Raman Scattering Studies of the Structural Phase Transitions in Single-Crystalline CH₃NH₃PbCl₃

Parallel Alignment of Methylammonium Cations in an Orthorhombic CH3NH3PbCl3 Single Crystal Observed by Polarized Micro-Raman Scattering Spectroscopy

“…However, the MA orientations in a MAPbX 3 single crystal have not yet been directly observed. It has been known that polarized Raman scattering spectroscopy is a powerful tool for studying the symmetry configuration of molecules and crystals. − For HOIPs, Raman spectra of MAPbX 3 were extensively studied for understanding MA molecular vibrations from which symmetry properties and structural phase transition information could be obtained. − ,, In this work, we report the direct experimental evidence of a specific directional orientation of MA ions and their parallel alignment in a MAPbCl 3 single crystal in the orthorhombic phase by using polarized Raman scattering spectroscopy. Our observation is completely consistent with DFT calculations, showing that the MA ions are indeed aligned toward a special direction of the crystal and the alignment of the MA ions leading to ferroelectricity in principle could be stabilized in typical HOIP samples.…”

“…CH 3 NH 3 PbX 3 has a crystal structure in which a methylammonium (MA, CH 3 NH 3 + ) ion is surrounded by a skeleton formed by eight octahedra of PbX 6 . The interaction between MA cations and surrounding PbX 6 dominantly affects the electronic and mechanical properties of MAPbX 3 , one of which is the temperature-dependent structural phase transition behavior observed in HOIPs. − For example, MAPbCl 3 undergoes a phase transition from a cubic ( Pm 3 m ) to a tetragonal ( P 4/ mmm ) structure at 179 K and a subsequent transition from a tetragonal to an orthorhombic ( P 222 1 ) structure at 172 K, − and the transitions are shown to be closely associated with the change in the hydrogen bonding characteristics of the material. ,− …”

“…Significant attention is also paid to the spatial configuration of the MA ions in MAPbX 3 . An isolated MA molecule has C 3 v point group symmetry, and interestingly, as a cation in HOIP it is reported that it can still be treated as an isolated molecule in terms of symmetry analysis. ,− Considering that the MA ions strongly interact with their surroundings via hydrogen bonding and that a MA ion has a finite dipole moment, the MA ions are thought to play an important role in the structural and electrostatic/electrodynamic properties of HOIP materials. The aforementioned temperature-dependent phase transitions of MAPbX 3 involve tilting and deformation of inorganic PbX 6 octahedra, which is closely associated with the orientations of MA cations in a PbX 6 cage. ,− In fact, the limitation of the degree of freedom of organic cations by the spatial alignment can greatly affect the electronic properties and device performance.…”

Anharmonic IR spectra of solvated ammonium and aminium ions: resemblance between water and bisulfate solvations

“…[1][2][3][4][5][6][7][8] The methylammonium ion (CH 3 NH 3 + , or denoted as MA-H + ) and related aminium species have been found to play an essential role in the organic-inorganic halide perovskite, which is a promising solar cell material. [9][10][11][12][13][14][15][16][17][18][19][20][21][22] And in the recent two decades, the amino-containing gas-phase species have attracted more attention because of their involvement in the new particle formation (NPF) of aerosols in the atmosphere. [23][24][25][26][27][28][29][30][31][32][33] From the aspect of atmospheric chemistry, the combination of these alkaline molecules with sulfuric acid forms cluster particles that are anticipated to be the seeds for aerosol nucleation.…”

“…† The simulated vibrational spectra were obtained by broadening each absorption peak with the Lorentzian function, where the full-width-athalf-maximum (FWHM) was set as 30 cm À1 for the NH stretching modes and 10 cm À1 for other bands according to the experimental observations for aminium species. 22…”