Ferroelectric Metal–Organic Frameworks

Photochromism of a Methyl Viologen Bismuth(III) Chloride: Structural Variation Before and After UV Irradiation

Polynuclear halide complexes of Bi(III): From structural diversity to the new properties

Imidazolium periodate (IPI) is found to be an improper ferroelectric. It shows bistable properties simultaneously in three channels of dielectricity, piezoelectricity, and second-harmonic generation within the temperature window 300-310 K.

Switchable dielectric, piezoelectric, and second-harmonic generation bistability in a new improper ferroelectric above room temperature.

Many order–disorder-type phase transitions in molecule-based ferroelectrics are related to changes of molecular dynamics. If the molecular motions do not involve reorientations of dipole moments, their ordering fails to contribute directly to spontaneous electric polarization. For understanding ferroelectric mechanisms in these systems, it is important to clarify how such molecular dynamics changes induce structurally symmetry-breaking phase transitions and thus the appearance of spontaneous electric polarization. Systematic characterization of an [18]crown-6 based host–guest inclusion compound, [(DIPA)([18]crown-6)]BF4 (DIPA = 2,6-diisopropylanilinium), shows it is an excellent ferroelectric with a large dielectric anomaly, significant pyroelectricity, and SHG response, and rectangular polarizaiton–electric field hysterisis loops. By the combination of variable-temperature single-crystal structural determination and solid-state NMR observation, it is found that the slowing down of the rotation of the [18...

Solid State Molecular Dynamic Investigation of An Inclusion Ferroelectric: [(2,6-Diisopropylanilinium)([18]crown-6)]BF4

Crystal structure, phase transitions and ferroelastic properties of [(CH3)2NH2]3[Bi2Cl9]

Differential scanning calorimetry, dilatometric, dielectric dispersion and linear birefringence measurements have been used to study the phase transition at 202 K in the (C5 H10 NH2 )SbCl6 (C5 H10 NH2 )Cl crystal. The x-ray studies show that at room temperature it crystallizes in the orthorhombic symmetry (space group Pccn ), whereas below 202 K the structure changes its symmetry to monoclinic (P 21 /c ). The mechanism of the phase transition is connected both with the disordering of the piperidinium cations and the essential change in the NH...Cl hydrogen bond system. The title crystal exhibits the ferroelastic domain structure in the monoclinic phase.

Structure and phase transition in the (C5H10NH2)SbCl6·(C5H10NH2)Cl crystal

Differential scanning calorimetry, dilatometric, dielectric and linear birefringence measurements have been used to study the ferroelastic [C(NH2)3]3Bi2Br9 crystal. The x-ray studies showed that it crystallizes at room temperature in the monoclinic symmetry, space group P21/m. The crystal undergoes a complex sequence of phase transitions: at 311 K, 333.5 K, 350 K, 415 K and 425 K. All phase transitions were found to be of first order type. The ferroelastic domain structure is maintained from room temperature up to 425 K. The temperature measurements of the linear birefringence and optical observations suggest the tetragonal symmetry of the parent paraelastic phase above 425 K.

http://iopscience.iop.org/article/10.1088/0953-8984/11/24/314/pdf

Structure and phase transitions in the ferroelastic [C(NH2)3]3Bi2Br9 crystal

Structural, dielectric and optical properties of the crystal C3N2H5ClO4 have been studied by X-ray diffraction, dielec-tric and birefringence measurements. On cooling, structural phase transitions occurring at 373 K (Tc1) and 210 K (Tc2) are of second and first order, respectively. It is considered from the structure and the dielectric behaviour that Phases I (T > Tc1) and II (Tc2 < T < Tc1) are paraelectric and ferroelectric, respectively, though a hysteresis loop is not found in Phase II. The crystal is destroyed below Tc2 by a large structure deformation. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Dielectric and optical properties related to phase transitions in an imidazolium perchlorate [C3N2H5ClO4] crystal

Single crystals of pyridinium periodate were grown, and their physical properties were studied. Anomalies of the electric permittivity and birefringence were observed at Tc1 = 321 K and T c2 = 211 K. These observations gave evidences for the existence of three phases denoted as I, II, and III. Hysteresis loops were observed both in phase II and III. Pyroelectric measurements showed two anomalies at Tc1 and T c2. The anomaly at Tc1 is related to the transition between a paraand ferroelectric phase, and the anomaly at Tc2 to the transition between two ferroelectric phases.

B. Kosturek

Papers

Crystal structure, phase transitions and ferroelastic properties of [(CH3)2NH2]3[Bi2Cl9]

Structure and phase transition in the (C5H10NH2)SbCl6·(C5H10NH2)Cl crystal

Structure and phase transitions in the ferroelastic [C(NH2)3]3Bi2Br9 crystal

Dielectric and optical properties related to phase transitions in an imidazolium perchlorate [C3N2H5ClO4] crystal

Ferroelectricity and Phase Transitions in Pyridinium Periodate Single Crystal