Ferroelectricity in Ethylammonium Bismuth-Based Organic–Inorganic Hybrid: (C₂H₅NH₃)₂[BiBr₅]

Abstract

The (C 2 H 5 NH 3 ) 2 [BiBr 5 ] (EBB) crystals adopt the one-dimensional (1D) polymeric anionic form [BiBr 5 ] ∞ 2− , which is preferred by halobismuthates(III) exhibiting polar properties and realized in R 2 MX 5 stoichiometry. Differential scanning calorimetry and dilatometric measurements reveal reversible structural phase transitions: at 160 K (phase I → phase II) and 120 K (phase II → phase III). The resolved crystal structures of EBB show the centrosymmetric space group in phase I (Aeam), polar (Pca2 1 ) in phase II, and polar (Aea2) in phase III. The presence of dielectric hysteresis loops in phases II and III evidence ferroelectric properties. The dielectric response [ε*(ω,T)] of EBB close to 160 K is characteristic of ferroelectrics with a critical slowing down process. The molecular mechanism of a paraelectric−ferroelectric phase transition at 160 K is explained as "order−disorder" (assigned to the dynamics of the ethylammonium cations) and dominating "displacive" (related to strong distortion of the 1D anionic network). The optical band gap obtained from UV−vis measurements is about 2.6 eV. The conduction band minimum is formed by the hybridized Bi 6p and Br 4p states. An analysis of the CSD results for haloantimonates(III) and halobismuthates(III) ferroelectrics characterized by [MX 4 ] − , [M 2 X 9 ] 3− , [MX 5 ] 2− , and [M 2 X 11 ] 5− anions is given.

Centimeter-Sized Single Crystal of a One-Dimensional Lead-Free Mixed-Cation Perovskite Ferroelectric for Highly Polarization Sensitive Photodetection

“…Inspired by traditional research on 1D nanowires and nanobelts for polarization-sensitive photodetectors (InP, ZnO, Sb 2 S 3 , and BaTiS 3 ), we constructed the prototype of a 1D lead-free perovskite on the basis of structural motifs resembling those of 1D hybrid perovskites, such as θ-[(CH 3 ) 2 C­(H)­NH 3 ] 3 SnI 5 and (C 2 H 8 N) 2 BiBr 5 . − A structural analysis reveals that I is a typical single-stranded conformational material, including 1D zigzag chains of corner-sharing SbBr 6 octahedra and organic cations of n -propylammonium along the a axis (Figure S1 in the Supporting Information). The antimony ion is located in the center of each octahedron and connects with two adjacent bridging and four terminal bromine atoms.…”

Efficient Lone-Pair-Driven Luminescence: Structure–Property Relationships in Emissive 5s2 Metal Halides

“…Further reducing the dimensionality to 1D compounds begets wholly different properties compared with the 3D perovskites because of the limitation of orbital overlap to a single crystallographic axis. While there are a variety of corner-connected octahedral structures ranging from straight trans-connected chains to zigzag cis-connected chains (Figure ) and corrugated double chains, their optical properties are relatively underexplored. The corrugated compounds Cs 3 M 2 Cl 9 (M = Sb, Bi) are known to be emissive at low temperatures only, whereas efficient STE emission from 1D metal halides has been obtained from edge-shared double chains …”

0D Bismuth(III)-Based Hybrid Ferroelectric: Tris(acetamidinium) Hexabromobismuthate(III)

“…The correlation between the dimensionality anionic network and the polarity of the crystal structure is visible if we take into account all possible anionic forms in a selected group. For example, in R 2 MX 5 - − or RMX 4 - type stoichiometries, despite their rich diversity of the anionic part, ferroelectricity is limited only to the 1D anionic network. The type of cation, its structure, symmetry, and size have only a limited impact on ferroelectricity generation.…”