Inhomogeneous distribution of uniaxial compacting pressure and its effects on transport properties of Bi1.65Pb0.35Sr2Ca2Cu3Oy superconductors

We have measured the temperature dependence of the electrical resistivity ρ(T,Ba) in polycrystalline Bi1.65Pb0.35 Sr2Ca2Cu3Oy superconductors under two conditions: Ba=0 and Ba=43 mT, where Ba is the applied magnetic field. Powders of this material were uniaxially pressed at 217 MPa and thermally treated to obtain cylindrical samples with similar dimensions. The physical properties of the two interfaces of these samples were investigated: the first, where the piston used in the compacting process has a direct mechanical contact with the powders, referred to as A, and the other one, which is parallel to the former, referred to as B. We have found appreciable differences in the degree of texture between these faces from X-ray diffractometry. For transport measurements, two specimens with slab form were cut from the same sample. The first was extracted from the face A and the second one was cut along the thickness of the samples, from the face A to B. The temperature dependence of the electrical resistivity at zero applied magnetic field shows similar values of the critical temperatures in both samples, but appreciable difference in the offset temperatures was observed when a magnetic field of 43 mT is applied. These features are discussed assuming an inhomogeneous distribution of uniaxial compacting pressure in these ceramic samples