Effects Of The Size Of Mg Powder On The Formation Of Mgb2 And The Superconducting Properties

The effect of the size and shape of magnesium(Mg) powder on the formation of MgB2 and the critical current density(J(c)) of MgB2 bulk was studied. As a precursor for the formation of MgB2, Mg and MgB4 powder, which was synthesized through the reaction of boron (B) with Mg powders, was used. MgB4 was mixed with Mg powders of various sizes, pressed into pellets and heat-treated at 650 degrees C-750 degrees C in flowing argon gas. The XRD analysis of the heat-treated MgB2 samples showed that the volume fraction of MgB2 was the highest as 92.74 % when spherical Mg powder with an average size of 25.7 mu m was used, whereas the volume fraction was the lowest as 79.64 % when plate-like Mg powder with a size of 34.1 mu m was used. The superconducting transition temperature (T-c) of MgB2 was not sensitive to the characteristics of the Mg powders used. All of the prepared MgB2 samples showed a high T-c of 38.3 K and a small superconducting transition width of 0.2 K-0.5 K. J(c) (5 K and 1 T) of MgB2 was the highest as 3.93x10(4)A/cm(2) when spherical Mg powder with a size of 25.7 mu m was used, whereas J(c) was the lowest as 2.18x10(4) A/cm(2) when plate-like Mg powder with a size of 34.1 mu m was used. The relationship between the J(c) of MgB2 and the characteristics of the Mg powders used was explained in terms of the volume fraction of MgB2 and the apparent density of the MgB2 pellets.