ULTRASONIC STUDIES ON HIGH Tc SUPERCONDUCTOR YBa₂Cu₃O_7-x

Ultrasonic attenuation and velocity measurements down to 77K were performed on high Tc superconductor Y-Ba-Cu-O samples with different sintering procedures. The change of sound velocity was found near Tc in two samples which have density of 94% of the theoretical density and excellent diamagnetism. In one of the samples an anomaly related to ultrasonic frequency was observed around Tc in the ultrasonic attenuation. Another sample also possesses an excellent diamagnetism, but no anomaly in ultrasonic attenuation was found near Tc. We did not observe anomaly in attenuation resulted from electron-phonon interaction in these two samples.