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Both ultrasonic attenuation and velocity as a function of temperature from 4.2 K to room temperature were measured on sinter-forged samples of YBa/sub 2/Cu/sub 3/O/sub 7- delta /, which have more than 80% alignment of the c-axis of the grains parallel to the forging axis. Strong anisotropy was found both in the attenuation and the velocity when propagating sound waves in different directions relative to the forging axis. Hysteresis was observed in the velocity changes. >

We report ultrasonic attenuation measurements on sinter-forged YBa/sub 2/Cu/sub 2/O/sub 7-//sub delta/ material, which differs from ordinary sintered material in that the crystallites are preferentially oriented to form a uniaxial sample. Three peaks in attenuation, at temperatures of 250, 180, and 70 K, were observed for longitudinal waves propagating perpendicular to the forging axis, which is similar to that reported in ordinary (isotropic) polycrystalline samples. However, for both transverse and longitudinal sound propagated along the forging axis we have a different behavior, with only one peak at 180 K, showing a strong anisotropy. It is suggested that sound waves traveling parallel to and normal to the Cu-O planes may account for the anisotropic effect, and a relaxation mechanism may explain the increase in shear wave attenuation which was seen with decreasing temperature.

Measurements of the attenuation of longitudinal ultrasound in superconducting UPt3, show a peak,below Hc2, which depends strongly on the orientation of the field relative to the c axis. We propose an explanation of this peak in terms of a vortex phase transition in an unconventional superconducting state, which is consistent with recent neutron-scattering data.

We have measured ultrasonic absorption in sinter-forged high Tc YBa2Cu3O7 − δ. Owing to the anisotropic properties of the sinter-forged samples, longitudinal ultrasonic attenuation measurements showed very strong anisotropy when waves were propagated parallel and perpendicular to the forging axis. Sound absorption was found to increase with decreasing temperature for shear waves travelling parallel to the forging axis.

Measurements of the attenuation of longitudinal ultrasound in superconducting UPt3, show a peak,below Hc2, which depends strongly on the orientation of the field relative to the c axis. We propose an explanation of this peak in terms of a vortex phase transition in an unconventional superconducting state, which is consistent with recent neutron-scattering data.