders, owing to the suppression of the reduction. The insufficient purity of the starting precursor and the high sensitivity of calcined powder to oxygen and moisture prevent further improvement in the J_c property.