Bidomain Ferroelectric Crystals: Properties and Prospects of Application

Lithium niobate (LiNbO 3 ) and lithium tantalate (LiTaO 3 ) are among the most important and most widely used materials of coherent and nonlinear optics, as well as acoustics. The strict requirements on the uniformity and reproducibility of characteristics have become the base of the industrial technology for the production of high-quality crystals, mastered by many enterprises around the world. However, using LiNbO 3 and LiTaO 3 is not limited to the areas listed above due to their pronounced piezo and ferroelectric properties. One of the promising areas of using crystals is the creation, based on them, of electromechanical converters for precision sensors and actuators. At the same time, the high thermal stability of the piezoelectric and mechanical properties, as well as the absence of hysteresis and creep, make it possible to create electromechanical transducers capable of operating in a wide temperature range unattainable for ferroelectric materials commonly used for these purposes. The main advantage of LiNbO 3 and LiTaO 3 over other monocrystalline piezoelectrics is the possibility of a directed effect on the characteristics of devices by controlling the ferroelectric domain structure of crystals. One of the most striking examples of the use of domain engineering to create electromechanical converters based on crystals is the formation in them of the so-called bidomain structure: two macroscopic domains located in one crystal plate, having oppositely directed vectors of spontaneous polarization separated by a charged domain wall. Highly coercive switching fields make the inverse domains stable up to the Curie temperature (about 1140°C for LiNbO 3 and 600°C for LiTaO 3 ). This review discusses the main achievements in the field of the formation of a bidomain structure and near-surface inverse domains in LiNbO 3 and LiTaO 3 crystals. Methods for visualizing the domain structure in crystals and nondestructive methods for monitoring the position of the interdomain boundary are presented. A comparative analysis of the methods for the formation of inverse domains in crystals is carried out, and the regularities and technological methods of controlling the domain structure are discussed. The main physical models proposed in the literature to explain the effect of the formation of inverse domains are presented, and their strengths and weaknesses are considered. Methods for choosing a crystallographic cut to create devices that use bidomain crystals (BCs) are briefly listed. Examples of implementation of devices based on BCs are given: actuators, sensors, acoustic transducers, and waste energy collection systems.