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