Ferroelectric ordering in imidazolium perchlorate

Imidazolium perchlorate has been synthesized and studied over a wide range of temperatures by differential scanning calorimetry, x-ray diffraction, proton magnetic resonance, optical observation, and dielectric spectroscopy. Polymorphic solid-solid phase transitions have been disclosed at 487, 373, and 247 K. The crystal structure at 298 K has been determined as trigonal, space group R (3) over barm, Z=1 with alpha=5.484(1) angstrom and alpha=95.18(2)degrees. The imidazolium cations are strongly disordered, while the perchlorate ions are well ordered. At 385 K the crystal structure remains trigonal, space group R (3) over barm, alpha=5.554(1) angstrom and alpha=95.30(2)degrees. Both ionic sublattices are orientationally disordered. Temperature evolution of the molecular dynamics of the imidazolium cation has been characterized. In spite of a high cationic disorder, dielectric measurements have revealed the polar properties of the crystal. It appears to be a new ferroelectric compound with the Curie point at 373 K. The spontaneous polarization originates predominantly from the behavior of slightly distorted perchlorate anion. (c) 2006 American Institute of Physics.