Potassium niobate single-domain crystals as piezoelectrics with low dielectric constants and high electromechanical coupling properties

Piezoelectric properties of potassium niobate (KNbO₃) crystals with the single-domain state were investigated. KNbO₃ crystals were cut, polished and sized into various shapes. The mechanical processing induced mechanical damage into the crystals. Remove of the stressed surface layers was very effective to achieve high mechanical quality factor (Q_m). After this treatment, KNbO₃ crystals were poled by the 2-step poling method. As a result, the domain state was almost single-domain. Using poled KNbO₃ single-domain crystals, the piezoelectric properties with k₃₂ modes were measured using a conventional resonance method. As a result, the [001]_o poled KNbO₃ crystals exhibited the electromechanical coupling factor (k₃₂) of almost 40%, the piezoelectric constant (d₃₂) of almost 18.5 pC/N, the dielectric constant (ε₃₃) of almost 48 and Q_m over 7,600. Thus, the KNbO₃ crystals are piezoelectrics with low dielectric constants and high electromechanical coupling properties, i.e., KNbO₃ crystal is a promising material for sensor application.