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

Masaru Nakamura; Yoshitaka Matsushita

doi:10.1007/s10853-026-12930-6

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

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Masaru Nakamura, Yoshitaka Matsushita. Polymorphism in high-temperature GeS2: identification and characterization of two distinct polymorphs. Journal of Materials Science. 2026, (), 10.1007/s10853-026-12930-6. https://doi.org/10.1007/s10853-026-12930-6

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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.