Rotationally Free and Rigid Sublattices of the Single Crystal Perovskite CH₃NH₃PbBr₃ (001): The Case of the Lattice Polar Liquid

Abstract

The dynamic motion, within the lattice of single crystal CH 3 NH 3 PbBr 3 (001) hybrid halide perovskite, was investigated using powder and single crystal x-ray diffraction, and x-ray photoemission spectroscopy. Single crystal x-ray diffraction studies indicate the methylammonium cation adopts multiple orientations within the crystal, at room temperature, evidence of a disordered methylammonium sublattice within a rigid and ordered PbBr 3 matrix lattice. From the Br 3d 5/2 core level photoemission temperature dependence, an effective Debye temperature of 160 ± 22 K can be estimated, while the Pb 4f 7/2 core-level Debye-Waller factor plots suggest an effective Debye temperature of 202 ± 131 K, indicative of a very rigid lattice along the (001) direction. The combination of x-ray diffraction with temperature dependent x-ray photoemission spectroscopy for bromine and lead core level peaks support the characterization of CH 3 NH 3 PbBr 3 as a lattice polar liquid crystal, as CH 3 NH 3 PbBr 3 does not meet the criteria required for a ferroelectric material.

Learning about the Structural Dynamics of Semiconductor Perovskites from Electron Solvation Dynamics

“…We have assigned these counterintuitive 300 fs dynamics to quantum confinement of charges due to the polaronic potential. Because of the liquid-like response observed in the works of Zhu et al. ,,, and in our 2DE line shape experiments, we suggest that the system forms a glassy, dynamical quantum dot on the time scale of polaron formation. The initially excited system is not a quantum dot, but the polaronically confined system is quantum confined, and hence we refer to it is a “quantum drop”.…”

Surface and dynamical properties of GeI2

“…A quantitative relationship between the XPS intensities and thermal motion of atoms is given by the Debye-Waller model. According to this model, the XPS intensity is an exponentially decaying function of temperature, and this function depends on the core-level's Debye-Waller factor (W (T)) as [11,[31][32][33][34][35][36]:…”

Probing the Electronic Structure of Hybrid Perovskites in the Orientationally Disordered Cubic Phase

“…However, if we use a ferro-ordering of the MA + ions along the (110) direction, the bandgap decreases by 0.04 eV and the 9-fold degeneracy is also lifted. These findings clearly indicate that the orientation of the MA + ion plays an important role in the electronic band structure by reducing the symmetry. − Comparison between experimental and theoretical band structures near the Γ point clearly shows a large discrepancy, the latter giving a gap between the top dispersing valence band and the flat band below it, the gap being ∼0.5–1.0 eV. Since in the cubic phase, orientation of the MA + cations is dynamically disordered (they are almost freely rotating), one has to sample the band structure for all possible orientations.…”