Metal-insulator transition and conduction mechanism in dysprosium doped Bi1.7Pb0.4Sr2Ca1.1Cu2.1O8+δ system

To explore the mechanisms behind the metal-insulator transition and charge transport in high temperature superconducting cuprates, a systematic study on the Bi1.7Pb0.4Sr2Ca1.1Cu2.1O8+delta compound was made by adding the rare-earth dysprosium at stoichiometric amounts (x) of 0.5 <= x <= 1. Phase analysis, determination of lattice parameters, microstructure analysis, and elemental analysis were carried out to evaluate the relative performance of the samples prepared by the solid state synthesis route. Charge transport in the insulating and superconducting samples were analyzed through resistivity measurements at (64-300 K). It is found that the x=0.5 sample is superconducting with a critical transition temperature of 94.8 K while for the samples with x>0.5 superconductivity is suppressed, along with an increase in their normal state resistivities. A metal-insulator transition is found to take place around 0.5 < x <= 6. A detailed analysis of the experimental data shows that the hole filling and disorder, induced by change in charge carrier concentration, lead to a metal-insulator transition in the present system. Also the conductivity of the semiconducting samples (x>0.5) at lower temperature is due to the two-dimensional variable range hopping mechanism of charge carriers between the spatially localized states. (C) 2008 American Institute of Physics.