Survey of Research on Ferroelectrics

Advanced experimental methods (e.g. inelastic neutron scattering and hyper-Raman scattering) have been applied effectively to studies of ferroelectrics, and several new concepts (e.g. soft modes of lattice vibrations and the dipole glass) have been introduced to understand the nature of ferroelectrics. Ferroelectric crystals have been widely used in capacitors and piezoelectric devices. Steady developments in crystal growth and in the preparation of ceramics and ceramic thin 

5-5 Number of research papers on ferroelectrics and related substances pubhshed in each year. The solid line indicates the number of papers concerning all ferroelectrics (crystals + liquid crystals -F polymers). The dashed line indicates the number of papers concerning liquid crystals and polymers alone. Prepared by Prof. K. Deguchi 

Corresponding to this intense development, many textbooks, monographs, and review articles have been published on ferroelectric research during recent years. Some of them, arranged according to the various research fields, are listed here  

Acoustic surface waves (ASWs) [5.36-39] Ferroelectric transducers and sensors [5.40] Memory applications [5.35] 

Ferroelectricity is caused by a cooperative interaction of molecules or ions in condensed matter. The transition to ferroelectricity is characterized by a phase transition. Depending on the mechanism of how the molecules or ions interact in the material, we can classify the ferroelectric phase transitions and also the ferroelectric materials themselves into three categories (I) order-disorder type, (II) displacive type, and (III) indirect type. In the order-disorder type (I), the spontaneous 

The ferroelectric effect was discovered in 1920 by Valasek, who obtained hysteresis curves for Rochelle salt analogous to the B-H curves of ferromagnetism [5.5], and studied the electric hysteresis and piezoelectric response of the crystal in some detail [5.6]. For about 15 years thereafter, ferroelectricity was considered as a very specific property of Rochelle salt, until Busch and Scherrer discovered ferroelectricity in KH2PO4 and its sister crystals in 1935. During World War II, the anomalous dielectric properties of BaTiOs were discovered in ceramic specimens independently by Wainer and Solomon in the USA in 1942, by Ogawa in Japan in 1944, and by Wul and Goldman in Russia in 1946. Since then, many ferroelectrics have been discovered and research activity has rapidly increased. In recent decades, active studies have been made on ferroelectric liquid crystals and high polymers, after ferroelectricity had been considered as a characteristic property of solids for more than 50 years. 

In second-order or nearly second-order phase transitions, the dielectric dispersion is observed to show a critical slowing-down a phenomenon in which the response of the polarization to a change of the electric field becomes slower as the temperature approaches the Curie point. Critical slowing-down has been observed in the GHz region in several order-disorder ferroelectrics (e.g. Figs. 4.5-8 and 4.5-9) and displacive ferroelectrics (e.g. Fig. 4.5-10). The dielectric constants at the Curie point in the GHz region are very small in order-disorder 

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