Papers by Author: Hirohiko Kumagai

Abstract: To induce fine engineered domain configurations into potassium niobate (KNbO3) single crystals, two kinds of methods were performed, i.e., (1) high DC electric field exposure along the opposite direction of polarization of KNbO3 single-domain crystals at room temperature, and (2) introduction of randomly oriented fine domain configuration by heat treatment at 700 °C and then high DC electric field exposure along [001]c direction of KNbO3 multidomain crystals at room temperature. When the method (1) was performed, finally, the poled KNbO3 crystals became to single-domain state again through the formation of multidomain state. On the other hand, the KNbO3 multidomain crystals were obtained by using the method (2), and an enhancement of piezoelectric-related properties was observed.

Abstract: For potassium niobate (KNbO3) single crystal, the 31 resonators with the highest piezoelectric constant d31 were designed using transformation of axis. We confirmed that the engineered domain configurations with maximum d31 of –55.1 pC/N was caused by a combination between two polarization with polar directions along [101]c and [-101]c directions. Moreover, if there are larger piezoelectric constants from domain wall region, we can expect the much higher piezoelectric properties. To induce the above domain configuration, a new poling method using patterning electrode was investigated. In this study, the two methods on the basis of temperature-induced phase transition at 207 °C and electric-field-induced phase transition at room temperature were investigated.