Effects of step-annealing in argon atmosphere on the superconducting properties of the 2212 Bi-Pb-Sr-Ca-Cu-O system

Abstract

Of the various classes of high temperature superconductors, the Bi-Sr-Ca-Cu-O class has the advantage of being compositionally and thermally stable. Less reactivity and less material costs make these materials highly suitable for practical applications. This compound was found to have three superconducting phases referred to by their cation ratio as 2201, 2212 and 2223 and whose transition temperatures have values of approximately 7 K, 80 K and 110 K, respectively. Several studies have been conducted in enhancing the transition temperature and critical current density ofthis compound by means ofemploying various ceramic processes and techniques. One such technique is by using an RF magnetron sputtering machine in the fabrication of superconducting thin films.
This study deals with determining the effects of step-annealing thin films of the superconducting Bi-Pb-Sr-Ca-Cu-O system in pure Argon and in air prepared from a single target RF magnetron sputtering. The target was prepared by mixing high purity (99.9%) Bi₂O₃, PbO, SrCO₃, CaCO₃ and CuO powders and calcining the mixture in air. The prereacted material was ground, pressed into a disk and sintered in air for about 8 hours. Prior to film deposition, presputtering of the target and etching of the substrate was conducted in order to clean the surface of the target and substrate. Film deposition was done for about 2 hours with a base pressure of approximately 1x10^-6 torr. The films were deposited on single-crystal MgO substrates and were subjected to several heat treatments at varying temperatures. The crystal orientation ofthe films were characterized by means of a Rigaku X-ray diffractometer (XRD) using monochromatod CuK_α radiation. Electrical resistivity measurements (ρ-T) were conducted by means of the standard four-probe using gold wires and silver paste for contact. Scanning Electron Microscopy and Energy Dispersive X-ray analysis (SEM-EDX) were conducted to determine the crystal shape, morphology and microstructures of the films. Inductively-Coupled Plasma Spectroscopy (ICPS) were also conducted to determine the chemical compositions of the films.