Preparation of Thin Films by Coevaporation and Phase Identification in Bi-Sr-Ca-Cu-O System

Abstract

Thin films of a Bi-Sr-Ca-Cu-O system were prepared on MgO substrate by coevaporation of Bi₂O₃, Sr_0.5Ca_0.5 alloy and Cu. The films were characterized by X-ray diffraction, dc resistivity and EPMA. By post-deposition annealing the film at 850°C for 12 hours, the film showed a superconducting transition with onset T _c of 91 K and zero resistance T _c of 82 K. The tetragonal phase Bi₂Sr₂CaCu₂O _x with a c-axis of 30.7 Å was responsible for this superconducting transition. The film annealed at 890°C for 5 hours showed a superconduting transition with onset T _c of 115 K and zero resistance T _c of 103 K. The tetragonal phase Bi₂Sr₂Ca₂Cu₃O _x with a c-axis of ∼37 Å was responsible for this superconducting transition.