Annealing effect on microstructure and superconductivity of K _xFe_ySe₂ synthesized by an easy one-step method

High-quality superconducting K_xFe_ySe₂ single crystals were synthesized using an easy one-step method. Detailed annealing studies were performed to make clear the phase formation process in K_xFe_ySe₂. Compatible observations were found in temperature-dependent X-ray diffraction patterns, back-scattered electron images and corresponding electromagnetic properties, which proved that good superconductivity performance was closely related to the microstructure of superconducting component. Analysis based on the scaling behavior of flux pinning force indicated that the dominant pinning mechanism was ΔT _c pinning and independent of connectivity. The annealing dynamics studies were also performed, which manifested that the humps in temperature-dependent resistance curves were induced by competition between the metallic/superconducting and the semiconducting/insulating phases.