Abstract:
Ferroelectric single crystals of LiNbO[inf 3] and LiTaO[inf 3] are widely used as substrates for ultrasonic and optoelectronic devices. Obtaining homogeneity in elastic and optical properties of the crystals is one of the most important problems for wafer production. Recently, inhomogeneities of commercial wafers/crystals have been investigated with data of velocity changes obtained by line-focus-beam acoustic microscopy. The variations of the elastic properties are considered to be due primarily to chemical composition changes and secondarily to residual multidomains. In this paper, a fundamental study of the differences in elastic properties between single- and multidomain crystals of LiTaO[inf 3] is conducted by measuring the longitudinal velocities for X-, Y-, and Z-cut specimens and the shear velocities for Z-cut specimens. Two sets of X-, Y-, and Z-cut specimens are prepared: One is for normal (single-domain) specimens and the other is for perfectly depoled (multidomain) specimens. For the longitudinal wave propagation directions along the Y and Z axes, the velocities for the single-domain specimens, due to the piezoelectricity, are 91.57 m/s (1.59%) and 92.70 m/s (1.50%) greater than those for the multidomain specimens, respectively. On the other hand, for the X-axis longitudinal and Z-axis shear wave propagation directions, the piezoelectricity is uncoupled, but very interesting velocity changes are found in that the longitudinal and shear velocities for the single-domain specimens are 48.45 m/s (0.87%) and 135.59 m/s (3.79%) lesser than those for the multidomain specimens, respectively.