The ordering of dipole moments of water molecules and the ferroelectric phase transition in potassium ferrocyanide and isomorphous crystals

Potassium ferrocyanide (KFCT) has a very complex twin habit and a strong tendency to twin. It is therefore difficult to establish the dipole moments of the water molecules in this material. A method was developed to select untwinned samples from PMR spectra. NMR data was used to study KFCT and K4Ru(CN)6 3H2O (KRuCT). From this study the dipolar configuration was obtained and compared with earlier work. The resultant model is discussed in detail. The ferroelectric behaviour of KRuCT may be connected with “C” type water molecules which would imply a macroscopic moment along [100]. This polarization direction was confirmed by dielectric reversible polarization measurements.