Dielectric and optical properties related to phase transitions in an imidazolium perchlorate [C 3 N 2 H 5 ClO 4 ] crystal

Structural, dielectric and optical properties of the crystal C 3 N 2 H 5 ClO 4 have been studied by X‐ray diffraction, dielec‐tric and birefringence measurements. On cooling, structural phase transitions occurring at 373 K ( T c1 ) and 210 K ( T c2 ) are of second and first order, respectively. It is considered from the structure and the dielectric behaviour that Phases I ( T > T c1 ) and II ( T c2 < T < T c1 ) are paraelectric and ferroelectric, respectively, though a hysteresis loop is not found in Phase II. The crystal is destroyed below T c2 by a large structure deformation. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)