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 tinIJII) 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.

Metastable cubic tin sulfide: A novel phonon-stable chiral semiconductor

“…33,34 An initial model of the crystal structure was prepared using the data in Ref. 15, and the atomic positions and cell volume optimized to a force tolerance of 10 2 eV Å 1 . Projector-augmented wave 35 (PAW) core potentials treating the S 3s and 3p and the Sn 5s, 4d, and 5p electrons as valence were used with the PBEsol exchange-correlation functional 21 and a plane-wave cutoff of 550 eV.…”

“…The equilibrium (DFT/PBEsol) lattice constant of 11.506 Å compares well to the value determined from X-ray diffraction at room temperature (11.603 Å). 15 Despite the cubic space group, the internal structure of π-SnS appears highly distorted. This originates from the stereochemical activity of the Sn(II) 5s 2 lone electron pair.…”

“…16 The assignment was further supported by X-ray diffraction data. 15 The cubic phase has reported optical bandgaps ranging from 1.6 to 1.8 eV, 11,13,17 and has been used to make a working solar cell. 18 Starting from the reported crystal structure parameters, we performed a local optimization of the structure (lattice vectors and internal positions) within density-functional theory (DFT) following a quasi-Newton minimization procedure.…”

“…Nonetheless, assignment of a zincblende phase of SnS continued in the literature, 13 until, recently, a new cubic crystal structure was resolved, using electron and X-ray diffraction, corresponding to a 2×2×2 supercell expansion of the rocksalt structure with large internal distortions. 15 The phase has been named π-SnS (see Figure 1).…”

Sulfurization Growth and HCl Etching Processes for Cubic‐Phase SnS Thin Films

“…Until now, most research on SnS for solar cells has been conducted using orthorhombic phase ( Pnma ) SnS thin films. Recently, thin film growth of cubic phase ( P2 1 3 ) SnS with a large lattice constant ( a = 1.15–1.17 nm) by using different growth techniques such as atomic layer deposition, chemical deposition, and thermal evaporation has been reported. For example Sanal et al deposited cubic SnS by chemical deposition and measured the band diagram of Zn(O,S)/cubic SnS by XPS measurement.…”