New Phase Transitions Driven by Soft Phonon Modes for CsPbBr₃: Density Functional Theory Study

Abstract

New phase transitions driven by the soft mode condensation from the Pm3m structure to related subgroup variants are predicted for CsPbBr3 from DFT calculations, performed by Raouia Ben Sadok and co‐workers (see article number http://doi.wiley.com/10.1002/pssb.202000289). The Pb2+ cation has only a small contribution to the structural distortions, which leaves an important role to Br– and Cs+ displacements in the structure stabilization. The ferroelectric distortion is found less favorable than the antiferrodistortive one, where the out‐of‐phase rotations of the PbBr6 octahedra may determine more stable structures than the in‐phase rotations. Nevertheless, the polar structure Pmc21 appears to be a candidate as ground state. All predicted structures show semiconductor character, with the band gap increasing when increasing the Pb–Br bond length and the angle of rotation of the PbBr6 octahedra. The optical dielectric constant and Born effective charges show low sensitivity to unit cell volume.