New Phase Transitions Driven by Soft Phonon Modes for CsPbBr3: Density Functional Theory Study. Issue 2 (18th October 2020)

• Record Type: Journal Article
• Authors: Ben Sadok, Raouia; Hammoutène, Dalila; Plugaru, Neculai
• Is Part Of: Physica status solidi. Volume 258:Issue 2(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-10-18
• Subjects: CsPbBr3 -- dielectric properties -- electronic properties -- phase transitions -- soft phonons; Solid state physics -- Periodicals; Solids -- Periodicals; Atomic structure -- Periodicals; 530.41
• DOI: 10.1002/pssb.202000289
• Languages: English
• ISSNs: 0370-1972

Abstract

Abstract : Using first‐principles lattice dynamics calculations, new phase transitions driven by soft phonon modes in CsPbBr3, from the high‐symmetry cubic structure P m 3 m to hypothetical structures, are predicted. The structural, electronic, and dielectric properties of the new phases are determined. A ferroelectric phase with P m c 2 1 symmetry is found to be more stable than the experimentally observed phases. It is suggested that it is a good candidate as a ground state. It is demonstrated that the out‐of‐phase rotations of the PbBr 6 octahedra determine a more stable crystal lattice than the in‐phase rotations. All predicted structures show semiconductor character, with bandgap values between 1.44 and 1.87 eV. The bandgap increases with increasing PbBr bond length and the angle of rotation of the PbBr 6 octahedron. The dielectric tensor, Born effective charges, and spontaneous polarization are also calculated. The optical dielectric constant shows low sensitivity to unit cell volume and symmetry of the structures. The Born effective charges are sensitive to lattice symmetry, as they are related to the directions of charge transfer between ions, whereas the cell volume has no significant effect on their values. The infrared and Raman vibration modes of the three structures are also determined. Abstract : Using density functional theory calculations, new phase transitions driven by soft mode condensation from the Pm3m symmetry to related structures are predicted for CsPbBr3 . The structural, electronic, and dielectric properties of the new phases are reported. The ferroelectric distortion is found less favorable than the antiferrodistortive one. PbBr6 octahedra out‐of‐phase rotations may determine more stable structures than the in‐phase rotations.