X-ray Study on the Disordered Structure above the Ferroelectric Curie Point in Potassium Nitrate

抄録

The disordered structure (phase I) above the ferroelectric Curie point (ca. 125°C) in KNO₃ was studied by analysing X-ray diffuse scattering. The single crystal was prepared by slow cooling from the melt in a small glass tube which was mounted on the sample holder of a camera. The observed intensity distribution of the diffuse scattering in reciprocal space was characterized by six diffuse maxima observed around each reciprocal lattice point. From its analysis a characteristic arrangement, in which two kinds of “micro-domains” whose polar axes are antiparallel are alternately stacked in the direction A, B or −(A+B), was proposed as basic arrangement. It was found that the local tendency to take such an arrangement was strong especially when the coexistence of the phase I and the ferroelectric phase III took place, and that such a tendency decreased gradually with the increase of temperature.