Abstract
Measurements will be presented of the ultrasonic wave velocity and attenuation in high-density polycrystalline samples of YBa2Cu3O7 at temperatures between 4.2 and 300 K. Both longitudinal and shear wave data were found to be characterized by thermal hysteresis and run-to-run variations. At temperatures below Tc, the hysteresis disappeared, the elastic constants increased, and the attenuation fell. The higher temperature measurements were affected by sample annealing and thermal history and exhibited recovery effects. The pressure dependence of the elastic constants was found to be very large and also to exhibit hysteresis effects. These phenomena are consistent with the suggestion that these ceramics are pseudoplastic solids in which the plasticity is attributed to the mobility of twin boundaries. Recent measurements of Bi-Ca-Sr-Cu-O superconductors will also be presented.
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