Proton Magnetic Resonance Study of Ferroelectric Potassium Ferrocyanide Trihydrate

Abstract

Proton magnetic resonance and vibrational spectra of potassium ferrocyanide trihydrate have been studied between 77° and 300°K. From the observed two sets of O–H stretching frequencies it has been possible to suggest the probable positions of four previously undetermined water molecules in the unit cell. Changes in the vibrational spectra and in the proton resonance second moment in the neighborhood of the Curie point indicate that the onset of ferroelectric behavior is associated with a dynamical orientational ordering of the hydrogen-bonded water molecules. Apparently there is also a contribution to the spontaneous polarization and internal field from displacements and polarizability of the K+ and Fe(CN)6—4 ions.

Effect of Nanoscale Confinement on the Crystallization of Potassium Ferrocyanide

“…45,46 KFCT also exhibits a number of unusual solid-state transitions, which have elicited considerable interest from a fundamental point of view. [47][48][49] Crystallization in Bulk Solution. Two precipitation methods were employed; evaporation of aqueous solutions or precipitation from aqueous solution by ethanol addition.…”

Vibration Spectra of Ferrocyanide Ions in the Paraelectric Phase of K4[Fe(CN)6] � 3H2O

“…Then by integrating these vibrations into the proper species of the factor group we can get the intermolecular vibrations of such ion. The particular ferrocyanide ion has octahedral O 1 h molecular symmmetry [17]. The site symmetry must be determined for each equivalent set of atoms in the molecule.…”

“…There has been a lot of confusion about the nature of the ferroelectric phase transition observed at %249 K. The order-disorder model was first suggested by Blinc et al [17] on the basis of the temperature dependence of NMR line-shapes and on an assumption of no structural variation at T c . Kiriyama et al [1] have shown that these lineshape anomalies do not occur at the transition.…”

“…At the transition, the major contribution to the spontaneous polarization arises along the [101] or [101] direction from the water molecular dipole moments in addition to a minor contribution due to the displacement and polarizability of K þ and Fe(CN) 4À 6 [17]. The water molecules are bound chiefly by relatively weak hydrogen bonds.…”

“…Raman and IR spectra of KFCT in different energy regions and at different temperatures were studied [26][27][28]. One of the most interesting features in the room temperature (paraelectric phase) IR spectra of KFCT is the appearance of two sets of water molecule bands, indicating the existence of two inequivalent sets of hydrogen bonds [17]. In the ferroelectric phase, however, the water sublattice contains three different "types" of water molecules.…”