Structure and dynamic dielectric behaviour of ferroelectric [NH₂(CH₃)₂]₃Sb₂Br₉(DMABA)

Abstract

The crystal structure of DMABA has been determined at 293 and 180 K. It crystallizes in the monoclinic P21/c space group. The structure was refined to R1 = 0.0466 for 1269 independent reflections at 293 K and R1 = 0.038 for 1728 reflections at 180 K. DMABA is isomorphous with the chlorine analogue, DMACA. Its anionic sublattice forms corrugated two-dimensional layers in the bc plane. There are two crystallographically independent, disordered dimethylammonium cations in the crystal structure. One of them occupies cavities inside the polyanionic layers; the other is located between the layers. The temperature dependence of lattice parameters has been determined between 100 and 290 K. The presence of the ferro-paraelectric phase transition at 164 K has been confirmed. The complex dielectric permittivity of DMABA single crystals in the frequency range 100 Hz-10 GHz between 10 K and 300 K has been measured. The dynamic dielectric behaviour of DMABA is found to be determined by the properties of two independent relaxators: a low frequency one (~1 MHz at Tc) with a critical slowing down of its dynamics and a high frequency one (~5 GHz), which is thermally activated and contributes to the electric permittivity at least from about 80 K.

Thermodynamic properties and molecular motions in ferroelectric (C3N2H5)5Sb2Br11

“…A special attention deserve haloantimonates(III) and halobismuthate(III) because many compounds described by the R 3 M 2 X 9 (2D dimensionality) and R 5 M 2 X 11 composition were found to exhibit the ferroelectric properties [9][10][11]. The later type of crystals is characterized by a discrete bioctahedral unit (0D).…”

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

“…It has turned out that the ferroelectric properties had some tendency to appear in the two-dimensional (2D) anionic sublayers encountered in the R 3 M 2 X 9 -type compounds. On the other hand, several synthesized ferroelectrics crystallize in R 5 M 2 X 11 composition, where the discrete bioctahedral units, M 2 X 5À 11 , constitute the anionic sublattice [6][7][8][9][10][11]. The role of the cations, their size and symmetry, is not fully recognized yet.…”

Tris(allylammonium) Hexabromobismuthate(III) – Crystal Structure, Phase Transitions and Thermal, Dielectric, Vibrational and 1H NMR Properties Over a Range of Temperatures

“…The hexabromobismuthate(III) anion, as well as two of the three crystallographically unrelated allylammonium cations are ordered. The N1-C2-C3-C4 and the N11-C12-C13ϪC14 torsion angles of the ordered cations are equal to 106.1 (9) and -112. 2c).…”

“…Experimental studies have shown that the ferroelectric properties have some tendency to appear in the 2D anionic substructures encountered in R 3 M 2 X 9 -type connections. [6][7][8][9] So far, several synthesised ferroelectrics were found to crystallise with a R 5 M 2 X 11 composition in which the anionic network con-(IV↔V) at 146/144 K. The ferroelastic domain structure was observed over one intermediate phase (III) below 215 K. The electric properties of ABB have been measured over a wide temperature range (105-310 K). Low frequency relaxation processes with dielectric increments Δε 1 ≈ 0.9 and Δε 2 ≈ 0.05 were observed within phases II and V, respectively.…”