Giant thermodynamical optical effect near ferroelastic phase transition point in Cs3Bi2I9 layered crystal

Strong Electron–Phonon Coupling and Self-Trapped Excitons in the Defect Halide Perovskites A3M2I9 (A = Cs, Rb; M = Bi, Sb)

“…This structure possesses hexagonal symmetry, as evidenced by the hexagonal channels filled by Cs cations (Figure a), but sacrifices the corner-sharing octahedra characteristic of perovskite-related structures in favor of disparate [Bi 2 I 9 ] 3– anions (Figure d). Despite its apparent structural simplicity, Cs 3 Bi 2 I 9 exhibits unusual ferroelastic phase transitions and optical properties which are hard to reconcile with its molecular nature. ,− …”

From molecular salt to layered network: cation-driven tuning of band gap, structure, and charge transport in A3Bi2I9 (A = Cs, Rb) perovskites

“…These assigned peak positions are consistent with values reported in previous studies. 35,36 Interestingly, the spectrum appears to lack a distinct peak corresponding to the E 0 (v 11 ) mode, which is expected for the antisymmetric stretching of bridging Bi-I bonds. However, the observed width of the E 00 (v 7 ) peak is broader compared to the E 00 and E 0 peaks assigned to terminal Bi-I bonds.…”

Low-Temperature Heat Capacity of CsPbI3, Cs4PbI6, and Cs3Bi2I9

“…Between 2004 and 2010, a series of studies into the optical behavior of the low-temperature phase of Cs 3 Bi 2 I 9 were furthermore reported by Motsnyi et al − Electron–phonon coupling was studied, as well as exciton–phonon coupling. , Exciton–phonon interaction resulted in the disappearance of the layered structure below the transition temperature. Phonon calculations using VASP were performed by Geng et al Until recently, no report on the low-temperature heat capacity of Cs 3 Bi 2 I 9 had been published, apart from statements on an undetectable anomaly or very small latent heat by Melnikova et al The recent work by Tailor and Satapathi is the first report of a heat capacity curve.…”