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arXiv · 2611.01830

Temperature-Dependent Raman Signatures of Local Symmetry Breaking in Vacancy Double Perovskite Cs$_2$SnI$_6$

Tomke E. Glier·Nicholas J. Weadock·Julian A. Vigil·Cole Shank·Xixi Qin·Gabriel J. Graf·Hemamala I. Karunadasa·Volker Blum·Michael F. Toney·Dmitry Reznik
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Abstract

Understanding and controlling the optical, thermal and mechanical properties of K$_2$PtCl$_6$-type double perovskites is essential for the design of lead-free, high-performance thermoelectric and optoelectronic materials. In this study, we investigate Cs$_2$SnI$_6$ using temperature-dependent near-resonance Raman scattering, complemented by density functional theory-based phonon calculations. The appearance of Raman-forbidden phonon modes in the Raman response at cryogenic temperatures provides strong evidence for local symmetry breaking that does not develop into a global structural phase transition. Through detailed analysis of phonon intensities, energies, and spectral lineshapes, we characterize the temperature evolution of the symmetry-broken structural response of Cs$_2$SnI$_6$. Below 200 K, multi-phonon scattering is strongly enhanced, and symmetry-forbidden Raman modes emerge. The temperature dependence of phonon intensities follows a phenomenological Arrhenius behavior, revealing an activation energy of 15-20 meV. These results establish temperature-dependent Raman spectroscopy as a sensitive probe of local structural distortions and anharmonic structural dynamics in Cs$_2$SnI$_6$, providing a robust experimental basis for discussing the microscopic origins of symmetry breaking and electron-phonon coupling in halide double perovskites.

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Tomke E. Glier, Nicholas J. Weadock, Julian A. Vigil, Cole Shank, Xixi Qin, Gabriel J. Graf, Hemamala I. Karunadasa, Volker Blum, Michael F. Toney, Dmitry Reznik. 2026-11-01. Temperature-Dependent Raman Signatures of Local Symmetry Breaking in Vacancy Double Perovskite Cs$_2$SnI$_6$. https://doi.org/10.1016/j.newton.2026.100724

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