Superconductivity and Phase Diagram in (Li${}_{0.8}$Fe${}_{0.2}$)OHFeSe${}_{1-x}$S${}_x$

Abstract

A series of (Li${}_{0.8}$Fe${}_{0.2}$)OHFeSe${}_{1-x}$S${}_x$ (0 $\le$ x $\le$ 1) samples were successfully synthesized via hydrothermal reaction method and the phase diagram is established. Magnetic susceptibility suggests that an antiferromagnetism arising from (Li${}_{0.8}$Fe${}_{0.2}$)OH layers coexists with superconductivity, and the antiferromagnetic transition temperature nearly remains constant for various S doping levels. In addition, the lattice parameters of the both a and c axes decrease and the superconducting transition temperature T${}_c$ is gradually suppressed with the substitution of S for Se, and eventually superconductivity vanishes at $x$ = 0.90. The decrease of T${}_c$ could be attributed to the effect of chemical pressure induced by the smaller ionic size of S relative to that of Se, being consistent with the effect of hydrostatic pressure on (Li${}_{0.8}$Fe${}_{0.2}$)OHFeSe. But the detailed investigation on the relationships between $T_{\mathrm{c}}$ and the crystallographic facts suggests a very different dependence of $T_{\mathrm{c}}$ on anion height from the Fe2 layer or $Ch$-Fe2-$Ch$ angle from those in FeAs-based superconductors.

6 pages, 6 figures