Molecular orientational melting within a lead-halide octahedra framework - the order-disorder transition in CH3NH3PbBr3

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 intra-molecular modes probed through high energy inelastic spectroscopy. Simultaneous Raman measurements, a strictly |Q|=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.

(10 pages, 10 figures, to be published in Phys. Rev. B)

References in corpus (8)

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• Giant Rashba Splitting in CH3NH3PbBr3 Organic-Inorganic Perovskite
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Cited by in corpus (8)

• Dynamic Shortening of Disorder Potentials in Anharmonic Halide Perovskites
• Upgrade to the MAPS neutron time-of-flight chopper spectrometer
• Common acoustic phonon lifetimes in inorganic and hybrid lead halide perovskites
• The Effect of Ionic Composition on Acoustic Phonon Speeds in Hybrid Perovskites from Brillouin Spectroscopy and Density Functional Theory
• Decoupled molecular and inorganic framework dynamics in CH${}_3$NH${}_3$PbCl${}_3$
• Lifetime-shortened acoustic phonons and static order at the Brillouin zone boundary in the organic-inorganic perovskite CH${}_3$NH${}_3$PbCl${}_3$
• Lattice dynamics and spin excitations in the metal-organic framework [CH${}_3$NH${}_3$][Co(HCOO)${}_3$]
• Broadband critical dynamics in disordered lead-based perovskites