Transport properties near the metal to insulator transition in samarium substituted (Bi,Pb)-2212 system

Abstract

The electrical transport properties of insulating and superconducting samples of Bi1.7Pb0.4Sr2−xSmxCa1.1Cu2.1O8+δ system is studied across the metal to insulator transition (MIT) region by varying the x values from 0.5 to 1.0 in steps of 0.1. X-ray diffraction analysis, scanning electron microscopy, energy dispersive x-ray analysis (EDAX), and electrical resistivity measurements have been employed for the characterization of all samples. The x-ray and EDAX analyses indicate that samarium (Sm) atoms are incorporated into the crystalline structure of Bi1.7Pb0.4Sr2Ca1Cu2O8+δ [(Bi,Pb)-2212]. Samples with x≤0.6 undergo superconducting transitions while those with 0.7≤x≤1.0 exhibit semiconducting behavior. The MIT is observed at 0.6<x≤0.7 with a suppression in superconductivity. The results show that with increase in temperature, the transport mechanism of the semiconducting samples transits from two dimensional variable range hopping to thermally activated conduction. A scaling model is presented for the MIT and the results are interpreted on the basis of hole filling and disorder due to the substitution of Sm at the strontium site of (Bi,Pb)-2212 system.