Preparation of superconducting Bi-Sr-Ca-Cu-O thin films by sequential electron beam evaporation and oxygen annealing

Abstract

Superconducting films with nominal composition Bi2Sr2Ca1Cu2Ox have been prepared on 〈100〉 MgO substrates by sequential electron beam evaporation of Cu, Bi, and Sr2/3 Ca1/3 F2, followed by annealing in flowing wet, then dry, O2. X-ray diffraction data show that the films contain the two Bi-Sr-Ca-Cu-O phases that have been identified in the literature as a superconducting phase with c∼31 Å and a semiconducting phase with c∼24 Å. Both phases are strongly textured with the c axis perpendicular to the substrate. For the best film, which was annealed at 870 °C for 30 min, zero resistance was observed at 90 K, and the critical current density increased from 0.8×105 A/cm2 at 77 K to 2.3×105 A/cm2 at 4.2 K.