Doping Controlled Metal to Insulator Transition in the (Bi, Pb)-2212 System

Abstract

We report on the details of the metal?insulator transition in the Bi1.7Pb0.4Sr2-xPrxCa1.1Cu2.1O8+?system, in the concentration range of x = 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.3 and 1.5. In addition to the electrical resistivity measurements at 6-300 K, the phase, microstructural and elemental analyses were also carried out to assess the relative performance of the samples. A detailed analysis of measurement results reveals that Pr atoms are successfully substituted at the strontium site of the (Bi, Pb)-2212 system. The system is found to be superconducting in the doping range of x ≤ 0.6 and semiconducting for x ≥ 0.7. A metal to insulator transition is found to occur in the doping range 0.6 < x ≤ 0.7, and the results reveal that a disorder induced transition leads to the localization of states in the vicinity of the Fermi level and to the said phenomenon in the Pr substituted (Bi, Pb)-2212 system. Resistivity in the insulating regime of samples was analyzed using a generalized hopping approach and the transport mechanism is found to be governed by the VRH mechanism. Superconductivity in conjunction with 2D VRH is observed near the superconductor?insulator boundary and is in agreement with a theoretical model that considers the competition between superconductivity and localization in a disordered system.