Rotational Displacement of IO₄ Tetrahedron in the Phase II of Pyridinium Periodate

Abstract

In order to investigate the displacement of the IO ₄ tetrahedron in the ferroelectric phase II of pyridinium periodate in detail, we performed X-ray structural analysis at 33 temperatures with the use of the estimated site occupancies of carbon and nitrogen atoms. We confirmed the continuous increase of the rotation angle of the IO ₄ tetrahedron about the a-axis with decreasing temperature in the phase II. This indicates that the IO ₄ tetrahedron acts as the displacive structural unit at the transition from phase I to phase II. It is found that the rotation of the IO ₄ tetrahedron is correlated with the reorientation of the pyridinium cation through the N-H─ O type hydrogen bond.

Keywords:

• Rotational displacement
• ordering of pyridinium
• structure analysis
• phase transition
• hydrogen bond