Structure and ferroelectric properties of [C₃N₂H₅]₅[Bi₂Br₁₁]

Abstract

A ferroelectric crystal [C3N2H5]5[Bi2Br11] has been synthesized and structurally characterized at 170 and 100 K. The crystal structure consists of discrete corner-sharing bioctahedra [Bi2Br11]5− and highly disordered imidazolium cations. The room temperature crystal structure has been determined as monoclinic, space group, P 21/n with: a = 9.257(2) Å, b = 15.157(3) Å, c = 13.865(3) Å and β = 97.73(3)°. The crystal undergoes two solid–solid phase transitions: at 355 K of first-order and at 155 K of second-order type. The later transition takes place between monoclinic phases: . The dielectric and pyroelectric measurements allow us to characterize the low temperature phase III as ferroelectric with the Curie temperature at 155 K. The saturated spontaneous polarization of the order of 2.6 × 10−3 C m−2 was measured along the a-axis (130 K). The ferroelectric phase transition mechanism at 155 K is due to the dynamics of three of five nonequivalent imidazolium cations.

Synthesis, crystal structure and phase transitions of a series of imidazolium iodides

“…The I-I distance of 3.5410(1) Å is significantly shorter then the sum of the van der Waals radii (4.12 Å), and the angle h 1 that is equal to 177.6u gives almost a linear configuration. The I … N distance is equal to 3.505(5) Å in N(1)-H(1) … I(1) bond and donor-to-acceptor angle equals 170 (7)u. The basic hydrogen and halogen bonded pattern is a ten membered ring.…”

Unprecedented solid-state chemical reaction—from . From centrosymmetric to non-centrosymmetric crystal structure

“…It is suggested that the lone pair (5s 2 -Sb(III) and 6s 2 -Bi(III)) has a key role in the collective properties of these ferroelectric materials [11]. Recently, we have synthesized three novel ferroelectrics from the haloantimonate(III) and halobismuthate(III) family of compounds crystallizing with the chemical composition R 5 M 2 X 11 , where R is the imidazolium cation [19,20]. It is rather intriguing that all known compounds (imidazolium, pyridinium, or methylammonium cations) with this composition have been found to exhibit ferroelectric properties, whereas formally very similar compounds crystallizing with H 2 O molecules, ðR 5 M 2 X 11 Á 2H 2 OÞ, do not reveal any ferroelectric properties [21,22].…”

Structural characterization, thermal, dielectric and vibrational properties of tris(allylammonium) hexabromoantimonate(III), (C3H5NH3)3SbBr6

“…It is known, however, that in the case of 2D ferroelectrics, characterized by the R 3 M 2 X 9 composition, their cations, such as monomethyl-, dimethyl-or trimethylammonium [12][13][14], are rather small. On the other hand, in the R 5 M 2 X 11 compounds the polar properties are found in either the small alkylammonium cations (methylammonium) or the aromatic ones (pyridinium and imidazolium) [15][16][17][18]. The ferroelectricity of these subgroups of crystals is due to the reorientational motion of the organic cations possessing a permanent dipole moment.…”