Relaxation behavior of ultrasonic attenuation in YBa2Cu 3O7

Temperature-dependent ultrasonic attenuation measurements have been performed on a pressed powder sample of YBa₂Cu₃ O₇ with frequencies at 10, 27, and 32 MHz. An attenuation anomaly occurs at temperature close to the superconducting transition temperature T_c (90 K) for each frequency. It is also found that the magnitudes of these attenuation peaks are of quadratic frequency dependence. With normalized attenuation data and by employing the Debye equation for relaxation type ultrasonic attenuation, the relaxation time is found to be exponentially dependent on temperature. Moreover, the velocity of a 10 MHz sound wave propagating in the sample generally increases with decreasing temperature while exhibiting a possible softening around T_c. These variations of attenuation and velocity at temperatures near T _c may be associated with the structural distortion of YBa₂Cu₃O₇ and may indirectly be a result of superconducting transition