Low temperature reentrant phase transition in the perovskite type layer compound (C₃H₇NH₃)₂PbCl₄

Synthesis, vibrational and optical properties of a new three-layered organic–inorganic perovskite (C4H9NH3)4Pb3I4Br6

“…In the low-frequency range (below 200 cm À1 ) a detailed assignment of the Raman bands is difficult because of their great number and their broadness. However, by comparison with previous works reported on similar compounds [26,27] we can distinguish between the Raman bands corresponding to the PbI 2 Br 4 octahedral motion and those associated with the C 4 chains. The bands observed between 400 and 3500 cm À1 in the Raman and infrared spectra are assigned to internal modes of the cations.…”

X-ray diffraction, vibrational and photoluminescence studies of the self-organized quantum well crystal H3N(CH2)6NH3PbBr4

“…The Raman study was focused on the 20-250 cm À1 frequency range which includes librational and translational vibrational modes of the organic and inorganic groups and of the Pb-Br stretching modes. Raman scattering by vibration modes associated with stretching and angular deformations of the organic cations is expected in the 400-4000 cm À1 frequency range [13,14]. However, a strong and broad luminescence probably due to impurity or defect states occurs in this frequency range which makes the Raman signal hardly detectable.…”

“…However, by comparison with the PbCl and PbBr-based perovskites, we may propose a tentative assignment of the observed bands. Indeed, by comparing C 3 PbBr 4 [13] and 2C 3 PbCl 4 [14], it clearly appears that the bands located at 55 and 88 cm À1 are due to Pb-Br stretching modes, and the peaks at 110 and 120 cm À1 are assigned to the organic cation motions. (Fig.…”

“…(Fig. 3) The assignment of the internal modes of the organic cations, observed in the infrared spectra, is based on the comparison with the well-documented spectra of the homologous compounds [13,14]. The broad absorption bands in the 2500-3500 cm À1 range are due to NH 3 stretching modes.…”

Optical properties and ab initio study on the hybrid organic–inorganic material [(CH3)2NH2]3[BiI6]

“…Raman scattering by vibration modes associated with stretching and angular deformations of the organic cations is expected in the 400-4000 cm À1 frequency range [22,23], however a strong and broad luminescence occurs in this frequency range which makes the Raman signal hardly detectable. Therefore we have recorded infrared absorption spectrum, which displays the characteristic bands of the (CH 3 ) 2 NH 2 cations.…”