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<p>High-temperature (HT-) GeS<sub>2</sub>, a promising layered 2<i>D</i> 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 <i>B</i> being approximately 6.1% shorter than that of Polymorph <i>A</i>. 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 <i>B</i> 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&#xa0;eV. This work necessitates a fundamental reassessment of the GeS<sub>2</sub> material system and highlights the complex interplay between structure and electronic properties in this layered 2<i>D</i> material.</p>

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

  • 期刊论文

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  • 发表日期：

    2026年5月17日

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  • Masaru Nakamura,
  • Yoshitaka Matsushita

摘要

High-temperature (HT-) GeS2, a promising layered 2D 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 GeS2 material system and highlights the complex interplay between structure and electronic properties in this layered 2D material.