Polymorph selectivity through halide precursors in the synthesis of metal chalcogenides nanomaterials

Controlling the crystal structure of a material remains a fundamental challenge in nanomaterials synthesis particularly when targeting metastable polymorphs with unique electrical, optical, magnetic, or catalytic properties. These structural variations play a critical role in applications across medicine, electronics, energy, and environmental science. While computational studies have predicted a wide range of possible crystal structures for many compounds, a significant number remain experimentally unrealized, especially metastable phases that are not thermodynamically favored under standard conditions. This project investigates synthetic strategies to intentionally stabilize metastable polymorphs of tin-based compounds (SnS), using a systematic trial and error approach. Key reaction parameters including the metal halide precursor, amine type, sulfur reagent, temperature, and reaction time were varied to examine their influence on polymorph formation. Inspired by previous findings in manganese-based systems (MnS), where the halide type strongly affected polymorph selectivity, we tested whether similar trends could be observed in tin systems and whether additional variables could be used to steer the reaction pathway. Crystal structures were characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD provided information on bulk phase composition, while TEM offered insight into nanoscale morphology and crystallinity. In tin sulfide systems, reaction conditions commonly yielded orthorhombic phases, though mixtures and occasional metastable forms, such as the pi-cubic structure, were also observed under specific conditions. These results suggest that subtle changes in precursor chemistry or reaction environment can dramatically influence structural outcomes. This study adds to the growing effort to control how materials crystallize, offering small but important steps toward more precise crystal engineering at the nanoscale.