Elastic constant anomalies in sinter-forged high-T_c superconductor YBa₂Cu₃O_{7 - δ}

The ultrasound velocity in the sinter-forged YBa₂Cu₃O_{7 - δ} superconductor was measured and the results showed evident anomalies as well as anisotropies. Both longitudinal and shear wave velocity along the c axis (the forging axis) showed a distinct thermal hysteresis from 65 K to 260 K. The velocity change ΔV V from room temperature to 4 K was 1.5%. The sound velocity along the "basal plane" reached a maximum around 160 K. No distinct thermal hysteresis was observed. ΔV V from room temperature to 4 K was 1%. All of these velocities were measured while sweeping the magnetic field up to 9 T at fixed temperatures of 4 K and 86 K respectively. No velocity change was observed. The shear wave velocity behaved similarly at 9 T during the thermal cycling between room temperature and 4 K.