Lithium Niobate / Lithium Tantalate acoustic crystals
Both lithium niobate and lithium tantalate are ferroelectric crystals which possess high Curie temperatures. These crystals exhibit excellent piezoelectric coupling coefficients, making them attractive for ultrasonic device applications. Both crystals are grown by the Czochralski technique which yields large, high quality single crystals in a number of different growth directions. After growth the crystals are poled into single domain at the Curie temperature. The result is a uniform, highly consistent piezoelectric transducer single crystal.
Lithium niobate possesses a number of useful cuts which are now extensively used in transducer applications. Two compressional cuts are popular, the z-cut and the 36° rotated y-cut. The shear mode cuts most commonly used are the x-cut and 163° rotated y-cut. Lithium tantalate also possesses useful cuts for compressional and shear wave mode transducers. The two most popular compressional cuts are the z-cut and the 47° rotated y-cut, while the x-cut and the 165° rotated y-cut are the most commonly used shear mode cuts.
Lithium niobate possesses very large electro-mechanical coupling coefficients – several times larger than quartz – and very low acoustic losses. Because of its Curie temperature of 1142°C, it can be utilized as a high temperature acoustic transducer, such as an accelerometer for jet aircraft. Acoustic wave delay lines and acousto-optic modulators, deflectors and filters now routinely employ lithium niobate for both shear and compressional wave generators because of its high efficiency, broad bandwidth capability, low dielectric constant for all orientations, and consistent repeatability.
Compared to quartz, lithium tantalate has a much larger electro-mechanical coupling and a number of zero temperature coefficient cuts of resonant frequency. As a result, it finds application in communications for acoustic resonator filters of broad bandwidth.
There exists an abundance of published physical property data on lithium niobate and lithium tantalate, much of it inconsistent. The following data comprise reports of varying validity of measured properties of congruent composition material. For information on the measurement tolerance associated with these data and for additional property data, consult the references below.