Giant k31 Relaxor Single-Crystal Plate and Their Applications

Abstract

Typical ferroelectric ceramics, lead zirconate titanate (PZT) ceramics are widely used for devices of electrical-mechanical energy conversion devices such as sensors and actuators, which correspond to the five senses and foot & hand of human being. Recently, these devices spread out in the computer controlled fields, for example, robotics and mechatronics. The research and development of ferroelectric ceramics, particularly PZT ceramics, have mainly focused on the material compositions to realize new electronic devices utilizing their piezoelectric properties. Many researchers in companies and institutes have carried out R & D on such chemical compositions since the discovery of piezoelectricity in PZT ceramics by Jaffe et al. in 1954. On the other hand, through the new research on DC poling field dependence of ferroelectric properties in PZT ceramics, the poling field has become an effective tool for evaluation and control of the domain structures, which fix the dielectric and ferroelectric properties of PZT ceramics. Therefore, PZT ceramics with different domain structures can be fabricated even though the ceramic compositions remain the same. These ceramics are called poling field domain controlled ceramic. It is thought that the domain controlled ceramics will lead to a breakthrough and the appearance of new ferroelectric properties. The study on the clarification of relationships between [compositions] vs [poling fields] vs [dielectric and piezoelectric properties] in hard and soft PZT ceramics was applied to other ferroelectric materials of lead titanate ceramics, lead-free ceramics such as barium titanate, alkali bismuth niobate, alkali bismuth titanate ceramics and relaxor single crystals of Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 (PZNT91/09) and Pb[(Mg1/3Nb2/3)0.74Ti0.26]O3 (PMNT74/26) compositions. This chapter describes how can be achieved the new ferroelectric properties such as giant transverse-mode electromecanical coupling factor of k31 over 80% and piezoelectric strain d31 constant of -2000 pC/N in PZNT91/09 and PMNT74/26 single crystals realized a monodomain single crystal by accurately controlling the domain structures. In addition, highefficiency piezoelectric unimorph and bimorph are also discribed as the devices using giant k31 single crystals.