Enhanced Piezoelectric Properties of Lead-free Ferroelectric Single Crystals with Engineered Domain Configurations

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In this study, our objectives are (I) an introduction of the engineered domain configurations into lead free ferroelectric single crystals and (II) occurrence of enhanced piezoelectric property by the engineered domain configurations. For these objectives, barium titanate single crystals were chosen as a typical lead-free ferroelectrics, and the relationship between the engineered domain configurations and piezoelectric property was investigated in detail. As a result, the following four points were found through this study. (1) a concept of the engineered domain configurations is universal, and this concept cam be applied into all of ferroelectric crystals. (2) the engineered domain configurations have several kinds and depend on the crystal structures such as tetragonal, orthorhombic and rhombohedral phase and crystallographic orientations such as [100], [110] and [111]. (3) In orthorhonbic barium titanate single crystals oriented along [001] direction, it was found that its piezoelectric properties was slightly larger than those of PZT ceramics. (4) In barium titanate single crystals with the engineered domain configurations, it was found that the piezoelectric properties become to larger with decreasing domain sizes. However, for barium titanate, its temperature dependence of the piezoelectric properties was not good because its low Curie temperature of 130℃ and phase transition around 5℃. Therefore, as tile feroelectrics with orthorhombic structure at room temperature and higher Curie temperature over 200℃, potassium niobate was chosen in this study. Up to date, the unknown piezoelectric properties of potassium niobate single-domain crystals was cleared through this study. At present, we investigated the introduction of the engineered domain configurations into potassium niobate crystals, and it can be expected that the much higher piezoelectric properties will be observed in the potassium niobate single crystals with the engineered domain configurations.