Pressure-induced strong ferroelectric polarization in tetra-phase perovskite CsPbBr3.

Ab initio simulations combined with the Berry phase method are employed to investigate ferroelectric polarization of tetragonal CsPbBr3 crystals by applying hydrostatic pressure varying from 0 to 19 GPa; we find that the object research belongs to the P4mm space group. The calculated results show that the materials undergo a paraelectric-ferroelectric phase transition when the pressure increases to a critical value 15 GPa. The polarization is strongly enhanced and attains a high value of about 23 μC cm-2, owing to the increase in the ionic and electric contributions to the polarization under compressive strain. We present a detailed theoretical investigation to analyze the origin of polarization. The ionic polarization is mainly ascribed to the central displacements of Pb2+ cations and Br- anions induced by a highly distorted octahedral PbBr6- framework. Electronic structure calculations suggest that asymmetric hopping p orbital electrons of Br(3) ions are responsible for the enhancement in electric polarization. These discoveries suggest that tetragonal CsPbBr3 has significant potential in future ferroelectric applications, and this can broaden the application field from optoelectronics to ferroelectrics.