Cooperative Nature of Ferroelectricity in Two-Dimensional Hybrid Organic–Inorganic Perovskites

Abstract

Two-dimensional (2D) ferroelectric (FE) hybrid organic− inorganic perovskites (HOIPs) are promising for potential applications as miniaturized flexible ferroelectric/piezoelectric devices. Recently, several 2D HOIPs [e.g., Ruddlensden−Popper type HOIP BA 2 PbCl 4 (BA = C 6 H 5 CH 2 NH 3 + )] were reported to possess room-temperature ferroelectricity. However, the underlying microscopic mechanisms for ferroelectricity in 2D HOIPs remain elusive. Here, by performing first-principles calculations and symmetry mode analysis, we demonstrate that there exists a cooperative coupling between A-site organic molecules and B-site inorganic Pb 2+ ions that is essential to the ferroelectricity in 2D BA 2 PbCl 4 . The nonpolar ground state of the closely related compounds BA 2 PbBr 4 and BA 2 PbI 4 can also be explained in terms of the weakened cooperative coupling. We further predict that 2D BA 2 PbF 4 displays in-plane ferroelectricity with a higher Curie temperature and larger electric polarization. Our work not only reveals the unusual FE mechanism in 2D HOIPs but also provides a solid theoretical basis for the rational design of 2D multifunctional materials.

Two-Dimensional Organic–Inorganic Room-Temperature Multiferroics

“…μC/cm 2 ), 36 while they are comparable to the value in 2D FE BA2PbCl4 (~5.65 μC/cm 2 ) 37,38 and CuInP2S6 (~4 μC/cm 2 ), 39 and larger than that of d1T-MoTe2 (~0.68 μC/cm 2 ). 40 Therefore, the Cr(hfpyz)2 monolayer can have a large potential for the applications in multi-state memory devices.…”

Progress on Emerging Ferroelectric Materials for Energy Harvesting, Storage and Conversion

“…Reproduced with permission. [ 181 ] Copyright 2021, American Chemical Society. e) Schematic Rashba splitting induced by spin‐orbit coupling and related optical transitions with circularly polarized light.…”

“…One should note that the out‐of‐phase octahedral rotations couple with the orientation of A‐site cations, leading to instantaneous symmetry‐broken nanostructures (1–3 nm) at room temperature and above. [ 180 ] By strengthening the corporative coupling, the ferroelectricity is further enhanced in 2D Ruddlesden–Popper‐type HOIPs, [ 181,182 ] for example, BA 2 PbCl 4 (space group Pb2 1 m, E g = 3.32 eV), which has vdW interlayer bonding and its polarization is ≈8 μC cm −2 along b axis (Figure 6d). Similar to FE BaTiO 3 and LiTaO 3 , [ 64 ] the 2D FE HOIPs also exhibit coexisting order‐disorder and displacive features owing to ordering of organic dipoles and Pb off‐center displacements.…”

“…d) Out-of-phase rotation of the BA = C 6 H 5 CH 2 NH 3 + cation and PbCl 6 octahedra as well as side view of the parallel aligned BA cations in 2D BA 2 PbI 4 . Reproduced with permission [181]. Copyright 2021, American Chemical Society.…”

Controlling screw dislocation evolution towards highly homogeneous quasi-two-dimensional (BA)2(MA)n−1PbnI3n+1 single crystals for high-response photo-detectors

“…This contributes to an in-depth understanding of the growth mechanism of quasi-2D (BA) 2 (MA) nÀ1 Pb n I 3n+1 SCs and the development and optimization of quasi-2D layered materials and devices for optoelectronics.Cs + , etc; 28,29 X is the halogen anion (Cl À , Br À , and I À ); and n stands for the thickness of the inorganic layer. [30][31][32][33][34] The size and shape of the organic cations A and B jointly determine the rotation and tilt of the Pb-I octahedron in the inorganic layer, which in turn changes the structure of the quasi-2D organicinorganic hybrid perovskite, thereby making the photoelectric properties of the perovskite change. [35][36][37][38] At present, the solution method is the most commonly used method to prepare organic-inorganic lead halide quasi-2D perovskite single crystals (SCs).…”