Structural and Phase Transition of ZnS to ZnO via Thermal Annealing

<jats:p>Zinc sulfide (ZnS) is a promising material for optoelectronic and photocatalytic applications, yet its thermal stability and phase transformation behavior are crucial for optimizing performance. In this study, ZnS was synthesized hydrothermally and annealed between 20 and 700°C. X-ray diffraction (XRD) confirmed cubic ZnS formation at room temperature, with peaks at 28.5°, 47.5°, and 56.3° corresponding to the (111), (220), and (311) planes. Upon annealing, mixed ZnS/ZnO phases appeared at 445–550°C, while complete transformation to hexagonal ZnO occurred above 600°C, indicated by new peaks at 31.7°, 34.4°, and 36.2° ((100), (002), and (101) planes). Energy-dispersive X-ray spectroscopy (EDX) revealed decreasing sulfur and increasing oxygen content with temperature, confirming oxidation and sulfur loss. Infrared spectroscopy showed the ZnS vibrational mode near 615 cm–1 red-shifted and disappeared at higher temperatures, consistent with the ZnS–ZnO transition. These results explain the temperature-dependent structural evolution of ZnS and highlight its potential for ZnS/ZnO heterostructure-based devices.</jats:p>