ULTRASONIC VELOCITY-MEASUREMENTS ON PRBA2CU3O7-DELTA (DELTA = 0.1, 0.5)

Ultrasonic longitudinal and shear velocities in polycrystalline PrBa2C u3O7-delta with an oxygen content of O-6.9 and O-6.5 were measured at 10 MHz between 80 and 300 K. Longitudinal velocity hysteresis was obse rved between 190 and 230 K in the O-6.9 (orthorhombic) sample but not in the O-6.5 (tetragonal) sample. Micrographs obtained from scanning e lectron microscopy showed no noticeable difference in the microstructu re of the samples under investigation. These results are explained in terms of possible oxygen ordering. By comparing our results with previ ous ultrasonic studies on the related materials which show superconduc ting properties, it is concluded that the oxygen content strongly infl uence the elastic property and the longitudinal velocity hysteresis. ( C) 1998 Elsevier Science B.V. All rights reserved.