Ultrasonic determination of the elastic moduli and their temperature and pressure dependences in YBa2Cu3O7-x/Ag (15 vol.%) composite

Abstract

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 B0 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 ( delta CL/ delta P)P=0 and ( delta mu / delta P)P=0 of the elastic stiffnesses and ( delta B/ delta P)P=0 of the bulk modulus are substantially smaller than those found previously for pure YBa2Cu3O7-x ceramics.