NORMAL-STATE RESISTIVITY DIAGNOSTIC FOR HIGH-TC SUPERCONDUCTORS

A resistivity versus temperature (rho-T) model that was applied successfully to the Li(x)Ni1-x(O) system has been extended to the La2-(x)Sr(x)CuO4 and YBa2Cu3O7 high-T(c) systems by fitting rho-T data with quantitative accuracy, and 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 (partial-rho/partial-T > 0 above T(c)) and the rho-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. Among the conclusions derived from the application of this theory: (i) normal phases cause increases in rho, but decreases in slope of rho(T)/rho(300), and (ii) metallic slopes may be achieved with less than ten percent effective volume of superconducting phase.