Effect of fine features of structure upon resistive and elastic properties of high-Tc superconductors

The methods of scanning electron microscopy (SEM), electron diffractometry X-ray microspectral analysis along with measurements of the temperature spectrum of the internal friction and shear modulus were employed to accomplish complex studies of yttrium and gadolinium HTS samples prepared by the ceramic technique. It is shown that all crystallites of the rhombic phase contain regularly arranged polysynthetic twins. Each crystallite has a shell of a different composition, through which the crystallites contact each other. The contact with water vapours first of all results in the destruction of shells. A strong peak of the internal friction is revealed in the region of 900 deg C along with the corresponding anomaly of the shear modulus. It is found that in the samples studied ρ(T) has a metallic character. As the temperature approaches Tc, the ρ value is observed to decrease sharply to some constant level. The temperature shift at which the sample has zero resistance, tends to saturation with increasing current density