Polymorphism in high-temperature GeS2: identification and characterization of two distinct polymorphs

Abstract High-temperature (HT-) GeS 2 , a promising layered 2 D material, has long been considered a single crystallographic phase. Here, we report the definitive identification of two distinct polymorphs, designated Polymorph A and B. A comprehensive structural and optical characterization revealed their contrasting properties. X-ray diffraction analysis showed that while both polymorphs possess a layered structure, their fundamental stacking periodicities are significantly different, with Polymorph B being approximately 6.1% shorter than that of Polymorph A . Furthermore, their Raman spectra, which primarily probe intra-layer vibrations, are completely dissimilar. Intriguingly, Polymorph A aligns with the crystallographically established structure, while the Raman spectrum of Polymorph B matches that widely reported in the literature. This finding resolves a long-standing discrepancy where crystallographic and spectroscopic reports have likely been examining different polymorphs unknowingly. Despite these pronounced structural differences in both inter-layer stacking and intra-layer arrangements, their optical band gaps were found to be nearly identical at ~ 3.32 eV. This work necessitates a fundamental reassessment of the GeS 2 material system and highlights the complex interplay between structure and electronic properties in this layered 2 D material.