title: Ferroelectric ordering in imidazolium perchlorate.
abstract: 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 R3m, Z=1 with a=5.484(1) A 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 R3m, a=5.554(1) A 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.
authors.affiliation: Institute of Physics, A. Mickiewicz University, 61-614 Poznań, Poland. zpajak@amu.edu.pl
authors.forename: Z
authors.initials: Z
authors.lastname: Pajak
authors.forename: P
authors.initials: P
authors.lastname: Czarnecki
authors.forename: B
authors.initials: B
authors.lastname: Szafrańska
authors.forename: H
authors.initials: H
authors.lastname: Małuszyńska
authors.forename: Z
authors.initials: Z
authors.lastname: Fojud