V(z) Evaluation of Crystallographic Orientations Effects on Elastic Properties of Sodium Cobalt Germanate Single Crystals

Abstract

Herein we report on the effect of anisotropy on the elastic acoustic parameters    (reflection coefficients R(θ), critical angles of wave excitation, acoustic signatures V(z), spatial periods, velocities) of sodium cobalt germanate Na₂CoGeO₄  single crystals with six crystallographic orientations  [100], [001], [010], [110], [101], and [011]. Simulations were carried out in the case of a scanning acoustic microscope at an operating frequency of 142MHz, a half opening angle of 50° and water couplant. Interesting results were found. Shear modes were first excited at  θ_S  ~ 26.8° on [100] direction. However, at other propagation directions  [001], [010], [110], [101],  and [011] the shear mode appears  at higher angles:  θ_S ~27.1°, 31°, 33.9°, 40.5°, 43° respectively. Propagation of acoustic waves showed a decrease of longitudinal waves velocities  from  5687 m/s for [101] direction to  4471 m/s for [011] direction. Similar behaviors were obtained with R(θ) and V(z) curves. These variations are due to either low or high atomic occupation of different orientations.