Ferro-Electric Materials: Trends & Applications

There has been a rapid progress in the field of ferro-electric materials and devices at all levels in research, development, production, discovering of new materials and development of new technologies. Although a large number of ferro-electric materials have been discovered, many of them are only of academic interest, whereas some have found innumerable applications as good transducer materials in piezo-electric, pyro-electric, and electro-optic applications. A review of such materials which are quite promising for device applications is presented in this article. In optical communication and office automation, there is an increasing demand for electrically-controlled component able to modulate or switch light. This function can be realized by using electro-optical effects in ferro-electric glass ceramics. They have good transparencies in the visible spectrum and near infra-red. Some of these materials are suitable for SAW devices, also. Pyro-electric materials find applications in point detectors and thermal imaging. Permanent piezo-electricity has been found in synthetic polymers and electrets which finds immense applications in underwater transducers. Inorganic fluorides with a general formula A5M3O9F5 form a new ferro-electric-ferro-elastic family. A2B2O7 type layer-structured crystals have high Curie points and also large piezo-electric and electro-optic constants. Semiconducting ferro-electrics such as SbSI are of interest because of the influence of carriers on ferro-electric properties. Many special purpose dielectrics e.g. high voltage, high temperature, low firing, microwave ceramics have been discussed.Relaxor ferro-electrics which have small thermal expansion, small electrostrictive co-efficients but very large permittivity, excel perovskite ferro-electrics such as PZT and barium titanate based ceramics. Relaxor ferro-electrics have the capability of producing enormous electrostriction, hence find applications in displacement transducers. Piezo-electric composites such as PZT/resin, PZT powder/rubber, Coral structured PZT/silicon rubber and the others have been developed which find growing applications as low density compliant flexible piezo-electric transducers.