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@ARTICLE{Songvilay:859544,
      author       = {Songvilay, M. and Bari, M. and Ye, Z.-G. and Xu, Guangyong
                      and Gehring, P. M. and Ratcliff, W. D. and Schmalzl, K. and
                      Bourdarot, F. and Roessli, B. and Stock, C.},
      title        = {{L}ifetime-shortened acoustic phonons and static order at
                      the {B}rillouin zone boundary in the organic-inorganic
                      perovskite {CH} 3 {NH} 3 {P}b{C}l 3},
      journal      = {Physical review materials},
      volume       = {2},
      number       = {12},
      issn         = {2475-9953},
      address      = {College Park, MD},
      publisher    = {APS},
      reportid     = {FZJ-2019-00396},
      pages        = {123601},
      year         = {2018},
      abstract     = {Lead halide hybrid perovskites consist of an inorganic
                      framework hosting a molecular cation located in the
                      interstitial space. These compounds have been extensively
                      studied as they have been identified as promising materials
                      for photovoltaic applications with the interaction between
                      the molecular cation and the inorganic framework implicated
                      as influential for the electronic properties. CH3NH3PbCl3
                      undergoes two structural transitions from a high temperature
                      cubic unit cell to a tetragonal phase at 177 K and then a
                      subsequent orthorhombic transition at 170 K. We have
                      measured the low-frequency lattice dynamics using neutron
                      spectroscopy and observe an energy broadening in the
                      acoustic phonon linewidth towards the high-symmetry point
                      QX=(2,12,0) when approaching the transitions. Concomitant
                      with these zone boundary anomalies is a hardening of the
                      entire acoustic phonon branch measured in the q→0 limit
                      near the (2, 0, 0) Bragg position with decreasing
                      temperature. Measurements of the elastic scattering at the
                      Brillouin zone edges QX=(2,12,0),QM=(32,12,0), and
                      QR=(32,32,52) show Bragg peaks appearing below these
                      structural transitions. Based on selection rules of neutron
                      scattering, we suggest that the higher 177 K transition is
                      displacive with a distortion of the local octahedral
                      environment and the lower transition is a rigid tilt
                      transition of the octahedra. We do not observe any critical
                      broadening in energy or momentum, beyond resolution, of
                      these peaks near the transitions. We compare these results
                      to the critical properties reported near the structural
                      transitions in other perovskites and particularly CsPbCl3
                      [Y. Fujii, S. Hoshino, Y. Yamada, and G. Shirane, Phys. Rev.
                      B 9, 4549 (1974)]. We suggest that the simultaneous onset of
                      static resolution-limited Bragg peaks at the zone boundaries
                      and the changes in acoustic phonon energies near the zone
                      center is evidence of a coupling between the inorganic
                      framework and the molecular cation. The results also
                      highlight the importance of displacive transitions in
                      organic-inorganic hybrid perovskites.},
      cin          = {JCNS-2 / PGI-4 / JARA-FIT / JCNS-ILL},
      ddc          = {530},
      cid          = {I:(DE-Juel1)JCNS-2-20110106 / I:(DE-Juel1)PGI-4-20110106 /
                      $I:(DE-82)080009_20140620$ / I:(DE-Juel1)JCNS-ILL-20110128},
      pnm          = {144 - Controlling Collective States (POF3-144) / 524 -
                      Controlling Collective States (POF3-524) / 6212 - Quantum
                      Condensed Matter: Magnetism, Superconductivity (POF3-621) /
                      6213 - Materials and Processes for Energy and Transport
                      Technologies (POF3-621) / 6G4 - Jülich Centre for Neutron
                      Research (JCNS) (POF3-623)},
      pid          = {G:(DE-HGF)POF3-144 / G:(DE-HGF)POF3-524 /
                      G:(DE-HGF)POF3-6212 / G:(DE-HGF)POF3-6213 /
                      G:(DE-HGF)POF3-6G4},
      experiment   = {EXP:(DE-Juel1)ILL-IN12-20150421},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000452319500002},
      doi          = {10.1103/PhysRevMaterials.2.123601},
      url          = {https://juser.fz-juelich.de/record/859544},
}