Acoustic microscopy evaluation of anisotropy effects on elastic properties of Na 2CoGeO 4 single crystals

Abstract

In this paper, we investigate anisotropy effects 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 Na 2CoGeO 4 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 142 MHz, 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. © Published under licence by IOP Publishing Ltd.