Effective Grüneisen constant in sodium fluoride crystals

Abstract

In this paper, we propose a new approach to determining the components of the Grüneisen tensor and establishing unambiguous relationships between the effective Grüneisen constant, which characterizes the nonlinearity of interatomic interaction forces, and the attenuation anisotropy of acoustic waves. The cubic crystals of sodium fluoride were taken as an object of study. Measurements were carried out by the method of Bragg diffraction of light by sound in the frequency range 0.4–1.6 GHz.The obtained values of velocity and attenuation of acoustic waves were used to determine the real and imaginary components of the elasticity tensor. Next, the acoustic damping coefficients and the independent components of the Grüneisen tensor in sodium fluoride crystals were determined. It is shown that the calculations performed trough the attenuation coefficients make it possible to determine the effective Grüneisen constants in two ways, and these results are in good agreement with each other. Thus, the components of the acoustical Grüneisen tensor for sodium fluoride crystals are determined for the first time and the dependence of the effective Grüneisen constant on the direction of propagation and polarization of acoustic waves is calculated.