Novel phases and superconductivity of tin sulfide compounds.

Tin sulfides, Sn<italic>x</italic>S<italic>y</italic>, 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<italic>x</italic>S<italic>y</italic> 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 P 3 ¯ m 1 symmetry remains stable up to 28 GPa. Another ambient phase, SnS, experiences a series of phase transformations including <italic>α</italic>-SnS to <italic>β</italic>-SnS at 9 GPa, followed by <italic>β</italic>-SnS to <italic>γ</italic>-SnS at 40 GPa. <italic>γ</italic>-SnS is a new high-pressure metallic phase with P m 3 ¯ m space group symmetry stable up to 100 GPa, which becomes a superconductor with a maximum T<italic>c</italic> = 9.74 K at 40 GPa. Another new metallic compound, Sn3S4 with I 4 ¯ 3 d space group symmetry, is predicted to be stable at pressures above 15 GPa, which also becomes a superconductor with relatively high T<italic>c</italic> = 21.9 K at 30 GPa. [ABSTRACT FROM AUTHOR]