Structural characterization and ferroelectric ordering in (C 3N 2H 5) 5Sb 2Br 11
Abstract
A ferroelectric crystal (C 3N 2H 5) 5Sb 2Br 11 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, P21/n with: a=9.139 A˚, b=15.150 A˚ and c=13.969 A˚ and β=96.19∘. The crystal undergoes three solid-solid phase transitions: (tetragonal?)⟷354/352P21/n (I↔II) discontinuous, P21/n⟷145Pn (II↔III) continuous and Pn⟷120/135Pn (III↔IV) discontinuous. The dielectric and pyroelectric measurements allow us to characterize the low temperature phases III and IV as ferroelectric with the Curie point at 145 K and the saturated spontaneous polarization value of the order of 1.8×10-3 C m-2 along the a-axis (135 K). The ferroelectric phase transition mechanism at 145 K is due to the dynamics of imidazolium cations.
- Publication:
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Journal of Solid State Chemistry France
- Pub Date:
- May 2008
- DOI:
- 10.1016/j.jssc.2008.02.029
- Bibcode:
- 2008JSSCh.181.1155P