ELASTIC PROPERTIES OF EuBa2Cu3O7-δ CERAMICS AT LOW TEMPERATURES

Ultrasonic velocity measurements on single-phase polycrystalline EuBa2Cu3O7-δ superconducting (δ ~ 0.1) and non-superconducting (δ ~ 0.7) samples have been performed at 9 MHz from 80 K to 280 K in longitudinal mode and from 80 K to 200 K in shear mode. The absolute longitudinal and shear velocities (at 80K) decreased when the oxygen content was reduced from O6.9 to O6.3. For the superconducting sample, a step-like anomaly was observed around 255 K indicating pronounced lattice stiffening in the longitudinal mode. However, a similar observation was not observed in the shear mode possibly due to the lower temperature limit. In addition, no elastic anomalies were observed for the non-superconducting sample in both longitudinal and shear modes. The elastic anomaly was discussed in terms of a phase transition involving oxygen ordering in Cu-O chains. Elastic moduli values and Debye temperature (θD) are also reported