Substitutional Sulfur and Its Vibrational Fingerprints in Sb ₂ Se ₃

The configurational behavior of sulfur in antimony triselenide (SbSe) isinvestigated by combining infrared absorption spectroscopy with density functional theory. Four sulfur‐related local vibrational modes (LVMs) are identified at 249, 273, 283, and 312 cm −1 in melt‐grown single crystals prepared from SbSe granulate. Their assignment to sulfur is confirmed through controlled indiffusion experiments using SbS and elemental sulfur, as well as isotope‐substitution studies with S, which produce the expected frequency shifts. Polarization‐resolved measurements, together with theoretical calculations of LVMs, demonstrate that the observed spectral features are fully consistent with substitutional sulfur on the three inequivalent selenium sites of SbSe.