Enhancement of Critical Current Density in low level Al-doped MgB2
  Two sets of MgB2 samples doped with up to 5 at. % of Al were prepared in different laboratories using different procedures. Decreases in the a and c lattice parameters were observed with Al doping confirming Al substitution onto the Mg site. The critical temperature (Tc) remained largely unchanged with Al doping. For 1 - 2.5 at.% doping, at 20K the in-field critical current densities (Jc's) were enhanced, particularly at lower fields. At 5K, in-field Jc was markedly improved, e.g. at 5T Jc was enhanced by a factor of 20 for a doping level of 1 at.% Al. The improved Jcs correlate with increased sample resistivity indicative of an increase in the upper critical field, Hc2, through alloying. 
A. Berenov, A. Serquis, X. Z. Liao, Y. T. Zhu, D.E. Peterson, Y.   Bugoslavsky, K. A. Yates, M.G. Blamire, L. F. Cohen, J.L....