Anomalous behaviour of sound velocity in the high T<inf> c</inf> superconductor YBa<inf>2</inf>Cu<inf>3</inf>O<inf>7</inf>

The longitudinal acoustic wave velocity in YBa2Cu3O7 has been measured in the range 300 to 85 K using the ultrasonic pulse superposition technique. The sound velocity shows a steep drop in its value at 260 K and decreases continuously till the superconducting transition temperature. Below T c the sound velocity increases steeply. A hysteresis is seen when the experiments are performed during a cooling-warming cycle. The results are compared with recent measurements by Ewert et al on the samples with the same chemical composition. © 1987 Indian Academy of Sciences.