All of the piezoelectric properties of KNbO₃ single-domain crystals

Abstract

Piezoelectric properties of KNbO₃ crystals with the single domain state were investigated. Prior to piezoelectric measurements, KNbO₃ crystals were cut, polished and sized into various shapes. However, it was confirmed that these mechanical processing induced the mechanical damage into the crystals. Thus, the optimum conditions for the mechanical processing of KNbO₃ crystals were investigated, and finally, the stressed surface layers of KNbO₃ crystals were successfully removed by the chemical etching processing. It was revealed that the remove of the stressed surface layers was very effective to achieve high mechanical quality factor (Q_m). After the treatment, KNbO₃ crystals were poled by the 2-step poling method. As a result, it was confirmed that the domain state was almost single-domain state. Using this poled KNbO₃ Single-domain crystals, the piezoelectric properties with k₃₂ modes were measured using a conventional resonance method. As a result, the [110]_c poled KNbO₃ crystals exhibited the electromechanical coupling factor (k₃₂) of almost 40 %, the piezoelectric onstant (d₃₂) of almost 18.5 pC/N, the dielectric constant (ε₃₃) of almost 48 and Q_m over 7,600. This result revealed that the KNbO₃ crystals were the piezoelectrics with the low dielectric and high electromechanical coupling properties, i.e., KNbO₃ crystal is one of the promising materials for sensor application.