Rotationally Free and Rigid Sublattices of the Single Crystal Perovskite CH3NH3 PbBr3 (001): The Case of the Lattice Polar Liquid

The dynamic motion, within the lattice of single crystal CH3NH3PbBr3 (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 PbBr3 matrix lattice. From the Br (3)d(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 supports the characterization of CH3NH3PbBr3 as a lattice polar liquid crystal, as CH3NH3PbBr3 does not meet the criteria required for a ferroelectric material.