Ultrasonic velocity anomalies in superconducting sinter-forged YBa2Cu3O/sub 7-//sub δ/

The velocity of ultrasound was measured on sinter-forged polycrystalline YBa2Cu3O/sub 7-//sub δ/ samples with a superconducting transition temperature of 91 K. The forging process results in crystallites which are preferentially aligned with their c axis aligned parallel to the forging axis as confirmed from optical and x-ray measurements. Sound-velocity measurements show that the material is elastically anisotropic. The temperature dependence of the sound velocity shows distinct anomalies. For propagation parallel to the forging axis, both longitudinal and shear waves displayed a thermal hysteresis between 65 and 260 K; however the longitudinal sound velocity with q in the basal plane showed a much smaller thermal hysteresis. No effect of a magnetic field was observed on sweeping the magnetic field to 7.2 T at temperatures of 4 and 86 K