Temperature Dependence of Spontaneous Polarization in Order−Disorder Pyridinium Periodate Extracted from ²H NMR Data

On the basis of occupancy factor data for nitrogen atoms in the pyridinium cation obtained from the structural study of PyHIO 4 by neutron diffraction, 4 the shape of the potential for cation reorientation about the axis perpendicular to its plane was found. The 2 H NMR spectra of d 5 PyHIO 4 taken over a wide range of temperatures have allowed the determination of potential minima populations. These data were used to obtain the temperature dependence of spontaneous polarization. The agreement between the spontaneous polarization calculated in this way and the measured values is very good and indicates that the ferroelectric crystal is of the order−disorder type.