Superconductivity in potassium and ammonia co-intercalated FeSe1-xTex

The origin of the ~40 and ~30 K superconducting phases in the metal-intercalated FeSe superconductors is still unclear. We report the synthesis of K0:3(NH3)y(FeSe1−xTex)2 and K0:6(NH3)y(FeSe1−xTex)2 with x=0-0.6 by using the liquid ammonia method at room temperature. The superconducting transition temperature Tc of the former remains 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 with Te doping. Superconductivity disappears for x ≥0.4 in both systems. Except for the different chemical pressure induced by substitution of Te for Se in both systems, we also observed distinct external pressure effect on superconductivity for both systems, with much more efficiency of suppressing Tc by external pressure in the former system. These dramatic differences of both chemical and external pressure effects on Tc between the ~30 and ~40 K superconducting phases revealed that the existence of the two superconducting phases can be ascribed to the moderate and negligible coupling between FeSe layers, respectively.