Annealing Effect on Microstructure and Superconductivity of KxFeySe2   Synthesized by an Easy One-step Method
  High-quality superconducting KxFeySe2 single crystals were synthesized using an easy one-step method. Detailed annealing studies were performed to make clear the phase formation process in KxFeySe2. 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 close related to the microstructure of superconducting component. Analysis based on the scaling behavior of flux pinning force indicated that the dominant pinning mechanism was delta(Tc) pinning and independent of connectivity. The annealing dynamics studies were also performed, which manifested that the humps in temperature-dependent resistance (RT) curves were induced by competition between the metallic/superconducting and the semiconducting/insulating phases. 
W. Zhou, X. Li, X. Zhou, F. F. Yuan, Y. Ding, J. C. Zhuang, Y. Sun, H.   L. Zhou, Z. X. Shi
cond-mat.supr-con