Structural characterization and ferroelectric ordering in (C3N2H5)5Sb2Br11

A ferroelectric crystal (C3N2H5)(5)Sb2Br11 has been synthesized. The single crystal X-ray diffraction studies (at 300, 155, 138 and 121 K) show that it is built up of discrete corner-sharing bioctahedra Sb2Br115- and highly disordered imidazolium cations. The room temperature crystal structure has been determined as monoclinic, space group, P2(1)/n with: a = 9.139 angstrom, b = 15.150 angstrom and c = 13.969 angstrom and beta = 96.19 degrees. The crystal undergoes three solid-solid phase transitions: (tetragonal?) (354/352)<-> P2(1)/n (I <-> II) discontinuous, P2(1)/n (145)<-> Pn (II <-> III) continuous and Pn (120/135)<-> Pn (III <-> IV) as ferroelectric with the Curie point at 145 K and the saturated spontaneous polarization value of the order of 1.8 x 10(-3) Cm-2 along the a-axis (135 K). The ferroelectric phase transition mechanism at 145 K is due to the dynamics of imidazolium cations. (C) 2008 Elsevier Inc. All rights reserved.