K-x(C2H8N2)yFe(2-z)S(2): synthesis, phase structure and correlation between K+ intercalation and Fe depletion

摘要

We report a new layered FeS compound K-x(C2H8N2)yFe(2-z)S(2) synthesized by intercalating K and C2H8N2 into tetragonal FeS via a simple sonochemical route. This new compound crystallizes in a body-centered tetragonal unit cell, with the K(C2H8N2) and FeS layers alternately stacking along the c direction. The nominal concentration of K, x, can be adjusted from 0.25 to 0.45, and the lattices a and c contract from 3.6971(9) and 20.667(5) angstrom to 3.691(1) and 20.566(7) angstrom, respectively. When x 0.45, K reacts with FeS directly to form K2Fe4S5 impurity. It is found that the C2H8N2 molecule has been co-intercalated in between the FeS layers along with K, evidenced by its content, y, having a linear dependence with x. Measurements indicate that K-x(C2H8N2)(y)Fe2-zS2 is a semiconductor and it shows a weak ferrimagnetism below 50 K. More importantly, Fe depletion resulting from the charged K+ intercalation was revealed by composition analysis, which leads to the formation of disordered Fe vacancies in the FeS layers and hence hinders the enhancement of original superconductivity in the FeS parent.