Fabrication of $\hbox{FeTe}_{0.5}\hbox{Se}_{0.5}$ Superconducting Wires and Tapes by a Chemical-Transformation PIT Process

We have fabricated single core superconducting FeTe
_0.5
Se
_0.5
wires and tapes using a process based on a chemical transformation from hexagonal Fe(Te
_0.5
Se
_0.5
)
_1+d
(nonsuperconducting) to tetragonal FeTe
_0.5
Se
_0.5
(superconducting) via an optimal supply of Fe from the Fe sheath by annealing. This process enhanced a packing density of wire core inside the sheath, owing to an expansion of the lattice volume via a chemical transformation from high-density hexagonal Fe(Te
_0.5
Se
_0.5
)
_1+d
to low-density tetragonal FeTe
_0.5
Se
_0.5
. An obvious correlation between annealing temperature (T
_a
) and phase transformation was observed. Transformation of wire core from hexagonal to tetragonal was observed above 500°C. Finally, the hexagonal phase completely transformed into the tetragonal phase by annealing at 700°C. The obtained superconducting wire showed superconductivity below ~13 K. The magnetic J
_c
value of 1.9 ×10
³
A/cm
²
at 4.2 K was obtained for the sample annealed at 500°C.