Unifying Low-Frequency Raman and Infrared Signatures across Perovskites
Abstract
Perovskites have been studied for a wide range of applications, from oxide-based ferroelectrics to halide-perovskite photovoltaics. Despite their diverse functionalities, these materials share strong lattice anharmonicity arising from structural instabilities such as polar off-centering and octahedral tilting. These anharmonic distortions strongly influence the low-frequency vibrational response and can be observed in infrared (IR) and Raman spectra. However, low-frequency IR and Raman signatures are typically investigated separately, hindering the development of a unified understanding of vibrational spectroscopy across perovskite classes. In this work, we use machine-learning-based molecular dynamics to simulate the IR and Raman spectra of oxide perovskites (SrTiO3 and BaTiO3), halide perovskites (CsPbBr3, CsSnBr3, and CsGeBr3) and double halide perovskites (Cs2AgAlBr6 and Cs2AgBiBr6). By comparing materials exhibiting polar, tilt-driven and mixed instabilities, we find that polar off-centering leads to enhanced low-frequency IR and dielectric responses, whereas nonpolar modes, particularly octahedral tilting, are associated with Raman central peaks. The strength of the low-frequency features also depends on how strongly the underlying modes couple to polarization or dielectric susceptibility. Finally, we show that the dynamics of these instabilities play an important role, with slow polar reorientations shifting the dielectric response to very low frequencies and overdamped tilting modes producing persistent Raman central peaks. These results establish a unified framework connecting low-frequency IR and Raman spectra to the symmetry, coupling and dynamics of their underlying anharmonic lattice instabilities.
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BibTeX
@misc{berger2026unifying,
title = {{Unifying Low-Frequency Raman and Infrared Signatures across Perovskites}},
author = {Ethan Berger and Erik Fransson and Apinya Ngoipala and Lucas Svensson and Priyanka Deswal and Mehmet Baskurt and Paul Erhart and Julia Wiktor},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.31830},
eprint = {2610.31830},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.31830},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Unifying Low-Frequency Raman and Infrared Signatures across Perovskites
AU - Ethan Berger
AU - Erik Fransson
AU - Apinya Ngoipala
AU - Lucas Svensson
AU - Priyanka Deswal
AU - Mehmet Baskurt
AU - Paul Erhart
AU - Julia Wiktor
PY - 2026
DA - 2026/10/22
PB - arXiv
DO - 10.48550/arxiv.2610.31830
UR - https://arxiv.org/abs/2610.31830
AB - Perovskites have been studied for a wide range of applications, from oxide-based ferroelectrics to halide-perovskite photovoltaics. Despite their diverse functionalities, these materials share strong lattice anharmonicity arising from structural instabilities such as polar off-centering and octahedral tilting. These anharmonic distortions strongly influence the low-frequency vibrational response and can be observed in infrared (IR) and Raman spectra. However, low-frequency IR and Raman signatures are typically investigated separately, hindering the development of a unified understanding of vibrational spectroscopy across perovskite classes. In this work, we use machine-learning-based molecular dynamics to simulate the IR and Raman spectra of oxide perovskites (SrTiO_3 and BaTiO_3), halide perovskites (CsPbBr_3, CsSnBr_3, and CsGeBr_3) and double halide perovskites (Cs_2AgAlBr_6 and Cs_2AgBiBr_6). By comparing materials exhibiting polar, tilt-driven and mixed instabilities, we find that polar off-centering leads to enhanced low-frequency IR and dielectric responses, whereas nonpolar modes, particularly octahedral tilting, are associated with Raman central peaks. The strength of the low-frequency features also depends on how strongly the underlying modes couple to polarization or dielectric susceptibility. Finally, we show that the dynamics of these instabilities play an important role, with slow polar reorientations shifting the dielectric response to very low frequencies and overdamped tilting modes producing persistent Raman central peaks. These results establish a unified framework connecting low-frequency IR and Raman spectra to the symmetry, coupling and dynamics of their underlying anharmonic lattice instabilities.
ER -