Normal-state resistivity diagnostic for high-Tc superconductors

A resistivity versus temperature (ρ-T) model that had been applied successfully to the Li_xNi_1-xO system has been extended to the La_2-xSr_xCuO₄ and YBa₂Cu₃O₇ high-T_c systems by fitting ρ-T data with quantitative accuracy. It may also serve as the basis for interpreting the varying slopes of multiphase superconductors. Calculated curves of a two-phase approximation fitted to reported experimental data show that the metallic slope (∂ρ/∂T>0 above T_c) and the ρ-axis intercept of the linear extrapolation are related to the electron hopping activation energy and carrier concentration and may also be used to estimate the volume ratio of effective superconducting phase to normal phase within a particular specimen. It is shown that normal phases cause increases in ρ, but decreases in slope of ρ(T)/ρ(300), and that metallic slopes may be achieved with less than 10% effective volume of superconducting phase