Elucidation of engineered domain structures of ferroelectric crystals and their high piezoelectricity

本研究的目的是利用假立方铁电晶体KNbO_3和高压电电的工程域结构，并利用开发域控制方法和压电电器件的高耦合因子。该项目中获得的结果已被总结为以下： 1。KNbO_3晶体对各种机电耦合因子的方向依赖性已被计算，并在所有已知的压电电子中找到了最高的耦合因子的切割。它展示了一条直线与一条电动曲线用于假立方体（001）_<pc>KNbO_3在低场有一个线性特征，但它是一个高场的非线性特征，在一个高场中有一个60度域的非线性特征，而且在理论上显示了一个比估计的更高的直线。3.用于去除微裂纹的晶体的化学蚀刻导致不存在60 °域的情况，在非半胱氨酸行为即使在高电场中也有结果。4.领域结构变化被审查时，被要求通过阶段过渡温度进行加热和冷却，并说明了质量。该方法是保持单域状态，当相位过渡温度被确定并被证明有效时加热的方法。5. Engineered domain structures were formed by applying an electric field along the （001）_<pc>axis while heating and cooling through the phase transition point。Piezoelectric behavior被证明是为了展示一个小歇斯底里。这个领域的结构是第一次展示两种90度层状域的概念。6.它被证明是因为KNbO_3超声波转换器具有更有效的和宽带特征，并与PZT陶瓷和LiNbO_3晶体的特性相比较。为了实现高频率超声波转换器的ECR-PLD系统，以实现高质量KNbO_3电影的外延增长。

The purpose of this research is to elucidate the engineered domain structures of pseudo-cubic ferroelectric crystal KNbO_3 and the high piezoelectricity, and to develop domain control methods and piezoelectric devices utilizing the high coupling factor. The results obtained in this project are summarized as follows: 1. The orientation dependence of various electromechanical coupling factors for KNbO_3 crystal have been calculated and the cut with the highest coupling factor among all known piezoelectrics for the thickness-extensional mode has been found. 2. It was shown that the strain vs. electric-field curve for the pseudo-cubic (001)_<pc> cut of KNbO_3 had a linear characteristic for a low field, but it was hysteretic due to occurrence of 60゜ domains for a high field and exhibited a much higher strain than that estimated theoretically. 3. Chemical etching of crystals for removing micro-cracks lead to no occurrence of 60゜ domain, resulting in non-hysteretic behaviors even for a high electric field. 4. Domain structural change was examined when subjected to heating and cooling through the phase transition temperature and was explained qualitatively. The method for keeping the single domain state when heating through the phase transition temperature was devised and demonstrated to work out. 5. Engineered domain structures were formed by applying an electric field along the (001)_<pc> axis while heating and cooling through the phase transition point. The piezoelectric behavior was demonstrated to exhibit little hysteresis. The domain structure was shown for the first time to consist of two kind of 90゜ laminar domains. 6. It was demonstrated that the KNbO_3 ultrasonic transducer has a more efficient and broader-band characteristic as compared with those of PZT ceramics and LiNbO_3 crystals. To realize higher frequency ultrasonic transducers an ECR-PLD system for epitaxial growth of high quality KNbO_3 films was developed.