Investigation of transport properties of superconducting MgB2/Fe wires fabricated by magnesium coating method

In this thesis, an experimental study which shows the effect of excess magnesium addition by evaporation technique on the current carrying properties of a single- core in-situ MgB2/Fe superconducting wire is presented. The initial excess magnesium was introduced by using a special evaporation technique in which a small amount of excess magnesium with <1wt. % was first coated by means of evaporation method into an empty iron tube, and then stoichiometric Mg + 2B precursor powder was packed into this Mg coated tube in powder or pellet forms. In order to make a comparison, the excess Mg was also introduced by a mixing method into the stoichiometric Mg + 2B powder in which the final mixture was packed into an empty iron tube by pellet-in-tube method again. The latter non- stoichiometric wires were prepared to contain different amount of excess magnesium with ratios 1wt. % and 5wt. % of the total Mg + 2B mixture weight. The reasons for the use of Mg-coating method are to ensure a uniform distribution of small amount of excess Mg along the wire and to reduce the formation of Fe2B in the core/sheath interface region. Transport measurements were carried out in order to determine the critical temperature, the engineering critical current density, the n-value, the resistivity and connectivity of the stoichiometric and non- stoichiometric wires produced by a cold wire drawing. The results revealed that the excess Mg significantly enhances the structural, superconducting, and transport properties of the MgB2/Fe wire. The most important result is that the Mg-coated sample has the best transport properties under the magnetic field. The highest Jce and n-values were obtained for the Mg-coated wire with the lowest starting excess Mg ratio between the non-stoichiometric wires. Discussions in this thesis are expected to make a contribution to the debates on Mg stoichiometry which influences the critical current density of MgB2 wires under the external magnetic field.