Evaluation of acoustic physical constants of LiNbO3 at hypersonic frequencies

Abstract

The velocity angular dispersion of bulk acoustic modes propagating parallel to the surfaces of X-, Y- and Z-cut crystal plates of LiNbO3 has been measured by Brillouin scattering. The elastic and piezoelectric stress constants of LiNbO3 at hypersonic frequencies, determined from a simultaneous fit to data from the three crystal cuts, are found to be only marginally more accurate than those based on only the X-cut data. Calculations based on the constants fitted to the X-cut data alone predicted accurately the velocity angular dispersion of the surface Rayleigh wave measured simultaneously. The first leaky surface wave on the Z-cut crystal is also experimentally observed whose velocity angular dispersion agrees with the theoretical dispersion computed from the fitted constants. Evidence of dispersion between ultrasonic and hypersonic velocities is found for both surface and bulk acoustic waves.