ANISOTROPY OF THE ELASTIC AND NONLINEAR ACOUSTIC PROPERTIES OF DENSE TEXTURED BI2SR2CACU2O8+Y

A description of the anistropy of elastic and nonlinear acoustic prope rties of dense (95% of theoretical), highly textured, sinter-forged, c eramic Bi2Sr2CaCu2O8+y (Bi-2-.2:1:2) high-T(c) superconductors is prov ided from measurements of the velocities of longitudinal and shear ult rasonic waves as functions of temperature and hydrostatic pressure. A high proportion of the grains are aligned preferentially with the c ax is along the forging direction in this material, while it is essential ly isotropic in the plane normal to the forging axis. A complete set o f the elastic stiffness tensor components has been determined as a fun ction of temperature from 10 to 290 K, treating this material as if it had cylindrical symmetry. The results are used to compute the orienta tion dependences of the Young's modulus and Poisson's ratio which are compared with those estimated for single crystal Bi-2:2:1:2. The main finding is a marked anisotropy of the elastic stiffness moduli and the ir dependences on pressure. The elastic and nonlinear acoustic propert ies of the textured and single-crystal Bi-2:2:1:2 comply with the beha vior expected for a layerlike material with rather weak interlayer bin ding forces: C-11 > C33, the linear compressibility and thermal expans ion along to the c axis, i.e., normal to the layers, being substantial ly larger than in the ab plane. The hydrostatic pressure derivative (p artial derivative C33/partial derivative P)=0(=21.3) of the elastic st iffness tensor component, which corresponds to a longitudinal wave pro pagated along the c axis, is larger than that (partial derivative C-11 /partial derivative P)p=0(=15.1), for such a wave propagated in the ab plane. The anisotropies of the linear compression and the acoustic mo de Gruneisen parameters are also typical of a layerlike material.