ULTRASONIC DETERMINATION OF THE ELASTIC-MODULI AND THEIR TEMPERATURE AND PRESSURE DEPENDENCES IN YBA2CU3O7-X/AG(15-VOL-PERCENT) COMPOSITE

The effects of temperature and hydrostatic pressure have been measured on the velocities of longitudinal and shear ultrasonic waves propagated in ceramic specimens of a composite comprising YBa2Cu3O7-x together with 15 vol.% metallic silver. At room temperature and atmospheric pressure the bulk modulus B(o) of the composite is 1.8 times larger than that of the pure YBa2CU3O7-x ceramic of similar porosity. The ultrasonic wave velocities increase smoothly with decreasing temperature from 300 to 10 K and do not show the anomalous step-like changes including the hysteresis effects in the temperature range 190-235 K, which characterize the elastic behaviour of pure YBa2Cu3O7-x ceramic. The ultrasonic attenuation shows peaks resembling those observed in YBa2CU3O7-x itself, which result from low-activation-energy anelastic relaxation processes. The effects of hydrostatic pressure on the velocities of ultrasonic waves propagated in the composite and hence the hydrostatic pressure derivatives (partial derivative C(L)/partial derivative P)P = O and (partial derivative-mu/partial derivative P)P = O of the elastic stiffnesses and (partial derivative B/partial derivative P)P = O of the bulk modulus are substantially smaller than those found previously for pure YBa2Cu3O7-x ceramics.