High-Pressure Structural Phase Transformation of Ferroelectric Bis-benzylammonium Lead Tetrachloride Studied by Raman Spectroscopy and X-ray Diffraction

Abstract

Hybrid organic−inorganic 2-D perovskite bis-benzylammonium lead tetrachloride (BALC) is a room-temperature ferroelectric semiconductor. A structural phase transformation from the ambient Cmc2 1 structure is evident at 1.8 GPa from the Raman spectra, and this is confirmed by our high-pressure Xray diffraction studies that point to a centrosymmetric structure Cmcm at 1.7 GPa. The ambient phase is recoverable on decompression. Using density functional theory calculations, we have studied the intermolecular and intramolecular vibrations to get an idea of the structural changes as a function of pressure. The high-pressure transition is identified to be due to a distortion in the PbCl 6 octahedra and a conformation change in the molecule. There are several discontinuities, broadening, and splitting of the Raman bands, corresponding to NH 3 units above 1.8 GPa that point to rearrangements in the hydrogen bond network in the new phase. The ambient structure shows anisotropic compressibility, with a bulk modulus of 14.5 ± 0.33 GPa. As the new phase is a centrosymmetric structure, BALC is expected to lose its ferroelectricity above ∼1.8 GPa.

Spacer-Dependent and Pressure-Tuned Structures and Optoelectronic Properties of 2D Hybrid Halide Perovskites

“…The mechanical compression of perovskites can result in modification of the Pb–X bond lengths and angles in the inorganic lattice. The subsequent change in orbital overlap results in modification of the observed optoelectronic properties. − The effects of high pressure on 3D HOIPs, such as MAPbI 3 and FAPbI 3 , have been studied extensively. − More recently, high-pressure studies have been conducted on 2D lead-halide-based HOIPs, mostly focused on those with BA (butylammonium), PMA (phenyl methylammonium), or PEA (phenyl ethylammonium) spacer cations. − However, the effects of different spacer cations on the pressure-tuned optoelectronic properties are still not well understood. For example, the PMA and PEA spacer cations differ only by a CH 2 group, yet the high-pressure behaviors of (PMA) 2 PbI 4 and (PEA) 2 PbI 4 are drastically different.…”

2-Chloroethylamine·trifluoromethanesulfonate combined with 18-crown-6: a ferroelectric with excellent dielectric switching properties

“…We performed a variable temperature Raman spectroscopy test in order to investigate the overall properties of compound 1 in relation to its temperature dependence. 37,38 Fig. S6 † shows the Raman spectra of compound 1 in the 3500-200 cm −1 region.…”

2D Antiferroelectric Hybrid Perovskite with a Large Breakdown Electric Field And Energy Storage Density

“…These phase transitions have also been confirmed optically by using Raman spectroscopy as shown in Figure 1e, where typical Raman peak positions (such as 14, and 35 cm −1 , etc.,) show changes across the phase transition near 150 K and 290 K as shown in Figure 1f. Note these low‐wavenumber Raman peaks mainly reflect the vibration modes of the inorganic [PbBr 6 ] octahedron, which include the libration of Pb 2 + at 14 cm −1 , [ 29 ] the bending and twisting of Pb–Br bonds in between 25 cm −1 and 80 cm −1 , and the stretching of Pb–Br bonds in between 80 and 140 cm −1 . [ 30 ] Generally, these vibration modes tend to soften (red‐shift) with increasing the temperature because of the thermal fluctuations, as the Raman modes at 35, 75, and 130 cm −1 .…”