Probing lattice vibrations of stabilized CsPbI₃ polymorphs via low-frequency Raman spectroscopy

Abstract

<p>The low-frequency Raman spectra of metal-halide perovskites are reported using a combination of a 976 nm laser and nanoconfinement to stabilize the crystals against temperature-induced polymorph transitions and humidity-induced degradation.</p>

Finite‐Temperature Dynamics in Cesium Lead Iodide Halide Perovskite

“…Let us now pay attention to the case of k 2 = −0.00258 (Figure 6c), which we believe to be the closest one to the real CsPbI 3 material, as aforementioned. One can first note that, for the smallest temperatures, v Rx,MF, Pnma and v Rx,HF, Pnma adopt values close to 24.0 and 34.0 cm −1 , respectively, which are very close to the first-principles results of 26.0 and 35.0 cm −1 for two low-in-frequency modes involving both iodine octahedra and displacements of Cs cations, [36] which attests of the accuracy of our numerical tools. Moreover, our results for the case of k 2 = −0.00258 is in overall qualitatively similar to that of k 2 = −0.00698 (Figure 6b) except for two noticeable features: v Mz,LF, P4/mbm and v Rx,LF, P4/mbm adopt very small values of about 8.0 and 1.0 cm −1 in the entire range of the intermediate P4/mbm phase.…”

Polymorphism in metal halide perovskites

“…77 Using lowfrequency Raman spectroscopy to monitor phonon modes in a CsPbI 3 crystalline film deposited via drop casting from dimethyl sulfoxide onto a SiO 2 substrate, we found this transition to occur within 6 minutes of air exposure ( Figure 4B). 78 The transition itself was rapid and completed within time resolution limit of the measurements (e.g. within one minute).…”

Pressure‐Induced Perovskite‐to‐non‐Perovskite Phase Transition in CsPbBr3

“…To rationalize the impact of isostatic pressing on the optical properties of CsPbBr 3 , we perform confocal Raman spectroscopy and assess the vibrational modes of the metal halide sublattice before and after compression ( Figures 3 ,a ). 1D δ‐CsPbBr 3 (as obtained after pressing) exhibits a series of low‐energy vibrational modes, with most intense peaks at 144 cm −1 (17.8 meV) and 63 cm −1 (7.8 meV), attributed to asymmetric Br−Pb−Br stretching and coupled Br−Pb−Br bending/stretching, respectively [32,49] . In contrast, the 3D γ‐CsPbBr 3 phase (present before pressing) features a broad central Raman peak, a strong peak around 72 cm −1 , along with a very weak peak at 127 cm −1 , assigned to local polar fluctuations and octahedral distortion and stretching, respectively [50–52] .…”