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

Piezoelectric properties of potassium niobate (KNbO/sub 3/) crystals with the single-domain state were investigated. KNbO/sub 3/ 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/sub m/). After this treatment, KNbO/sub 3/ crystals were poled by the 2-step poling method. As a result, the domain state was almost single-domain. Using poled KNbO/sub 3/ single-domain crystals, the piezoelectric properties with k/sub 32/ modes were measured using a conventional resonance method. As a result, the [001]/sub o/ poled KNbO/sub 3/ crystals exhibited the electromechanical coupling factor (k/sub 32/) of almost 40%, the piezoelectric constant (d/sub 32/) of almost 18.5 pC/N, the dielectric constant (/spl epsiv//sub 33/) of almost 48 and Q/sub m/ over 7,600. Thus, the KNbO/sub 3/ crystals are piezoelectrics with low dielectric constants and high electromechanical coupling properties, i.e., KNbO/sub 3/ crystal is a promising material for sensor application.