Ultrasonic Attenuation in Al2O3 at Ultrahigh Frequencies and Low Temperatures

Abstract

Ultrasonic propagation in Al₂O₃ at low temperatures and high frequencies (to 3000 Mc/sec) is discussed in terms of the relations given by Woodruff and Ehrenreich. Phonon relaxation times calculated from thermal conductivity measurements are used. The measured low‐temperature attenuation values at 1315 Mc/sec agree with the calculated values. A comparison of attenuation as a function of frequency is made among Al₂O₃, Ge, Si, and quartz. On comparing experimental values of attenuation for pure Al₂O₃ and impure Al₂O₃ (ruby) it is found that impurities lead to an increase in the attenuation as would be predicted from the corresponding effect of impurities on the thermal phonon relaxation time.