  We discuss here a comparative study of the role of local structure and/or
nature of local magnetic coupling on the electrical transport properties of Mn
site substituted La-Ca-Mn-O perovskites. Particular emphasis is being paid to
explore the strong correlation between the insulator-metal transition (TIM) and
the residual resistivity (rhoo) upon substitution. There exists an inverse
relationship between ro and TIM in the compounds under present discussion. Best
fit for TIM Vs ro could be obtained for the compounds understudy to a first
order exponential decay with a functional form TIM = TIMO + Aexp (-rhoo/t) than
that to a power law. There is a previous report wherein the similar correlation
in the case of rare earth substituted manganites has been attributed to
Anderson-type electron localization. The "universal behavior" as has been
observed between ro and TIM irrespective of the electronic, magnetic and
chemical nature of the substituting elements in the Mn site substituted
La-Ca-Mn-O perovskites needs a rigorous theoretical investigation.
