Correlation of normal and superconducting transport properties on textured Bi-2212 ceramic thin rods

The electric and thermal properties well above and below T_c of Bi-2212 textured ceramics have been correlated through a careful analysis of the microstructure and the transport measurements. Thin rods with the same Bi-2122 stoichiometry and textured by a laser floating zone technique have been studied with that aim. By changing the growth parameters, it has been possible to produce strong changes in microstructure and critical current density, J_c, with small variations in the thermal conductivity. The existence of phase and composition gradients across the thin rods, which explains the variations of T_c, makes the relation difficult between the normal state resistivity and J_c (77 K). A simple qualitative analysis that takes into account the observed microstructure has been developed to correlate the electric transport properties in the normal and in the superconducting states.