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New Phase Transitions Driven by Soft Phonon Modes for CsPbBr 3 : Density Functional Theory Study
Author(s) -
Ben Sadok Raouia,
Hammoutène Dalila,
Plugaru Neculai
Publication year - 2021
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.202000289
Subject(s) - phonon , condensed matter physics , ferroelectricity , dielectric , raman spectroscopy , band gap , phase transition , soft modes , octahedron , materials science , density functional theory , semiconductor , ground state , polarization (electrochemistry) , crystal structure , chemistry , optics , physics , atomic physics , computational chemistry , crystallography , optoelectronics
Using first‐principles lattice dynamics calculations, new phase transitions driven by soft phonon modes in CsPbBr 3 , 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 1symmetry 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 thePbBr 6octahedra 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 PbBr bond length and the angle of rotation of thePbBr 6octahedron. 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.