Abstract
The coupling between the organic CH3NH3+ cations and inorganic perovskite PbBr3- framework in a large single crystal of (CH3NH3)PbBr3 weighting 13 g was studied using neutron diffraction and inelastic neutron scattering. Two lattice incommensurate (ICM) phases were found, one at higher temperatures, marked ICMHT, which appeared between 147 and 135 K. The second one, marked ICMLT, developed below 143 K and remained at 75 K. The transition from the ICMLT to ICMHT phase upon warming gave rise to extremely large lattice shrinking, followed by extremely large lattice expansion of the tetragonal basal plane of the PbBr3 lattice. There was a progressive decrease in the width of the Bragg peaks from the PbBr3 lattice upon warming, which can be described using a critical exponent for each type of Bragg peak to show complete ordering of the atoms into a (CH3NH3)PbBr3 lattice at 194 K. (CH3NH3)PbBr3 exhibits six definitive acoustic-like phonon branches at 75 K. The six branches renormalizes into two at 200 K, with the frequencies of both the transverse and longitudinal modes greatly enhanced. The asymmetric structure of the CH3NH3 ions helps to understand the observed behaviors.
Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
