Synthesis of Denser In Situ $\hbox{MgB}_{2}$ Bulks Using $ \hbox{MgB}_{4}$ Precursor

We have synthesized
$\hbox{MgB}_{2}$
bulks from a laboratory-made
$\hbox{MgB}_{4}$
precursor that have higher packing factor (relative density) compared to conventional in situ
$\hbox{MgB}_{2}$
bulks from boron.
$\hbox{MgB}_{4}$
precursor with less MgO content can be obtained by decomposition of
$\hbox{MgB}_{2}$
under low magnesium partial pressure.
$\hbox{MgB}_{2}$
bulks fabricated by heating the mixed powders of Mg and
$\hbox{MgB}_{4}$
showed improved packing factor
$\sim$
61%, high connectivity
$K = 17\%$
, and
$J_{\rm c} = 2.7 \time 10^{5}\ \hbox{A/cm}^{2}$
at 20 K under self-field. Both
$K$
and
$J_{\rm c}$
are the highest among the literatures for samples synthesized from
$\hbox{MgB}_{4}$
precursor. Our results suggest that the
$\hbox{Mg/MgB}_{4}$
in situ reaction route is effective for densification of in situ
$\hbox{MgB}_{2}$
, and much higher connectivity and
$J_{\rm c}$
can be reasonably expected by further optimization of the preparation of the
$\hbox{MgB}_{4}$
precursor and reaction conditions.