Enhanced Piezoelectric Properties of Piezoelectric Single Crystals by Domain Engineering

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Enhanced Piezoelectric Properties of Piezoelectric Single Crystals by Domain Engineering Satoshi Wada, Koichi Yako, Hirofumi Kakemoto and Takaaki Tsurumi Department of Metallurgy and Ceramics Science, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo 152-8552, Japan ABSTRACT For tetragonal barium titanate (BaTiO3) single crystals, an electric field (E-field) applied along [111]c direction can induce an engineered domain configuration. In this study, the engineered domain structures with different domain sizes were induced into BaTiO3 single crystals, and their piezoelectric properties were investigated as a function of a domain size. Prior to this study, the dependence of domain configuration on the temperature and the E-field was investigated using a polarizing microscope in order to understand the optimum condition for fine and coarse domain structures. As a result, above Curie temperature (Tc) of 132.2 ˚C, when the E-field over 6 kV/cm was applied along [111]c direction, the engineered domain configuration with fine domain structure appeared. Moreover, it was also found that this fine domain structure was still stable at room temperature without E-field. On the other hand, the coarse domain structure was obtained by poling at just below Tc. Finally, the piezoelectric properties were measured using the 31 resonators with different kinds of domain sizes. As the result, it was found that the piezoelectric properties such as d31 and k31 increased significantly with decreasing domain sizes.

[111]

E-field

INTRODUCTION Domain engineering is very important technique to obtain the enhanced piezoelectric and ferroelectric related properties for ferroelectric single crystals. It was reported that in [001]c oriented rhombohedral PZN-PT single crystals, ultrahigh piezoelectric activities were found by Park et al. [1-3] and Kuwata et al. [4,5] with the strain over 1.7 %, the piezoelectric constant d33 over 2,500 pC/N, the electromechanical coupling factor k33 over 93 % and the hysteresis-free strain vs electricfield behavior. These ultrahigh piezoelectric properties were originated from one of the domain engineering techniques, i.e., "the engineered domain configuration". This engineered domain configuration technique uses the anisotropy of the ferroelectric single crystals as a function of the crystallographic orientation. The crystal structures are also very important factor for the engineered domain configurations [6]. BaTiO3 single crystals have a tetragonal P4mm phase at room temperature. To induce an engineered domain configuration into tetragonal crystals, E-field should be applied

Fig. 1 Schematic engineered domain configuration for tetragonal crystal.

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along [111]c direction as shown in Fig. 1. Thus, the piezoelectric properties were investigated using the [111]c oriented tetragonal BaTiO3 crystals [7,8]. As the results, the d33 of the [111]c poled tetragonal BaTiO3 crystal with the engineered domain configuration was almost 203 pC/N, and this value was almost twice larger than 90 pC/N

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