Doping dependent metal to insulator transition in the (Bi,Pb)-2212 system: The evolution of structural and electronic properties with europium substitution

The present work investigates the effect of europium substitution onthe (Bi, Pb)-2212 system in the concentration range 0.5 ≤ x ≤1.0. Phase analysis and lattice parameter calculations on thepowder diffraction data and the elemental analysis of EDX show thatthe Eu atoms are successfully substituted into the (Bi, Pb)-2212system. Resistivity measurements (64--300~K) reveal that thesystem exhibits superconductivity at x ≤ 0.5 andsemiconductivity at x > 0.5. With the complete suppression ofsuperconductivity which is known to be a quasi-two dimensionalphenomenon in these materials, a metal to insulator transition takesplace at x=0.6 and the predominant conduction mechanism is foundto be variable range hopping between localized states, resultingin macroscopic semiconducting behaviour. The results of electricaland structural properties of the doped (Bi, Pb)-2212 compoundssuggest that the decrease of charge carrier concentration and theinduced structural disorder are the more effective and dominantmechanisms in the origin of the metal to insulator transition andsuppression of superconductivity due to Eu substitution at itsSr site.