Critical current properties of an ex-situ MgB2/TiB2 sample fabricated by spark plasma sintering using MgB2

A critical current density, Jc, of an in-situ processed MgB2 is known to be improved by doping or adding Ti, in which Ti does not substitute for Mg-site but rather creates a thin layer of TiB2 on the surface of the MgB2 grain. For this study, we fabricated the in-situ (1−x)MgB2/xTiB2 samples from the mixture of (Mg1−xTixB2) (x=0 and 0.1), and then confirmed that the Jc of the Ti10% (x=0.1) sample was higher than that of the pristine (x=0) sample. To obtain a higher Jc(B), we prepared the dense ex-situ (1−x)MgB2/xTiB2 samples using a spark plasma sintering (SPS) method from the above powdered (1−x)MgB2/xTiB2 precursors. Contrary to the in-situ samples, the ex-situ Ti10% sample showed a degraded Jc compared to the ex-situ pristine sample. The microstructural analysis revealed that the grain growth of MgB2 occurred in the ex-situ Ti10% sample, which identifies the decrease of the number density of grain boundaries acting as the predominant pinning centers. We propose a possible mechanism that the TiB2 in the in-situ precursor powder promoted grain growth for the ex-situ Ti10% sample during the SPS process.