Fabrication of FeTe0.5Se0.5 Superconducting Wires and Tapes by a Chemical-Transformation PIT Process

We have fabricated single core superconducting FeTe0.5Se0.5 wires and tapes using a process based on a chemical transformation from hexagonal Fe (Te0.5Se0.5)(1+d) (nonsuperconducting) to tetragonal FeTe0.5Se0.5 (superconducting) via an optimal supply of Fe from the Fe sheath by annealing. This process enhanced a packing density or wire core inside the sheath, owing to an expansion of the lattice volume via a chemical transformation from high-density hexagonal Fe(Te0.5Se0.5)(1+d) to low-density tetragonal FeTe0.5Se0.5. 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 degrees C. Finally, the hexagonal phase completely transformed into the tetragonal phase by annealing at 700 degrees C. The obtained superconducting wire showed superconductivity below similar to 13 K. The magnetic J(c) value of 1.9 x 10(3) A/cm(2) at 4.2 K was obtained for the sample annealed at 500 degrees C.