The origin of the $\sim$40 and $\sim$30 K superconducting phases inthe metal-intercalated FeSe superconductors is still unclear. Wereport the synthesis ofK$_{0.3}$(NH$_3$)$_y$(FeSe$_{1-x}$Te$_x$)$_2$ andK$_{0.6}$(NH$_3$)$_y$(FeSe$_{1-x}$Te$_x$)$_2$ with $x$=0-0.6 byusing the liquid ammonia method at room temperature. Thesuperconducting transition temperature $T_{\rm~c}$ of the formerremains about 43 K for all the nominal Te content less than 0.3,while that of the latter is about 30 K and obviously decreases withTe doping. Superconductivity disappears for $x\geq$0.4 in bothsystems. Except for the different chemical pressure induced bysubstitution of Te for Se in both systems, we also observed distinctexternal pressure effect on superconductivity for both systems, withmuch more efficiency of suppressing $T_{\rm~c}$ by external pressurein the former system. These dramatic differences of both chemicaland external pressure effects on $T_\text{c}$ between the $\sim$30 and$\sim$40 K superconducting phases revealed that the existence of thetwo superconducting phases can be ascribed to the moderate andnegligible coupling between FeSe layers, respectively.
This work was supported by the National Natural Science Foundation of China (Grants Nos. 11374252, 11604278, 11534010, and 91422303), the National Key Rrm D Program of the MOST of China (Grant No. 2017YFA0303001), the Hefei Science Center Chinese Academy Sciences (Grant No. 2016HSC-IU001), and the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (Grant No. XDB04040100).
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