Date of this Version
The Journal of the Acoustical Society of America 84, S111 (1988); doi: 10.1121/1.2025678
Sinter‐forged YBa2Cu3O7 exhibits rotational symmetry about the forging axis with the c axis of 80% of the crystallites aligned within 2° of the forging axis. Attenuation measurements as a function of temperature of longitudinal waves propagating perpendicular to the forging axis exhibit it three broad relative maxima at 70, 180, and 250 K. Attenuation measurements with either longitudinal or transverse waves propagating along the forging axis exhibit only one maximum at about 180 K. The absence of the other two maxima along this orientation indicates that they could be produced by interaction mechanisms that may be associated with the Cu‐O planes, while the 180‐K maximum may be produced by an isotropic interaction mechanism. Sound velocity measurements show the sinter‐forged material to be elastically anisotropic. The temperature dependence of the sound velocity shows distinct hysteresis curves that flatten out if the sample is not warmed above 250 K. Upon cooling, lattice softening is observed to start at temperatures much higher than Tc, and to stop below Tc.