Influence of milling energy of in-situ precursor powder on the properties of Ti-doped MgB2

Abstract

The effect of Ti-doping on the electrical properties of MgB2 bulks was studied in dependence on the milling energy of the used in-situ precursor powder. Ti-powder was added to a mixture of Mg- and B-powder before milling in three different concentrations related to the atomic weight of Mg (Mg1-xTixB2 with x = 0.025/0.05/0.1). From each doping concentration two different powders were milled with a planetary ball mill (for 1 resp. 10 h, rotation speed 250 rpm). This corresponds to a milling energy of 5⋅108 J/kg resp. 5⋅109 J/kg. The electrical resistivity in normal state of the bulk samples is increasing by Ti-doping. The most interesting point is the influence of Ti-doping on the magnetic field dependence of the critical current density jc of samples prepared with powders milled with different energy. A remarkable increase of jc was found with increasing Ti-content at 4.2 K and external fields higher than around 4 T for the powder with lower milling energy. Not any effect could be measured at the powder milled with higher energy. If we take into account that the grain sizes of the samples prepared with higher energy milled powder is remarkably smaller than that of the other sample it can be noticed that Ti-doping has only a distinct effect on the grain size, like discussed in [1], of samples with coarser powder, not on high energy milled powders.