Kx(C2H8N2)yFe2−zS2: synthesis, phase structure and correlation between K+ intercalation and Fe depletion

Abstract

We report a new layered FeS compound K_x(C₂H₈N₂)_yFe_2−zS₂ 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) Å to 3.691(1) and 20.566(7) Å, respectively. When x < 0.25, the parent FeS is residual and 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)_yFe_2−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.