  The ubiquitous coexistence of majority insulating 245 phases and minority
superconducting (SC) phases in AxFe2-ySe2 (A = K, Cs, Rb, Tl/Rb, Tl/K) formed
by high-temperature routes makes pure SC phases highly desirable for studying
the intrinsic properties of this SC family. Here we report that there are at
least two pure SC phases, KxFe2Se2(NH3)y (x ~ 0.3 and 0.6), determined mainly
by potassium concentration in the K-intercalated iron selenides formed via the
liquid ammonia route. K0.3Fe2Se2(NH3)0.47 corresponds to the 44 K phase with
lattice constant c = 15.56(1) angstroms and K0.6Fe2Se2(NH3)0.37 to the 30 K
phase with c = 14.84(1) angstroms. With higher potassium doping, the 44 K phase
can be converted into the 30 K phase. NH3 has little, if any, effect on
superconductivity. Thus, the conclusions should apply to both K0.3Fe2Se2 and
K0.6Fe2Se2 SC phases. K0.3Fe2Se2(NH3)0.47 and K0.6Fe2Se2(NH3)0.37 stand out
among known superconductors as their structures are stable only at particular
potassium doping levels, and hence the variation of Tc with doping is not
dome-like.
