Precise Determination of Acoustical Physical Constants of LiNbO_3 and LiTaO_3 Single Crystals

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In this study, we have developed a new method of determining the acoustical physical constants associated with piezoelectric crystals, using two systems of line-focus-beam acoustic microscopy and bulk ultrasonic spectroscopy, and have determined precisely all the independent constants of LiNbO_3 and LiTaO_3 single crystals, including the density.1. In order to improve reliability and reproducibility of the two systems, the measurement environment of temperature has been stabilized and a laser interferometer has been introduced to measure the absolute distance. Absolute accuracy of better than (]SY.+-。[)0.01% in velocity has been achieved.2. Many crystalline plane specimens of LiNbO_3 and LiTaO_3 with optically polished surfaces and excellent parallelism of front and back surfaces have been prepared from one ingot for each crystal.3. A new method of determining the acoustical physical constants, viz., stiffness, piezoelectric, and dielectric constants, has been developed using the two systems for velocity measurements.4. The acoustical physical constants of LiNbO_3 and LiTaO_3 have been determined, which provide five significant digits for bulk and surface acoustic wave velocities.5. The elastic constants for multi-domain LiTaO_3 crystals have been also determined, for the first time, and have been compared with those for single-domain LiTaO_3 crystals. It has been shown that the poling operation to introduce piezoelectricity is responsible for the differences of elastic properties between single-and multi-domain crystals.