Deuteron Magnetic Resonance of Ferroelectric Potassium Ferrocyanide Trihydrate

The quadrupolar splittings and linewidths of the deuteron magnetic resonance of single crystals of ferroelectric K4Fe(CN)6·3D2O(KFCT) have been measured from −100° to 58°C. At low temperatures eight pairs of resonance lines are observed corresponding to four types of water molecules A, B, C, D, and their ac plane enantiomorphs A+, B+, C+, D+. The molecules are undergoing a fast 180° flip motion about the bisectrix of the DOD bond angle. At temperatures above the Curie temperature (−20°C) only two pairs of lines are observed which are shown to result from fast molecular reorientations within the sets A, C, A+, C+ and B, D, B+, D+. Molecular orientations are determined at low temperatures from rotation patterns and these become shifted for the C- and D-type molecules in the transition to the paraelectric phase. A structure for ferroelectric KFCT is proposed based on the deuteron resonance data. Activation energies and frequency factors for the 180° flip, AC, and AA+ averaging motions are derived and discussed. The temperature dependence of proton resonance second-moment data and the single-crystal spectra at 25°C are interpreted in terms of the motions deduced from the deuteron resonance experiments and compared with the results of inelastic neuteron scattering experiments.