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

这项研究的目的是解决工程领域的结构pseudo-cubicferroelectric crystal knbo_3 and the high piezoelectricityand 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 havebeen calculated and the cut with the highest coupling factor among all known piezoelectrics for thethickness-extensional mode has been found. 2.这应该是strain vs. electron -field curvefor 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 higherstrain than that estimated theoretically. 3. Chemical etching of crystals for removing microcrackslead to no occurrence of 60 domain，resulting in non-hysteretic behaviors even for a high electric field. 4. Domain structural changewas examined when subjected to heating and cooling through the phase transition temperature and wasexplained qualitatively. The method for keeping The单一domain state when heating through The5.工程域的阶段转换temperature已定义和定义工作。structures were formed by applying an electric field along the (001)_<pc> axis while heating andcooling through the phase transition point. the piezoelectric behavior was demonstrated to exhibitlittle hysteresis. The domain structure was shown for The first time to consist of two kind of 90laminar domains. 6.它解释了knbo_3 ultrasonic transducer已经有了更多的效率和broader-band characteristic as compared with those of PZT ceramics and linbo_3 crystals. Torealize higher frequency ultrasonic transducers an ECR-PLD system for epitaxial growth of highquality knbo_3 films was developed。

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.