Crystal structure of a large cubic tin monosulfide polymorph: an unraveled puzzle

Abstract

We present the atomic arrangement of 64 atoms within a simple cubic unit cell crystalline structure of lattice constant 11.6 Å, observed in tin sulfide (SnS) thin films. Thin films of 260 or 550 nm in thickness were deposited at 17 °C from a chemical bath containing tin(II) chloride and thioacetamide. The X-ray diffraction (XRD) patterns of these thin films are consistent with those of a simple cubic structure of lattice constant 11.600 ± 0.025 Å (as-prepared) or 11.603 ± 0.007 Å (after 400 °C heating). The said recently discovered “π-SnS” structure was adopted from previous reports, using the present, newly acquired experimental data to obtain the atomic positions. This structural assignment unravels a puzzle originated by inconsistencies among the XRD patterns of some SnS thin films and nanocrystals prepared via certain chemical routes, and the zinc blende, rock salt or pseudo-tetragonal structures previously assigned to them. In addition to its relevance as a stable solar cell material, salient features of this SnS polymorph arising from its lack of centro-symmetry are discussed.