OXYGEN RELATED ULTRASONIC-ATTENUATION AND ELASTIC ANOMALIES IN EUBA2CU3O7-DELTA (DELTA-SIMILAR-TO-0.02 AND 0.45)

Ultrasonic shear velocity and attenuation measurements on superconduct ing (delta similar to 0.02) and non-superconducting (delta similar to 0.45) polycrystalline EuBa2Cu3O7-delta have been performed at 7-8 MHz between 80 K and 220 K. Enhanced attenuation and softening tendency wa s observed near 170 K in the superconducting material. The attenuation peak is greatly suppressed and no softening tendency was observed in the non-superconducting sample. The reduction of oxygen content from O -6.98 to O-6.55 caused the absolute shear velocity to decrease. The O- 6.98 sample showed a 2.25% change in shear velocity between 80 K and 2 20 K while the O-6.55 sample showed a 3.75% change within the same tem perature range. These anomalies are discussed in terms of possible oxy gen ordering. The acoustic Debye temperature of the superconducting sa mple in the void-free approximation is estimated to be Theta(D)similar to 457 K. (C) 1998 Elsevier Science S.A.