ROTATION OF IO4 IN THE PHASE II OF PyIO4

In order to investigate the displacement of the IO4 tetrahedron in the ferroelectric phase II of pyridinium periodate in detail, we performed X-ray structural analysis with the use of the estimated site occupancies of carbon and nitrogen atoms at many temperatures. We confirmed the continuous increase of the rotation angle of the IO4 tetrahedron about the a-axis with decreasing temperature in the phase II. This indicates that the IO4 tetrahedron acts as the displacive structural unit at the transition from phase I to phase II. It is found that the rotation of the IO4 tetrahedron is correlated with the reorientation of the pyridinium cation through the N-H...O type hydrogen bond.