Some Studies on Ferroelectricity in KNO3and Related Compounds

(NH 4 ) x K 1- x NO 3 mixed crystals have been found to show ferroelectricity for a wide range of concentration. Dielectric measurements and infrared absorption studies were carried out. The librational behaviors of the NO 3 radical about the 3-fold axis and the axes perpendicular to the 3-fold axis were analysed. The librational frequency and the mean declination angle of the radical were estimated. The Lorentz correction for various rhombohedral angles was calculated, and the ferroelectric effect in the KNO 3 type ferroelectrics was discussed in terms of the local field. The ferroelectric transition has been explained to occur when the rhombohedral angle reaches a particular value.