Molecular orientational melting within a lead-halide octahedron framework: The order-disorder transition in CH3NH3PbBr3

K. L. Brown*, S. F. Parker, I. Robles Garcia, S. Mukhopadhyay, V. Garcia Sakai, C. Stock

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Lead-halide organic-inorganic perovskites consist of an inorganic host framework with an organic molecule occupying the interstitial space. The structure and dynamics of these materials have been heavily studied recently due to interest in their exceptional photovoltaic properties. We combine inelastic neutron scattering, Raman spectroscopy, and quasielastic neutron scattering to study the temperature dependent dynamics of the molecular cation in CH3NH3PbBr3. By applying high resolution quasielastic neutron scattering, we confirm the [CH3NH3](+) ions are static in the low temperature orthorhombic phase yet become dynamic above 150 K where a series of structural transitions occur. This molecular melting is accompanied by a temporal broadening in the intramolecular modes probed through high energy inelastic spectroscopy. Simultaneous Raman measurements, a strictly vertical bar Q vertical bar = 0 probe, are suggestive that this broadening is due to local variations in the crystal field environment around the hydrogen atoms. These results confirm the strong role of hydrogen bonding and also a coupling between molecular and framework dynamics.

Original languageEnglish
Article number174111
Number of pages10
JournalPhysical Review B
Volume96
Issue number17
DOIs
Publication statusPublished - 22 Nov 2017

Keywords

  • LOW-TEMPERATURE PHASE
  • LIQUID-CRYSTAL FILMS
  • HYBRID PEROVSKITES
  • CATION REORIENTATION
  • NEUTRON-SCATTERING
  • ORGANIC CATIONS
  • SINGLE-CRYSTAL
  • PLASTIC PHASE
  • SOLAR-CELLS
  • METHYLAMMONIUM

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