Fabrication of Large and High-Performance FeSe Bulk Superconductors by a Simple Liquid–Solid Diffusion Method

FeSe polycrystalline superconductors with dimensions over
$10\times 10 \times 3\ \hbox{mm}^{3}$
were fabricated by diffusing liquid Se into an iron tablet at 650
$^{\circ}\hbox{C}$
. Scanning electron microscopy and X-ray diffraction analyses were performed on the FeSe samples, and they showed that the main phase throughout the bulk is tetragonal
$\beta$
-FeSe and the grains are well crystallized and connected. The critical transition temperature (onset) was determined to be 12 K, with a transition width of 3 K, by a resistivity measurement. The upper critical fields
$H_{c2}(0)$
was estimated to be 40 T, and the intragranular critical current density estimated from the Bean model is about
$1.5 \times 10^{5}\ \hbox{A/cm}^{2}$
at 4 K in self-field. These results suggest that liquid–solid diffusion is a promising technique for fabricating large and high-quality FeSe bulk superconductors.