Development of ${\hbox {MgB}}_{2}$ Powders and Study of the Properties and Architecture of Ex-Situ PIT Wires

MgB₂ tapes and wires have been synthesized through the ex-situ Powder-In-Tube (PIT) method. We studied the effects of using different metallic materials for the sheaths in new round or square shaped multifilamentary wires; enhanced critical currents in 19 filaments wires are reported. The influence of the starting powders on the superconducting properties of the final conductors was thoroughly investigated in order to improve their behavior in magnetic field. In particular we analyzed the effect of controlling the grain size in the powders by high energy ball milling and by lowering the synthesis temperature. TEM analysis results are shown that highlight the role played by the amorphous layer at the grain boundaries.