Effect of Te doping on the structure and superconductivity of K_0.8Fe₂Se_2-zTe_z single crystals

We report the structure, transport, and magnetic properties of K_xFe_2−ySe_2−zTe_z single crystals grown by optical floating zone technique. The phase separation phenomena were observed in the Te-doped samples. With increasing Te doping level, the c-axis lattice parameter expands for both insulating/semiconducting and superconducting phases. The critical current density was estimated to be ≈10³–10⁴ A/cm² for the all doped samples. The capability of carrying superconducting current is reduced towards high magnetic field with increase of Te doping.