Fabrication of FeTe0.4Se0.6 superconducting tapes by a chemical-transformation PIT process

We have fabricated single core superconducting FeTe0.4Se0.6 tapes using a process based on a chemical phase transformation from hexagonal Fe(Te0.4Se0.6)1.4 (non-superconducting) to tetragonal FeTe0.4Se0.6 (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, due to an expansion of the lattice volume via the transformation from high-density hexagonal Fe(Te0.4Se0.6)1.4 to low-density tetragonal FeTe0.4Se0.6. An obvious correlation between annealing temperature (Ta) and phase transformation was observed. Transformation of tape cores from hexagonal to tetragonal were observed above 500 °C. Finally, the hexagonal phase completely transformed into the tetragonal phase by annealing at 600 °C. The obtained superconducting tape showed superconductivity below ∼13.5 K. The magnetic Jc value of 3.0 × 103 A/cm2 at 4.2 K was obtained for the sample prepared by annealing at 525 °C for 3 h followed by annealing at 200 °C for 2 h.