Structure and mechanism of ferroelectric phase transition in tris (dimethylammonium)-nonachlorodiantimonate (III)

Abstract
The X-ray diffraction studies were carried out for the crystals of [NH2(CH3)2]3Sb2Cl9 at 293 K in paraelectric phase. The crystals are monoclinic, space group P21/a, with the unit cell parameters: a = 14.045(4), b = 9.018(3), c = 9.670(2) Å, β = 95.47(2)° and Z = 2. The SbCl6 distorted octahedra form infinite polyanion layers via chlorine bridges. The cavities in a twelve-membered (‒Sb‒Cl‒)6 rings are occupied by disordered dimethylammonium cations. The IR spectra and dielectric relaxation studies confirm the mechanism of para-ferroelectric phase transition in which the main role play the reorientations of dimethylammonium cations around 180° and their freezing below Tc = 242 K.

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