The possibility of the “giant” isotope effect for ultrasound absorption in crystals

The effect of isotopic disorder on ultrasound absorption in germanium, silicon, and diamond crystals is considered. The “giant” isotope effect is predicted in the ultrasound absorption coefficient (in contrast to the isotope effect in the thermal conductivity and thermopower) of these crystals. The parameters determining the ultrasound absorption coefficients for the crystals under study with different degrees of isotopic disorder are determined from the known values of elastic moduli of the second and third order. The ultrasound absorption coefficients are analyzed as functions of temperature and wavevector for isotopically modified crystals. The possibility of experimental observation of this effect is considered.