Novel phases and superconductivity of tin sulfide compounds

Tin sulfides, Sn S , are an important class of materials that are actively investigated as novel photovoltaic and water splitting materials. A first-principles evolutionary crystal structure search is performed with the goal of constructing the complete phase diagram of Sn S and discovering new phases as well as new compounds of varying stoichiometry at ambient conditions and pressures up to 100 GPa. The ambient phase of SnS₂ with $$ symmetry remains stable up to 28 GPa. Another ambient phase, SnS, experiences a series of phase transformations including α-SnS to β-SnS at 9 GPa, followed by β-SnS to γ-SnS at 40 GPa. γ-SnS is a new high-pressure metallic phase with $$ space group symmetry stable up to 100 GPa, which becomes a superconductor with a maximum T = 9.74 K at 40 GPa. Another new metallic compound, Sn₃S₄ with $$ space group symmetry, is predicted to be stable at pressures above 15 GPa, which also becomes a superconductor with relatively high T = 21.9 K at 30 GPa.