Transverse ultrasound absorption in cubic crystals with positive and negative anisotropies of second-order elasticity moduli

TL;DR

This paper investigates how transverse ultrasound absorption varies with direction in cubic crystals, considering defect scattering and anharmonic processes, revealing qualitative differences based on anisotropy types.

Contribution

It introduces an analysis of ultrasound absorption anisotropy in cubic crystals considering both defect and anharmonic scattering mechanisms, highlighting their distinct angular behaviors.

Findings

Absorption anisotropy differs qualitatively for positive and negative elastic anisotropies.

The dominant relaxation mechanism can be identified by angular dependence patterns.

Inverse angular dependence behaviors distinguish defect scattering from anharmonic scattering.

Abstract

The transverse ultrasound absorption in cubic crystals with positive and negative anisotropies of the second-order elasticity moduli is analyzed. The scattering of the ultrasound by defects and during anharmonic scattering processes is considered. The transverse ultrasound absorption is analyzed as a function of the wave-vector direction in terms of the anisotropic continuum model. The Landau-Rumer mechanism is considered for anharmonic scattering processes. Known values of the second- and third-order elasticity moduli are used to calculate parameters determining the ultrasound absorption. It is shown that the angular dependences of the transverse ultrasound absorption differ qualitatively if the anharmonic scattering processes dominate in cubic crystals with positive and negative anisotropies of the second-order elasticity moduli. For the scattering by defects and the anharmonic scattering processes, the angular dependences of the transverse ultrasound absorption exhibit the inverse behavior, making it possible to determine the dominating mechanism of the ultrasound relaxation in the crystals under study.