Ultrasonic attenuation in Lanthanum Monochalcogenides

Ultrasonic attenuation due to phonon-phonon interaction and thermoelastic r elaxation are studied in Lanthanum Monochalcogenides in (110) direction at different higher temperatures. For evaluation of ultrasonic absorption coef ficients the second and third order elastic constants (SOEC) and (TOEC) are also calculated. Shear wave attenuation shows maximum along (110) propagat ion direction with polarized along (110) and the attenuation increases at h igher temperatures. Thermo-elastic loss is very small compared to phonon-vi scosity loss. Behavior of temperature dependence of the absorption is the s ame as in case of pure metals and dielectric crystals.