Ferroelectric order in hybrid organic-inorganic perovskite NH4PbI3 with non-polar molecules and small tolerance factor

Abstract

The appropriate theoretical picture of describing the ferroelectric order in hybrid organic-inorganic perovskite remains attractive and under intense debate. We rationalize the interaction between organic molecule sublattice and inorganic frame from first-principles. Through systematic investigations on the NH4PbI3, we show that the non-polar octahedral rotation dominates the process of stabilizing of the lattice with small value of tolerance factor. The direct coupling between molecules is negligible. With the help of hydrogen bonding to the inorganic cage, molecule sublattice will eventually build long-range ferroelectric or anti-ferroelectric order under the constrain of the inorganic cage and further polarize the inorganic frame as the feedback. These results also clarify that to build ferroelectricity the polar molecule is helpful but not crucial. As the general rule for hybrid organic-inorganic perovskite, we identified the fundamental mechanism that can be considered as a critical pre-step forward to further controlling the related physics in functional materials.