Understanding doping, vacancy, lattice stability and superconductivity   in KxFe2-ySe2
  Metal-intercalated iron selenides are a class of superconductors that have received much attention but are less understood in comparison with their FeAs-based counterparts. Here, the controversial issues such as Fe vacancy, the real phase responsible for superconductivity, and lattice stability have been addressed based on first-principles calculations. New insights into the distinct features in terms of carrier doping have been revealed. 
Yu Liu, Gang Wang, Tianping Ying, Xiaofang Lai, Shifeng Jin, Ning Liu,   Jiangping Hu and Xiaolong Chen
cond-mat.supr-con cond-mat.mtrl-sci