Pajak Z, Czarnecki P, Szafrańska B, Małuszyńska H, Fojud Z
Institute of Physics, A. Mickiewicz University, 61-614 Poznań, Poland.
J Chem Phys. 2006 Apr 14;124(14):144502. doi: 10.1063/1.2185098.
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.
通过差示扫描量热法、X射线衍射、质子磁共振、光学观察和介电谱等方法，在很宽的温度范围内合成并研究了高氯酸咪唑鎓。已发现在487K、373K和247K时存在多晶型的固-固相变。298K时的晶体结构已确定为三方晶系，空间群R3m，Z = 1，a = 5.484(1) Å，α = 95.18(2)°。咪唑鎓阳离子强烈无序，而高氯酸根离子有序排列。在385K时，晶体结构仍为三方晶系，空间群R3m，a = 5.554(1) Å，α = 95.30(2)°。两个离子亚晶格均存在取向无序。已对咪唑鎓阳离子的分子动力学的温度演变进行了表征。尽管阳离子无序度很高，但介电测量揭示了该晶体的极性性质。它似乎是一种新的铁电化合物，居里点为373K。自发极化主要源于轻微畸变的高氯酸根阴离子的行为。
